Crack analysis in thermite welding of cathodic protection

For protection of steel pipes that are exposed to corrosion, cathodic protection is commonly used. Joint between steel surface and copper conductor is done by thermite welding. During the welding process and due to the nature of it, steel surface in the solid state comes in contact with liquid copper. Contact of steel with liquid metal (copper, zinc) in some cases cause phenomenon known as the liquid–metal embrittlement or LME. Phenomenon was previously studied in cases such as soldering or hot-dip galvanizing but for thermite welding no records were found in accessible literature. The purpose of this paper is to draw attention to some irregularities and consequences arising from it, which in this type of welding can occur. At the end of article some measures to reduce these risks are given.

► Thermite welding used for cathodic protection installation can cause liquid–metal embrittlement.
► Microcracks are observed in weld area, due to microstructural changes in steel.
► Martensite structure, hardness and microcracks can be reduced by preheating prior welding.
► Due to microcracks some minor reduction of strength can be expected.