Has anyone had any bad experiences with LME as it relates to zinc galvanizing and carbon steel? We have a large piece of high pressure equipment which was galvanized many years ago. Now we need to repair and PWHT (1150 degrees). Could we expect LME problems? Our findings thus far indicate that this could be a problem.

Travis LME possibility exists if you do not remove the galvanizing in the portions of the weld area . It is essential that you remove the galvanizing portions before start of welding repairs and during PWHT. Mr. Dhendrix, had rightly cautioned about this to remove locally the areas to be repair welded and post weld heat treated - including the HAZ and the portions which will effectively exceed a temperature above 400 deg cent while doing PWHT. Zinc being a low melting metal can penetrate the HAZ/Weld or in the portions heated > 400 deg cent . I guess that you should remove at least 150-200 mm of the galvanized portions of the steel before welding and PWHT. If due to conducted heat the PWHT portions exceed > 400 deg cent, you might have to remove additional areas of galvanizing to prevent possible Zn penetration in steel . If by chance you are performing or intendeing to do repair weld using Stainless Steel filler metals (dissimilar materials welding) , you have to exercise abundant caution. For repair welding using S.S electrodes at site for a high pressure carbon steel shell material, , this becomes a "must" as LME due to Zn in S.S is a well known embrittlement. In that case, repair welding using S.S filler wire, you have to be doubly sure that no zinc traces are left or present at the portions of weld repair and also at portions which are PWHT for the higher thickness Carbon steel high pressure shell material Trust this answers your question C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai India Sept 25,2004 E-mail:nishi@vsnl.com/nishi@hathway.com >Travis: > >We have no personal experience with LME of carbon steel in >contact with zinc as a galvanized product. Our review of >the literature also does not suggest that LME of carbon >steel by liquid zinc is a problem. However, if practical, >as a safety precaution, you might consider removing the >galvanizing in the area of the weld repair, if the PWHT can >be done locally. > >Hope this helps! > > > >David Hendrix >The Hendrix Group Inc.