UNUSUAL FAILURES INVOLVING COPPER DEPOSITION IN BOILER TUBING

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-degrees-C (1600-degrees-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.