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C100 Cryomodule End Can Piping Design per ASME B31.3 Gary G. Cheng and Edward F. Daly

Introduction

This technical note analyzes the C100 cryomodule (CM) end can piping design in accordance with the American Society of Mechanical Engineers (ASME) code B31.3 for process piping. The C100 cryomodule is aimed at being used in the ongoing CEBAF 12GeV upgrade project. The end can design is based on the past design of CEBAF cryomodule. Despite the fact that similar end can designs had been built and performed properly and safely, this note serves as an in-depth review of the pressurized piping systems inside the end cans in terms of provisions from ASME standards.

The supply and return end can piping consists of the primary circuit, which provides cooling

fluid to the superconducting cavities, and the shield circuit that cools the nominal 50K thermal shield. The gas/fluid circuits consist of pipes, tubes, fittings, and valves. The design pressure for the primary circuit is 5.0 atm and 20.0 atm for the shield circuit. The ASME B31.3 code comprehensively defines design requirements in various aspects: material selection, component pressure and temperature ratings, fabrication, assembly, erection, etc. In this note, end can piping and components are examined in reference to pertinent code sections.

I. Supply End Can Piping Design

1. Primary Circuit Figure 1 shows a schematic of the supply end can primary circuit. The circuit includes

helium pipeline and pressure relief pipeline.

Straight Pipe Minimum Wall Thickness For straight pipes in the primary circuit, B31.3 para 304.1.2(a) equation (3a) can be used for

calculating the minimum required wall thickness for straight pipes under internal pressure:

( )YPWESODPt

***2*

+=

where t -------- Minimum required wall thickness

P-------- Design pressure, P = 5.0*14.7 psi for the primary circuit. OD ----- Outer diameter of pipe

S -------- Material allowable stress from B31.3 Table A-1. For 304 stainless steel, S = 16700 psi

E -------- Quality factor for longitudinal weld from Table A-1B, herein E = 1.0. W ------- Weld strength reduction factor, herein W = 1.0. Y -------- Coefficient from Table 304.1.1, Y = 0.4 for steels at low temperatures.

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Fig. 1 Supply end can primary circuit

The calculations of minimum required wall thicknesses for pipe segments are tabulated in

Table 1. All pipe wall thicknesses are found to be sufficient.

Table 1 Minimum pipe/tube wall thicknesses in supply end can primary circuit

Piping assy name Reference drawing #

OD of main run

(in.)

Wall of main run

(in.)

B31.3 required wall

(in.) Safety factor

HELIUM INLET BAFFLE 115310-1043D 4.00 0.12 0.00879 13.7

PIPING SPOOL #2 115310-1023D 0.84 0.083 0.00185 45.0

PIPING SPOOL #1 115310-1022D 0.84 0.083 0.00185 45.0 2K 1-1/2 FEMALE BAYONET ASSY 115310-1084E 1.5 0.035 0.00330 10.6

SPOOL E (S) ASSY 115310-1021C 0.25 0.035 0.00055 63.7

SPOOL B (S) 115310-1017C 0.25 0.035 0.00055 63.7

3K He gas

To supply header

Bayonet

J-T valve assembly

Spool B(S)

Relief valve

NUPRO® purge valve

J-T valvebody

Piping spool #1

Piping spool #2

Corrugated hose

4.0" OD tube

Helium inlet baffle Check valve

Spool E(S) ASSY

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Strength of Branch Connections B31.3 para 304.3 requires strength verification of branch connections if necessary. From

Table 1, it is seen that with current pipe dimensions, substantial safety factors on pipe wall thicknesses are achieved. In the primary circuit, there exists one branch connection from the piping spool #2 to the helium inlet baffle. B31.3 para. 304.3.2 Strength of Branch Connections states “Unless the wall thickness of the run pipe is sufficiently in excess of that required to sustain pressure at an intersection not manufactured in accordance with a listed standard, it may be necessary to provide added material as reinforcement.” Because the actual pipe thicknesses of the involved pipes are >10 times over the required minimum, it is safe to say that no reinforcement material is needed in welding up these two subassemblies.

