Evaluation of High-Temperature Cracking Risk of Stainless Steels in the Presence of Zinc Silicate Primer

The zinc-containing primers, especially zinc silicate, are widely used on the carbon steel for both onshore and offshore environments.  Their use on stainless steels is not recommended since there is a risk of embrittlement by molten zinc in case of fire due to low melting point. Zinc silicate contains metallic zinc particles which can diffuse into the stainless steel if the particles melt. However, zinc quantity may not be sufficient (the thickness is 60 to 90 microns) to initiate a significant cracking. Also the oxidation of zinc particles, which are very small, before they reach melting temperature, would not permit cracking of stainless steels. In order to confirm these possibilities some tests were carried out on three types of stainless steels painted with 60 to 90 microns of zinc silicate and heated to temperatures 400 to 650^oC. No cracking was observed on painted samples but cracking was experienced on stainless steel samples when a piece of zinc is placed on the stainless steel surface. This paper summarizes the test results and discusses the possible reasons of non-cracking.

Key words: liquid metal embrittlement, zinc silicate, stainless steel.