A NOVEL APPROACH TO INSTALLING SACRIFICIAL ANODES TO PROTECT GLASS FLAKE LINED STEEL LARGE DIAMETER SEAWATER PIPELINE SYSTEMS

摘要

Seawater is used for cooling in almost all industries. Most systems are of large diameter spiral welded pipelines which are internally coated to prevent corrosion. As no lining is 100% perfect, it is only a primary defence and there is no guarantee that the lining can be kept free of defects - particularly at the welds. Such defects lead to internal corrosion and later leaks, thus emphasizing that internal coatings alone do not always provide a complete guarantee of leak free service in the absence of a secondary defence like cathodic protection. Temporary control of large leaks in buried pipelines requires massive excavation to clamp and wrap the leaks and can require several days of plant shutdown for long-term repairs. Cathodic protection is the only secondary line of defence which can reduce or even prevent such corrosion, unscheduled shutdowns and production losses. Friction stud welding was used for the installation of sacrificial anodes inside buried glass flake lined seawater piping to avoid damage to both the internal lining as well as external organic coating. Al-Zn-In alloy anodes of the stand-off type were designed to be installed using friction welded studs and optimized to protect the buried portions of the pipe. The use of a portable friction welding tool was pivotal to retrofitting the anodes quickly and welding through the coating without damaging or further risking the integrity of the pipeline. This paper also provides an overview of portable friction stud welding, discusses the metallurgy of the process and weld zone and methodology of anode installation. A fully bonded solid phase weld is produced without the need for pre or post weld heat treatment. A major benefit of friction stud welding is the relatively low temperature of the process, preventing damage to the external coating and minimizing damage to the internal lining. This method has recently been used to install anodes inside seven sea water pipelines in an onshore gas processing facility.