except as permitted in Part UCL (see Appendix F). UG …€¦ · ASME B&PVC sec81$$u10 06-02-99...

ASME B&PVC sec81$$u10 06-02-99 16:28:04 pd: sec81 Rev 14.04

UG-24 PART UG — GENERAL REQUIREMENTS UG-27

are to be used in vessels to contain lethal substances(UW-2).

(a) Castings of cast iron (UCI-2) and cast ductileiron (UCD-2) are prohibited.

(b) Each casting of nonferrous material permit-ted by this Division shall be radiographed at all criticalsections (see footnote 1, Appendix 7) without revealingany defects. The quality factor for nonferrous castingsfor lethal service shall not exceed 90%.

(c) Each casting of steel material permitted bythis Division shall be examined per Appendix 7 forsevere service applications [7-3(b)]. The quality factorfor lethal service shall not exceed 100%.

(b) Defects. Imperfections defined as unacceptableby either the material specification or by Appendix 7,7-3, whichever is more restrictive, are considered tobe defects and shall be the basis for rejection of thecasting. Where defects have been repaired by welding,the completed repair shall be subject to reexaminationand, when required by either the rules of this Divisionor the requirements of the castings specification, therepaired casting shall be postweld heat treated and, toobtain a 90% or 100% quality factor, the repairedcasting shall be stress relieved.

(c) Identification and Marking.Each casting to whicha quality factor greater than 80% is applied shall bemarked with the name, trademark, or other traceableidentification of the manufacturer and the casting identi-fication, including the casting quality factor and thematerial designation.

UG-25 CORROSION

(a) The user or his designated agent (see U-2) shallspecify corrosion allowances other than those requiredby the rules of this Division. Where corrosion allow-ances are not provided, this fact shall be indicated onthe Data Report.

(b) Vessels or parts of vessels subject to thinningby corrosion, erosion, or mechanical abrasion shall haveprovision made for the desired life of the vessel by asuitable increase in the thickness of the material overthat determined by the design formulas, or by using someother suitable method of protection. (See Appendix E.)

NOTE: When using high alloys and nonferrous materials either forsolid wall or clad or lined vessels, refer to UHA-6, UCL-3, andUNF-4, as appropriate.

(c) Material added for these purposes need not beof the same thickness for all parts of the vessel ifdifferent rates of attack are expected for the various parts.

(d) No additional thickness need be provided whenprevious experience in like service has shown that

23

corrosion does not occur or is of only a superficialnature.

(e) Telltale Holes.Telltale holes may be used toprovide some positive indication when the thicknesshas been reduced to a dangerous degree. Telltale holesshall not be used in vessels which are to contain lethalsubstances [see UW-2(a)], except as permitted by ULW-76 for vent holes in layered construction. When telltaleholes are provided, they shall have a diameter of1⁄16

in. to 3⁄16 in. (1.6 mm to 4.8 mm) and have a depthnot less than 80% of the thickness required for aseamless shell of like dimensions. These holes shallbe provided in the opposite surface to that wheredeterioration is expected. [For telltale holes in clad orlined vessels, see UCL-25(b).]

(f) Openings for Drain.Vessels subject to corrosionshall be supplied with a suitable drain opening at thelowest point practicable in the vessel; or a pipe maybe used extending inward from any other location towithin 1⁄4 in. (6 mm) of the lowest point.

UG-26 LININGS

Corrosion resistant or abrasion resistant linings,whether or not attached to the wall of a vessel, shall notbe considered as contributing to the strength of the wallexcept as permitted in Part UCL (see Appendix F).

UG-27 THICKNESS OF SHELLS UNDERINTERNAL PRESSURE

(a) The thickness of shells under internal pressureshall be not less than that computed by the followingformulas.14 In addition, provision shall be made forany of the other loadings listed in UG-22, when suchloadings are expected. (See UG-16.)

(b) The symbols defined below are used in theformulas of this paragraph.

tp minimum required thickness of shell, in.Pp internal design pressure (see UG-21), psiRp inside radius of the shell course under con-

sideration,15 in.Sp maximum allowable stress value, psi (see UG-

23 and the stress limitations specified in UG-24)

14Formulas in terms of the outside radius and for thicknesses andpressures beyond the limits fixed in this paragraph are given in 1-1 to 1-3.15For pipe, the inside radiusR is determined by the nominal outsideradius minus the nominal wall thickness.


UG-27 1998 SECTION VIII — DIVISION 1 UG-28

Ep joint efficiency for, or the efficiency of, appro-priate joint in cylindrical or spherical shells, orthe efficiency of ligaments between openings,whichever is less.

For welded vessels, use the efficiency speci-fied in UW-12.

For ligaments between openings, use the ef-ficiency calculated by the rules given in UG-53.

(c) Cylindrical Shells.The minimum thickness ormaximum allowable working pressure of cylindricalshells shall be the greater thickness or lesser pressureas given by (1) or (2) below.

(1) Circumferential Stress (Longitudinal Joints).When the thickness does not exceed one-half of theinside radius, orP does not exceed 0.385SE, thefollowing formulas shall apply:

t pPR

SE− 0.6Por P p

SEt

R + 0.6t(1)

(2) Longitudinal Stress (Circumferential Joints).16

When the thickness does not exceed one-half of theinside radius, orP does not exceed 1.25SE,the followingformulas shall apply:

t pPR

2SE+ 0.4Por P p

2SEt

R − 0.4t(2)

(d) Spherical Shells.When the thickness of the shellof a wholly spherical vessel does not exceed 0.356R,or P does not exceed 0.665SE, the following formulasshall apply:

t pPR

2SE− 0.2Por P p

2SEt

R + 0.2t(3)

(e) When necessary, vessels shall be provided withstiffeners or other additional means of support to preventoverstress or large distortions under the external loadingslisted in UG-22 other than pressure and temperature.

(f) A stayed jacket shell that extends completelyaround a cylindrical or spherical vessel shall also meetthe requirements of UG-47(c).

(g) Any reduction in thickness within a shell courseor spherical shell shall be in accordance with UW-9.

16These formulas will govern only when the circumferential jointefficiency is less than one-half the longitudinal joint efficiency, orwhen the effect of supplementary loadings (UG-22) causing longitudi-nal bending or tension in conjunction with internal pressure is beinginvestigated. An example illustrating this investigation is given inL-2.1 and L-2.2.

24

UG-28 THICKNESS OF SHELLS ANDTUBES UNDER EXTERNALPRESSURE

(a) Rules for the design of shells and tubes underexternal pressure given in this Division are limited tocylindrical shells, with or without stiffening rings, tubes,and spherical shells. Three typical forms of cylindricalshells are shown in Fig. UG-28. Charts used in determin-ing minimum required thicknesses of these componentsare given in Subpart 3 of Section II, Part D.

(b) The symbols defined below are used in theprocedures of this paragraph:

Ap factor determined from Fig. G in Subpart 3 ofSection II, Part D and used to enter the applica-ble material chart in Subpart 3 of Section II,Part D. For the case of cylinders havingDo/tvalues less than 10, see UG-28(c)(2).

Bp factor determined from the applicable materialchart in Subpart 3 of Section II, Part D formaximum design metal temperature, psi [seeUG-20(c)]

Dop outside diameter of cylindrical shell course ortube, in.

Ep modulus of elasticity of material at design tem-perature, psi. For external pressure design inaccordance with this Section, the modulus ofelasticity to be used shall be taken from theapplicable materials chart in Subpart 3 of Sec-tion II, Part D.17 (Interpolation may be madebetween lines for intermediate temperatures.)

Lp total length, in., of a tube between tubesheets,or design length of a vessel section betweenlines of support (see Fig. UG-28.1). A line ofsupport is:

(1) a circumferential line on a head (ex-cluding conical heads) at one-third the depth ofthe head from the head tangent line as shownon Fig. UG-28;

(2) a stiffening ring that meets the require-ments of UG-29;

(3) a jacket closure of a jacketed vesselthat meets the requirements of 9-5;

(4) a cone-to-cylinder junction or aknuckle-to-cylinder junction of a toriconicalhead or section which satisfies the moment ofinertia requirement of 1-8.

Pp external design pressure, psi [see Note inUG-28(f)]

17Note that the modulus of elasticity values listed in UF-27 of thisDivision shall not be used for external pressure design.

A99


FIG. UG-28 DIAGRAMMATIC REPRESENTATION OF VARIABLES FOR DESIGN OF CYLINDRICAL VESSELSSUBJECTED TO EXTERNAL PRESSURE

Pap calculated value of maximum allowable exter-nal working pressure for the assumed value oft, psi [see Note in (f) below]

Rop outside radius of spherical shell, in.tp minimum required thickness of cylindrical shell

or tube, or spherical shell, in.tsp nominal thickness of cylindrical shell or tube,

in.(c) Cylindrical Shells and Tubes.The required mini-

mum thickness of a cylindrical shell or tube underexternal pressure, either seamless or with longitudinalbutt joints, shall be determined by the following pro-cedure.

(1) Cylinders havingDo/t values ≥ 10:Step 1. Assume a value fort and determine the

ratios L/Do and Do/t.Step 2.Enter Fig. G in Subpart 3 of Section II, Part

D at the value ofL/Do determined in Step 1. Forvalues of L/Do greater than 50, enter the chart at avalue of L/Do p 50. For values ofL/Do less than0.05, enter the chart at a value ofL/Do p 0.05.

Step 3.Move horizontally to the line for the valueof Do/t determined in Step 1. Interpolation may bemade for intermediate values ofDo/t. From this pointof intersection move vertically downward to determinethe value of factorA.

Step 4.Using the value ofA calculated in Step 3,enter the applicable material chart in Subpart 3 of

25

Section II, Part D for the material under consideration.Move vertically to an intersection with thematerial /temperature line for the design temperature(see UG-20). Interpolation may be made between linesfor intermediate temperatures.

In cases where the value ofA falls to the right ofthe end of the material /temperature line, assume anintersection with the horizontal projection of the upperend of the material /temperature line. For values ofAfalling to the left of the material /temperature line, seeStep 7.

Step 5. From the intersection obtained in Step 4,move horizontally to the right and read the value offactor B.

Step 6.Using this value ofB, calculate the valueof the maximum allowable external working pressurePa using the following formula:

Pa p4B

3(Do / t )

Step 7.For values ofA falling to the left of theapplicable material /temperature line, the value ofPa

can be calculated using the following formula:

Fig. UG-28.1 1998 SECTION VIII — DIVISION 1

FIG. UG-28.1 DIAGRAMMATIC REPRESENTATION OF LINES OF SUPPORT FOR DESIGN OF CYLINDRICALVESSELS SUBJECTED TO EXTERNAL PRESSURE

26



Pa p2AE

3(Do / t )

Step 8.Compare the calculated value ofPa obtainedin Steps 6 or 7 withP. If Pa is smaller thanP, selecta larger value fort and repeat the design procedureuntil a value of Pa is obtained that is equal to orgreater thanP. An example illustrating the use of thisprocedure is given in L-3(a).

(2) Cylinders havingDo/t values <10:Step 1.Using the same procedure as given in UG-

28(c)(1), obtain the value ofB. For values ofDo/tless than 4, the value of factorA can be calculatedusing the following formula:

A p1.1

(Do / t )2

For values ofA greater than 0.10, use a value of 0.10.Step 2.Using the value ofB obtained in Step 1,

calculate a valuePa1 using the following formula:

Pa1 p 3 2.167

(Do / t )− 0.08334 B

Step 3.Calculate a valuePa2 using the followingformula:

Pa2 p2S

Do / t 31 −1

Do / t4

where S is the lesser of two times the maximumallowable stress value in tension at design metal temper-ature, from the applicable table referenced in UG-23,or 0.9 times the yield strength of the material at designtemperature. Values of yield strength are obtained fromthe applicable external pressure chart as follows:

(a) For a given temperature curve, determinethe B value that corresponds to the right hand sidetermination point of the curve.

(b) The yield strength is twice theB valueobtained in (a) above.

