ABSTRACT
Coating systems for the corrosion protection of buried steel pipelines extensively use Fusion Bonded Epoxy (FBE) either as a standalone coating or as the base layer in dual or multi-layer coatings. The application of these systems in a coating plant generally requires heating of the steel pipe to temperatures in excess of 230°C, followed by cooling back to ambient after a coating cure time. Although, this thermal cycle occurs for a short duration, it has been shown to affect the strain aging behavior of the steel with a more significant effect on higher strength grades. A desirable attribute to the application of these coatings is to lower the application temperature, preferably to less than 200°C due to: (1) grades of steel such as X100 and X120 cannot be heated above 200°C for long durations without significant change to their stress-strain behavior that is critical in strain based pipeline design; (2) difficulty in heating heavy wall pipe uniformly to temperatures in excess of 200°C without compromising production line speed; (3) improvement of material usage and product throughput for 3LPE/PP; and (4) energy savings. This paper discusses the experience in coordinating with powder suppliers in the development of Low Application Temperature (LAT) FBE materials and the enhancement and process controls for the corresponding application process to constrain temperatures that the steel pipe experiences in a coating plant. Multi-layer coating systems using LAT FBE have been used in several projects around the world. This paper also presents the performance characteristics, production, commercial track record and experience of these systems.
INTRODUCTION
Fusion Bonded epoxy (FBE) coatings has been widely used in pipeline corrosion protection for more than three decades. They are commonly used as stand-alone coatings, as base layer for dual or multi-layer FBE coatings, and as base layer for multi-layer polyethylene/polypropylene coatings. FBE is a powder coating applied by electrostatic spraying onto preheated steel pipes where the powder melts, flow (wet), fuse and react/crosslink to form a solid protective coating. One of the most important factors to achieve proper adhesion between the steel pipe and the coating is the melt-flow-wet process, which is mainly governed by the temperature of the pipe and the melt-fuse characteristics of the FBE. Typical application temperatures for conventional FBE coatings are in excess of 230°C.
