Dear all,
Thanks to all of you for your technical guidance.
On my job there is a Heat recover steam generator (HRSG). The side wall panels are welded (to AWS D1.1) to the stack from out side as per the approved drawing. There is a requirement in the company standard that the welding attachments shall be seal welded.
There are some comments from inspection side that the HRSG duct welded to stack is an external attachment and therefore should be seal welded. I do have doubt to call it an external attachment and I am thinking that in technical terms, the attachment is referred to relatively small items like, nozzles, lugs, instrument ports, stair attachments etc.
Please correct me if I am wrong. Can some one guide me where to find the technical definition of welding attachments?
Secondly what do you think of welding the exhaust duct side panels to Stack from outside only and leaving it with out welding from inside. Do you think it will cause the chances of corrosion in those pockets? HRSG is working on the exhaust of the gas turbine
Thanks,
I have never seen the "technical" definition, but I'll give it a shot: If the weld is not designed to carry load, but merely to stop the passage of gas (or liquid); it is a seal weld. If you think the weld is part of the structural strength of the assembly, ask your chain of command to clear it up for you. Chances are, someone knows the answer. It is always a good practice to maintain a questioning attitude.
As for welding on one side only (for seal welds); it is a practice done all the time. I don't necessarily agree with it, for the reason you stated, but it does cut down on half the welding.
Charles
My concern with welding 1 side only is that the proper side is chosen to exclude the corrosive materials from the crevices of the joint, not just to prevent leekage. If the material is sensitive to crevis corosion, and the exhaust gasses are corosive, My country boy reasoning would suggest seal welding at least on the inside, but I am not an engineer.
I agree with your reasoning, but my experience is that the designers of HRSG (which have a life expectancy of 25 - 30 years) always choose the "cheap" option in their design philosophy. It could be based on as simple a choice as : "it's easier (ie - will cost less) to weld from the outside.
Still, there is no reason why the question couldn't be asked in an RFI to the owner's engineer.
Charles
Definition of a seal weld per ASME section IX.
QW/QB-492
seal weld -- any weld designed primarily to provide
a specific degree of tightness against leakage
AWS 3.0
seal weld. Any weld intended primarily to provide a specific
degree of tightness against leakage.
Regards,
Gerald
Thanks all for your technical guidance and sharing with me your expertise.
In spite of the Designer statement that the welding is needed from outside only, The Company Inspector remained adamant to see welding from inside even after all explanations.
To avoid delay in the next construction activity, the contractor agreed to go ahead with the demand of Inspector and did the welding from Inside also.
My opinion: The inspectors should be with enough field experience (if they do not have specific reference) to support their stand. Otherwise the demand will be considered as a wrong use of their authority and an exploitation of the position of contractor.
I Have come across the same thing , The state inspector wanted to see more than what was put on the print So I said No problem, but your agency will receive The Bill..........That ended that.
Mike has a very good answer for inspectors trying to impose their unjustifiable wills. Money talks, bull*&^% walks.
Be polite and respectful. And then submit a polite and respectfull invoice.
I hate to spill cold water, but before you assume that you will be paid because an Inspector tells you to do something that is not in the contract scope; remember that most contracts require changes in writing (from an approval officer) before they will be honored.
The point is well taken, but make sure you document it in writing and get approval before you change the scope.
Charles
Isn't the job of the inspector to provide quality assurance? In no way does the inspector have the right to make you do something that will cost your company more money. The outside inspector should have no communication with the workers on the production line. The only person the inspector should be in contact with is the QC person in the company, who takes into account all problems and then makes a decision based on the code governing the project.
I just tell 'em to show me in the job specs. or in the code where it says that I have to do it, and I'll do it. That's usually the end of it.
By 803056 
Date 02-19-2008 22:49
Edited 02-19-2008 22:52
Whether the weld is a load carrying component of the assembly or just to "keep the weather out", if the welding is per D1.1 it has to meet the minimum joint penetration requirements, based on the thickness of the components, per the table for PJP listed in Section 2.
As for the inspector's demands; I would ask that he submit a request for a change. If his request is ligit, he shouldn't have an issue with asking for the change in writing. Sometimes they have ligitimate concerns. Once they are reviewed by the owner (engineer) the change order can be issued through proper channels.
It is a rare project that I don't see something that doesn't look correct. I submit my concerns to the EOR and ask for clarification. Sometimes the engineer tells me that the design meets his needs, other times they make a change and the contractor implements the change and collects the "extras" from the owner. It is a win-win for everyone.
best regards - Al
By br549
Date 02-20-2008 12:16
"In no way does the inspector have the right to make you do something that will cost your company more money."
They can bust you for something you've done wrong per spec or code. That can in fact cost you money.
