ASME B31.4 PWHT Issue 2

[yukon09]

I have questions regarding PWHT on ASME B31.4 piping welding
"434.8.9 Stress Relieving (a) Welds shall be stress relieved when the effective weld throat (see Fig. 434.8.6-2) exceeds 1 1/4 in. (32 mm)..."

But there is another clause:
"The thickness to be used to determine the stress-relieving requirements of branch connections or slip-on flanges shall be the thickness of the pipe or header."
I have a branch connection with 1 1/4" pipe header, 1" reinforcement pad, and a branch pipe (see attachment). The contractor insists that stress relieving is not required because the pipe header is not above 1 1/4". They weld the branch to header first, MT and grind the weld, and then weld the repad. The WPS and filler metal are all the same. They think the welds are two separate welds. But to my understanding, the welds are a single weld, the effective weld throat exceeds 1 1/4" and will need stress relieving.
My questions are:
The weld branch connection with repad is a single weld or separate welds? Does PWHT required or not per the code.
I appreciate your great help.

 

[DekDee]

yukon09,
My opinion and I stress opinion only is 2 x welds.
If the repad was fitted onto the header first and the repad was prepared so that there was a 2 1/4" single bevel weld then it would be considered a single weld.
However, if the branch is welded first and then MT tested the first weld is deemed complete.
When you add a repad the weld joining the repad to the header would be considered an additional weld.

As per the clause you have noted - "The thickness to be used to determine the stress-relieving requirements of branch connections or slip-on flanges shall be the thickness of the pipe or header."
The repad is neither pipe nor header.
Cheers,
Shane

 

[metengr]

First, based on your sketch, the alignment of the branch connection groove weld with the repad fillet weld would be a combined weld deposit. Why? Because if you look at other codes and standards the groove and fillet welds when deposited one on top of the other are in alignment and are taken in total length. Does the total weld length deposited radially in a plane really matter if the welds are deposited sequentially? No.

If the repad had been sized larger in diameter and away from the branch groove weld, this would follow DekDee's logic, which I agree. However, these are clearly not separate welds as deposited with one on top of the other.

So, in this case based on the total weld deposit thickness exceeding 1.25" with no preheat or 1.5" with a 200 deg F preheat per B31.4 434.8.9, PWHT is required. Plus, I would require it regardless because of the size of the weld and residual stress with a reinforced branch connection....

 

[DekDee]

I do not have a copy of B31.4 so I have used B31.3 as an example.

328.5.4 Welded Branch Connections
(h) Examination and any necessary repairs of the
completed weld between branch and run shall be made
before adding a pad or saddle.

That supports my original statement regarding completed weld.

However,
The thickness requirements for PWHT as per 331.1.3 state thickness is calculated using a combination of the run pipe thickness, repad thickness and covering fillet well throat thickness.

Therefore metengrs comments are correct - PWHT is required (if B31.4 requirements are in line with B31.3)

 

[yukon09]

Hi, DekDee, and Metengr, I appreciate your great insight on this PWHT issue. I have compared B31.3 and B31.4 and found the discrepancies between the codes.
From B31.3, as mentioned by Dekdee, PWHT requirements are based on "control thickness". For the branch connection with repad, the control thickness would be a combination of the run pipe thickness, repad thickness, and fillet weld throat thickness as per 331.1.3 (5) for the Fig. 328.5.4D illustration (4).
From B31.4, clause specifies "The thickness to be used to determine the stress-relieving requirements of branch connections or slip-on flanges shall be the thickness of the pipe or header." No matter how thick a final weld is, the stress-relieving requirement is relied only on the pipe or header. I think it makes no sense.
For my case, the thickness of run pipe is 1 1/4", and the repad is 1". the contractor has done a groove weld to weld the branch to run pipe, MT the weld, and then ground flush the weld to fit up the repad. They completed another grove weld plus a fillet weld to weld the repad to the branch. The contractor insists that they are two separate welds, a groove weld and a groove weld + fillet weld. They have the same point with DekDee, the groove weld is deemed finished after MT and flush grinding. Since the run pipe is 1 1/4", it is compliance with the B31.4 code with no preheat and PWHT.
Is it a loop hole of B31.4? considering the actual weld thickness, PWHT should be in place but not required by current 31.4 code. I am going to send a letter to B31.4 Committee.

 

[yukon09]

There is another issue regarding the branch connection weld. some engineers consider the groove weld of branch to run pipe as pressure containment weld, and the groove weld+ fillet weld of repad to branch is non-pressure containment weld/ attachment weld/ Weld reinforcement. IS this reason for B31.4 to consider only run pipe thickness for PWHT reuqirement?

 

[gtaw]

The weld isn't complete until the post weld heat treatment is complete. Grinding and performing MT on the weld doesn't mean the weld is complete. I would consider it to be an in-process operation.

Does it mean the weld is completed because someone grinds a root bead to improve the weld profile and performs MT on the root bead to ensure it isn't cracked? Of course not, it simply prudent to make sure the root bead is acceptable before proceeding to deposit additional weld. This is no different.

This contractor would no doubt try to peddle the notion that the groove weld is separate from the reinforcing fillet weld. Nice snow job if he's dealing with a "newbie."

Best regards - Al

 

[metengr]

yukon09;
I understand your frustration being involved with several standards committees. Sometimes code language is developed and most scenarios are covered, other possible scenarios are not and that is where engineering judgement is necessary.

In your sketch, the branch connection is inserted full thickness into the main pipe run and is full penetration welded. The weld for the repad, which is required by area reinforcement to ensure adequate strength to the main pipe run - so it is part of the main pipe run to contain pressure, happens to be tied in directly to the original full penetration weld. This is not discussed specifically in B31.4 regarding controlling thickness for PWHT. Silence does not mean PWHT is exempted.

 

[yukon09]

Hi, Metengr, great point regarding code language and engineering judgement. It is always good to have questioning attitude about the codes and standards.

 

[DekDee]

It appears it is a contractual arguement that will cost one party or the other time and money.
If the requirements of B31.4 are only " The thickness to be used to determine the stress-relieving requirements of branch connections or slip-on flanges shall be the thickness of the pipe or header." and nothing else I would side with the contractor.

Forget everything about what we all think is right (and also what I posted from B31.3)- if it ended up in arbitration because the contractor claimed the client unfairly imposed additional costs not mandated by the code I would think the contractor had a fair case.

I also am involved with a code committee and sometimes I struggle with the decisions made and the wording involved but it is a group of volunteers doing the best they can and it is impossible to cover every possible scenario.
Based on the detailed "controlling thickness" requirements of B31.3 I think the B31.4 committee need to do a bit more work on clarifying their code requirements.
Cheers,
Shane

 

[gtaw]

If it was too easy, it wouldn't be fun.

Best regards - Al

 

[yukon09]

Cost is not an issue and do right thing to avoid Loss of Containment is the most important. A single leaking will cost money to fabricate thousands of spools and also an environmental disaster.

 

[Trestala]

So, would this also be applicable for ASME Boiler and Pressure Vessel Code vessels (Div.1 and Div.2)? Where shell thickness + reinforcing pad thickness exceeds 38 mm?

 

[metengr]

So, would this also be applicable for ASME Boiler and Pressure Vessel Code vessels (Div.1 and Div.2)? Where shell thickness + reinforcing pad thickness exceeds 38 mm?

First, please start a new thread versus hijacking an existing thread. Second comment - no. ASME B&PV Code, Section VIII, Div 1 and 2 have their own PWHT requirements apart from ASME B31.4.