Step 4.The smaller of the values ofPa1 calculatedin Step 2, orPa2 calculated in Step 3 shall be usedfor the maximum allowable external working pressurePa. ComparePa with P. If Pa is smaller thanP, selecta larger value fort and repeat the design procedureuntil a value for Pa is obtained that is equal to orgreater thanP.

(d) Spherical Shells.The minimum required thicknessof a spherical shell under external pressure, either

27

seamless or of built-up construction with butt joints,shall be determined by the following procedure:

Step 1.Assume a value fort and calculate the valueof factor A using the following formula:

A p0.125

(Ro / t)

Step 2.Using the value ofA calculated in Step 1,enter the applicable material chart in Subpart 3 ofSection II, Part D for the material under consideration.Move vertically to an intersection with the material /temperature line for the design temperature (see UG-20). Interpolation may be made between lines forintermediate temperatures.

In cases where the value atA falls to the right ofthe end of the material /temperature line, assume anintersection with the horizontal projection of the upperend of the material /temperature line. For values atAfalling to the left of the material /temperature line, seeStep 5.


Step 4.Using the value ofB obtained in Step 3,calculate the value of the maximum allowable externalworking pressurePa using the following formula:

Pa pB

(Ro / t)



Pa p0.0625E

(Ro / t )2

Step 6.ComparePa obtained in Steps 4 or 5 withP. If Pa is smaller thanP, select a larger value fortand repeat the design procedure until a value forPa

is obtained that is equal to or greater thanP. Anexample illustrating the use of this procedure is givenin L-3(b).

(e) The external design pressure or maximum allow-able external working pressure shall not be less thanthe maximum expected difference in operating pressurethat may exist between the outside and the inside ofthe vessel at any time.

(f) Vessels intended for service under external workingpressures of 15 psi (103 kPa) and less [see U-1(c)(2)(h)]may be stamped with the Code Symbol denoting compli-ance with the rules for external pressure provided



all the applicable rules of this Division are satisfied.When the Code Symbol is to be applied, the user orhis designated agent shall specify the required maximumallowable external working pressure.18 The vessel shallbe designed and stamped with the maximum allowableexternal working pressure.

(g) When there is a longitudinal lap joint in acylindrical shell or any lap joint in a spherical shellunder external pressure, the thickness of the shell shallbe determined by the rules in this paragraph, exceptthat 2P shall be used instead ofP in the calculationsfor the required thickness.

(h) Circumferential joints in cylindrical shells maybe of any type permitted by the Code and shall bedesigned for the imposed loads.

(i) Those portions of pressure chambers of vesselswhich are subject to a collapsing pressure and whichhave a shape other than that of a complete circularcylinder or formed head, and also jackets of cylindricalvessels which extend over only a portion of the circum-ference, shall be fully staybolted in accordance withthe requirements of UG-47 through UG-50 or shall beproof tested in compliance with UG-101(p).

(j) When necessary, vessels shall be provided withstiffeners or other additional means of support to preventoverstress or large distortions under the external loadingslisted in UG-22 other than pressure and temperature.

UG-29 STIFFENING RINGS FORCYLINDRICAL SHELLS UNDEREXTERNAL PRESSURE

(a) Except as exempted in (f) below, the availablemoment of inertia of a circumferential stiffening ringshall be not less than that determined by one of thefollowing two formulas:

Is p [Do2Ls(t + As / Ls)A] / 14

Is′ p[Do2Ls(t + As / Ls)A] / 10.9

Isp required moment of inertia of the stiffening ringcross section about its neutral axis parallel tothe axis of the shell, in.4

Is′p required moment of inertia of the combinedring-shell cross section about its neutral axisparallel to the axis of the shell, in.4

Ip available moment of inertia of the stiffening

18It is recommended that a suitable margin be provided whenestablishing the maximum allowable external working pressure toallow for pressure variations in service.

28

ring cross section about its neutral axis parallelto the axis of the shell, in.4

I ′p available moment of inertia of combined ring-shell cross section about its neutral axis parallelto the axis of the shell, in.4 The nominal shellthicknessts shall be used and the width of shellwhich is taken as contributing to the momentof inertia of the combined section shall not be

greater than 1.10√Dots and shall be taken aslying one-half on each side of the centroid ofthe ring. Portions of the shell plate shall not beconsidered as contributing area to more thanone stiffening ring.

CAUTIONARY NOTE: Stiffening rings may be subject tolateral buckling. This should be considered in addition to therequirements forIs and I ′s [see U-2(g)].

If the stiffeners should be so located that the maximumpermissible effective shell sections overlap on eitheror both sides of a stiffener, the effective shell sectionfor that stiffener shall be shortened by one-half of eachoverlap.

Asp cross-sectional area of the stiffening ring, sq in.Ap factor determined from the applicable chart in

Subpart 3 of Section II, Part D for the materialused in the stiffening ring, corresponding to thefactorB, below, and the design temperature forthe shell under consideration

Bp factor determined from the applicable chart inSubpart 3 of Section II, Part D for the materialused for the stiffening ring, psi [see UG-20(c)]

Lsp one-half of the distance from the center line ofthe stiffening ring to the next line of supporton one side, plus one-half of the center linedistance to the next line of support on the otherside of the stiffening ring, both measured paral-lel to the axis of the cylinder, in. A line ofsupport is:

(1) a stiffening ring that meets the require-ments of this paragraph;

(2) a circumferential connection to ajacket for a jacketed section of a cylindricalshell;

(3) a circumferential line on a head at one-third the depth of the head from the head tangentline as shown on Fig. UG-28;

(4) a cone-to-cylinder junction.

P, Do, E, t, and ts are as defined in UG-28(b).


The adequacy of the moment of inertia for a stiffeningring shall be determined by the following procedure.

Step 1.Assuming that the shell has been designedand Do, Ls, and t are known, select a member to beused for the stiffening ring and determine its cross-sectional areaAs. Then calculate factorB using thefollowing formula:

B p 3⁄4 1 PDo

t + As / Ls2

Step 2.Enter the right-hand side of the applicablematerial chart in Subpart 3 of Section II, Part D forthe material under consideration at the value ofBdetermined by Step 1. If different materials are usedfor the shell and stiffening ring, use the material chartresulting in the larger value ofA in Step 4, below.

Step 3. Move horizontally to the left to thematerial /temperature line for the design metal tempera-ture. For values ofB falling below the left end of thematerial /temperature line, see Step 5.

Step 4.Move vertically to the bottom of the chartand read the value ofA.

Step 5.For values ofB falling below the left end of thematerial /temperature line for the design temperature, thevalue ofAcan be calculated using the formulaAp 2B/E.

Step 6a. In those cases where only the stiffeningring is considered, compute the required moment ofinertia from the formula forIs given above.

Step 6b.In those cases where the combined ring-shell is considered, compute the required moment ofinertia from the formula forIs′ given above.

Step 7a. In those cases where only the stiffeningring is considered, determine the available moment ofinertia I as given in the definitions.

Step 7b.In those cases where the combined ring-shell is considered, determine the available moment ofinertia I ′ as given in the definitions.

NOTE: In those cases where the stiffening ring is not attached tothe shell or where the stiffening ring is attached but the designerchooses to consider only the ring, Step 6a and Step 7a are considered.In those cases where the stiffening ring is attached to the shell andthe combined moment of inertia is considered, Step 6b and Step 7bare considered.

Step 8.If the required moment of inertia is greater thanthe available moment of inertia for the section selected,for those cases where the stiffening ring is not attached orwhere the combined ring-shell stiffness was not consid-ered, a new section with a larger moment of inertia mustbe selected; the ring must be attached to the shell and thecombination shall be considered; or the ring-shell combi-nation which was previously not considered together shall

29

be considered together. If the required moment of inertiais greater than the available moment of inertia for thosecaseswhere thecombinedring-shellwasconsidered,anewring section with a larger moment of inertia must be se-lected. In any case, when a new section is used, all of thecalculationsshallbe repeatedusing thenewsectionproper-ties of the ring or ring-shell combination.

If the required moment of inertia is smaller than theactual moment of inertia of the ring or ring-shellcombination, whichever is used, that ring section orcombined section is satisfactory.

An example illustrating the use of this procedure isgiven in L-5.

(b) Stiffening rings shall extend completely aroundthe circumference of the cylinder except as permittedin (c) below. Any joints between the ends or sectionsof such rings, such as shown in Fig. UG-29.1(A) and(B), and any connection between adjacent portions ofa stiffening ring lying inside or outside the shell asshown in Fig. UG-29.1(C) shall be made so that therequired moment of inertia of the combined ring-shellsection is maintained.

(c) Stiffening rings placed on the inside of a vesselmay be arranged as shown in Fig. UG-29.1(E) and (F)provided that the required moment of inertia of thering in (E) or of the combined ring-shell section in(F) is maintained within the sections indicated. Wherethe gap at (A) or (E) does not exceed eight times thethickness of the shell plate, the combined moment ofinertia of the shell and stiffener may be used.

Any gap in that portion of a stiffening ring supportingthe shell, such as shown in Fig. UG-29.1(D) and (E),shall not exceed the length of arc given in Fig. UG-29.2 unless additional reinforcement is provided asshown in Fig. UG-29.1(C) or unless the followingconditions are met:

(1) only one unsupported shell arc is permittedper ring; and

(2) the length of the unsupported shell arc doesnot exceed 90 deg.; and

(3) the unsupported arcs in adjacent stiffening ringsare staggered 180 deg.; and

(4) the dimensionL defined in UG-28(b) is takenas the larger of the following: the distance betweenalternate stiffening rings, or the distance from the headtangent line to the second stiffening ring plus one-thirdof the head depth.

(d) When internal plane structures perpendicular tothe longitudinal axis of the cylinder (such as bubbletrays or baffle plates) are used in a vessel, they mayalso be considered to act as stiffening rings providedthey are designed to function as such.


FIG. UG-29.1 VARIOUS ARRANGEMENTS OF STIFFENING RINGS FOR CYLINDRICAL VESSELS SUBJECTEDTO EXTERNAL PRESSURE

30


FIG. UG-29.2 MAXIMUM ARC OF SHELL LEFT UNSUPPORTED BECAUSE OF GAP IN STIFFENING RING OFCYLINDRICAL SHELL UNDER EXTERNAL PRESSURE

(e) Any internal stays or supports used as stiffenersof the shell shall bear against the shell of the vesselthrough the medium of a substantially continuous ring.

NOTE: Attention is called to the objection to supporting vesselsthrough the medium of legs or brackets, the arrangement of whichmay cause concentrated loads to be imposed on the shell. Verticalvessels should be supported through a substantial ring secured tothe shell (see G-3). Horizontal vessels, unless supported at or closeto the ends (heads) or at stiffening rings, should be supported throughthe medium of substantial members extending over at least one-thirdof the circumference, as shown at (K) in Fig. UG-29.1.

Attention is called also to the hazard of imposing highly concen-trated loads by the improper support of one vessel on another orby the hanging or supporting of heavy weights directly on the shellof the vessel. (See Appendix G.)

(f) When closure bars or other rings are attachedto both the inner shell and outer jacket of a vessel,with pressure in the space between the jacket and inner

31

shell, this construction has adequate inherent stiffness,and therefore the rules of this paragraph do not apply.

UG-30 ATTACHMENT OF STIFFENINGRINGS

(a) Stiffening rings may be placed on the inside oroutside of a vessel, and shall be attached to the shellby welding or brazing. Brazing may be used if thevessel is not to be later stress relieved. The ring shallbe essentially in contact with the shell and meet therules in UG-29(b) and (c). Welding of stiffening ringsshall comply with the requirements of this Divisionfor the type of vessel under construction.

(b) Stiffening rings may be attached to the shell bycontinuous, intermittent, or a combination of continuous


and intermittent welds or brazes. Some acceptable meth-ods of attaching stiffening rings are illustrated in Fig.UG-30.

(c) Intermittent welding shall be placed on both sidesof the stiffener and may be either staggered or in-line.Length of individual fillet weld segments shall not beless than 2 in. (51 mm) and shall have a maximumclear spacing between toes of adjacent weld segmentsof 8t for external rings and 12t for internal rings wheret is the shell thickness at the attachment. The totallength of weld on each side of the stiffening ringshall be:

(1) not less than one-half the outside circumferenceof the vessel for rings on the outside; and

(2) not less than one-third the circumference ofthe vessel for rings on the inside.

