1.SCOPE

Engineering StandardsStandard8370

Page

1 of 2

ADJOININGIssue Date

UNEQUAL WALL PIPE

06/86

Rev. No.3

Date07/93

1.SCOPE

This standard establishes the allowed joint design alternatives for welding pipe sections that have unequal wall thickness.

2.CODES AND STANDARDS

49 CFR Part 192, paragraph 192.235

GPTC Guide for Gas Transmission and Distribution Systems, Appendix G-5

3.DESIGN PRESSURE

3.1The SMYS and wall thickness of the pipe sections to be joined must meet design requirements for the maximum pressure but need not be equal.

3.2The maximum allowable wall thickness (tD) for design calculation of the maximum design pressure is 1.5 times the thinner wall thickness (t); however, the nominal wall thickness (T) may actually be greater.

4.UNEQUAL INTERNAL DIAMETERS (See Drawings 1, 2, 3, 4 ,5 & 6)

4.1If the hoop stress at the maximum design pressure is less than 20 percent SMYS and the nominal wall thickness of adjoining pipe ends do not differ by more than 1/8" (0.125"), no special treatment is necessary.

4.2If the hoop stress at the maximum design pressure is 20 percent SMYS or more and the nominal wall thickness of adjoining pipe ends do not differ by more than 3/32" (0.094"), no special treatment is necessary.

4.3When the nominal wall thickness of adjoining pipe ends differ in excess of 3/32" (1/8" for hoop stress less than 20 percent), but not more than 1/2 the thickness of the thinner section, the transition shall be made by a tapered cut or tapered weld as shown in Drawings 3 and 4, respectively. If the internal offset exceeds 1/2 the thickness of the thinner section, the transition shall be made by a taper cut or by a combination taper cut and tapered weld as shown in Drawings 3 and 5, respectively. Taper cutting shall be by mechanical tool or machine torch.

5.UNEQUAL EXTERNAL DIAMETERS (See Drawings 6 & 7)

5.1For external offset 1.5 times the thinner wall thickness (t) the transition shall be made in the girth weld and a 30 tapered preparation.

6.UNEQUAL EXTERNAL AND INTERNAL DIAMETERS (See Drawing 8)

When both internal and external offsets are encountered, both Sections 4 and 5 of this standard apply as shown in Drawing 8.

* Indicates revised paragraph, this Rev. No.