Determining Discontinunities under Galvanizing

[Rich2001]

I have a project to inspect several erected steel structures that have been galvanied. There is a high probability that there exist multiple serious discontinuities under the galvanizing. This appears to be a liquid metal embrittlement problem caused by the addition of tin to the galvanizing bath.

Welds are 100% MT'ed prior to galvanizing. After galvanizing cracks are detected. The cracks in the steel are filled with the galvanizing. An SEM analysis of the crack material deposits show high levels of Tin.

Along with looking for cracks in welds, I need to locate any crack in plates, & and other structral members. I am currently using AC yoke, dry MT techniques. Can anyone else think of a better method?

 

[Rjeffery]

Have you thought of Lambda Wave UT. (plate wave) Is this thick enough to use Shear Wave UT? (greater than 1/4 inch)

 

[quadswift]

I am not over-keen on MPI, unless on hot root cut-backs etc. I think you would have better results with wet MPI or fluorescent ink and UV.