Defects and holidays in mainline coatings necessitate the use of repair coatings for all coated pipelines. This includes both newly coated pipelines just out of the plant as well as existing buried lines in need of small repairs. The repair coating must provide corrosion protection for the steel, lessen the demand on the cathodic protection system, and provide good long-term service. In short, the repair coating must protect the pipe to the same extent as the mainline coating. Two additional requirements for repair coatings are that they adhere not only to the steel but also to the existing mainline...
Defects and holidays in mainline coatings necessitate the use of repair coatings for all coated pipelines. This includes both newly coated pipelines just out of the plant as well as existing buried lines in need of small repairs. The repair coating must provide corrosion protection for the steel, lessen the demand on the cathodic protection system, and provide good long-term service. In short, the repair coating must protect the pipe to the same extent as the mainline coating. Two additional requirements for repair coatings are that they adhere not only to the steel but also to the existing mainline coating, and that they be field-applicable under varying ambient conditions. Repair coatings sometimes also have to adhere to non-ideal surfaces, including poorly prepared welds, thermite welds, and flash rusted steel. The compatibility of commercially available repair coatings applied to common mainline pipe coatings was investigated by a laboratory investigation. The mainline coatings investigated were fusion bond epoxy (FBE), coal tar enamel, asphalt enamel, cold-applied polyethylene tape wrap, and extruded polyethylene. Specific combinations ofmainline coatings with different types repair coatings were evaluated for chemical compatibility and adhesion strength in three different scenarios:· As applied to a new pipeline coating, simulating initial repairs made at a coating plant or on a job site prior to installation· As applied to an artificially aged pipeline coating, simulating repairs made to a mainline coating which has been in buried service· After artificially aging a repaired mainline coating, simulating the longer term service of an initial repair made at a coating plant or job site prior to installation.