Backing Bar Materials
Backing Bar Materials
(OP)
I'm revisiting what should be a simple question. We typically use 1/4" thk backing bars on circ. seams (heat exchanger closing seams) since the material is SA-36 and comliant with UG-(5)(a) and UCS-12. The question has come up if we can use thinner material that is easier to work with (3/16" or 1/8"), but that material only comes in HR strip. HR strip has chemicals and cert of compliance, but the backing bar is integral with a pressure boundary and subject to pressure.
Can HR strip material be used? What code section(s) allow this?
Can HR strip material be used? What code section(s) allow this?





RE: Backing Bar Materials
Your proposed material is HR strip of what? SA-36? Isn't SA-36 strip and bar normally hot-rolled?
Are you saying that the backing bar would be removed in one case and left in place in the other case? That could make a difference to your joint efficiencies and your welding procedure qualification.
What objection has been raised? That might help us understand the problem.
RE: Backing Bar Materials
Regards,
Mike
RE: Backing Bar Materials
Question (1): Are backing strips left in place after completion of the vessel considered to be material subject to stress due to pressure?
Reply (1): Yes.
Question (2): Are backing strips, whether removed or left in place, considered nonpressure parts, such as skirts, baffles, and supporting lugs?
Reply (2): No.
[question 3 ommitted]
However, UCS-5(b) does allow you to use non-code material for backing strips, with conditions.
RE: Backing Bar Materials
In that case it seems UW-5(a), UCS-5(b), etc. would govern.
Thanks,
Mike
RE: Backing Bar Materials
I think that might be an overzealous interpretation of the interpretation. It doesn't actually say that a removed backing strip is a pressure part. But even if it is a pressure part, ("materials used in the construction of welded pressure vessels" per UW-5,) it clearly is not "material subject to stress due to pressure," which is how UG-5, UCS-5, etc., are worded. So it could still be made of non-code material of proven weldable quality. (Otherwise UCS-5(b) would make no sense.)
I'm not sure what the impact would be of treating it as a pressure part. Maybe the intent is just to require identification of the removed backing strip? Maybe that's what UG-116(l) is getting at? I've puzzled over that one before and never really figured it out.
RE: Backing Bar Materials
Probably the only "pressure" a removed backing strip is going to be subjected to is when it gets crushed at the scrapyard. At that point nobody cares about it:)
Have a good weekend, all.
Mike
RE: Backing Bar Materials
If c/s A/SA 36 to any other similar metals, not a problem.
finally: check with your AI for approval.
I see no Code violations for Sect VIII-1 here.
On the other hand there section I will not allow A/SA36.