A novel fusion bonded epoxy (FBE) coating based on brominated epoxy resin with a high glass transition temperature (Tg) was developed for pipeline protection. Properties of this FBE coating related to high temperature service are described in this paper. The new FBE coating has a glass transition temperature greater than 150°C as determined by differential scanning calorimetry (DSC). It performs significantly better in cathodic disbondment (CD) and water soak tests than conventional FBE coatings when tested at 95°C for 28 days. With brominated epoxy resin as the main binder, the new FBE coating has improved UV resistance. The new FBE should be used where superior cathodic disbondment performance at high temperature is needed.
Fusion bonded epoxy is a superior coating material for underground pipeline protection since it has excellent adhesion to steel, good chemical resistance, low oxygen permeability and good flexibility . FBE has been used for this purpose for decades on pipes to transport gas, oil and water. As reservoirs go deeper and the oil temperatures get higher, requests for FBE to work under higher temperatures with longer life are increasing [2-3]. Conventional FBE with a glass transition temperature (Tg) less than 110°C is typically not used for pipelines operating above 95°C. Conventional FBE primer (Tg<110°C), adhesive and polypropylene three layer system, on the other hand, have been reported to operate safely at 140]>°C, although the CD performance was improved when a higher Tg FBE primer was used.
Most FBE coatings for pipe have a glass transition temperature less than 110° C. When the coating is subjected to service temperatures above its Tg, it softens and reduces its mechanical properties such as cohesive strength, penetration and impact resistance. When the coating's mechanical property is reduced, pipe movement, due to thermal expansion, may lead the coating to disbond . This has prompted the development of products with high glass transition temperature for use at high service temperatures. While current technology can produce high Tg FBE products by increasing the crosslinking density with polyfunctional resin or hardeners, such coatings do not offer the level of flexibility and adhesion to steel required by the pipeline industry. Accordingly, an approach to raise the Tg of the FBE coating by increasing the stiffness of the polymer backbone was carried out. In this paper, we report the properties of a novel high Tg fusion bonded epoxy coating based on brominated epoxy resin. Glass transition temperature, cathodic disbondment performance and water soak adhesion of this FBE coating are evaluated. Accelerated weathering resistance of this material is also studied.
Both the conventional and the new high Tg FBE powders used here were Nap-Gard® ¹ products. Both products had a 16-second gel time per CSA Z245.20-02. Substrate panels for CD test have a dimension of 10cm x 10cm x 0.6cm ( 4 inch x 4 inch x 0.25 inch) and 63~100 micron anchor profile. Sodium chloride and other chemicals were reagent grade and used without further purification.