Pipe Fittings Pressure Design

Pipe/tube fittings, such as tees, elbows, reducers, are used at junctions of pipes/tubes in the

primary circuit. The B31.3 para 303 refers to a few acceptable fittings manufacturing and validation standards that are listed in Table 326.1 of B31.3. For buttwelding fittings, the ASME B16.9 standard is suggested. In the main run of the primary circuit, excluding pressure relief pipeline, there are five 90o elbows, one equal-end tee, and one concentric reducer. All these buttweld fittings are to be fabricated and rated in compliance with ASME code B16.9 as specified in drawings. In the relieving pipeline, fittings from CAJON Co. (now Swagelok®), such as union tee, bellows valve, nuts, connectors, weld gland, etc., are used. According to Swagelok catalog, all pipe fittings have been designed, manufactured, and tested conforming to ASME B31 codes for pressure/process piping.

The J-T valve body can be treated as an equal-end tee. The pressure design of this special tee

is in reference to that of a straight pipe with similar outer diameter. Therefore, information in Table 1 is sufficient to substantiate the robustness of the J-T valve body subjected to the design pressure of 5.0 atm.

One APOLLO check valve manufactured by Conbraco Industries Inc. is modified for use in

the pressure relieving pipeline. The valve from vendor has a pressure rating of 400 psig, which is over 5 times higher than the design pressure of 5.0 atm. The original Reinforced Teflon™ ball in the check valve is replaced by a stainless steel ball. This simple modification does not degrade the structural integrity of this valve as demonstrated by pressure tests and operations.

Pressure Relieving

Pressure relieving devices are required by B31.3 para 301.2.2 and also in para. 322.6.3,

where detailed design requirements for such devices are set forth. A pressure relieving valve is mounted in the primary circuit through 0.25" OD pipes, i.e. SPOOL E(S) and SPOOL B(S) assemblies in Table 1. The B31.3 para. 322.6.3 requires that the pressure relieving devices shall be in accordance with the related provisions in the Boiler & Pressure Vessel Code, Section VIII, Division 1. The vendor of these relief valves, Circle Seal Controls Inc., has obtained ASME certification for manufacturing pressure vessel pressure relief valves. The relief valve is therefore trusted to be acceptable per either BPV or B31.3 code. The set pressures on the relief valves in

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the primary circuit are determined according to rules in BPV code.

Flexibility, Stress, and Support The primary circuit is mainly made of 304 stainless steel (SS). According to B31.3 para

302.3.5, the system allowable displacement stress due to thermal load can be evaluated as follows:

Thermal cycles < 7,000 f := 1.0 Sc for 304 SS at 2K<100F, B31.3 Table A-1 Sc = 16,700 psi Sh for 304 SS at 300K<200F, B31.3 Table A-1 Sh = 16,700 psi SA for the system is (302.3.5 Eq. (1b)):

SA = f*(1.25*Sc+0.25*Sh) SA = 25,050 psi B31.3 para 319.4 requires flexibility analysis for piping systems that cannot be excluded by

para. 319.4.1, in which Eq. (16) is used as a criterion:

( ) 12 KULyD

≤−

Where D = outside diameter of pipe, mm Ea = reference modulus of elasticity at 21 oC (70 oF), MPa(ksi)

K1 = 208000 SA/Ea, (mm/m)2 L = developed length of piping between anchors, m(ft) SA = allowed displacement stress range, MPa(ksi) U = anchor distance, straight line between anchors, m(ft) y = resultant of total displacement strains, mm(in.), to be absorbed by the piping system The primary circuit as shown in Fig. 1 consist four subassemblies: 1) the J-T valve

subassembly, 2) piping spool # 1 that has one tee, one reducer, and three elbows, 3) piping spool #2 that has two elbows and one corrugated hose, and 4) the bayonet assembly.

