ABSTRACT
Pipelines that operate at high temperatures require new coating materials for protection. Development of those coating materials requires new chemistry. It also requires the development of new test methods. This paper reviews coating requirements and existing test procedures applicable to high temperature coatings. It proposes new test methods for better evaluation of the new coatings. It also provides test data and results from example candidate coatings for high operating temperature pipelines. Key Words: fusion-bonded epoxy, FBE, pipecoating, semi-interpenetrating network, semi-ipn, high temperature, glass transition, cathodic disbondment, adhesives.
INTRODUCTION
Single layer fusion-bonded epoxy (FBE)
Dual layer FBE
3-layer polypropylene (PP)
3-layer PP insulation systems
Multi-layer insulated systems
Many pipelines operate at temperatures far above ambient. There are several reasons that include high-temperature materials coming out of the ground and materials that must maintain a high temperature. Examples include tar-sand hydrocarbons and gas with hydrates. Depending on the circumstances and environment, the pipeline coating may be:In the case of FBE systems without a polyolefin overcoat, the corrosion coating must have a glass transition temperature, Tg, above the operating temperature of the pipeline to prevent damage from pipe movement. In the case of systems with a thick polymer overcoat, the FBE is protected from damage and may be serviceable on pipelines operating above the Tg of the corrosion coating. The insulated system may be foamed or syntactic polyurethane over an FBE corrosion coating and not necessarily bonded to it. Other systems include multilayered coatings with either foamed or syntactic PP insulation layers incorporated as part of the coating system. Whatever type of material selected, it must not only meet "normal" pipecoating requirements, but it must also provide long term performance at temperature not seen historically by underground and underwater pipeline coatings. There are many potential technologies that may address these requirements. This paper will review new FBE and PP adhesive (part of a three-layer PP system) coating technology designed for high temperature pipelines. Potential high-temperature technologies. Due to the severity of new anticorrosion coating service temperatures, new materials must be developed to survive these more difficult environments. Common fusion bonded epoxies, customarily utilized for oil and gas pipeline protection, encounter problems because of their relatively low glass transition temperatures, which lead to issues of maintaining adhesion to steel substrates. Multifunctional epoxy resins have commonly been used to produce highly crosslinked coatings with high glass transition temperatures. FBE coatings formulated with these resins exhibit poor flexibility, poor impact resistance, and reduced adhesion to steel. However recent advances in epoxy technology have made the formulation of FBE coatings with high glass transition temperatures, good adhesion, and good mechanical properties possible. In addition to epoxy resins, other materials may be suitable for use in high temperature pipecoating applications. One approach to making high glass transition temperature thermosetting materials has been the use of acrylonitrile-butadiene rubber toughened vinyl ester resins. Vinyl ester precursors ranging in number average molecular weight from 3600 to 3800 have been made into toughened coatings having glass transition temperatures a few degrees above 140°C. 1
