1 Answer

I would contact one of the companies that supply pre-formed backing strips for welding certification test coupons for pipe. That way you would get pre-formed (rolled) backing strips shipped to the site,  that are similar in composition, and would also help with alligning the tubes for welding.

You could order a small amount for immediate delivery to hold you over until a larger main shipment arrived at a later date. The added benefit to all this would be that you could order them made to the specific diameter you need. Just google "pipe welding certification test materials."  Hope this helps you. My experience has always been with open root, and primarily intermediate-sized structural steel structures.