The J-T valve assembly has a bellows at its warm end. When thermal contraction occurs, the

bellows will be compressed to absorb such displacement. Assuming the cold end of the J-T valve is fixed (worst scenario), the force developed in bellows can be calculated as follows:

Length of J-T valve inner tube is L_300K = 31.177 in Axial spring rate of the bellows is k_belw = 39 lbf/in 304 stainless steel linear expansion is

310071.3300_

2_300_ −×=−

KLKLKL

Thermal contraction in inner tube is ΔL = L_300K-L_2K = 0.096 in Force in bellows is F_belw = ΔL*k_belw = 3.74 lbf

Obviously, this force would not induce any significant stresses in a stainless steel structure.

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The corrugated hose, an ANAMET (now HYSPAN®) product, in piping spool #2 is

restrained from axial movements by braided stainless steel sleeve. Therefore, there will be no thrust force passing on to the adjacent pipe elements. Hose bending is not restrained so that piping spool#2 is actually free of thermal stress during contractions.

The bayonet has a built-in double wall structure. Inside the bayonet, the cold gas keeps the

inner tube chilled so that not much thermal stress is expected to develop. For the piping spool #1, at the worst scenario, it can be assumed to be fixed at two interfaces:

the reducer end face connecting to J-T valve bottom and the elbow face connecting to the bottom of bayonet. Apply Eq. (16) in B31.3 para 319.4:

Outside diameter of pipe is D = 0.84 in Reference modulus of elasticity at 21oC(70oF) Ea = 29,000 ksi K1 = 30 SA/Ea K1 = 0.0259 (in/ft)2 Developed length of piping between anchors L = 7.53+11.03+5+3.1=26.66 in Anchor distance, straight line between anchors

222 )0.50()03.111.3()5.153.7( −+−+−=u u=11.14656 in. Resultant of total displacement to be absorbed by the piping system Assumed to be triple of contraction in J-T valve y = 0.3 in. Apply Eq. (16):

0259.000105.0)15.1166.26(

3.0*84.0)(

122 =<=−

=−

KuLyD

Therefore, no formal flexibility analysis is needed for piping spool #1.

2. Shield circuit Figure 2 shows the supply end can shield circuit.

Straight Pipe Minimum Wall Thickness The design pressure for shield circuit is 20 atm. Equation (3a) in B31.3 para 304.1.2(a) is

applied to calculate the minimum required wall thickness for straight pipes in this circuit. The results are listed in Table 2. All straight pipe wall thicknesses are found to be sufficient according to Table 2.

Pipe Fittings Pressure Design

There are seven elbows and one tee in the main run of this circuit. These are required to be

B16.9 buttwleding fittings that are acceptable by B31.3. In the relief/gauge pipeline, there are again some CAJON tube fittings that are certified to conform to B31 codes by the vendor − Swagelok. The pressure rating of the temperature sensor feedthrough was in question. To

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validate the strength of temperature sensor feedthroughs under 20 atm design pressure, a Jefferson Lab Temporary Operational Safety Procedure (TOSP) has been composed and enforced. The procedure of this TOSP requires cold shock of the circuit using liquid nitrogen before pressure test up to 23.4 atm (330 psig) for the primary circuit and 6 atm (74 psig) for the primary return circuit. Leak check is performed after the pressure test. The pressure rating of 20 atm was verified using the TOSP.

Fig. 2 Supply end can shield circuit

Table 2 Minimum pipe/tube wall thicknesses in supply end can shield circuit

Piping assy name Reference drawing #

OD of main run

(in.)

Wall of main run

(in.)

B31.3 required wall

(in.) Safety factor

PIPING SPOOL #3 115310-1057D 0.84 0.083 0.00734 11.3

PIPING SPOOL #3 115310-1057D 1.05 0.083 0.00918 9.0

PIPING SPOOL #4 115310-1025D 0.84 0.083 0.00734 11.3 SHIELD 1-1/2 FEMALE

BAYONET ASSY 115300-1052E 1.5 0.035 0.01311 2.7

SPOOL C (S) 115310-1019C 0.25 0.035 0.00219 16.0 SPOOL BA (S) 115310-1018D 0.25 0.035 0.00219 16.0

Pressure gauge

Relief valve

NUPRO® (purge) valves

Piping spool #3

Piping spool #4

Relief/gauge pipeline

Heat station rings

35K He gas

Piping spool #4

Bayonet

Temperature sensor feedthrough

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Pressure Relieving One pressure relief valve is installed in parallel with a pressure gauge for monitoring pressure

levels in the shield circuit. The set pressure of the relief valve is decided per BPV code provisions.

