DBP Forum

Having encountered some problems with LAMC (Liquid Metal Assisted Cracking) during galvanizing steelwork recently we have been baffled by why, all of a sudden, this phenomenon has started to affect us following years of trouble free Galvanizing. After talking to several experts and reading reams and reams of none committal reports we have finally got an answer that seems to make sense. Apparently some galvanisers have started to increase the Tin content in the bath to help increase the shine of the finished product and this could well be the major cause. Having compared the Tin content of baths where we have had the problem to ones which have been trouble free this appears to be correct. It looks like if you want to be free of LMAC then you may have to settle for a slightly duller finish, which is a small price to pay for peace of mind. Has anyone else found this to be the case as there is so little information available on probable causes?

Well it's happened again, twice in the last 2 weeks and the bath tin contents this time were below the recommended 0.1% so now I'm even more confused. Having spoken in length with some technical members of the Galvanizing Association there are 14 items which can increase the chances of LMAC ranging from speed of dipping to the temperature of steel but the 5 main items seem to be as follows:-

1. Percentage Tin content and others misc trace metals in the bath above recommendations.
2. The grade of steel S355 is more prone to cracking than S275.
3. The subgrade of the steel JO & J2 are less likely to crack than JR.
4. Notching quality of beams especially in the K zone (Route Radius Area).
5. More LMAC problems reported because there is far more inspection being carried out - Fair Point!

My own opinion is that the main reasons for our recent LMAC problems is the inceased use of S355 steel as the notch details used have been common practice for decades now. We are looking at increasing notch radiuses to try and reduce any further LMAC problems and looking at JO minimum standards for the larger notched beams.

Anyone else had problems with LMAC that they wish to share?

Having compared the Tin content of baths where we have had the problem to ones which have been trouble free this appears to be correct. It looks like if you want to be free of LMAC then you may have to settle for a slightly duller finish, which is a small price to pay for peace of mind. Has anyone else found this to be the case as there is so little information available on probable causes?

We have made a point of monitoring the tin content over the last few years and we have been LMAC free so it would appear that the tin content is a major player. We have also been using bigger radius notches on deeper beams so the evidence appears to be that both items must have helped.