Section VIII imp details.docx

7/27/2019 Section VIII imp details.docx

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UG-4

Material subject to stress shall conform to one of the specifications given in Section II, part D, subpart 1,

Tables 1A, 1B and 3

Materials for non pressure parts such as skirts, lugs etc need not conform to the specification of the

material to which they are attached nor to a specification permitted in code. The allowable stress value

for material not identified in accordance with UG 93, shall not exceed 80% of max allowable stress value

permitted for similar material in subsection C

UG 8

Finned tubes may be supplied in the as fabricated condition, WHEN SPECIFIED i.e finned portion in

cold worked temper (as finned) resulting from finning operation and unfinned portion in temper of tube

prior to finning.

Max allowable stress value for finned tubes shall be same as unfinned tube. Any higher stress value can

be used provided additional mechanical tests conducted on the finned sample establishes that such

higher stress values are in conformance to one of the governing specification in Section II

Max allowable internal and external working pressure shall correspond to root diameter and minimum

wall thickness of the finned section. MAWP for integral fins may be established in accordance with

Appendix 23

Each tube after finning shall be subjected to either a hydrostatic test or pneumatic test. Pneumatic test

pressure of a minimum of 250 psi shall be applied for 5 sec without any evidence of leak, which shall be

established by immersion of tubes in water. Hydrostatic test shall be conducted in accordance with UG

99.

A material identified with a specification not permitted by the code may be accepted when certified by

an organisation other than the vessel or part manufacturer, provided all physical and chemical

requirements of the specification to which it is recertified is met. The copy of certificates and a

certification to that effect is given to vessel manufacturer.

A material identified with a specification not permitted by the code may be accepted when certified by

vessel manufacturer when above conditions are met. Also the metallurgical and mechanical property

and deoxidation requirement are as per specification to which it is being recertified.

If documentation mentioned above is not available and still if a material is to be certified as per aspecification in Section II, then outside agencies cannot certify the same. Vessel manufacturer can do

the certification after satisfactory testing of the material to establish its conformance to a specification

as per section II.

UG 11


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Prefabricated or preformed pressure parts supplied by other vendors shall satisfy all the requirements of

the code and also submission of partial data reports as per UG 120 c. If the name plate provided on the

prefabricated piece obstructs with further fabrication, same can be removed and shall be noted in the

remarks section of vessel manufacturers data report. The parts which are manufactured as per ANSI/

ASME standards like pipe fittings, flanges, caps etc need not be identified separately and partial data

reports are not required for the same. Such materials shall be marked with trade mark of the parts

manufacturer, which shall be considered as parts manufacturers certification that the part complies with

requirement of the code.

Parts of small fittings for which it is difficult to identify material by marking and that which do not affect

the safety of the vessel, may be used for relatively unimportant parts which is stressed to not more than

50% of stress value permitted by code

Such parts need not be manufactured by a certificate of authorization holder

UG 14

Upto a size of 4, hollow cylindrical shaped parts can be machined from rolled or forged bars. However,

this is not applicable for flanges, eq tees, elbows etc

UG 15

An equivalent material specification mentioned in subsection C may be used in place of a material spec

which is not included in the code, if the physical, chemical, heat treating requirements, deoxidation

requirements, grain size requirements etc conform to approved spec in subsection C. In case of welded

tubing made of plate, sheet or strip without the addition of filler metal, the appropriate stress values

shall be multiplied with 0.85, in such cases. Pipes or tubes fabricated by fusion welding with addition of

filler metal shall not be substituted similarly, unless the part has been fabricated as per rules of the

code.

UG 16 DESIGN

The minimum thickness of shells and heads after forming shall not be less than 1.5 mm excluding

corrosion allowance.

The above condition is not applicable for heat transfer plates of plate type heat exchangers and to inner

pipe of double pipe heat exchangers where pipe sizes are 6 and less.

The minimum thickness of shells and heads of unfired boilers shall be a minimum of 6 mm, exclusive ofcorrosion allowance.

The minimum thickness of shells and heads used in compressed air, steam and water service shall be a

minimum of 2.5 mm, excluding corrosion allowance.

This minimum thickness requirement shall not apply to tubes in air cooled and cooling tower heat

exchangers, if


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Tubes are not used for lethal services

Tubes are protected by fins

Tube OD is between 10 mm and 38 mm

The reduction in thickness of plates due to mill under tolerance shall be permissible upto the smaller

value of 0.25 mm or 6% of ordered thickness for application of full design pressure

The pipe reduction in thickness on account of mill under tolerance shall be as per pipe specifications

The dimensions of all thickness indicated in design formulas in the code represents dimensions in

corroded conditions.

UG 19

A combination unit is a pressure vessel that consist of more than one independent pressure chamber

operating at same or different pressures and temperatures. Each element including the commonelement shall be designed for the most severe conditions of coincident pressure and temperatures. A

lower pressure /temperature is allowed only when the common element design conditions can be

controlled

Vessels having special shapes other than cylindrical and spherical for which design rules are not

provided in the code may be designed as per U-2

If no design rules are available and if the strength cannot be calculated, then the maximum allowable

pressure shall be determined as per UG 101

UG 20

The maximum design temperature shall not be less than mean metal temperature through the

thickness, expected during service, except as provided in UW 2 d(3). Similarly for minimum temperature

shall correspond to the minimum expected operating conditions except under provisions of UCS 66, UCS

160 and UG 116 foot note 37.

MDMT marked on name plate shall correspond to maximum MAWP

The design temperatures which exceeds the value given in Section II part D subpart 1, tables 1 A, 1B and

3, are not allowed. Similarly the maximum temperature given on external pressure charts also shall not

be exceeded.

Impact testing is not required if the following conditions are satisfied

Material is limited to P no 1 and shall not exceed 13 mm for materials listed under curve A of UCS 66.

For materials under curve B, C or D the thickness shall not exceed 25 mm

Vessel shall be subjected to hydrostatic test per UG 99


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Design temperatures shall be within 345 deg C and -29 deg C

Thermal and mechanical shock loadings are not present

Cyclical loading is not present

UG 23

Maximum allowable stress value

The maximum allowable TENSILE stress value for a material shall be selected from the maximum

allowable tensile stress value for various materials listed in subpart 1 of section II, Part D. A listing of

these materials is given in subsection C of section VIII. (UCS-23, UNF-23 etc)

The maximum allowable longitudinal COMPRESSIVE stress value to which a cylindrical shell or tube is

subjected shall be the smaller of following.

The maximum stress value as determined above

The value of factor B determined from applicable material /temperature chart in Section II, subpart 3,

Part D from the value of A determined from the formula A= 0.125

(R0/t)

R0 is the outside RADIUS of shell or tube

t is the minimum required thickness of shell or tube

If the value of A falls to the right of the end of material /temperature line, assume an intersection with

horizontal projection of upper end of the material /temperature line

If value of A falls to the left of material /temperature line, the value of B shall be found as follows

B=AE

2

If value of B as determined above is with the computed longitudinal compressive stress using the

selected values of R0 and t. If the value of B is less than the computed longitudinal compressive stress,

higher value of t will have to be used.


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