Chemical facilities face a number of issues when dealing with corrosion and harsh chemicals. The conventional method of addressing these issues is to adequately-prepare the steel surface and then apply the proper coating to protect it from the elements. However, in chemical facilities, harsh chemicals are essential to the process and require adequate containment and reliable service in order to keep the facilities operational. This article addresses the issues that these facilities face when dealing with severe chemical exposure and protection; namely, with respect to the nonmetallic linings and construction materials where high-priced alloys and thin coatings are not strong enough to withstand the constant thermocycling and harsh facility operations.
By Michael Yee
Material selection determination is made based on existing tanks and secondary containment areas that are primarily made out of steel and concrete. They also can be further addressed by selecting stand-alone chemical resistant fiberglass. The chemicals that require special attention include, but are not limited to, sulfuric acid, chlorine, phosphoric acid, hydrochloric acid, sodium hydroxide, sodium hypochlorite (bleach), potassium hydroxide, brine, white and black liquor, hydrocarbon solvents and alcohols. The containment of these chemicals requires materials that are considered unique, but continue to be rigorously used around the world, like fiberglass-reinforced polymers (FRP), rubber linings and resin-rich flake glass liners.
While there are many resins on the market, the primary resin used in linings is the thermosetting resin. Thermosetting resins cure to produce an infusible solid material that does not melt when heated. The most commonly-used thermoset resin system is epoxy vinyl ester with a chemically-resistant glass as the corrosion-protection layer for caustic service. For stronger acids, the novalac epoxy vinyl ester is commonly-used due to its chemical resistance. These combinations can also be used as the liners for steel tanks, though a solid FRP-construction will traditionally see a longer service life and lower installed cost due to the labour reductions associated with automation in fabrication shops. Additionally, there is limit to the vessel size and logistics costs when the vessels grow past the 40’-diameter mark.
Fiber-Reinforced Polymers (FRPs)
FRPs are used daily in hostile environments. While the majority of FRP applications and uses are located in Asia, it is equally-matched to the demand in the United States, Canada and Europe. The use of chemically-resistant resins with glass has been around since its introduction in the 1950’s by Dow Chemical, as well as several other Japanese companies that have been incorporating composites. FRP was created for its use in hostile, chemical environments and thus, different product lines were created to address different services for each environment. Today, a lot of these resins are being added to coatings to provide a similar level of chemical protection to steel and concrete surfaces. Technology has not changed much since the 1970’s and there are numerous case studies that show that a properly-designed FRP vessel and lining with excellent quality, properly maintained, inspected, and operated can reliably last for over 20 years.
The full article was published in the September/October 2016 edition of Managing Aging Plants magazine. To receive the article, please contact Jolanda Heunen.