Traditional internal coating systems relied on phenolic, novolac, epoxy or blended resin systems. These tended to provide good barrier properties in the environments they were developed for, but as with all materials, there were limitations. One of those limitations that had to be overcome during the development and application process was that during the curing process, they can tend to shrink, so greater surface preparation processes must be followed to ensure that the system adhesion far outweighs the residual stress in the coating system. In the presence of higher concentrations of hydrogen sulfide, there can be a negative effect on the adhesion of most of these resin type coating systems allowing the residual stress to play a role in blistering and disbondment. A new and novel resin system has been developed that does not shrink during the curing process and can be applied as a primer-less system. Coatings developed with this new resin, benzoxazine, allows the coating system to maintain good adhesion and barrier properties in H2S concentrations two to three times greater than the current leading H2S resistant coating systems on the market today. This paper is the second in a series on the development of this product into a coating solution. Building on technology progress, new materials are now being developed and rolled out providing insulation to protect downhole electronics for high temperature applications
During the 72-year history of using high performance coating systems for pipe internal corrosion control, there has been a slow introduction of different resin chemistries that serve as the backbone of these coating systems. While phenolic resins systems were the primary starting point, it transitioned to include epoxies, novolacs, nylons, urethanes and others. As needs outside corrosion control like deposit mitigation and wear resistance arose, coatings based on other specialty resin chemistries, like from the fluoropolymer family, were developed. While each of these systems could provide the protection and performance required for most environments, there was one environmental component that could negatively affect the long-term performance of the coating system. The presence of hydrogen sulfide (H2S) in a given environment can affect the long-term life expectancy of a coating system. The concentration that a coating can withstand will depend primarily on the pressure, but also on the maximum temperature of exposure. In most instances, the H2S does not directly affect the integrity of the coating film or its ability to provide barrier properties against most corrosive species. What the H2S does is migrate through the film and react with the steel substrate without the presence of water. The resulting reaction product reduces the adhesion of the coating to the steel substrate. Several upgrades have historically helped the coating system withstand limited H2S concentrations. The first improvement has been the development and implementation of higher performing primers better designed for specific topcoat systems. These primers can benefit in two ways. One benefit is to aid in the physical and chemical blocking of the H2S so that is it does not reach the steel substrate. The second benefit is the increase in adhesion that can stop or delay the negative effects of the reaction product forming on the surface. Another upgrade is the use of different filler morphology that can act as a physical barrier to the H2S, preventing it or delaying it from reaching the surface. A third path to improvement starts to look at the resin chemistry itself to help in the protection process. The development and use of resin systems that possessed greater crosslink density could also slow the ingression into the coating film. While all three of these upgrades can allow current coating systems to provide the intended performance requirements in the presence of H2S, under enough system pressure and/or under high enough H2S concentration, these coatings could also experience reduced life expectancy.
