The coating and cathodic protection protect pipeline against the corrosion. The failure of these two defense systems leads to corrosion failure of pipelines. Any changes in chemical, physical or electrochemical properties of coating which affect their properties to isolate tFhe pipes from the corrosive atmosphere is considered as failure of coating. The failure mechanism and the gap analysis need to be continuously done for improvements in specifications and its executions. Majority of the global oil and gas pipelines are being protected externally with either 3-Layer Polyolefin coating system or fusion bonded coatings. Some of the gas pipelines are provided with a flow improvement internal coatings considering nil corrosive challenges on internal surfaces. The failures in the external coating appear in the form of edge disbondment from cutbacks and near holidays, complete loss of adhesion of coating, loss of cohesion within coating, cracking in the coating, swelling & blistering around holidays, distortions in the coating, electro osmosis, electrophoresis and highly alkaline atmosphere near holidays, continual increase in CP currents and corrosion of the substrate. The internal surfaces of pipes are suffering corrosion mainly due to presence of corrosive gases viz. carbon dioxide, oxygen, condensates and other corrosive substances even in traces. The common methods like Dehydration, Inhibitors, Buffering, Biocide and Cleaning pigs are not adequate to protect the pipelines to from the corrosion. A very thin internal flow coat can hardly resist any corrosion and gets failed.
This paper presents the in-depth analysis of the major causes of coating failures and the improvements required in the external and internal coating selections, specifications, coating applications, testing and its maintenance.
