Examination of external weld deposition repair for internal wall loss

There are significant economic and environmental incentives for performing maintenance and repair welding on pipelines without removing them from service. From an economic viewpoint, a shutdown involves revenue loss from the loss of pipeline throughput, in addition to that from the gas lost to the atmosphere. Since methane is a so-called greenhouse gas, there are also environmental incentives for avoiding the venting of large quantities of gas to the atmosphere. The objective of this work was to develop broadly applicable guidelines to safely repair internal wall loss of operating pipelines by external deposition of weld metal. To accomplish this, non-linear finite element analyses (FEA) were conducted to determine the effects of wall loss on burst pressure. The size of the wall loss was characterized by its depth, width along the circumference, and the length along the pipe axis. Both straight pipe sections and elbows were analyzed. Experiments were conducted to validate the FEA results for straight sections of pipe and elbows, and to expand the results to tees. The first experiment involved an instrumented burst test of an unrepaired straight section of pipe with internal wall loss. The remaining experiments involved burst tests of elbows and a tee with internalmore » wall loss that were repaired by external deposition of weld metal using a technique developed in a previous program.« less