Study of Qualification of Coating Procedure Specifications as Per Din 30670 for 3lpe Coating of 8 Inch Diameter Erw Pipe

Abstract

In present study qualification of 3 layer polyethylene coating procedure is discussed which is adopted for the corrosion protection of API 8 Inch ERW line pipes. API monogrammed bare pipes were supplied by the local manufacturer while coating was performed as per DIN 30670 standard. Raw materials including surface preparation and coating raw materials steel grit, acid and chromate, epoxy, adhesive, HDPE and bare pipes were tested and compared with the manufacturer testing certificate for specification compliance check, results are presented in tables 1-4. Physical inspections of bare pipes were carried out before assigning unique identification number to each pipe. Surface preparation including pre-heating of pipes at least 3oC above dew point temperature, steel grit blasting of pipes to get the desired Sa 2.5 surface with 50 to 80 microns profile, acid washing of pipes to remove excess chloride ions, Rinsing of pipes after acid washing with RO water, drying of pipes through blowers, induction heating of pipes up to the epoxy manufacturer recommended temperature which is 200 to 220 degree celsius, first layer epoxy powder application through electrostatic spray gun technique, second layer of adhesive and third layer of Polyethylene film application through side extrusion process, quenching of coated pipes, full length coating holiday inspection and in the end Final inspection of coated pipes. Four test pipes were selected for coating procedure qualification. Out of these 4 test pipes, First pipe coated with adhesive layer for adhesive layer thickness measurement, Second pipe coated with epoxy layer for epoxy layer thickness measurement, third pipe coated with Polyethylene layer for polyethylene layer thickness measurement along with sampling for indentation hardness test, fourth pipe coated with all three layers and tested for thickness measurement of combined three layers, holiday detection, peel adhesion strength test, impact test and cathodic disbondment test. All testing were evaluated to check compliance against the standard DIN 30670 requirements and coating procedure specifications.