(d) A continuous full penetration weld is permittedas shown in sketch (e) of Fig. UG-30. Continuous filletwelding or brazing on one side of the stiffener withintermittent welding or brazing on the other side ispermitted for sketches (a), (b), (c), and (d) of Fig.UG-30 when the thicknesstw of the outstanding stiffen-ing element [sketches (a) and (c)] or widthw of thestiffening element mating to the shell [sketches (b) and(d)] is not more than 1 in. (25 mm). The weld segmentsshall be not less than 2 in. (51 mm) long and shallhave a maximum clear spacing between toes of adjacentweld segments of 24t.

(e) Strength of Attachment Welds.Stiffening ringattachment welds shall be sized to resist the full radialpressure load from the shell between stiffeners, andshear loads acting radially across the stiffener causedby external design loads carried by the stiffener (ifany) and a computed radial shear equal to 2% of thestiffening ring’s compressive load. See Example L-5of Appendix L.

(1) The radial pressure load from shell, lb /in., isequal toPLs.

(2) The radial shear load, lb, is equal to 0.01PLsDO.(3) P, Ls, and DO are defined in UG-29.

(f) Minimum Size of Attachment Welds.The filletweld leg size shall be not less than the smallest ofthe following:

(1) 1⁄4 in. (6 mm);(2) vessel thickness at the weld location;(3) stiffener thickness at weld location.

UG-31 TUBES, AND PIPE WHEN USEDAS TUBES OR SHELLS

(a) Internal Pressure.The required wall thicknessfor tubes and pipe under internal pressure shall be

32

determined in accordance with the rules for shells inUG-27.

(b) External Pressure.The required wall thicknessfor tubes and pipe under external pressure shall bedetermined in accordance with the rules in UG-28.

(c) The thickness as determined under (a) or (b)above shall be increased when necessary to meet thefollowing requirements.

(1) Additional wall thickness should be providedwhen corrosion, erosion, or wear due to cleaning opera-tions is expected.

(2) Where tube ends are threaded, additional wallthickness is to be provided in the amount of 0.8/n in.(where n equals the number of threads per inch).

NOTE: The requirements for rolling, expanding, or otherwise seatingtubes in tube plates may require additional wall thickness and carefulchoice of materials because of possible relaxation due to differentialexpansion stresses.

UG-32 FORMED HEADS, AND SECTIONS,PRESSURE ON CONCAVE SIDE

(a) The required thickness at the thinnest point afterforming19 of ellipsoidal, torispherical, hemispherical,conical, and toriconical heads under pressure on theconcave side (plus heads) shall be computed by theappropriate formulas in this paragraph20 (see UG-16).In addition, provision shall be made for any of theother loadings given in UG-22.

(b) The thickness of an unstayed ellipsoidal or tori-spherical head shall in no case be less than the requiredthickness of a seamless hemispherical head divided bythe efficiency of the head-to-shell joint.

(c) The symbols defined below are used in theformulas of this paragraph:

tp minimum required thickness of head after form-ing, in.

Pp internal design pressure (see UG-21), psiDp inside diameter of the head skirt; or inside length

of the major axis of an ellipsoidal head; or insidediameter of a conical head at the point under

19In order to ensure that a finished head is not less than the minimumthickness required, it is customary to use a thicker plate to takecare of possible thinning during the process of forming. The neckof an opening in a head with an integrally flanged opening will thinout due to the fluing operation. This is permissible provided theneck thickness is not less than the thickness required for a cylindricalshell subject to internal and/or external pressure, as applicable, andhaving an inside diameter equal to the maximum diameter of theopening [see UG-38(a) and UG-46(j)].20Formulas in terms of outside dimensions and for heads of otherproportions are given in 1-4 together with illustrative examples.

98

PART UG — GENERAL REQUIREMENTS Fig. UG-30

FIG. UG-30 SOME ACCEPTABLE METHODS OF ATTACHING STIFFENING RINGS

33


consideration, measured perpendicular to thelongitudinal axis, in.

Dip inside diameter of the conical portion of a to-riconical head at its point of tangency to theknuckle, measured perpendicular to the axis ofthe cone, in.

p D − 2r (1 − cosa)rp inside knuckle radius, in.Sp maximum allowable stress value in tension as

given in the tables referenced in UG-23, psi,except as limited in UG-24 and (e) below.

Ep lowest efficiency of any joint in the head; forhemispherical heads this includes head-to-shelljoint; for welded vessels, use the efficiencyspecified in UW-12

Lp inside spherical or crown radius, in.ap one-half of the included (apex) angle of the cone

at the center line of the head (see Fig. 1-4)(d) Ellipsoidal Heads.The required thickness of a

dished head of semiellipsoidal form, in which half theminor axis (inside depth of the head minus the skirt)equals one-fourth of the inside diameter of the headskirt, shall be determined by

t pPD

2SE− 0.2Por P p

2SEt

D + 0.2t(1)

An acceptable approximation of a 2:1 ellipsoidal headis one with a knuckle radius of 0.17D and a sphericalradius of 0.90D.

(e) Torispherical Heads.The required thickness ofa torispherical head for the case in which the knuckleradius is 6% of the inside crown radius and the insidecrown radius equals the outside diameter of the skirt,[see (j) below], shall be determined by

t p0.885PL

SE− 0.1Por P p

SEt

0.885L + 0.1t(2)

Torispherical heads made of materials having aspeci-fied minimum tensile strength exceeding 80,000 psishall be designed using a value ofS equal to 20,000psi at room temperature and reduced in proportion tothe reduction in maximum allowable stress values attemperature for the material (see UG-23).

(f) Hemispherical Heads.When the thickness of ahemispherical head does not exceed 0.356L, or P doesnot exceed 0.665SE,the following formulas shall apply:

34

t pPL

2SE− 0.2Por P p

2SEt

L + 0.2t(3)

(g) Conical Heads and Sections (Without TransitionKnuckle). The required thickness of conical heads orconical shell sections that have a half apex-angleanot greater than 30 deg. shall be determined by

t pPD

2 cosa(SE− 0.6P)or P p

2SEtcosa

D + 1.2t cosa(4)

A reinforcing ringshall be provided when required bythe rule in 1-5(d) and (e).

Conical heads or sections having a half apex-anglea greater than 30 deg. without a transition knuckleshall comply with Formula (4) and 1-5(g).

(h) Toriconical Heads and Sections.The requiredthickness of the conical portion of a toriconical heador section, in which the knuckle radius is neither lessthan 6% of the outside diameter of the head skirt norless than three times the knuckle thickness, shall bedetermined by Formula (4) in (g) above, usingDi inplace of D.

The required thickness of the knuckle shall be deter-mined by Formula (3) of 1-4(d) in which

L pDi

2 cosa

Toriconical heads or sections may be used when theanglea ≤ 30 deg. and are mandatory for conical headdesigns when the anglea exceeds 30 deg., unless thedesign complies with 1-5(g).

(i) When an ellipsoidal, torispherical, hemispherical,conical, or toriconical head is of a lesser thicknessthan required by the rules of this paragraph, it shallbe stayed as a flat surface according to the rules ofUG-47 for braced and stayed flat plates.

(j) The inside crown radius to which an unstayedhead is dished shall be not greater than the outsidediameter of the skirt of the head. The inside knuckleradius of a torispherical head shall be not less than6% of the outside diameter of the skirt of the headbut in no case less than 3 times the head thickness.

(k) A dished head with a reversed skirt may be usedin a pressure vessel provided the maximum allowableworking pressure for the head is established in accor-dance with the requirements of UG-101.

(l) All formed heads, thicker than the shell andconcave to pressure, intended for butt welded attach-ment, shall have a skirt length sufficient to meet therequirements of Fig. UW-13.1, when a tapered transition


is required. All formed heads concave to pressure andintended for butt welded attachment need not have anintegral skirt when the thickness of the head is equalto or less than the thickness of the shell. When a skirtis provided, its thickness shall be at least that requiredfor a seamless shell of the same inside diameter.

(m) Heads concave to pressure, intended for attach-ment by brazing, shall have a skirt length sufficientto meet the requirements for circumferential joints inPart UB.

(n) Any taper at a welded joint within a formedhead shall be in accordance with UW-9. The taper ata circumferential welded joint connecting a formedhead to a main shell shall meet the requirements ofUW-13 for the respective type of joint shown therein.

(o) If a torispherical, ellipsoidal, or hemisphericalhead is formed with a flattened spot or surface, thediameter of the flat spot shall not exceed that permittedfor flat heads as given by Formula (1) in UG-34, usingC p 0.25.

(p) Openings in formed heads under internal pressureshall comply with the requirements of UG-36 throughUG-46.

(q) A stayed jacket that completely covers a formedinner head or any of the types included in this paragraphshall also meet the requirements of UG-47(c).

UG-33 FORMED HEADS, PRESSURE ONCONVEX SIDE

(a) General.The required thickness at the thinnestpoint after forming [see footnote 20, UG-32(a)] ofellipsoidal, torispherical, hemispherical, toriconical, andconical heads and conical segments under pressure onthe convex side (minus heads) shall be computed bythe appropriate formulas given in this paragraph (seeUG-16). In addition, provisions shall be made for anyother loading given in UG-22. The required thicknessfor heads due to pressure on the convex side shall bedetermined as follows.

(1) For ellipsoidal and torispherical heads, therequired thickness shall be the greater of the following:

(a) the thickness computed by the proceduregiven in UG-32 for heads with pressure on the concaveside (plus heads) using a design pressure 1.67 timesthe design pressure on the convex side, assuming ajoint efficiency E p 1.00 for all cases; or

(b) the thickness as computed by the appropriateprocedure given in (d) or (e) below.

In determining the maximum allowable working pres-sure on the convex side of ellipsoidal or torispherical

35

TABLE UG-33.1VALUES OF SPHERICAL RADIUS FACTOR Ko FOR

ELLIPSOIDAL HEAD WITH PRESSURE ONCONVEX SIDE

Interpolation Permitted for Intermediate Values

Do/ 2ho . . . 3.0 2.8 2.6 2.4 2.2Ko . . . 1.36 1.27 1.18 1.08 0.99

Do/ 2ho 2.0 1.8 1.6 1.4 1.2 1.0Ko 0.90 0.81 0.73 0.65 0.57 0.50

heads, reverse the procedures in (a)(1)(a) and (a)(1)(b)above, and use the smaller of the pressures obtained.

(2) For hemispherical heads, the required thicknessshall be determined by the rules given in (c) below.

(3) For conical and toriconical heads and conicalsections, the required thickness shall be determined bythe rules given in (f) below.

(b) Nomenclature.The nomenclature defined belowis used in this paragraph. Figure 1-4 shows principaldimensions of typical heads.

A, B, E, and P are as defined in UG-28(b)Dopoutside diameter of the head skirt, in.

Do / 2hopratio of the major to the minor axis ofellipsoidal heads, which equals the outsidediameter of the head skirt divided by twicethe outside height of the head (see TableUG-33.1)

tepeffective thickness of conical section, in.pt cos a

Lcpaxial length of conical section, excludingthe knuckle, of a toriconical head or section(see Fig. UG-33.1), in.

Lepequivalent length of conical section, in.p(L /2)(1 + Ds /DL)

Lpaxial length of cone or conical section (seeFig. UG-33.1), in., [for a toriconical heador section, see UG-33(g)].

Dspoutside diameter at small end of conicalsection under consideration, in.

DLpoutside diameter at large end of conicalsection under consideration, in.

hopone-half of the length of the outside minoraxis of the ellipsoidal head, or the outsideheight of the ellipsoidal head measured fromthe tangent line (head-bend line), in.

Kopfactor depending on the ellipsoidal headproportionsDo / 2ho (see Table UG-33.1)

Ropfor hemispherical heads, the outside ra-dius, in.


FIG. UG-33.1 LENGTH L OF SOME TYPICAL CONICAL SECTIONS FOR EXTERNAL PRESSURE

Ropfor ellipsoidal heads, the equivalent outsidespherical radius taken asKoDo, in.

