Can I weld supports to repad after hydrotest? 8

[ljas]

Do to time restraints and scheduling of the outside inspectors I would like to weld the supports onto the re-pads of a pressure vessel after we hydrotest the shell. Is this ok since the welds from the pads to the shell are already done?

Thanks

 

[Duwe6]

Call up YOUR AI and ask him/her. The answer should be 'Yes', but it is up to the AI. Repad is 'structural' not 'pressure boundary', thus the weep hole in it.

 

[jte]

Now let's not go around leaving the client / owner / user out of this!

Yes, the AI should be involved, but a modestly savvy client will have issued purchase documentation which would have included a vessel spec as well. This issue may be addressed in the spec.

A further complication can arise from PWHT requirements - the assumption would be that these welds would not require PWHT if they were Code boundary, but this is not made clear in the original post.

 

[ljas]

AI said no. None of us understand why and will talk to him more tomorrow about it. We ended up putting off all testing until the supports could be fully welded. There is no PWHT on this unit and the pads are really only poison pads since there is a 1/4 weep hole in them.

Thanks for the replies.

 

[Duwe6]

NO those repads are not "poison pads" due to the weep hole. But they are much closer to a structural attachment than a pressure boundary due to that [mandatory] weep hole. Repads are a mandatory part of a design, 'poison pads' are just there to prevent rust streaking at the s/s to c/s interface. ASSuming that the c/s got properly prepped & painted.

Did somebody get the AI upset? And thank you for posting the resolution to your issue. Not many folks will do that. And we do prefer to be able to 'close the loop' on problems.

 

[doct9960]

ljas ,

AI said no. None of us understand why and will talk to him more tomorrow about it.

I would say no too. If the Code of Construction is ASME Section VIII Div. 1, read UG-99(a).

Hints:
"all fabrication has been completed"
"all examinations have been performed"

 

[gr2vessels]

Well, I wouldn't scrap a pressure vessel if I damaged lightly a pipe support right after the hydrotest. I would cut it off and replace it, carefully to not affect the pressure envelope and I would clearly document the repair work, tests, etc. Afterall, the intent of UG-99(a) was to ensure no significant work was undertaken after hydrotest, affecting the pressure envelope. I have also seen a new nozzle being added to the pressure vessel when brand new equipment was installed on site and required an additional nozzle. No, API 510 did not apply.
I believe an engineer should be able to argue with the AI and prevail his good judgement and experience over the simple following a letter of the code.
Cheers,
gr2vessels

 

[moltenmetal]

A recent thread made this murky area a little clearer for me. I used to take UG-99 as an absolute requirement for a re-hydro after any welding to the pressure envelope- even for studs for insulation attachment etc. just like doct9960. I guess it depends on whether the vessel has been completed, making the new work an R stamp repair, or whether it's considered additional work required to complete the vessel. And that distinction is arbitrary enough when the vessel hasn't left the vessel shop yet to make me feel like more of a lawyer than an engineer, which is a situation which always makes my skin crawl a bit.

From a purely engineering perspective, setting aside treating these code rules as if they were carved in stone tablets and given to Moses, or Acts of Parliament (incidentally they ARE given the force of legal regulation by some jurisdictions): assuming the modification doesn't substantially alter the design of the vessel by introducing significant loads previously unaccounted for, and the work (welding) is permitted (i.e. no PWHT required, the vessel isn't lined etc.), are done properly and inspected (and documented) in a way that ensures the soundness of the pressure envelope metal is maintained, I'm not sure why on earth we'd prohibit this kind of modification and absolutely require a huge vessel to be re-hydro'd instead. But in the OP's case, that's a matter for discussion with the AI, whose profession makes him or her more of a "stone tablet" kind of person in my experience.

 

[Duwe6]

Well said, MM.

And yes, some AI's have the "Tablets of Stone" mentality, some have more of a "Functional Engineering" mentality. But the final responsibility resides with them and their company [not really the fab shop], so they must have that authority. Things get disfunctional pretty quickly when responsibility and authority are not kept togather.

 

[doct9960]

ASME Section VIII, Division 1 is a "Design by Rules" code. You either follow the rules or not. No matter how much you argue with the AI and talk some engineering sense to him, he needs to abide by the rules.

The AI cannot sign the Manufacturer's Data Report if the vessel is not constructed to the rules of ASME VIII Div 1. It is as simple as that.

