PWHT for Tube-Tubesheet Joint 1

[Afox88]

Hi Guys,

We are quoting a replacement tube bundle for a high pressure steam generator (BKU), whose service clearly falls under UW-2(C) for unfired steam boilers. This bundle was already replaced once in 2014, and the tube-tubesheet joint at that time was strength welded but PWHT was not performed. The only welding that will take place on the replacement component is the tube-tubesheet weld.

What is your thoughts on this joint? Are we required to PWHT the tube-tubesheet joint in order to comply with UW-2(C)?

Thanks in advance.

 

[Afox88]

Forgot to mention, that this is all CS.

 

[SnTMan]

Afox88, I can't provide a specific exemption, but PWHT of a tube-TS joint is rarely (if ever) done, falling under UW-2(c) or not.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Afox88]

Thanks SnTman for the response.

I have seen many cases where non-removable bundles (like a BEM or NEU) have undergone PWHT with the exchanger in order to comply with the PWHT requirements of the shell, etc. I have never thought about it for just a U-bundle as I have never had a situation arise where I had the exchanger be CS, removable bundle, have strength weld, and be either lethal service or an unfired steam boiler. I have never had all 4 apply to one job, until now.

I will run it by my AI to see his thoughts.

 

[metengr]

Look at UW-2 a 1(a), these welds would be internal to the heat exchanger, therefore exempt from PWHT.

 

[Afox88]

Metengr,

Pardon my ignorance, but I don't see the relevance from that section to the question of PWHT. It applies only to lethal service, which this is not, and only says that internal tubes do not need to have butt welded long seams. I don't see the connection, even if this were a lethal service exchanger.

Please elaborate.

 

[metengr]

My mistake, but I thought you cited UW-2 SERVICE RESTRICTIONS in your original post, which pertains to lethal service under all of UW-2 including 2(c). If you mean U-2 (c) under the Scope, this pertains to vessels where steam is generated. Correct?

 

[metengr]

PWHT requirements would fall under UCS-56 for CS pressure vessels unless UW-2 Service Restrictions is mandated. Since this does not fall under UW-2, nominal thickness definition under UW-40 would be followed for PWHT. So, no PWHT would be required.

 

[Afox88]

My understanding is that UW-2(a) refers to lethal service and UW-2(c) refers to unfired steam generators, and they are completely isolated and separate. The U-bundle I am working on is in steam generating service.

U-2(c) in the scope pertains to mixing and matching materials and fabrication methods in one pressure vessel.

 

[metengr]

Afox88
I think you better look again at UW-2 (a) and information that follows. The service restrictions are applicable to lethal service only and nothing more. My response to your post above is correct regarding UCS-56 for PWHT requirements.

 

[Afox88]

metengr,

I am agreeing that lethal service UW-2(a) does not apply in this case, in its entirety.

The specific requirement I am referring to is UW-2(c)(3), which is calling for PWHT and does not have any exception with regards to tube-tubesheet joint or anything else.

 

[metengr]

Afox88
First my apologies, I had a senior moment for referencing U-2 because I thought it was a misprint when you referenced UW-2 (c). I am not an expert on Section VIII, Div 1 like I am with BPV I because I sit on BPV I standards committee. With that said, I do know several BPV VIII members and I recall discussing the applicability of UW-2 and the restrictions in all of UW-2 were applicable to any exposure to lethal service application.

 

[Afox88]

Metengr,

No problem. I am just glad to know that I am not crazy. I read your posts on this forum all the time, and was starting to think I might be.

Of all the service cases in UW-2, lethal services is by far the most stringent, but the section does clearly differentiate between the different service cases.

That being said, my AI will be in my office tomorrow anyway and I will just wait to ask him.

Thank You,

 

[SnTMan]

Afox88, please post your result, it will be of interest to myself and others I am sure.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Afox88]

I will let you guys know when this is resolved. It is being passed around the inspection agency.

Our AI wasn't sure but thought no PWHT required.
His boss wasn't sure but thought yes, PWHT required.

I will get to the bottom of this. They will have to give me an answer eventually as they will have to sign the U-2 in the end of the day.

 

[Afox88]

My inspection agency has pointed me to Table UCS-56-1. In the general notes (b)(3)(b), it says the following:

(b): Post weld heat treatment is mandatory under the following conditions:
(b)(3): For welded joints of all thicknesses if required by UW-2, except postweld heat treatment is not mandatory under the conditions specified below:
(b)(3)(b): for groove welds not over 1/2 in. in size or fillet welds with a throat thickness of 1/2 in. or less that attach tubes to a tubesheet when the tube diameter does not exceed 2 in. A preheat of 200°F minimum must be applied when the carbon content of the tubesheet exceeds 0.22%.

So for my case, the strengths welds are not close to exceeding 1/2" thk so I would not need PWHT, but there are cases that would require it. For other steel P-numbers, this exemption may not be there.

 

[EdStainless]

Thanks for getting back and running this one to ground.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[SnTMan]

Ditto

The problem with sloppy work is that the supply FAR EXCEEDS the demand