Longitudinal Welded Pipe in LNG Applications

[numberfive]

Under the heading "9.7.3 Welded Pipe Tests" NFPA 59A, 2009 Edition states in para. 9.7.3.1 - Longitudinal welded pipe that is subjected to service temperatures of -20 deg. F (-29 deg. C) shall meet one of the following requirements:
1 - It shall have a design pressure of less than two-thirds the mill proof test pressure or subsequent shop or field hydrostatic test pressure.
2 - It shall be subjected to 100 percent radiographic or ultrasonic inspection of the longitudinal or spiral weld.

Question 1 - Is the "mill proof test" refering to the hydrostatic test required by most ASME & ASTM pipe & tube material specifications (ex: SA-312) or is this an additional test performed by the material manufacturer?

Question 2 - Is it acceptable to use longitudinal welded pipe that has had a nondestructive electric test (eddy current not RT or UT) in lieu of a hydrostatic test as allowed in the material specification (ex: SA-312 Type 304/304L) when the pipe will not receive a shop or field hydrostatic test at 1.5 times the design pressure, but rather a pneumatic test at 1.1 times the design pressure per B31.3.

Any input would be greatly appreciated.

Thanks!

 

[BigInch]

1) yes.

2) you sure about no hydrotest? Air test only??? I believe that is allowed under special circumstances when it is impossible to do a hydro. Is it really impossible, or are you just saying so to avoid the hydro.

From "BigInch's Extremely simple theory of everything."

 

[stanweld]

2) No. 100% RT or UT is required - not meerly Eddy Current. NFPA 59A supercedes B31.3.

 

[numberfive]

B31.3 allows pneumatic testing when the owner considers a hydrostatic leak test "impracticable" - 345.1 (b). This piping will be constructed outside in sub-freezing temperatures - freezing of the water in the lines during a hydrostatic leak test and total evacuation of any residual water left in the system is of concern.

 

[BigInch]

I suppose you got no water heater or antifreeze either.
So no chem plant constructed in the winter was ever tested with water. Right.

From "BigInch's Extremely simple theory of everything."

 

[numberfive]

So if I understand 9.7.3.1 correctly, we have four options for pipe subjected to service temperatures below -20 deg. F:

1 - Order longitudinal welded pipe hydrostatically tested to a pressure at least 1.5 times greater than the system design pressure from the manufacturer (mill proof test).

2 - Order longitudinal welded pipe that is not hydrostatically tested by the manufacturer and upon receipt shop or field hydro test the pipe ourselves to a pressure at least 1.5 times greater than the system design pressure.

3 - Order longitudinal welded pipe that is fully examined by either RT or UT.

4 - Order seamless pipe in which case 9.7.3.1 is not applicable.

 

[stanweld]

numberfive,
In the USA, NFPA 59A trumps B31.3 for testing requirements. NFPA 59A has added testing requirements beyond those established in B31.3.

If the LNG facility is outside the USA and NFPA 59A is invoked in the Contract, the Owner may possibly permit deviation from NFPA 59A requirements provided the jurisdiction does not invoke NFPA 59A as part of its regulations.

 

[numberfive]

This system is in the USA and the contract spec. requires construction and testing in accordance with B31.3. However compliance with NFPA 59A is mandatory in the jurisdiction, therefore on the issue of longitudinal welded pipe I feel that we must comply with one of the four options that I listed previously.

The material specifications are called out in the contract spec. but seamless or welded is not.

 

[Duwe6]

Don't you love contract specs that just say A-53? What they need, and posibly wanted, is SA-53 Gr. B Smls [or SA-106 Gr. B]. Obviously not written/reviewed by a pipe engineer. Plus the omission of NFPA 59A further shows that whoever wrote that contract was less than competent in this area. Happens all the time.

Destructive testing has regularly proved that even with a circ. weld with Incomplete Penetration all the way around, the Long seam is still the weakest part of the pipe. Thus, with the danger of a BLEVE - Boiling Liquid Vapor Explosion - avoiding Longitudinal seams is the prudent choice of a cognizant, conservative engineer. The ONLY seamed pipe I would use is SA-53 Gr. B, with 100% UT shearwave of each seam by a certified 3rd-Party NDT firm. Unless your pipe is rather large, seamless will be cheaper.

 

[stanweld]

49CFR Part 193 governs design, construction and operation of LNG facilities. It is the LAW!! Part 193 specifically mandates NFPA 59A. Regardless of what your contract stated, the OWNER must comply with the added testing requirements defined therein.

Your company may have recourse to recover additional costs - but I doubt it.