The Optimization Of Three Layers PE Coating For Steel Pipepine

3 layers PE coating has become one of the coatings firstly chose for new oil &gas pipeline in the world. but the 3 layers PE coating specification now utilized inchina is followed the west country's standards,it doesn't conform with the pipelinestatus of our country. The non-conformities are as follows: 1,the thickness of FBElayer is thin, the FBE coating material can not cover the steel surface entirely. 2,according the 3LPE specification now utilizing, the coating thickness over weldingseam only can be up to 10% less than the normal pipe coating thickness. So theconsumed coating material is too large. 3,the coating cost is high. so it is needed tooptimize the 3 layers coating to conform to the actual status of pipeline projects in ourcountry.During the optimization,we tested the FBE samples and PE samples by utilizingthe technology of electrochemical impedance spectroscopy,and understood thefunctions of each layer of 3 layers PE coating, finally we decided the minimum FBEthickness. Synthesizing the utilizing experience of china and other countries and theactual status of pipes in china,we decided the requirements for the coating thicknessover welding seam. After several application tests in coating mill, we are sure that thenewly optimized 3 layers PE coating specification is suitable.From the results of this study, we can get the following conclusions:(1) the anticorrosion function of 3 layers PE coating is mostly depend on theouter PE layer,the most function for FBE layer is to give strong adhesive andexcellent Cathodic disbonding resistances.(2) the FBE primer layer thickness should not less than 100μm ,so as to makesure the FBE layer is continual, and the FBE layer can have the essential ability foranticorrosion。(3)for huge dimension pipes,the coating thickness over welding seam can beup to 30% less than the normal pipe coating thickness. This requirement cann'tweaken the coating's performance.(4)after application tests in coating mill, the optimizing structure of 3LPE isconformed to the actual conditions of production.By the utilizing in west-to-east gas pipeline project, all of the above changes of3LPE coating not only can conform to the requirements for anticorrosion, but also canreduce the production cost greatly.