Flexibility, Stress, and Support

Fig. 3 Supply end can during refurbishment activities

Piping spool #4 is attached to the supply end can 50K shield by copper thermal straps as

shown in Fig. 3. In fact, both piping spool #3 and #4 are anchored by such straps and heat station rings at multiple places. The bayonet is welded to the outer box of the supply end can. The 50K shield box is made of 0.094" thick copper. Due to the flexibility of such thin-walled copper frame, thermal contractions in this circuit will be absorbed without causing high residual thermal stresses. On the other hand, there should not be much thermal displacement developed in this circuit in view of the small temperature gradient: the bayonet isolates room temperature from cold helium gas and the rest of the circuit should have a temperature in approximately 35K to 50K range. Observing above factors, stress calculations per B31.3 are waived.

Copper straps

Bayonet welded to end can outer box

Thin-wall copper 50K shield box J-T valve

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II. Return End Can Piping Design

1. Primary Circuit A schematic of the return end can primary circuit is shown in Fig. 4. The relief system shown

has been tested previously to assure that it can properly vent helium in case of an upset condition (Wiseman, 1994).

Fig. 4 Return end can primary circuit

Straight Pipe Minimum Wall Thickness

Design pressure in end can primary circuit is 5 atm or 73.5 psi. Minimum wall thicknesses

for straight pipes in this circuit are calculated from B31.3 para 304.1.2(a) equation (3a) and the results are presented in Table 3. Note that for the check valve, wall thicknesses are computed using both the maximum OD at the middle pipe and the minimum OD at its exits. From Table 3, appreciable safety factors are achieved in all pipes in this circuit.

Helium return cap

Piping spool #1

Temperature sensor feedthrough

Check valve

Subatmospheric bayonet

Gate valve

NUPRO® (purge) valves Relief stack assembly

Parallel plate assembly with shroud

Relief valve

Pressure transducers

Instrument piping spool assembly

0.25" OD × 0.035" wall tubes

Piping spool #4

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Strength of Branch Connections The branch connection between piping spool #1 and helium return cap is also waived from

strength verification since the wall thicknesses of the pipes are excessively thick comparing to the B31.3 required minimum. For the same reason, the branch connection from the temperature sensor feedthrough tube, which is of 0.75" OD × 0.035" wall, to piping spool #4 is also waived from further analysis.

Table 3 Minimum pipe/tube wall thicknesses in return end can primary circuit

Piping assy name Reference drawing #

OD of main

run (in.)

Wall of main run

(in.)

B31.3 required wall

(in.) Safety factor

HELIUM RETURN CAP 115300-1012D 4.00 0.12 0.00879 13.7

PIPING SPOOL #1 115300-1004C 2.38 0.109 0.00522 20.9

PIPING SPOOL #4 115300-1007D 2.375 0.109 0.00522 20.9

3-1/8 SUB-ATMOSPHERIC FEMALE BAY 115300-1053E 3.125 0.035 0.00686 5.1

CHECK VALVE 11131-D-0084 4.5 0.083 0.00989 8.4

CHECK VALVE 11131-D-0084 2.38 0.083 0.00523 15.9

RELIEF STACK ASSY 115300-1055E 2.375 0.109 0.00522 20.9 TUBE 0.25 OD X 0.035

WALL 115300-1001E

ITEM 33 0.25 0.035 0.00055 63.7

INSTRUMENT PIPING SPOOL ASSEMBLY 115300-1054D 0.375 0.035 0.00082 42.5

Pipe Fittings Pressure Design

B16.9 conformable tees and elbows, as well as CAJON pipe fittings, are used to join the

pipes. As explained earlier, they are acceptable by B31.3 code.

Pressure Relieving A safety relief and primary relief are provided in this circuit. The safety relief valve is a

Circle Seal relief valve and the primary relief is a parallel plate relief type with double O-ring seal. The pressure settings are dictated by rules in ASME BPV code.