Ropfor torispherical heads, the outside radiusof the crown portion of the head, in.

tpminimum required thickness of head afterforming, in.

apone-half the apex angle in conical headsand sections, deg.

(c) Hemispherical Heads.The required thickness ofa hemispherical head having pressure on the convexside shall be determined in the same manner as outlinedin UG-28(d) for determining the thickness for a sphericalshell. An example illustrating the use of this procedureis given in L-6.3.

36

(d) Ellipsoidal Heads.The required thickness of anellipsoidal head having pressure on the convex side,either seamless or of built-up construction with buttjoints, shall not be less than that determined by thefollowing procedure.

Step 1.Assume a value fort and calculate the valueof factor A using the following formula:

A p0.125

Ro / t

Step 2.Using the value ofA calculated in Step 1,follow the same procedure as that given for spherical


shells in UG-28(d), Steps 2 through 6. An exampleillustrating the use of this procedure is given in L-6.1.

(e) Torispherical Heads.The required thickness ofa torispherical head having pressure on the convexside, either seamless or of built-up construction withbutt joints, shall not be less than that determined bythe same design procedure as is used for ellipsoidalheads given in (d) above, using the appropriate valuefor Ro. An example illustrating the use of this procedureis given in L-6.2.

(f) Conical Heads and Sections.The required thick-ness of a conical head or section under pressure onthe convex side, either seamless or of built-up construc-tion with butt joints, shall be determined in accordancewith the following subparagraphs.

(1) When a is equal to or less than 60 deg.:(a) cones havingDL /te values ≥ 10:

Step 1. Assume a value forte and determine theratios Le/DL and DL /te.

Step 2. Enter Fig. G of Subpart 3 of Section II,Part D at a value ofL/Do equivalent to the value ofLe/DL determined in Step 1. For values ofLe/DL greaterthan 50, enter the chart at a value ofLe/DL p 50.

Step 3.Move horizontally to the line for the valueof Do/t equivalent to the value ofDL /te determined inStep 1. Interpolation may be made for intermediatevalues ofDL /te. From this point of intersection movevertically downwards to determine the value of factorA.

Step 4.Using the value ofA calculated in Step 3,enter the applicable material chart in Subpart 3 ofSection II, Part D for the material under consideration.Move vertically to an intersection with the material /temperature line for the design temperature (see UG-20). Interpolation may be made between lines forintermediate temperatures.

In cases where the value ofA falls to the right of the endof the material /temperature line, assume an intersectionwith the horizontal projection of the upper end of thematerial /temperature line. For values ofA falling to theleft of the material /temperature line, see Step 7.


Step 6.Using this value ofB, calculate the valueof the maximum allowable external working pressurePa using the following formula:

Pa p4B

3(DL / te)



37

Pa p2AE

3(DL / te)

Step 8.Compare the calculated value ofPa obtainedin Steps 6 or 7 withP. If Pa is smaller thanP, selecta larger value fort and repeat the design procedureuntil a value of Pa is obtained that is equal to orgreater thanP. An example illustrating the use of thisprocedure is given in L-6.4.

Step 9.Provide adequate reinforcement of the cone-to-cylinder juncture according to 1-8.

(b) cones havingDL /te values <10:Step 1.Using the same procedure as given in (f)(1)(a)

above, obtain the value ofB. For values ofDL /te lessthan 4, the value of factorA can be calculated usingthe following formula:

A p1.1

(DL / te)2

For values ofA greater than 0.10, use a value of 0.10.Step 2.Using the value ofB obtained in Step 1,

calculate a valuePa1 using the following formula:

Pa1 p 3 2.167

(DL / te)− 0.08334 B

Step 3.Calculate a valuePa2 using the followingformula:

Pa2 p2S

DL / te31 −

1

DL / te4

whereSp the lesser of two times the maximum allowable

stress value in tension at design metal tempera-ture, from the applicable Table referenced byUG-23, or 0.9 times the yield strength of thematerial at design temperature, psi

Values of yield strength are obtained from the applicableexternal pressure chart as follows.

(a) For a given temperature curve, determinethe B value that corresponds to the right hand sidetermination point of the curve.

(b) The yield strength is twice theB valueobtained in (a) above.

Step 4.The smaller of the values ofPa1 calculatedin Step 2, orPa2 calculated in Step 3 shall be usedfor the maximum allowable external working pressurePa. ComparePa with P. If Pa is smaller thanP, selecta larger value fort and repeat the design procedure


until a value for Pa is obtained that is equal to orgreater thanP.

Step 5.Provide adequate reinforcement of the cone-to-cylinder juncture according to 1-8. When the cone-to-cylinder juncture is a line of support, the momentof inertia at the cone-to-cylinder shall be provided inaccordance with 1-8.

(2) When a of the cone is greater than 60 deg.,the thickness of the cone shall be the same as therequired thickness for a flat head under external pressure,the diameter of which equals the largest diameter ofthe cone (see UG-34).

(3) The thickness of an eccentric cone shall betaken as the greater of the two thicknesses obtainedusing both the smallest and largesta in the calculations.

(g) The required thickness of a toriconical headhaving pressure on the convex side, either seamless orof built-up construction with butt joints within the head,shall not be less than that determined from (f) abovewith the exception thatLe shall be determined asfollows.

(1) For sketch (c) in Fig. UG-33.1,

Le p r1 sin a +Lc

2 1DL + Ds

DLs2

(2) For sketch (d) in Fig. UG-33.1,

Le p r2Dss

DL

sin a +Lc

2 1DL + Ds

DL2

(3) For sketch (e) in Fig. UG-33.1,

Le p 1r1 + r2Dss

DL s2 sin a +

Lc

2

(DL + Ds)

DLs

When the knuckle-to-cylinder juncture is a line ofsupport, the moment of inertia at the knuckle-to-cylinderjuncture shall be provided in accordance with 1-8.

(h) When lap joints are used in formed head construc-tion or for longitudinal joints in a conical head underexternal pressure, the thickness shall be determined bythe rules in this paragraph, except that 2P shall beused instead ofP in the calculations for the requiredthickness.

(i) The required length of skirt on heads convex topressure shall comply with the provisions of UG-32(l)and (m) for heads concave to pressure.

(j) Openings in heads convex to pressure shall com-ply with the requirements of UG-36 through UG-46.

38

UG-34 UNSTAYED FLAT HEADS ANDCOVERS

(a) The minimum thickness of unstayed flat heads,cover plates and blind flanges shall conform to therequirements given in this paragraph. These require-ments apply to both circular and noncircular21 headsand covers. Some acceptable types of flat heads andcovers are shown in Fig. UG-34. In this figure, thedimensions of the component parts and the dimensionsof the welds are exclusive of extra metal required forcorrosion allowance.

(b) The symbols used in this paragraph and in Fig.UG-34 are defined as follows:

Cp a factor depending upon the method of attach-ment of head, shell dimensions, and other itemsas listed in (d) below, dimensionless. The fac-tors for welded covers also include a factor of0.667 which effectively increases the allowablestress for such constructions to 1.5S.

Dp long span of noncircular heads or covers mea-sured perpendicular to short span, in.

dp diameter, or short span, measured as indicatedin Fig. UG-34, in.

Ep joint efficiency, from Table UW-12, of any Cat-egory A weld as defined in UW-3(a)(1)

hGp gasket moment arm, equal to the radial distancefrom the center line of the bolts to the line ofthe gasket reaction, as shown in Table 2-5.2, in.

Lp perimeter of noncircular bolted head measuredalong the centers of the bolt holes, in.

mp the ratiotr /ts, dimensionlessPp internal design pressure (see UG-21), psirp inside corner radius on a head formed by flang-

ing or forging, in.Sp maximum allowable stress value in tension, psi,

from applicable table of stress values referencedby UG-23

tp minimum required thickness of flat head orcover, in.

tfp nominal thickness of the flange on a forgedhead, at the large end, as indicated in Fig. UG-34 sketch (b), in.

thp nominal thickness of flat head or cover, in.trp required thickness of seamless shell, for pres-

sure, in.tsp nominal thickness of shell, in.twp thickness through the weld joining the edge of

a head to the inside of a vessel, as indicated inFig. UG-34 sketch (g), in.

21Special consideration shall be given to the design of shells, nozzlenecks or flanges to which noncircular heads or covers are attached[see U-2(c)].


FIG. UG-34 SOME ACCEPTABLE TYPES OF UNSTAYED FLAT HEADS AND COVERSThe Above Illustrations Are Diagrammatic Only. Other Designs That Meet

the Requirements of UG-34 Are Acceptable.

39


t1p throat dimension of the closure weld, as indi-cated in Fig. UG-34 sketch (r), in.

Wp total bolt load, lb, given for circular heads forFormulas (3) and (4), 2-5(e)

Yp length of flange of flanged heads, measuredfrom the tangent line of knuckle, as indicatedin Fig. UG-34 sketches (a) and (c), in.

Zp a factor of noncircular heads and covers thatdepends on the ratio of short span to long span,as given in (c) below, dimensionless

(c) The thickness of flat unstayed heads, covers, andblind flanges shall conform to one of the followingthree requirements.22

(1) Circular blind flanges conforming to any ofthe flange standards listed in Table U-3 and furtherlimited in UG-44 shall be acceptable for the diametersand pressure–temperature ratings in the respective stan-dard when the blind flange is of the types shown inFig. UG-34 sketches (j) and (k).

(2) The minimum required thickness of flat un-stayed circular heads, covers and blind flanges shallbe calculated by the following formula:

t p d√CP / SE (1)

except when the head, cover, or blind flange is attachedby bolts causing an edge moment [sketches (j) and(k)] in which case the thickness shall be calculated by

t p d√CP / SE+ 1.9WhG / SEd3 (2)

When using Formula (2), the thicknesst shall becalculated for both operating conditions and gasketseating, and the greater of the two values shall beused. For operating conditions, the value ofP shall bethe design pressure, and the values ofS at the designtemperature andW from Formula (3) of 2-5(e) shallbe used. For gasket seating,P equals zero, and thevalues of S at atmospheric temperature andW fromFormula (4) of 2-5(e) shall be used.

(3) Flat unstayed heads, covers, or blind flangesmay be square, rectangular, elliptical, obround, segmen-tal, or otherwise noncircular. Their required thicknessshall be calculated by the following formula:

t p d√ZCP / SE (3)

22The formulas provide safe construction as far as stress is concerned.Greater thicknesses may be necessary if deflection would causeleakage at threaded or gasketed joints.

40

where

Z p 3.4 −2.4d

D(4)

with the limitation thatZ need not be greater than twoand one-half (2.5).

Formula (3) does not apply to noncircular heads,covers, or blind flanges attached by bolts causing abolt edge moment [sketches (j) and (k)]. For noncircularheads of this type, the required thickness shall becalculated by the following formula:

t p d√ZCP / SE+ 6WhG / SELd2 (5)

When using Formula (5), the thicknesst shall becalculated in the same way as specified above forFormula (2).

(d) For the types of construction shown in Fig. UG-34, the minimum values ofC to be used in Formulas(1), (2), (3), and (5) are:

Sketch (a). Cp 0.17 for flanged circular and noncir-cular heads forged integral with or butt welded to thevessel with an inside corner radius not less than threetimes the required head thickness, with no specialrequirement with regard to length of flange, and wherethe welding meets all the requirements for circumferen-tial joints given in Part UW.

C p 0.10 for circular heads, when the flange lengthfor heads of the above design is not less than

Y p 11.1 − 0.8ts2

th22 √dth (6)

C p 0.10 for circular heads, when the flange lengthY is less than the requirements in Formula (6) but theshell thickness is not less than

ts p 1.12th !1.1 − Y/√dth (7)

for a length of at least 2√dts.WhenC p 0.10 is used, the taper shall be at least 1:3.Sketch (b-1). Cp 0.17 for forged circular and

noncircular heads integral with or butt welded to thevessel, where the flange thickness is not less than twotimes the shell thickness, the corner radius on the insideis not less than three times the flange thickness, andthe welding meets all the requirements for circumferen-tial joints given in Part UW.

