Chapter 17 - Welding and NDT

Abstract

Welding plays a major role in the construction, modification, and repair of hazardous liquid pipelines and natural gas pipelines. Even though there has been a large amount of research and development (R&D) related to the advancement of semi automatic and automatic pipe welding machines, which should significantly increase weld deposition rate and improve pipeline production, most pipeline welding today is still being done manually, using stick (SMAW) electrodes. There has also been a large amount of R&D work in the field of nondestructive testing (NDT) and especially for pipeline weld inspection using ultrasonic methods. Butradiographic NDT (X-ray) is still preferred to evaluate pipe weld integrity, in both large and small pipeline projects. Automatic (or mechanized) welding is starting to be used on large diameter gas pipeline construction to improve production rate and reduce cost. Big diameter pipeline projects, such as the 36-in. Cheyenne Plains Natural Gas Pipeline Project and the 36-in. Alliance Natural Gas Pipeline system, used automatic welding, and they both selected a highly accurate and automated ultrasonic testing system (AUT) to ensure girth weld integrity. AUT was necessary to provide quality inspection with speed sufficient to keep up with the automatic weld production. Even so, X-ray inspection was required on all pipeline tie-ins.