 

[jte]

doct-

Ok, let me pose two and a half scenarios for you and please provide us with your interpretation:

1) A vessel with a weld-end nozzle is provided to a client. A connecting pipe is welded to the nozzle stub. Does this vessel require a hydrotest for Section VIII Div. 1 reasons? On the basis of which paragraph?

2) A vessel is provided with pads on the bottom shell/head to which legs are attached. The vessel is delivered to the field and the legs are found to be too long. The legs are cut short and new baseplates are welded to them. Does this vessel require a hydrotest for Section VIII Div. 1 reasons? On the basis of which paragraph?


2)a) A vessel is provided with pads on the bottom shell / head, the sole intent of these pads is to allow for a "landing" for legs which will be welded on in the field. The pads are not intended to meet any Section VIII Div. 1 requirement. After welding the legs on to the pads, does this vessel require a hydrotest for Section VIII Div. 1 reasons? On the basis of which paragraph?

 

[MrPDes]

A reinforcing pad around a nozzle plays a critical role in reinforcing the opening. The Re-Pad contributes to retaining the internal presure. If it is altered by welding, it needs to be re-hydrotested.

If on the other hand a doubler pad is welded onto the shell before the hydrotest and then supports are welded on top of it that after the hydrotest then this is okay as the doubler pad does not contribute to retaining the internal pressure.

That is my interpretation. Of course you might find an AI that is Okay with a few tack welds.

 

[doct9960]

Hi jte,

The OP is about a vessel that has not left the vessel manufacturer shop. The scenarios you mentioned are post-construction activities. In my opinion, after a vessel leaves the shop, any modifications or alterations to it are no longer in the scope of ASME Section VIII Div 1. I guess they would fall under a Repair Code like NBIC.

For Scenario 2, let us say the vessel is still in the manufacturer shop. In my opinion, the modifications to the legs does not require re-hydro because the modifications are done on structural components, not on a vessel component like the repad mentioned in the OP. Although the repads are for non-pressure attachments, I consider them as vessel components that are essential to the structural integrity of the vessel. Why else would they provide repads for the mentioned supports? Those repads are probably required to minimize local stress at the attachment areas.

 

[metengr]

Section VIII is fairly clear on rules regarding when fabrication is completed. It is unfortunate that the hydrotest was not better planned in that schedule and time constraints are not reasons or excuses to allow for what the rules state regarding after a hydrotest.

I do not agree with the rules in Section VIII, Div 1, but since I am a member of Section I standards committee we do allow for post hydro welding with no re-hydrotest, as defined in PW-54. Maybe Section VIII needs to follow the "mother code" for common sense. Boy, I hope I don't open a can of worms with my fellow code volunteers on Section VIII.

 

[sanshu1111]

U 1 (e)(2) -where non pressure parts are welded directly to either the internal or external pressure retaining surface of a pressure vessel, this scope shall include the design, fabrication, testing, and material requirements established for non pressure part attachments by the applicable para-graphs of this Division(3)

End note 3- These requirements for design, fabrication, testing, and material for non pressure part attachments do not establish the length, size, or shape of the attachment material. Pads and stand offs are permitted and the scope can terminate at the next welded or rmechanical joint

A doubler/ pad plate is a non pressure structural attachment. Based on the footnote 3, ASME Sec VIII scope ends at next welded or mechanical joint which will be a welded joint between pad and support. In line with U1(e)(1)(a) which allow scope termination at first welded joint with external piping, I would guess that "next weld" which is the scope termination for non pressure pad, can be allowed after hydotest.

 

[Duwe6]

Da Questions, da answere:

1) That connection weld is specifically under the piping Code
2) Structural item, with the weld well-removed from any pressure-boundary atachment
2a) "The pads are not intended to meet any Section VIII Div. 1 requirement. . ." so again, not a pressure boundary item.

New Ques. #3) ljas wants to attach to a repad, not near the repad-to-vessel weld. Legal?
per sanshu1111's Code citation, it depends if in the opinion if the repad is "non-pressure boundary" or not. For this instance, the cognizant AI feels it is, sanshu & I do not.

