In the past, the service temperature for the large diameter external pipeline coatings has tended to be below 65 °C. Both FBE (fusion bonded epoxy) and 3LPE (3 layer polyethylene) have performed reasonably well at these temperatures. In recent years however, higher service temperature pipeline coatings have been requested by end users worldwide. In response to this demand, coating manufacturers have fabricated several new FBE coatings of high glass transition temperatures and phenolic epoxy coatings for this market. However, as yet there is no publicly accepted test protocol to qualify these newly developed high temperature coatings. In addition to FBE and phenolic epoxy, 3 layer polypropylene (3LPP) is also a candidate coating system for high service temperatures. PP coating manufacturers specify service temperatures in the range of 110 °C to 140 °C. However, 3LPP cracking and disbondment and PP girthweld joint coating cracking at lower service temperatures have been reported in the literature.
The purpose of this work is to develop a new test protocol to prequalify candidate high temperature mainline and field joint coatings. The test protocol focuses on two critical coating properties: material stability and coating-steel interfacial adhesion durability in the hygrothermal and thermo-oxidative environments. This test protocol has already been used to qualify the high service temperature pipeline coatings for major oil and gas operators, including gas transfer lines with a design temperature of 110°C.