Temperature Limits for Asphalt Coated Flowlines: A Design Approach

The 18” flowline from the Mikkel template in the North Sea was coated with asphalt enamel for corrosion protection and an external concrete coating for weight. The high internal temperature of 85 °C close to the template can give relative thermal movements between the outer concrete coating and the inner steel pipe. The case is considered to be similar to an adhesive joint between two tubular members. The strength approach is based on the analysis of the shear stress distribution in this “adhesive” joint. The material stiffness (shear modulus) of the asphalt was used to determine the upper temperature limit for the asphalt coating. The hotter part of the flowline had to be coated with polypropylene instead of asphalt.