 

[jte]

sanshu

Nice post! This is exactly what I was driving at in my previous post. Whether or not the vessel has left the shop doesn't really matter. The point in my mind would be that just as Section VIII Div. 1 allows for a weld directly to the pressure boundary - pipe to weld end nozzle - without a Section VIII mandated hydrotest, a weld of a support to a repad should not fall within the scope of Section VIII either. Clearly, the support itself is excluded from the scope - I don't think anybody would argue that.

So the question is whether or not a weld may be made to a repad provided for the purpose of attaching supports post-hydrotest. I think the reference above clearly answers that.


metengr

Agree that cost and schedule are nothing but attempts at an excuse and are no reason at all for arguing for breaking the rules. I think the question here lies in interpretations of what the rules are, and I think sanshu helped to clarify that quite a bit in this case in the post above.

The "mother code" eh? I think some of the folks down the hall would perhaps agree - and comment that "mother" should get up to speed with the modern world! This would make for a good discussion over a beer.

 

[jte]

Hi Duwe

Didn't see your post earlier - I suppose we were both typing at the same time.

For the record, I agree with your thoughts on my questions. That doesn't necesserely make us right, but at least there are two of us who agree on this.

I think my 2)a) question answers your 3) question. If one could legally perform this weld in the field, then why on earth would it not be ok to do in a shop, either before or after the U stamping ceremony? doct was indicating he felt there would be a distinction; I don't see it. Once the U stamp is on then NBIC governs. I get it. But as far as I know, NBIC claims no more scope than VIII-1 does. Thus, it doesn't matter.

 

[doct9960]

Hi jte,

It's Friday and I'm down to my fifth pint of beer, so forgive me if I am incoherent.

I love these healthy discussions, especially when experts and experienced people like you and metengr are involved. Since I've joined Eng-Tips back in 2006, I have valued the technical insights and opinions from both of you. (For those who are new to the forum, check out who the top 2 MVP's in the forum are.)

jte said:

If one could legally perform this weld in the field, then why on earth would it not be ok to do in a shop, either before or after the U stamping ceremony? doct was indicating he felt there would be a distinction;

jte, I strongly believe there should be a distinction. It all boils down to accountability. I believe that after a vessel is completed, stamped and got out of the vessel shop...anything unfortunate that happens to it as a result of alterations/modifications or as a result of stupidity done by others, the damage done to the vessel is no longer the responsibility of the original Code of Construction and the vessel manufacturer. In my line of work in the vessel drafting/designing, we call it CYA...cover your ass. (I first heard the term from a Parsons/ex-Fluor vessel engineer back in the 90's when I was a fresh grad)

The footnote #3 in U-1(e)(2) still befuddles me. I didn't find it in ASME VIII-Div.2 or other codes. I believe that footnote can only be found in ASME VIII-Div.1. I have a different interpretation to the sentence, "Pads and standoffs are permitted and the scope can terminate at the next welded or mechanical joint." For example, we have a platform clip with a repad. In my opinion, the scope of ASME and the responsibility of the vessel manufacturer is up to the clip. The bolting and the platform that attaches to the clip are outside the scope of ASME. If you say the scope of ASME is just up to the weld of the clip, then who is responsible for sizing the clip and the weld? The structural engineer who stamps my L&P drawings does not want to be responsible for the vessel clips and welds, whether they are on the vessel or on the repads.

Going back to the OP, it was not mentioned what type of supports are welded on the repads.
1. To jte & Duwe6, allow me to pose this scenario and let me know your interpretations:
Put yourselves in the shoes of the AI. If Ijas wants to weld support saddles or support lugs on the repads of the vessel after the hydrotest, would you allow it and would you sign the Manufacturer's Data Report and certify that to the best of your knowledge and belief, the Manufacturer has constructed the vessel in accordance with ASME BPV Code? (By support saddles and lugs, I mean the structural supports that hold the vessel in place.)

2. To Ijas, since you were gracious enough for informing us that the AI rejected your request to weld the supports after hydro...can you share why the AI rejected it?. When you mentioned "supports" in your OP, what type of supports are they?

Thanks,
doct

 

[Duwe6]

"If Ijas wants to weld support saddles or support lugs on the repads. . ."
For minor loads, unreservedly YES*. For a major load, probably not. And if allowed, it would be treated as an 'oops' and not automatically allowed whenever they paint themselves into a corner.

*ASSumes that it gets attached by the "A" team of fitters & welders, not the guy running a broom or grinder.