Proper welding procedure for internally Fusion-Bonded Epoxy Coated water lines

Abstract

The main purpose of this work is to develop an appropriate welding procedure for the installation of full encirclement repair sleeves on in-service, internally coated water lines. The new proposed welding procedure should be followed with no harm on the Fusion-Bonded Epoxy Coating (FBE) on the internal surface of the carbon steel pipe. Any possible damage of FBE can lead to frequent leaks due to internal corrosion. Prevention of coating damage will increase the reliability of the supply/injection water system. The cost saving can be observed in the increase in the remaining life of girth welds and defective trunk lines. In particular, full encirclement sleeve repair is a well known repair method but its effect on internal coating has never been evaluated previously. Thus, no proper welding procedure was hitherto developed to sleeve-repair the internally coated water pipes. To identify the optimum combined welding parameters which avoid harming the internal pipe coating, an experiment is conducted. Multiple weld passes are applied circumferentially and longitudinally to weld the sleeve on in-service pipelines (API 5L X STD. of 12" diameter x 0.375" thickness). This experiment is carried out on coated pipes with internal pressure of 185 psig and raw water temperature of 180°F which are the maximum parameters in operation. From the actual observation and all possible cases performed, a specific and safe sleeve repair procedure is addressed in this report. This procedure can be adequately applied to eliminate or reduce any susceptibility of damage to the coating on the internal water pipe surface.