Flexibility, Stress, and Support

The relief stack assembly has triple walls, as illustrated in Fig. 4. Superinsulation materials

are wrapped in between any two of the three pipes so that the inner tube will not subject to severe temperature gradient. The bayonet has double walls and therefore the temperature in the inner tube is not expected to vary dramatically either. The strain relief for return end can primary circuit relies mainly on the thin-walled 50K shield, as shown in Fig. 5. The displacement stress, as termed in B31.3 for stress induced by thermal loads, is negligible in this circuit.

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Fig. 5 Return end can during refurbishment activities

The piping spool #1 contains a corrugated hose like the one used in supply end can primary

circuit. This hose is also protected by braided stainless steel screen that restrains the hose’s axial movement. No significant thrust force will be passed on to the contiguous pipes. No other components in this circuit can generate appreciable mechanical forces or moments. It is thus safe to say that the sustained load stress, as termed in B31.3 for stresses caused by pressure and gravity loads, is negligible. Actually, a calculation based on B31.3 para 319.4.1(c) equation (16) can be done for piping spool #4, like what was done for the supply end can primary circuit piping spool #1. The tee interface to piping spool #1 can be assumed to be free since the hose does not limit the deformation so much. Provided that there is a total of 0.3" thermal displacement to be absorbed:

Outside diameter of pipe is D = 2.375 in Reference modulus of elasticity at 21oC(70oF) Ea = 29,000 ksi K1 = 30 SA/Ea K1 = 0.0259 (in/ft)2 Developed length of piping between anchors L = 8+3+6=17 in Anchor distance, straight line between anchors

222 )0.30.3()0.80()0.60( −+−+−=u u=10 in. Total displacement to be absorbed by the piping system y = 0.3 in.

Gate valve

Thin-walled copper shield

Temperature sensor feedthrough

Relief stack assembly

Copper straps

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Apply Eq. (16):

0259.00145.0)1017(

3.0*375.2)(

122 =<=−

=−

KuLyD

Therefore, no formal flexibility analysis is needed for piping spool #4. 2. Shield circuit

Figure 6 shows the shield circuit in return end can. The entire circuit has three subassemblies:

piping spool #2, piping spool #3, and the bayonet assembly. Piping spool #2 contains a corrugated hose for strain relief.

Fig. 6 Return end can gas shielding circuit

Straight Pipe Minimum Wall Thickness The minimum pipe wall thicknesses for straight pipes in this circuit are calculated per B31.3

para 304.1.2(a) equation (3a). Design pressure for this circuit is 20 atm. The results are listed in Table 4. Large safety factors are achieved.

Piping spool #2 Piping spool #3

Bayonet

Corrugated hose

Heat station rings

Heat station sleeves

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Table 4 Minimum pipe/tube wall thicknesses in return end can shield circuit

Piping assy name Reference drawing #

OD of main

run (in.)

Wall of main run

(in.)

B31.3 required wall

(in.) Safety factor

PIPING SPOOL #2 115300-1005E 0.84 0.083 0.00734 11.3 PIPING SPOOL #2 115300-1005E 1.05 0.083 0.00918 9.0 PIPING SPOOL #3 115300-1006D 0.84 0.083 0.00734 11.3

SHIELD 1-1/2 FEMALE BAYONET ASSY 115300-1052E 1.5 0.035 0.01311 2.7

Strength of Branch Connections

No branch connections exist in this circuit.

Pipe Fittings Pressure Design Pipes and the bayonet assembly are connected by B16.9 conformable tees and elbows. They

are acceptable to B31.3 code.

Pressure Relieving No pressure relief devices are equipped in this circuit. The pressure relief for shield circuit is

done in the supply end can where a relief valve is installed.

Flexibility, Stress, and Support In Fig. 5, it can be seen that the piping spool #3 is strapped to the thin-walled 50K copper

shield. There are three heat station sleeves and two heat station rings in this circuit. They are all strapped/welded to the 50K copper shield located inside or outside of the return end can. The bayonet outer wall is welded onto the outer box of the end can. Flexibility is provided by the corrugated hose and the thin-walled copper shield. The heat stations will add heat into the gas flow so that the temperatures in the circuit may vary from 35K to 50K, as estimated. The resulted thermal displacement will be absorbed by the hose and thermal shield so that no significant residual thermal stress would develop. No sources of severe mechanical loads are present in this circuit.

