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Re: A Welding question

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On Jan 25, 2008, at 1:38 AM, Ed Najjarine, SE wrote:

I have a situation where we specified an aluminum
railing system consisting of welded members. The
system is manufactured in china and shipped to the US
for installation. what kinds of tests should we
request to insure that foreign welding is appropriate.
Tough job. If it were a pressure vessel job, I'd request copies of all the QA documents, the welding procedures and procedure qualifications. Then I'd probably do some quick met testing over here to make sure the materials themselves are what the supplier said they were. I'd also request design documents showing that the original designers knew enough about aluminum design. And because I'm a bit nosy, I'm real curious why you specified the system without some guarantee that the system would be welded properly and that it would meet the Aluminum Association structural spec. If you've already contracted for the railing, any testing you do may be irrelevant if it's not in the original purchase documents.

Welding aluminum isn't exactly rocket science, but it has to be done properly or you get serious problems. Aluminum undergoes a significant loss in strength when it's welded and there may be a loss in ductility depending on the welding consumables. There can be distortion issues and because aluminum has a low melting temperature, sometimes there are procedural problems.

OTOH, I've been riding a bike with a welded aluminum frame and put about 7000 miles on it and it's done pretty well. The bike was designed in the US and made in Taiwan, although it appears that each frame was welded and heat treated to restore the strength of the aluminum, presumably by the manufacturer. This isn't your everyday approach to aluminum welding but it seems to work out.

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)

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