Modern offshore facilities in the Gulf of Mexico can be vast, with a significant amount of hot processing equipment that requires insulation for personnel protection and energy conservation. For personnel protection where the service temperature is <350 °F (177 ºC), a primer plus an acrylic insulative coating may be used. The insulative coating system is typically a waterborne acrylic coating with a protective primer on the metal surface. When an insulative coating is repaired, equipment shut-down is not typically done, requiring the primer to be applied on hot steel (250 ºF [121 ºC] to 350 ºF) and still maintain high film integrity. Liquid coatings are normally formulated to spray at temperatures ranging from 40 to 100 ºF (5 to 40 ºC). On hot steel, however, a liquid coating could dry too quickly to form a porous-free film, so the primers sprayed onto hot steel must have good thermal stability, and the entire insulative coating system must have good corrosion resistance and thermal shock resistance for withstanding rainfall.
For energy conservation, the main insulation system choice has traditionally been the use of a protective coating system applied on the steel surface that is wrapped with a thick insulation material (e.g., mineral wool) and enclosed with metal jacketing. Water can permeate the jacketing, however, and over time moisture penetrates the insulation to reach the steel surface, particularly where the insulation is joined or damaged, and cause corrosion under insulation (CUI). The protective coating system underneath, therefore, must have good thermal stability, good water immersion resistance, and good hot/cold and dry/wet cycling corrosion resistance. When coating repairs are performed for CUI, equipment operated at 300 to 440 ºF (149 to 226 ºC) needs to be shut down for safety reasons, and the protective coating system is applied under ambient conditions.
A laboratory test protocol program was developed for coatings used for each type of insulation method—insulative coatings and traditional insulation. Using the test protocols, which have identified failure modes such as blistering, holidays, mud cracking, cracking, and inter-coat delamination, candidate coating systems can be evaluated and best in class products can be selected to mitigate CUI.
The new test protocol for the coatings under traditional insulation includes a method to test the thermal stability of the coating, the corrosion resistance of the coating when immersed in DI water and seawater, and the corrosion resistance of the coating when placed under wet insulation. Similarly, the new test protocols for insulative coatings include a method to test the thermal stability of primers on hot surfaces, the corrosion resistance of a primer applied on hot steel, the corrosion resistance of the complete primer and insulative coating system in a test environment, and the corrosion resistance of the complete primer and insulative coating system in simulated field conditions. Test protocols for both types of coating systems include acceptance criteria.
More information on the new test protocols are presented in CORROSION 2016 paper no. 7804, “Evaluation of Protective Coatings to Mitigate Corrosion under Insulation,” by Y. Yang, A.B. Bodington, and B.T.A. Chang.