Unusual Failures Involving Copper Deposition in Boiler Tubing

Abstract

Abstract Unusual case histories are presented in which boiler tube failure mechanisms involved copper deposition on waterside surfaces. Three case histories on copper-induced liquid metal embrittlement (LME) are reviewed. For copper to cause LME of plain carbon steel boiler tubing, metal temperatures must exceed 871°C (1600°F). Therefore, copper embrittlement of boiler equipment is usually associated with a rapid, high-temperature overheating incident (e.g., flame impingement, sudden loss in normal circulation) or, more commonly, a welding repair process. Grain-boundary penetration of liquid copper via LME can result in severe intergranular cracking and brittle fracture of normally ductile steel tubing. Another case history discusses overheating damage (bulging) of a tube that was promoted by thick waterside deposits containing multiple layers of copper alloy corrosion products. The majority of copper was probably transported into the boiler system during shutdown/start-up cycles.