Sketch (b-2). Cp 0.33m but not less than 0.20 forforged circular and noncircular heads integral with or


butt welded to the vessel, where the flange thicknessis not less than the shell thickness, the corner radiuson the inside is not less than the following:

rmin p 0.375 in. forts ≤ 11⁄2 in.

rmin p 0.25ts for ts > 11⁄2 in. but need not begreater than3⁄4 in.

The welding shall meet all the requirements for circum-ferential joints given in Part UW.

Sketch (c). Cp 0.13 for circular heads lap weldedor brazed to the shell with corner radius not less than3t and Y not less than required by Formula (6) andthe requirements of UW-13 are met.

C p 0.20 for circular and noncircular lap weldedor brazed construction as above, but with no specialrequirement with regard toY.

C p 0.30 for circular flanged plates screwed overthe end of the vessel, with inside corner radius notless than 3t, in which the design of the threadedjoint against failure by shear, tension, or compression,resulting from the end force due to pressure, is basedon a factor of safety of at least four, and the threadedparts are at least as strong as the threads for standardpiping of the same diameter. Seal welding may beused, if desired.

Sketch (d). Cp 0.13 for integral flat circular headswhen the dimensiond does not exceed 24 in. (610 mm),the ratio of thickness of the head to the dimensiondis not less than 0.05 or greater than 0.25, the headthicknessth is not less than the shell thicknessts, theinside corner radius is not less than 0.25t, and theconstruction is obtained by special techniques of upset-ting and spinning the end of the shell, such as employedin closing header ends.

Sketches (e), (f), and (g). Cp 0.33m but not lessthan 0.20 for circular plates, welded to the inside ofa vessel, and otherwise meeting the requirements forthe respective types of welded vessels. If a value ofm less than 1 is used in calculatingt, the shell thicknessts shall be maintained along a distance inwardly from

the inside face of the head equal to at least 2√dts.The throat thickness of the fillet welds in sketches (e)and (f) shall be at least 0.7ts. The size of the weldtwin sketch (g) shall be not less than 2 times the requiredthickness of a seamless shell nor less than 1.25 timesthe nominal shell thickness but need not be greaterthan the head thickness; the weld shall be depositedin a welding groove with the root of the weld at theinner face of the head as shown in the sketch.

41

C p 0.33 for noncircular plates, welded to the insideof a vessel and otherwise meeting the requirements forthe respective types of welded vessels. The throatthickness of the fillet welds in sketches (e) and (f)shall be at least 0.7ts. The size of the weldtw in sketch(g) shall be not less than 2 times the required thicknessof a seamless shell nor less than 1.25 times the nominalshell thickness but need not be greater than the headthickness; the weld shall be deposited in a weldinggroove with the root of the weld at the inner face ofthe head as shown in the sketch.

Sketch (h). Cp 0.33 for circular plates welded tothe end of the shell whents is at least 1.25tr and theweld details conform to the requirements of UW-13(e)and Fig. UW-13.2 sketches (a) to (g) inclusive. Seealso UG-93(d)(3).

Sketch (i). Cp 0.33m but not less than 0.20 forcircular plates if an inside fillet weld with minimumthroat thickness of 0.7ts is used and the details of theoutside weld conform to the requirements of UW-13(e)and Fig. UW-13.2 sketches (a) to (g) inclusive, inwhich the inside weld can be considered to contributean amount equal tots to the sum of the dimensionsa and b. See also UG-93(d)(3).

Sketches (j) and (k). Cp 0.3 for circular andnoncircular heads and covers bolted to the vessel asindicated in the figures. Note that Formula (2) or (5)shall be used because of the extra moment applied tothe cover by the bolting.

When the cover plate is grooved for a peripheralgasket, as shown in sketch (k), the net cover platethickness under the groove or between the groove andthe outer edge of the cover plate shall be not less than

d√1.9WhG / Sd3

for circular heads and covers, nor less than

d√6WhG / SLd2

for noncircular heads and covers.Sketches (m), (n), and (o). Cp 0.3 for a circular

plate inserted into the end of a vessel and held inplace by a positive mechanical locking arrangement,and when all possible means of failure (either by shear,tension, compression, or radial deformation, includingflaring, resulting from pressure and differential thermalexpansion) are resisted with a factor of safety of atleast four. Seal welding may be used, if desired.

Sketch (p). Cp 0.25 for circular and noncircularcovers bolted with a full-face gasket, to shells, flangesor side plates.

98

UG-34 1998 SECTION VIII — DIVISION 1 UG-35.2

Sketch (q). Cp 0.75 for circular plates screwedinto the end of a vessel having an inside diameterdnot exceeding 12 in. (305 mm); or for heads havingan integral flange screwed over the end of a vesselhaving an inside diameterd not exceeding 12 in.(305 mm); and when the design of the threaded joint,against failure by shear, tension, compression, or radialdeformation, including flaring, resulting from pressureand differential thermal expansion, is based on a factorof safety of at least four. If a tapered pipe thread isused, the requirements of Table UG-43 shall also bemet. Seal welding may be used, if desired.

Sketch (r). Cp 0.33 for circular plates having adimension d not exceeding 18 in. inserted into thevessel as shown and otherwise meeting the requirementsfor the respective types of welded vessels. The end ofthe vessel shall be crimped over at least 30 deg., butnot more than 45 deg. The crimping may be done coldonly when this operation will not injure the metal. Thethroat of the weld shall be not less than the thicknessof the flat head or shell, whichever is greater.

Sketch (s). Cp 0.33 for circular beveled plateshaving a diameterd not exceeding 18 in., inserted intoa vessel, the end of which is crimped over at least 30deg., but not more than 45 deg., and when the under-cutting for seating leaves at least 80% of the shellthickness. The beveling shall be not less than 75% ofthe head thickness. The crimping shall be done whenthe entire circumference of the cylinder is uniformlyheated to the proper forging temperature for the materialused. For this construction, the ratiots/d shall be notless than the ratioP/Snor less than 0.05. The maximumallowable pressure for this construction shall not exceedP p S/5d.

This construction is not permissible if machined fromrolled plate.

UG-35 OTHER TYPES OF CLOSURES

UG-35.1 Spherically Dished Covers

Requirements for design of circular spherically dishedheads with bolting flanges are given in 1-6.

UG-35.2 Quick-Actuating (Quick-Opening)Closures

UG-35.2(a) DefinitionsUG-35.2(a)(1) Quick-actuating or quick-opening

closures are those that permit substantially faster accessto the contents space of a pressure vessel than wouldbe expected with a standard bolted flange connection(bolting through one or both flanges). Closures with

42

swing bolts are not considered quick-actuating (quick-opening).

UG-35.2(a)(2) Holding elements are structuralmembers of the closure used to attach or hold thecover to the vessel.

UG-35.2(a)(3)Locking components are structuralitems that are used to prevent opening of the closurewhile pressure is applied. Locking components mayalso be used as holding elements.

UG-35.2(a)(4)The locking mechanism or lockingdevice consists of a combination of locking components.

UG-35.2(b) General Design RequirementsUG-35.2(b)(1) Quick-actuating closures shall be

designed, such that the failure of a single lockingcomponent while the vessel is operating, will not:

(a) release the cover;(b) result in the failure of any other locking

component or holding element; and(c) increase the stress in any other locking

component or holding element by more than 50% abovethe allowable stress of the component.

UG-35.2(b)(2) Quick-actuating closures shall bedesigned and installed such that it may be determinedby visual external observation that the holding elementsare in good condition.

UG-35.2(b)(3)The closures shall also be designedso that all locking components can be verified to befully engaged by visual observation or other meansprior to the application of pressure to the vessel.

UG-35.2(b)(4)When installed, all vessels havingquick-actuating closures shall be provided with a pres-sure indicating device visible from the operating area.

UG-35(c) Specific Design RequirementsUG-35(c)(1)Quick-actuating closures that are held

in position by positive locking devices and that arefully released by partial rotation or limited movementof the closure itself or the locking mechanism and anyclosure that is other than manually operated shall be sodesigned that when the vessel is installed the followingconditions are met:

(a) The closure and its holding elements arefully engaged in their intended operating position beforepressure can be built up in the vessel.

(b) Pressure tending to force the closure clearof the vessel shall be released before the closure canbe fully opened for access.

(c) In the event that compliance with (a) and(b) above is not inherent in the design of the closureand its holding elements, provisions shall be made sothat devices to accomplish this can be added when thevessel is installed.

UG-35(c)(2) It is recognized that it is impracticalto write requirements to cover the multiplicity of devices


98

UG-35.2 PART UG — GENERAL REQUIREMENTS UG-36

used for quick access, or to prevent negligent operationor the circumventing of safety devices. Any device ordevices which will provide the safeguards broadlydescribed in (1)(a), (1)(b), and (1)(c) above will meetthe intent of this Division.

UG-35(d) Alternative Designs for Manually OperatedClosures

UG-35(d)(1)Quick-actuating closures that are heldin position by a locking mechanism designed for manualoperation shall be so designed that there will be leakageof the contents of the vessel prior to disengagementof the locking components and release of the closure.

UG-35(d)(2)Manually operated closures need notsatisfy (c)(1)(a), (c)(1)(b), or (c)(1)(c) above, but suchclosures shall be equipped with an audible or visiblewarning device that will warn the operator if pressureis applied to the vessel before the holding elementsand locking components are fully engaged in theirintended position or if an attempt is made to disengagethe locking mechanism before the pressure within thevessel is released.

OPENINGS ANDREINFORCEMENTS 23

(Typical examples of the application of these rulesare given in Appendix L.)

UG-36 OPENINGS IN PRESSURE VESSELS

(a) Shape of Opening24

(1) Openings in cylindrical or conical portions ofvessels, or in formed heads, shall preferably be circular,elliptical, or obround.25 When the long dimension ofan elliptical or obround opening exceeds twice theshort dimensions, the reinforcement across the shortdimensions shall be increased as necessary to provideagainst excessive distortion due to twisting moment.

(2) Openings may be of other shapes than thosegiven in (1) above, and all corners shall be provided

23The rules governing openings as given in this Division are basedA99on the stress intensification created by the existence of a hole in anotherwise symmetrical section. External loadings such as those dueto the thermal expansion or unsupported weight of connecting pipinghave not been evaluated. These factors should be given attention inunusual designs or under conditions of cyclic loading.24The opening made by a pipe or a circular nozzle, the axis ofwhich is not perpendicular to the vessel wall or head, may beconsidered an elliptical opening for design purposes.25An obround opening is one which is formed by two parallel sidesand semicircular ends.

43

with a suitable radius. When the openings are of suchproportions that their strength cannot be computed withassurance of accuracy, or when doubt exists as to thesafety of a vessel with such openings, the part of thevessel affected shall be subjected to a proof hydrostatictest as prescribed in UG-101.

(b) Size of Openings(1) Properly reinforced openings in cylindrical

shells are not limited as to size except with the followingprovisions for design. The rules in UG-36 through UG-43 apply to openings not exceeding the following: forvessels 60 in. (1520 mm) inside diameter and less,one-half the vessel diameter, but not to exceed 20 in.(508 mm); for vessels over 60 in. (1520 mm) insidediameter, one-third the vessel diameter, but not toexceed 40 in. (1000 mm). For openings exceeding theselimits, supplemental rules of 1-7 shall be satisfied inaddition to UG-36 through UG-43.

(2) Properly reinforced openings in formed headsand spherical shells are not limited in size. For anopening in an end closure, which is larger than one-half the inside diameter of the shell, one of the followingalternatives to reinforcement may also be used:

(a) a conical section as shown in Fig. UG-36sketch (a);

(b) a cone with a knuckle radius at the largeend as shown in Fig. UG-36 sketch (b);

(c) a reverse curve section as shown in Fig.UG-36 sketches (c) and (d); or

(d) using a flare radius at the small end asshown in Fig. UG-33.1 sketch (d).

The design shall comply with all the requirementsof the rules for reducer sections [see (e) below] insofaras these rules are applicable.

(c) Strength and Design of Finished Openings(1) All references to dimensions in this and suc-

ceeding paragraphs apply to the finished constructionafter deduction has been made for material added ascorrosion allowance. For design purposes, no metaladded as corrosion allowance may be considered asreinforcement. The finished opening diameter is thediameterd as defined in UG-37 and in Fig. UG-40.

