Using the direct current voltage gradient technology as a quality control tool during construction of new pipelines

Abstract

External coatings on buried pipelines offer the first line of defence against corrosion with cathodic protection systems in place to protect bare metal at coating defects. Holiday detection, before pipelaying, does not guarantee pipelines are without coating defects after pipelaying. The coating is more than likely to be damaged during pipe construction. The DC voltage gradient (DCVG) method, to locate coating defects on underground pipelines, was initially used for rehabilitation of older pipelines. This technique is now increasingly gaining popularity as a good quality control tool when used on newly laid pipelines to detect coating damage, most of which could be attributed to construction work. On a recently built 50 km long gas pipeline coated with fusion bonded epoxy (FBE), it was proved that more than 80% of defects located after pipelaying were due to mechanical damage during construction. The factory related defects seen were in the form of pinholes or pimples most of which could not be seen by the naked eye and relied on holiday detection for identification.