PWHT requirement for longitudinal weld on a Hot Tap Split Tee 1

[shanib154]

As per ASME B31.8 para 825.3 Welds in all carbon steel shall be stress relieved when the nominal walthickness exceeds 1.25inch.

I am working on a sales gas pipeline project, where a 48 inch Hot tap connection is to be made on 56" pipeline.
The Hot tap split tee vendor has proposed a split tee of 2 inch wall thickness ,which by code requires stress relieving, which is not practical to do on live gas line with 960 PSIG maop.

When i pointed out this issue with the vendor , they came up with the solution to machine the split tee near the longitudinal weld weld to a wall thickness of 1.25 inch.

can some one please advice if this is allowed ?

Design pressure is 960 psig
design factor is 0.5
split tee is 56"x48"x2"thick 96.375 inch long
material WPHY 70, FLANGE IS ASME B16.47A ,ASTM A707 L5 CL3

 

[Ripz]

Remember this is a construction code, not a welding-while-in-service code.

The major purpose of your stress relieving is to prevent the weld from cooling too rapidly which may result in cracking. There is also the issue of residual stresses.

What is your operating temperature?

If your temperature is sufficient to prevent rapid cooling of your weldment, then an engineering assessment can be done to forego the Stress relieving.

 

[shanib154]

Hi Ripz ,

Thanks for the response..

The operating temperature during Hot Tap will be around 150deg F.

By "Engineering Assessment" did u mean FEA analysis of the weld and tee ? or is there a simpler way to prove that stress relieving is not required?

 

[Ripz]

My opinion, is that the weld will cool to quickly with your 150F fluid. The fluid flow with also provide much faster cooling that if exposed to ambient air. Thus the possibility of cracking while cooling exists.

Not sure of how else to help you. Sorry.