(2)(a) Openings in cylindrical or conical shells, orformed heads shall be reinforced to satisfy the require-ments in UG-37 except as given in (3) below.

(b) Openings in flat heads shall be reinforcedas required by UG-39.

(3) Openings in vessels not subject to rapid fluctu-ations in pressure do not require reinforcement otherthan that inherent in the construction under the followingconditions:



FIG. UG-36 LARGE HEAD OPENINGS — REVERSE-CURVE AND CONICAL SHELL-REDUCER SECTIONS

(a) welded or brazed connections attached inaccordance with the applicable rules and with a finishedopening not larger than:

31⁄2 in. (89 mm) diameter — in vessel shells orheads3⁄8 in. (10 mm) or less in thickness;

23⁄8 in. (60 mm) diameter — in vessel shells orheads over3⁄8 in. (10 mm) in thickness;

(b) threaded, studded, or expanded connectionsin which the hole cut in the shell or head is not greaterthan 23⁄8 in. (60 mm) diameter;

(c) no two isolated unreinforced openings, inaccordance with (a) or (b) above, shall have theircenters closer to each other than the sum of theirdiameters;

(d) no two unreinforced openings, in a clusterof three or more unreinforced openings in accordance

44

with (a) or (b) above, shall have their centers closerto each other than the following: for cylindrical orconical shells,

(1 + 1.5 cosu)(d1 + d2);

for doubly curved shells and formed or flat heads,

2.5(d1 + d2)

whereu p the angle between the line connecting the center

of the openings and the longitudinal axis ofthe shell

d1,d2 p the finished diameters of the two adjacentopenings



(d) Openings Through Welded Joints.Additional pro-visions governing openings through welded joints aregiven in UW-14.

(e) Reducer Sections Under Internal Pressure(1) The formulas and rules of this paragraph

apply to concentric reducer sections wherein all thelongitudinal loads are transmitted wholly throughthe shell of the reducer. Where loads are trans-mitted in part or as a whole by other elements, e.g.,inner shells, stays, or tubes, the rules of this paragraphdo not apply.

(2) The thickness of each element of a reducer,as defined in (4) below, under internal pressure shallnot be less than that computed by the applicable formula.In addition, provisions shall be made for any of theother loadings listed in UG-22, where such loadingsare expected.

(3) The symbols defined in either UG-32(c) orbelow are used in this paragraph (see Fig. UG-36).

tp minimum required thickness of the consideredelement of a reducer after forming, in.

RLp inside radius of larger cylinder, in.Rsp inside radius of smaller cylinder, in.rLp inside radius of knuckle at larger cylinder, in.ap one-half of the included (apex) angle of a coni-

cal element, deg.rsp radius to the inside surface of flare at the small

end, in.(4) Elements of a Reducer.A transition section

reducer consisting of one or more elements may beused to join two cylindrical shell sections of differentdiameters but with a common axis provided the require-ments of this paragraph are met.

(a) Conical Shell Section.The required thicknessof a conical shell section, or the allowable workingpressure for such a section of given thickness, shallbe determined by the formulas given in UG-32(g).

(b) Knuckle Tangent to the Larger Cylinder.Where a knuckle is used at the large end of a reducersection, its shape shall be that of a portion of anellipsoidal, hemispherical, or torispherical head. Thethickness and other dimensions shall satisfy the require-ments of the appropriate formulas and provisions ofUG-32.

(5) Combination of Elements to Form a Reducer.When elements of (4) above, having different thick-nesses are combined to form a reducer, the jointsincluding the plate taper required by UW-9(c) shall lieentirely within the limits of the thinner element beingjoined.

(a) A reducer may be a simple conical shellsection, Fig. UG-36 sketch (a), without knuckle, pro-vided the half-apex anglea is not greater than 30 deg.,

45

except as provided for in 1-5(g). A reinforcement ringshall be provided at either or both ends of the reducerwhen required by the rules of 1-5.

(b) A toriconical reducer, Fig. UG-36 sketch(b), may be shaped as a portion of a toriconical head,UG-32(h), a portion of a hemispherical head plus aconical section, or a portion of an ellipsoidal head plusa conical section, provided the half-apex anglea isnot greater than 30 deg., except as provided for in 1-5(g). A reinforcement ring shall be provided at thesmall end of the conical reducer element when requiredby the rules in 1-5.

(c) Reverse curve reducers, Fig. UG-36 sketches(c) and (d), may be shaped of elements other thanthose of (e)(4) above. See U-2(g).

(f) Reducers Under External Pressure.The rules ofUG-33(f) shall be followed, where applicable, in thedesign of reducers under external pressure.

(g) Oblique Conical Shell Sections Under InternalPressure.A transition section reducer consisting of anoblique conical shell section may be used to join twocylindrical shell sections of different diameters andaxes, provided the following requirements are used.

(1) The required thickness shall be determined bythe formulas given in UG-32(g).

(2) The anglea to be used shall be the largestincluded angle between the oblique cone and theattached cylindrical section [see Fig. UG-36 sketch (e)]and shall not be greater than 30 deg.

(3) Diametrical dimensions to be used in the designformulas shall be measured perpendicular to the axisof the cylinder to which the cone is attached.

(4) A reinforcement ring shall be provided at eitheror both ends of the reducer when required by the rulesof 1-5.

UG-37 REINFORCEMENT REQUIREDFOR OPENINGS IN SHELLS ANDFORMED HEADS

(a) Nomenclature.The symbols used in this para-graph are defined as follows:

Ap total cross-sectional area of reinforcement re-quired in the plane under consideration, sq in.(see Fig. UG-37.1) (includes consideration ofnozzle area through shell ifSn/Sv<1.0)

A1p area in excess thickness in the vessel wall avail-able for reinforcement, sq in. (see Fig. UG-37.1)(includes consideration of nozzle area throughshell if Sn/Sv<1.0)

A2p area in excess thickness in the nozzle wall avail-able for reinforcement, sq in. (see Fig. UG-37.1)

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FIG. UG-37 CHART FOR DETERMINING VALUE OFF, AS REQUIRED IN UG-37

A3p area available for reinforcement when the noz-zle extends inside the vessel wall, sq in. (seeFig. UG-37.1)

A41, A42,A43p cross-sectional area of various welds available

for reinforcement, sq in. (see Fig. UG-37.1)A5p cross-sectional area of material added as rein-

forcement, sq in. (see Fig. UG-37.1)cp corrosion allowance, in.

Dp inside shell diameter, in.Dpp outside diameter of reinforcing element, in. (ac-

tual size of reinforcing element may exceed thelimits of reinforcement established by UG-40;however, credit cannot be taken for any materialoutside these limits)

dp finished diameter of circular opening or finished

46

dimension (chord length at midsurface of thick-ness excluding excess thickness available forreinforcement) of nonradial opening in the planeunder consideration, in. [see Figs. UG-37.1 andUG-40]

Ep 1 (see definitions fortr and tr n)E1p 1 when an opening is in the solid plate or in a

Category B butt joint; orp joint efficiency obtained from Table UW-12

when any part of the opening passes throughany other welded joint

Fp correction factor which compensates for thevariation in internal pressure stresses on differ-ent planes with respect to the axis of a vessel. Avalue of 1.00 shall be used for all configurationsexcept that Fig. UG-37 may be used for inte-grally reinforced openings in cylindrical shellsand cones. [See UW-16(c)(1).]

hp distance nozzle projects beyond the inner sur-face of the vessel wall, in. (Extension of thenozzle beyond the inside surface of the vesselwall is not limited; however, for reinforcementcalculations, credit shall not be taken for mate-rial outside the limits of reinforcement estab-lished by UG-40.)

K1p spherical radius factor (see definition oftr andTable UG-37)

Lp length of projection defining the thickened por-tion of integral reinforcement of a nozzle neckbeyond the outside surface of the vessel wall[see Fig. UG-40 sketch (e)]

Pp internal design pressure (see UG-21) psiRp inside radius of the shell course under consider-

ation, in.Rnp inside radius of the nozzle under consider-

ation, in.Sp allowable stress value in tension (see UG-23),

psiSnp allowable stress in nozzle, psi (seeS, above)Svp allowable stress in vessel, psi (seeS, above)Spp allowable stress in reinforcing element (plate),

psi (seeS, above)frp strength reduction factor, not greater than 1.0

[see UG-41(a)]fr1pSn /Sv for nozzle wall inserted through the

vessel wallfr1p1.0 for nozzle wall abutting the vessel wall

and for nozzles shown in Fig. UG-40,sketch (j), (k), (n) and (o).

fr 2pSn/Sv

fr 3p(lesser ofSn or Sp) /Sv

fr 4pSp /Sv


PART UG — GENERAL REQUIREMENTS Fig. UG-37.1

98 FIG. UG-37.1 NOMENCLATURE AND FORMULAS FOR REINFORCED OPENINGS(This Figure Illustrates a Common Nozzle Configuration and Is NotIntended to Prohibit Other Configurations Permitted by the Code.)

47



TABLE UG-37VALUES OF SPHERICAL RADIUS FACTOR K1Equivalent spherical radius p K1D;D/ 2h p axisratio. For definitions, see 1-4(b). Interpolation

permitted for intermediate values.

D/2h . . . 3.0 2.8 2.6 2.4 2.2K1 . . . 1.36 1.27 1.18 1.08 0.99

D/2h 2.0 1.8 1.6 1.4 1.2 1.0K1 0.90 0.81 0.73 0.65 0.57 0.50

tp specified vessel wall thickness,61 (not includingforming allowances), in. For pipe it is the nomi-nal thickness less manufacturing undertoleranceallowed in the pipe specification.

tep thickness or height of reinforcing element, in.(see Fig. UG-40)

tip nominal thickness of internal projection of noz-zle wall, in.

trp required thickness, in., of a seamless shell basedon the circumferential stress,or ofa formedhead,computed by the rules of this Division for thedesignated pressure, usingE p 1, except that:

(1) when the opening and its reinforce-ment are entirely within the spherical portionof a torispherical head,tr is the thickness re-quired by 1-4(d), usingM p 1;

(2) when the opening is in a cone,tr isthe thickness required for a seamless cone ofdiameterD measured where the nozzle axispierces the inside wall of the cone;

(3) when the opening and its reinforce-ment are in an ellipsoidal head and are locatedentirely within a circle the center of which coin-cides with the center of the head and the diame-ter of which is equal to 80% of the shell diame-ter, tr is the thickness required for a seamlesssphere of radiusK1D, whereD is the shell diam-eter andK1 is given by Table UG-37.

tnp nozzle wall thickness,61 in. Except for pipe, thisis the wall thickness not including forming al-lowances. For pipe, use the nominal thickness[see UG-16(d)].

tr np required thickness of a seamless nozzle wall, in.Wp total load to be carried by attachment welds, lb

(see UG-41)(b) General. The rules in this paragraph apply to

all openings other than:(1) small openings covered by UG-36(c)(3);(2) openings in flat heads covered by UG-39;

61In the corroded condition, see UG-16(e).A99

48

(3) openings designed as reducer sections coveredby UG-36(e);

(4) large head openings covered by UG-36(b)(2);(5) tube holes with ligaments between them con-

forming to the rules of UG-53.Reinforcement shall be provided in amount and distri-

bution such that the area requirements for reinforcementare satisfied for all planes through the center of theopening and normal to the vessel surface. For a circularopening in a cylindrical shell, the plane containing theaxis of the shell is the plane of greatest loading dueto pressure. Not less than half the required reinforcementshall be on each side of the center line of singleopenings.

(c) Design for Internal Pressure.The total cross-sectional area of reinforcementA required in any givenplane through the opening for a shell or formed headunder internal pressure shall be not less than

A p dtr F + 2tntr F(1 − fr1)

(d) Design for External Pressure(1) The reinforcement required for openings in

single-walled vessels subject to external pressure needbe only 50% of that required in (c) above, wheretris the wall thickness required by the rules for vesselsunder external pressure and the value ofF shall be1.0 in all external pressure reinforcement calculations.

