Low Application Temperature Graded Structure Polyolefin Coating System Based on a Next Generation FBE for Strain-Based Design Pipelines Using High Strength Steel

Pipelines combining strain-based design with the use of thin walled, high strength steel (X80 or higher) present a significant challenge in terms of the availability of suitable coating systems. FBE-based coatings typically require the pipe to be heated to temperatures in the range of 230°C to 250°C for a period of up to 10 minutes in order to achieve optimum properties. The problem is that some of the key properties of such steels can change when they are subjected to such a heat cycle, resulting in a reduction in the tensile elongation at yield, a key requirement with strain-based design pipelines. When such pipelines are being constructed in remote areas, such as Northern Canada, there is the additional requirement that the coating must be robust enough to withstand transportation, handling and construction damage, and be bendable to temperatures as low as −50°C. Graded Structure Polyolefin Systems (GSPO) such as Bredero Shaw’s High Performance Composite Coating (HPCC) have established an excellent track record on pipelines constructed in very cold conditions through very rough terrain. However, such coatings are historically based on conventional fusion-bonded epoxy coatings designed for optimum performance when applied to pipes heated to 230 to 250°C. This paper describes a new version GSPO coating which can be produced without having the pipe temperature exceed 200°C at any point in the process, and which provides performance virtually identical to that of the standard GSPO product. It is the result of a cooperative development between Bredero Shaw and DuPont Powder Coatings, and is based on a new generation of FBE which can be processed at temperatures as low as 175°C with very little sacrifice in resistance to adhesion, as characterized by hot cathodic disbondment. Because the FBE has primary responsibility for providing corrosion resistance, the performance of the new generation FBE applied at low application temperatures was first compared to that of well-established FBE applied at their recommended application temperatures. Cathodic Disbondment (CD) was selected as the key performance test for adhesion because it simulates field conditions for disbonding of a coating from a pipeline with impressed current cathodic protection. Because the measurement of disbondment is on a continuous numerical scale, statistical analysis is possible. The new generation FBE coating performs significantly better in CD testing than conventional FBE when applied at lower application temperatures. Its performance is comparable to the best conventional FBE when applied at 240°C. This performance is maintained in the Low Application Temperature GSPO coating.