DEVELOPING A DESIGN METHODOLOGY FOR REINFORCING CRACK-LIKE DEFECTS IN THE LONGITUDINAL ELECTRONIC RESISTANCE WELDED SEAMS OF TRANSMISSION PIPELINES

Abstract

Vintage oil and gas transmission pipelines manufactured between 1920 and 1970 were typically constructed using a welding process known as electronic resistance welding, or ERW. At the time, this welding process was susceptible to multiple quality control problems which created small inclusions and flaws at the longitudinal weld seam at the time of manufacture. When the pipes were placed in service, cyclic pressure cycles and environmental corrosion would weaken these flaws, forming crack-like defects. The longitudinal weld seam also exhibits brittle behavior due to the heat affected zone formed by the welding process. As a result, the crack-like defects that form at or near the weld seam grow from cyclic fatigue until they reach a critical size and rupture. It has been shown that carbon-epoxy reinforcements are economical and effective reinforcements for improving the cyclic fatigue performance as well as restoring the burst pressure near the flaw. The following thesis explores the state of the art research related to carbon-epoxy reinforcements and fracture mechanics, and then recommends a design methodology that could be adapted by pipeline operators and regulators to address this special threat to pipeline integrity. Future work in modeling the crack growth of reinforced flaws is discussed.