(2) The reinforcement required for openings ineach shell of a multiple-walled vessel shall complywith (1) above when the shell is subject to externalpressure, and with (c) above when the shell is subjectto internal pressure, regardless of whether or not thereis a common nozzle secured to more than one shellby strength welds.

(e) Design for Alternate Internal and External Pres-sure. Reinforcement of vessels subject to alternateinternal and external pressures shall meet the require-ments of (c) above for internal pressure and of (d)above for external pressure.

(f) Details and formulas for required area and avail-able area are given in Fig. UG-37.1.

UG-38 FLUED OPENINGS IN SHELLSAND FORMED HEADS

(a) Flued openings in shells and formed heads madeby inward or outward forming of the head plate shallmeet the requirements for reinforcement in UG-37.The thickness of the flued flange shall also meet therequirements of UG-27 and / or UG-28, as applicable,

98


FIG. UG-38 MINIMUM DEPTH FOR FLANGE OFFLUED IN OPENINGS

where L as used in UG-28 is the minimum depth offlange as shown in Fig. UG-38. The minimum thicknessof the flued flange on a vessel subject to both internaland external pressure shall be the larger of the twothicknesses as determined above.

(b) The minimum depth of flange of a flued inopening exceeding 6 in. (152 mm) in any inside dimen-sion, when not stayed by an attached pipe or flue,shall equal 3tr or (tr + 3) in., whichever is less, wheretr is the required shell or head thickness. The depthof flange shall be determined by placing a straightedge across the side opposite the flued opening alongthe major axis and measuring from the straightedge tothe edge of the flanged opening (see Fig. UG-38).

(c) There is no minimum depth of flange requirementfor flued out openings.

(d) The minimum width of bearing surface for agasket on a self-sealing flued opening shall be inaccordance with UG-46(j).

UG-39 REINFORCEMENT REQUIREDFOR OPENINGS IN FLAT HEADS

UG-39(a) General.The rules in this paragraph applyto all openings in flat heads except opening(s) whichdo not exceed the size and spacing limits in UG-36(c)(3) and do not exceed one-fourth the head diameteror shortest span.

UG-39(b) Single and multiple openings in flat headsthat have diameters equal to or less than one-half thehead diameter may be reinforced as follows.

UG-39(b)(1)Flat heads that have a single openingwith a diameter that does not exceed one-half the headdiameter or shortest span, as defined in UG-34, shall

49

have a total cross-sectional area of reinforcement forall planes through the center of the opening not lessthan that given by the formula

A p 0.5dt + ttn (1 − fr1)

where d, tn, and fr1 are defined in UG-37 andt inUG-34.

UG-39(b)(2)Multiple openings none of which havediameters exceeding one-half the head diameter andno pair having an average diameter greater than one-quarter the head diameter may be reinforced individuallyas required by (1) above when the spacing betweenany pair of adjacent openings is equal to or greaterthan twice the average diameter of the pair.

When spacing between adjacent openings is less thantwice but equal to or more than 11⁄4 the average diameterof the pair, the required reinforcement for each openingin the pair, as determined by (1) above, shall be summedtogether and then distributed such that 50% of the sumis located between the two openings. Spacings of lessthan 11⁄4 the average diameter of adjacent openingsshall be treated by rules of U-2(g).

UG-39(b)(3)In no case shall the width of ligamentbetween two adjacent openings be less than one-quarterthe diameter of the smaller of the two openings in thepair. The width of ligament between the edge of anyone opening and the edge of the flat head (such asU3 or U5 in Fig. UG-39) shall not be less than one-quarter the diameter of that one opening.

UG-39(c) Flat heads which have an opening with adiameter that exceeds one-half the head diameter orshortest span, as defined in UG-34, shall be designedas follows.

UG-39(c)(1)When the opening is a single, circularcentrally located opening in a circular flat head, thehead shall be designed according to Appendix 14 andrelated factors in Appendix 2. The head-to-shell junctionmay be integral, as shown in Fig. UG-34 sketches (a),(b-1), (b-2), (d), and (g). The head may also be attachedby a butt weld or a full-penetration corner weld similarto the joints shown in Fig. UW-13.2 sketches (a), (b),(c), (d), (e), or (f). The large centrally located openingmay have a nozzle which is integrally formed orintegrally attached by a full penetration weld or maybe plain without an attached nozzle or hub. The headthickness does not have to be calculated by UG-34rules. The thickness that satisfies all the requirementsof Appendix 14 meets the requirements of the Code.

UG-39(c)(2)Opening(s) may be located in the rimspace surrounding the central opening. See Fig. UG-39.Such openings may be reinforced by area replacement in

Fig. UG-39 1998 SECTION VIII — DIVISION 1

FIG. UG-39 MULTIPLE OPENINGS IN RIM OF HEADS WITH A LARGE CENTRAL OPENING

50



accordance with the formula in (b)(1) above using asa required head thickness the thickness that satisfiesrules of Appendix 14. Multiple rim openings shall meetspacing rules of (b)(2) and (b)(3) above. Alternatively,the head thickness that meets the rules of Appendix14 may be increased by multiplying it by the squareroot of two (1.414) if only a single opening is placedin the rim space or if spacingp between two suchopenings is twice or more than their average diameter.For spacing less than twice their average diameter, thethickness that satisfies Appendix 14 shall be dividedby the square root of efficiency factore, where e isdefined in (e)(2) below.

The rim opening(s) shall not be larger in diameterthan one-quarter the differences in head diameter lesscentral opening diameter. The minimum ligament widthU shall not be less than one-quarter the diameter ofthe smaller of the two openings in the pair. A minimumligament width of one-quarter the diameter of the rimopening applies to ligaments designated asU2, U4,U3, and U5 in Fig. UG-39.

UG-39(c)(3)When the large opening is any othertype than that described in (c)(1) above, there are nospecific rules given. Consequently, the requirements ofU-2(g) shall be met.

UG-39(d) As an alternative to (b)(1) above, thethickness of flat heads and covers with a single openingwith a diameter that does not exceed one-half the headdiameter may be increased to provide the necessaryreinforcement as follows.

UG-39(d)(1) In Formula (1) or (3) of UG-34(c),use 2C or 0.75 in place ofC, whichever is the lesser;except that, for sketches (b-1), (b-2), (e), (f), (g), and(i) of Fig. UG-34, use 2C or 0.50, whichever is thelesser.

UG-39(d)(2) In Formula (2) or (5) of UG-34(c),double the quantity under the square root sign.

UG-39(e) Multiple openings none of which havediameters exceeding one-half the head diameter andno pair having an average diameter greater than one-quarter the head diameter may be reinforced as follows.

UG-39(e)(1)When the spacing between a pair ofadjacent openings is equal to or greater than twice theaverage diameter of the pair, and this is so for allopening pairs, the head thickness may be determinedby rules in (d) above.

UG-39(e)(2) When the spacing between adjacentopenings in a pair is less than twice but equal to orgreater than 11⁄4 the average diameter of the pair, therequired head thickness shall be that determined by(d) above multiplied by a factorh, where

51

h p √0.5/e

e p [( p − dave) /p]smallest

wheree p smallest ligament efficiency of adjacent opening

pairs in the headp p center-to-center spacing of two adjacent

openingsdave p average diameter of the same two adjacent

openingsUG-39(e)(3)Spacings of less than 11⁄4 the average

diameter of adjacent openings shall be treated by rulesof U-2(g).

UG-39(e)(4)In no case shall the width of ligamentbetween two adjacent openings be less than one-quarterthe diameter of the smaller of the two openings inthe pair.

UG-39(e)(5) The width of ligament between theedge of any one opening and the edge of the flat head(such asU3 or U5 in Fig. UG-39) shall not be lessthan one-quarter the diameter of that one opening.

UG-40 LIMITS OF REINFORCEMENT

(a) The boundaries of the cross sectional area inany plane normal to the vessel wall and passing throughthe center of the opening within which metal must belocated in order to have value as reinforcement aredesignated as the limits of reinforcement for that plane(see Fig. UG-37.1). Figure UG-40 depicts thicknessest, te, and tn, or ti and diameterd used in establishingthe limits of reinforcement.

(b) The limits of reinforcement, measured parallelto the vessel wall, shall be at a distance, on each sideof the axis of the opening, equal to the greater of thefollowing:

(1) the diameterd of the finished opening in thecorroded condition;

(2) the radiusRn of the finished opening in thecorroded condition plus the nominal thickness of thevessel wallt, plus the nominal thickness of the nozzlewall tn.

(c) The limits of reinforcement, measured normal tothe vessel wall, shall conform to the contour of thesurface at a distance from each surface equal to thesmaller of the following:

(1) 21⁄2 times the vessel wall thickness less corro-sion allowance;

98

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Fig. UG-40 1998 SECTION VIII — DIVISION 1

98

A99

FIG. UG-40 SOME REPRESENTATIVE CONFIGURATIONS DESCRIBING THE REINFORCEMENT DIMENSION teAND THE OPENING DIMENSION d

52


98FIG. UG-40 SOME REPRESENTATIVE CONFIGURATIONS DESCRIBING THE REINFORCEMENTDIMENSION te AND THE OPENING DIMENSION d (CONT’D)

53


(2) 21⁄2 times the nominal nozzle wall thicknessless corrosion allowance, plus the thicknesste as definedin Fig. UG-40.

(d) Metal within the limits of reinforcement that maybe considered to have reinforcing value shall includethe following:

(1) metal in the vessel wall over and above thethickness required to resist pressure and the thicknessspecified as corrosion allowance. the area in the vesselwall available as reinforcement is the larger of thevalues ofA1 given by the formulas in Fig. UG-37.1.

(2) metal over and above the thickness requiredto resist pressure and the thickness specified as corrosionallowance in that part of a nozzle wall extending outsidethe vessel wall. The maximum area in the nozzle wallavailable as reinforcement is the smaller of the valuesof A2 given by the formulas in Fig. UG-37.1.

All metal in the nozzle wall extending inside thevessel wallA3 may be included after proper deductionfor corrosion allowance on all the exposed surface ismade. No allowance shall be taken for the fact that adifferential pressure on an inwardly extending nozzlemay cause opposing stress to that of the stress in theshell around the opening:

(3) metal in attachment weldsA4 and metal addedas reinforcementA5.

(e) With the exception of studding outlet type flanges,bolted flange material within the limits of reinforcementshall not be considered to have reinforcing value.

UG-41 STRENGTH OF REINFORCEMENT

(a) Material used for reinforcement shall have anallowable stress value equal to or greater than that ofthe material in the vessel wall, except that when suchmaterial is not available, lower strength material maybe used, provided the area of reinforcement is increasedin inverse proportion to the ratio of the allowable stressvalues of the two materials to compensate for the lowerallowable stress value of the reinforcement. No creditmay be taken for the additional strength of any reinforce-ment having a higher allowable stress value than thatof the vessel wall. Deposited weld metal outside ofeither the vessel wall or any reinforcing pad used asreinforcement shall be credited with an allowable stressvalue equivalent to the weaker of the materials con-nected by the weld. Vessel-to-nozzle or pad-to-nozzleattachment weld metal within the vessel wall or withinthe pad may be credited with a stress value equal tothat of the vessel wall or pad, respectively.

(b) On each side of the plane defined in UG-40(a),the strength of the attachment joining the vessel wall

54

and reinforcement or any two parts of the attachedreinforcement shall be at least equal to the smaller of:

(1) the strength in tension of the cross section ofthe element or elements of reinforcement being consid-ered (seeW1-1, W2-2, and W3-3 of Fig. UG-41.1 forexamples and L-7 for numerical examples);

(2) the strength in tension of the area defined inUG-37 less the strength in tension of the reinforcingarea which is integral in the vessel wall as permittedby UG-40(d)(1) (seeW of Fig. UG-41.1 for examplesand L-7 for numerical examples);

(3) for welded attachments, see UW-15 for exemp-tions to strength calculations.

(c) The strength of the attachment joint shall beconsidered for its entire length on each side of theplane of the area of reinforcement defined in UG-40.For obround openings, consideration shall also be givento the strength of the attachment joint on one side ofthe plane transverse to the parallel sides of the openingwhich passes through the center of the semicircularend of the opening.

