My question arose from a desire to easily remove the backer bar for this particular structural application rather than better penetration.
The foreman in the field desired to use brass backing material and other ironworkers were highly recommending it.
My hesitation comes from the fact that the D1.1 does not discuss the use of brass for backing material unless you consider the statement in 5.10 ",or similar materials" would apply. Copper is mentioned in 5.10. However, in the C5.10, it states that any material besides steel for a prequalified groove weld needs to be qualified.
The WPS that I created for this particular application (splice welds in W trusses - 2 splices each end - top and bottom chord) calls for steel backing per D1.1.
Although the workers out in the field are preferring brass, I hesitate to deviate from the WPS for the above reasons. In addition, as G Roberts stated, the concern for weld contamination exists with copper or brass. The AWS Welding Handbook, Volume 4, "Metals and their Weldability" considers the risks associated with the use of copper or brass in the welding process.
In the replies I have received thus far as well as the research, brass is ruled out and if we go with copper, we will need to qualify it.
I appreciate any input on this. Thanks.
By -
Date 05-15-2001 17:33
I am not sure if I understand your question properly, so I will give you the "fundamental" answer. Tell me if I am aiming too low!
As with any backing, the idea is to ensure a complete penetration of your weld in a consistent manner because you have something to "weld against". This requires much less skill in achieving full penetration welds than without backing. When using steel backing, the backing strip will fuse into the weld. On the other hand, when using a material that has a very high co-efficient of thermal conductivity, it conducts the heat away fast enough so that the backing material does not melt. You then have the benefits of full penetration without having to remove the backing strip by grinding. Obviously, there are the problems as mentioned by some of the others.
If your question rather revolves around "better" penetration, then I do not believe that you actually get "better" penetration. You just get other benefits than is the case with steel backing.
Regards
Niekie