IV. Fabrication and Assembly The B31.3 Chapter V “Fabrication, Assembly, and Erection” extensively listed the basic

qualifications for welders and welding procedures. Jefferson Lab has established its own welding requirements and standards. The two are found being compatible to each other. Fillet and butt welds are typically specified for all circuit components. Because of the thin wall thickness of both supply and return end cans, according to ASME B16.25, the butt welding of these pipes can be done with square or slightly chamfered pipe end preparations.

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ASME B31.3 para. 328.5.4 Welded Branch Connections requires that the branch connections shall be attached by fully penetrated groove welds. And the welds shall be finished with cover fillet welds having a throat dimension not less than tc.

The minimum tc for the branch connection in supply end can primary circuit joint between

the helium inlet baffle and piping spool #2 (refer to Fig. 1) can be easily calculated as follows (see B31.3 Figure 328.5.4D (2) for definitions of parameters):

The piping spool #2 pipe is of 0.5" IPS SCH 10S:

308.0 ′′=bT 1058.07.0 ′′== bc Tt

In the return end can primary circuit, there is a branch connection between helium return cap and piping spool #1, see Fig. 4. The weld minimum throat thickness can be calculates as

The piping spool #1 pipe is of 2.0" IPS SCH 10S:

910.0 ′′=bT 3076.07.0 ′′== bc Tt

Suppose the weld length L = 0.12 in. and the welded parts are orthogonal and center lines intersect, the weld throat is:

.0848.045cos inLt othroat ==

The throat thickness of 0.12" is thus sufficient for the supply or return end can branch

connections. In the piping spool #4 of the return end can primary circuit (refer to Fig. 4), there is a 0.75"

OD × 0.035" wall tube connecting to a 2" IPS SCH 10S 90o elbow. The B31.3 required minimum weld throat thickness for this branch connection is

The sensor mounting tube wall thickness is 0.035":

503.0 ′′=bT 0245.07.0 == bc Tt

To fulfill this requirement, a weld length between 0.08 and 0.10 is suggested:

.0287.069cos08.0 int othroat ==

V. Summary

The C100 cryomodule end can piping design has been reviewed per ASME B31.3 code for processing pipes. Piping, fittings, and valves are examined in various aspects including B31.3 required minimum wall thickness, branch connections strength, pipe fittings manufacturing standards and pressure ratings, pressure relieving system, and pipe system flexibility, stress, and

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support. It is found that all piping in end cans meets design requirements of B31.3. Special components such as feedthroughs and reliefs have been validated by operational experience in the CEBAF accelerator. Using of B16.9 fittings is necessary in order to standardize piping junctions that satisfy B31.3. Most of the pipes or tubes in end cans have wall thicknesses which yield abundant safety factors. Welding lengths at branch connections are calculated in accordance with B31.3 provisions for minimum throat thicknesses. REFERENCES

[1]. ASME B31.3-2004 “Process Piping”, ASME code for pressure piping, B31. The American Society of Mechanical Engineers.

[2]. G. E. Woods and R. B. Baguley, “CASTI Guidebook to ASME B31.3”, Fourth Edition, CASTI Publishing Inc.

[3]. E. F. Daly, “TOSP-Upgrade Cryomodule – Supply End Can Cold Feddthrough Pressure Test,” Jefferson Lab, Newport News, VA.

[4]. M. Wiseman, K. Crawford, M. Drury, K. Jordan, J. Preble, Q. Saulter, and W. Schneider, “Loss of Cavity Vacuum Experiment at CEBAF,” Advances in Cryogenic Engineering, Vol. 39, Edited by P. Kittle, Plenum Press, New York, 1994.

[5]. ASME B16.9 “Factory-Made Wrought Steel Buttwelding Fittings”, The American Society of Mechanical Engineers.

[6]. ASME B16.25 “Buttwelding Ends”, The American Society of Mechanical Engineers.