Abstract
Copper contamination in pipeline girth welds was experienced in the construction of onshore high strength steel transmission pipelines with mechanized welding using gas metal arc welding short-circuit transfer (GMAW-S) on root pass welds with copper backing, gas metal arc welding pulsed spray transfer (GMAW-P) on fill and cap pass welds, and flux cored gas-shielded arc welding (FCAW-G) on fill and cap pass welds. Copper contamination may result in copper contamination cracking, which is a type of liquid metal embrittlement (LME), or copper inclusions which have elevated hardness.
Traditionally, pipeline girth welds were made using manual shielded metal arc welding (SMAW), which is generally not susceptible to copper contamination, as copper is not present in the weld zone. However, mechanized welding requires the use of copper materials in the weld zone, including the contact tip, gas nozzle, and backing bar when using the copper backup clamp (CBU) system.
Copper contamination cracking in mechanized girth welds occurs in specific weld passes and weld locations, with distinct characteristics detectable by common nondestructive examination (NDE) methods, including visual testing (VT), radiographic testing (RT), and ultrasonic testing (UT). Copper contamination cracking of production welds may be effectively controlled when it is recognized and appropriate actions are taken to optimize mechanized welding procedure qualification, welding operator training and production controls, and tailor NDE methods and personnel training to improve detection.
