Abstract
Corrosion under insulation (CUI) is a serious external corrosion issue experienced both onshore and offshore. Modern offshore facilities in the Gulf of Mexico can be vast with many oil/gas processing equipment. Insulation is required on hot processing equipment for two main reasons; (1) personnel protection and (2) energy conservation. For personnel protection, the water borne acrylic insulative coating system is increasingly being used compared to the traditional insulation which is still used. When an insulative coating is applied, equipment shut-in is not typically required, preventing deferred production losses in most cases. Hence, primers and acrylic insulative coatings sprayed on hot steels (250°F and 350°F) are needed. For energy conservation, the main choice has traditionally been the use of a protective coating system applied on the steel surface wrapping with a thick traditional insulation material (e.g., mineral wool), and enclosed with a metal jacketing. Over time, moisture penetrates the insulation to reach equipment steel surfaces, particularly at damaged insulation areas and termination points. When this occurs, the equipment operated at 300°F and 440°F, needs to be shut down for safety reasons to allow repair work to be performed by applying the protective coating system under ambient conditions.
A laboratory test protocol program was developed for the coatings to be used underneath each of the two types of insulation (i.e., insulative coating and traditional insulation). The test protocol for the insulative coatings includes: (1) thermal stability of hot primers, (2) accelerated corrosion of hot primers, (3) accelerated corrosion of insulative coating systems, and (4) corrosion resistance of the hot applied insulative coating system in a simulation test condition. The test protocol for CUI coatings includes: (1) thermal stability, (2) DI water & seawater immersion resistance, and (3) CUI simulation test. As a result of these newly developed test protocols, several failure modes have been identified: (1) blistering, (2) holidays (3) mud cracking, (4) cracking, (5) rusting, and (6) inter-coat delamination. Using the test protocols, candidate coating systems can be evaluated and best in class product(s) can be selected to mitigate CUI.