(d) For detailed requirements for welded and brazedreinforcement see the appropriate paragraphs in theParts devoted to these subjects (see UW-15 and UB-19).

UG-42 REINFORCEMENT OF MULTIPLEOPENINGS

(See UG-39 for multiple openings in flat heads.)(a) When any two openings are spaced at less than

two times their average diameter, so that their limitsof reinforcement overlap [see Fig. UG-42 sketch (a)],the two openings shall be reinforced in the planeconnecting the centers, in accordance with the rules ofUG-37, UG-38, UG-40, and UG-41 with a combinedreinforcement that has an area not less than the sumof the areas required for each opening. No portion ofthe cross section is to be considered as applying tomore than one opening, nor to be considered morethan once in a combined area.

(1) The overlap area shall be proportioned betweenthe two openings by the ratio of their diameters.

(2) If the area of reinforcement between the twoopenings is less than 50% of the total required for thetwo openings, the supplemental rules of 1-7 shallbe used.

(3) A series of openings all on the same centerline shall be treated as successive pairs of openings.

(b) When more than two openings are spaced as in(a) above [see Fig. UG-42 sketch (b)], and are to beprovided with a combined reinforcement, the minimumdistance between centers of any two of these openings

PART UG — GENERAL REQUIREMENTS Fig. UG-41.1

FIG. UG-41.1 NOZZLE ATTACHMENT WELD LOADS AND WELD STRENGTH PATHS TO BE CONSIDERED

55


FIG. UG-41.1 NOZZLE ATTACHMENT WELD LOADS AND WELD STRENGTH PATHS TO BE CONSIDERED(CONT’D)

56


FIG. UG-42 EXAMPLES OF MULTIPLE OPENINGS

shall be 11⁄3 times their average diameter, and the areaof reinforcement between any two openings shall beat least equal to 50% of the total required for the twoopenings. If the distance between centers of two suchopenings is less than 11⁄3 times their average diameter,no credit for reinforcement shall be taken for any ofthe material between these openings. Such openingsmust be reinforced as described in (c) below.

(c) Alternatively, any number of adjacent openings,in any arrangement, may be reinforced by using anassumed opening enclosing all such openings. Thelimits for reinforcement of the assumed opening shallbe those given in UG-40(b)(1) and (c)(1). The nozzlewalls of the actual openings shall not be consideredto have reinforcing value. When the diameter of theassumed opening exceeds the limits in UG-36(b)(1),the supplemental rules of 1-7 shall also be used.

(d) When a group of openings is reinforced by athicker section butt welded into the shell or head, theedges of the inserted section shall be tapered as pre-scribed in UW-9(c).

(e) When a series of two or more openings in acylindrical shell are arranged in a regular pattern,

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reinforcement of the openings may be provided perthe rules of ligaments in UG-53.

UG-43 METHODS OF ATTACHMENT OFPIPE AND NOZZLE NECKS TOVESSEL WALLS

(a) General. Nozzles may be attached to the shellor head of a vessel by any of the methods of attachmentgiven in this paragraph, except as limited in UG-36.

(b) Welded Connections.Attachment by welding shallbe in accordance with the requirements of UW-15 andUW-16.

(c) Brazed Connections.Attachment by brazing shallbe in accordance with the requirements of UB-17through UB-19.

(d) Studded Connections.Connections may be madeby means of studs. The vessel shall have a flat surfacemachined on the shell, or on a built-up pad, or on aproperly attached plate or fitting. Drilled holes to betapped shall not penetrate within one-fourth of the wallthickness from the inside surface of the vessel after


TABLE UG-43MINIMUM NUMBER OF PIPE THREADS FOR CONNECTIONS

Size of pipe 1⁄2 & 3⁄4 1, 11⁄4 & 11⁄2 2 21⁄2 & 3 4–6 8 10 12connection, NPS

Threads engaged 6 7 8 8 10 12 13 14

Min. plate thickness 0.43 0.61 0.70 1.0 1.25 1.5 1.62 1.75required, in.

deducting corrosion allowance, unless at least the mini-mum thickness required as above is maintained byadding metal to the inside surface of the vessel. Thetapped holes shall also conform to the requirements of(g) below. Studded connections shall meet the require-ments for reinforcement in UG-36 through UG-42.

(e) Threaded Connections.Pipes, tubes, and otherthreaded connections that conform to the ANSI/ASMEStandard for Pipe Threads, General Purpose, Inch(ANSI/ASME B1.20.1) may be screwed into a threadedhole in a vessel wall, provided the pipe engages theminimum number of threads specified in Table UG-43 after allowance has been made for curvature of thevessel wall. The thread shall be a standard taper pipethread except that a straight thread of at least equalstrength may be used if other sealing means to preventleakage are provided. A built-up pad or a properlyattached plate or fitting may be used to provide themetal thickness and number of threads required inTable UG-43, or to furnish reinforcement when required.

Threaded connections larger than 4 in. pipe size(DN 100) shall not be used in vessels that containliquids having a flash-point below 110°F (43°C), orflammable vapors, or flammable liquids at temperaturesabove that at which they boil under atmosphericpressure.

Threaded connections larger than 3 in. pipe size(DN 80) shall not be used when the maximum allowableworking pressure exceeds 125 psi (861 kPa), exceptthat this 3 in. pipe size (DN 80) restriction does notapply to plug closures used for inspection openings,end closures, or similar purposes, or to integrally forgedopenings in vessel heads meeting the requirement ofUF-43.

(f) Expanded Connections.A pipe, tube, or forgingmay be attached to the wall of a vessel by insertingthrough an unreinforced opening and expanding intothe shell, provided the diameter is not greater than 2in. pipe size (DN 50). A pipe, tube, or forging notexceeding 6 in. (152 mm) in outside diameter may be

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attached to the wall of a vessel by inserting througha reinforced opening and expanding into the shell.

Such connections shall be:(1) firmly rolled in and beaded; or(2) rolled in, beaded, and seal-welded around the

edge of the bead; or(3) expanded and flared not less than1⁄8 in.

(3.2 mm) over the diameter of the hole; or(4) rolled, flared, and welded; or(5) rolled and welded without flaring or beading,

provided:(a) the ends extend at least1⁄4 in. (6 mm), but

no more than3⁄8 in. (10 mm), through the shell;(b) the throat of the weld is at least3⁄16 in.

(4.8 mm), but no more than5⁄16 in. (8 mm).When the tube or pipe does not exceed 11⁄2 in.

(38 mm) in outside diameter, the shell may be chamferedor recessed to a depth at least equal to the thicknessof the tube or pipe and the tube or pipe may be rolledinto place and welded. In no case shall the end of thetube or pipe extend more than3⁄8 in. (10 mm) beyondthe shell.

Grooving of shell openings in which tubes and pipeare to be rolled or expanded is permissible.

Expanded connections shall not be used as a methodof attachment to vessels used for the processing orstorage of flammable and/or noxious gases and liquidsunless the connections are seal-welded.

(g) Where tapped holes are provided for studs, thethreads shall be full and clean and shall engage thestud for a length not less than the larger ofds or

0.75ds ×

Maximum allowable stress value ofstud material at design temperature

Maximum allowable stress value oftapped material at design temperature

in which ds is the nominal diameter of the stud, exceptthat the thread engagement need not exceed 11⁄2ds.


UG-44 FLANGES AND PIPE FITTINGS

The following standards covering flanges and pipefittings are acceptable for use under this Division inaccordance with the requirements of UG-11. Pressure–temperature ratings shall be in accordance with theappropriate standard except that the pressure–tempera-ture ratings for ASME B16.9 and ASME B16.11 fittingsshall be calculated as for straight seamless pipe inaccordance with the rules of this Division includingthe maximum allowable stress for the material. Thepressure–temperature ratings of ASME/ANSI B16.28fittings shall be 80% of that calculated for straightseamless pipe in accordance with the rules of thisDivision unless 100% rating has been established bythe fitting manufacturer in accordance with para. 9 ofASME B16.9. The thickness tolerance of the ASMEstandards shall apply.

UG-44(a) ASME/ANSI B16.5, Pipe Flanges andFlanged Fittings [see UG-11(a)(2)]

UG-44(b)ASME B16.9, Factory-Made Wrought SteelButtwelding Fittings

UG-44(c) ASME B16.11, Forged Fittings, Socket-Welding and Threaded

UG-44(d) ANSI/ASME B16.15, Cast BronzeThreaded Fittings, Classes 125 and 250

UG-44(e)ASME B16.20, Metallic Gaskets for PipeFlanges — Ring-Joint, Spiral-Wound, and Jacketed

UG-44(f) ASME B16.24, Cast Copper Alloy PipeFlanges and Flanged Fittings, Class 150, 300, 400,600, 900, 1500, and 2500

UG-44(g)ASME/ANSI B16.28, Wrought Steel Butt-welding Short Radius Elbows and Returns

UG-44(h) ASME/ANSI B16.42, Ductile Iron PipeFlanges and Flanged Fittings, Class 150 and 300

UG-44(i) ASME B16.47, Large Diameter SteelFlanges, NPS 26 Through NPS 60

UG-45 NOZZLE NECK THICKNESS

UG-45(a) The minimum wall thickness of a nozzleneck or other connection (including access openingsand openings for inspection) shall not be less than thethickness computed from the applicable loadings inUG-22 plus the thickness added for corrosion allowanceon the connection.

UG-45(b) Additionally, the minimum thickness of anozzle neck or other connection (except for accessopenings and openings for inspection only) shall notbe less than the smallest of the following:

UG-45(b)(1) for vessels under internal pressureonly, the thickness (plus corrosion allowance) requiredfor pressure (assumingE p 1.0) for the shell or head

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at the location where the nozzle neck or other connectionattaches to the vessel but in no case less than theminimum thickness specified for the material in UG-16(b);

UG-45(b)(2) for vessels under external pressureonly, the thickness (plus corrosion allowance) obtainedby using the external design pressure as an equivalentinternal design pressure (assumingE p 1.0) in theformula for the shell or head at the location where thenozzle neck or other connection attaches to the vesselbut in no case less than the minimum thickness specifiedfor the material in UG-16(b);

UG-45(b)(3)for vessels designed for both internaland external pressure, the greater of the thicknessesdetermined by (b)(1) or (b)(2) above;

UG-45(b)(4) the minimum thickness26 of standardwall pipe plus the thickness added for corrosion allow-ance on the connection; for nozzles larger than thelargest pipe size included in ANSI/ASME B36.10M,the wall thickness of that largest size plus the thicknessadded for corrosion allowance on the connection.

UG-45(c) The allowable stress value for shear inthe nozzle neck shall be 70% of the allowable tensilestress for the nozzle material.

UG-46 INSPECTION OPENINGS27

(a) All pressure vessels for use with compressed airand those subject to internal corrosion or having partssubject to erosion or mechanical abrasion (see UG-25),except as permitted otherwise in this paragraph, shallbe provided with suitable manhole, handhole, or otherinspection openings for examination and cleaning.

Compressed air as used in this paragraph is notintended to include air which has had moisture removedto provide an atmospheric dew point of −50°F (−46°C)or less.

Inspection openings may be omitted in vessels cov-ered in UG-46(b), and in the shell side of fixed tubesheetheat exchangers. When inspection openings are notprovided, the Manufacturer’s Data Report shall includeone of the following notations under remarks:

26The minimum thickness for all materials is that wall thicknesslisted in Table 2 of ANSI /ASME B36.10M, less 121⁄2%. For diametersother than those listed as standard (STD) in the Table, this shall bebased upon the next larger pipe size. When a material specificationdoes not specify schedule weights conforming to ANSI /ASMEB36.10M, the pipe weight indicated as regular shall be used whenso designated in the specification. If not so designated, the heaviestschedule listed shall be used even though this is less than thethickness of standard weight pipe of ANSI /ASME B36.10M.27All dimensions given, for size of vessel on which inspectionopenings are required, are nominal.

except as permitted in Part UCL (see Appendix F). UG …€¦ · ASME B&PVC sec81$$u10 06-02-99...

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Transcript of except as permitted in Part UCL (see Appendix F). UG …€¦ · ASME B&PVC sec81$$u10 06-02-99...