L51763 Repair of Pipelines by Direct Deposition of Weld Metal - Further Studies

The objective of this project was to establish the feasibility of repairing defects, especially corrosion-caused wall loss, by direct deposition of weld metal in pressurized pipelines without removing them from service. From experiments conducted to establish limiting parameters, it appears this type of repair technique is feasible for remaining wall thickness as small as 0.125 inches, with internal pressures as high as 900 psig. Heat input limits were established as a function of remaining wall thickness and electrode diameter. This work confirms previous findings by British Gas and others. It is concluded that repairs by deposited weld metal are feasible and should be considered for approval by the various regulations and design codes. Welding parameters that may be safely used are limited in terms of burn-through potential. Burn-through potential is dependent on welding current level as well as welding heat input. To investigate the integrity of repairs, cyclic pressure testing of the two vessels, fabricated from pipe in which areas of simulated corrosion damage ha been introduced and repaired, has been carried out. Metallographic analysis and fatigue life assessment of the repairs in both vessels were done to verify restoration of pipe integrity.