ABSTRACT
In Oil and Gas plant facilities, protective coating system selection for cyclic temperature condition and under insulation has become a key concern in recent years. Severe cyclic temperature conditions in LNG plant facility is observed in Dehydration Unit where operating temperatures ranges from +25 °C to +300 °C with a few cycles per day, for carbon steel components with and without insulation.
In such severe conditions, there are few protective coating systems available for carbon steel surfaces. NACE(1) Standard SP01981, ”The Control of Corrosion Under Thermal Insulation and Fireproofing Materials – A Systems Approach”, includes such as TSA: Thermal Spray Aluminum (CS-5), IMM: Coating with Inert Multi-Polymeric Matrix (CS-6) or IOZ: Inorganic Zinc Primer with topcoat (CS-8).
These protective coating systems will be applied at several locations such as vendor shops, module yards and shops/fields at construction sites. After completion of coating works, these articles are exposed to corrosive atmospheric environment during storage, transportation and construction until plant start-up, typically after a couple of years. Thus, consideration must also be given to the protective coating durability at ambient temperature in corrosive environments.
A comparison between ”TSA”, ”IMM”, and ”IOZ with IMM”, with respect to both cyclic temperature heat resistance and ambient temperature corrosion protection is investigated in this paper.
In conclusion, it is suggested that ”TSA” and ”IOZ with IMM” are optimum protective coating system for cyclic temperature service in coastal area corrosive environment. In addition, IMM without IOZ may also be applied with sufficient evaluation beforehand.
INTRODUCTION
In Oil & Gas plant facilities, there are several operating temperature conditions available such as cryogenic (below 0°C), ambient temperature, high temperature (above 100°C) and cyclic temperature. As for LNG plant facility, severe temperature cycling is observed in dehydration unit where typical operating temperatures range is from +25 °C to +300 °C with a few cycles per day with carbon steel components, both insulated and non-insulated. From the view point of protective coating system selection, it is important to understand actual operating temperature condition of each component during engineering phase.
In general, protective coating systems are selected based on substrate material, operating temperature and insulation. Protective coating system selection for ”Cyclic Temperature Service” and protection against Corrosion Under Insulation (CUI) are among the most severe problems in Oil & Gas industries. CUI is caused by several factors e.g. corrosive environmental condition, insulation material, coating system, operation condition, chloride salt concentration, etc. CUI risk is described in some international industrial standards such as NACE SP0198, API(2) RP5832, CINI(3) Manual ”Insulation for Industries”3, etc. These standards say that high CUI risk is expected in temperature range from 50 °C to 175 °C and the most severe condition is ”Cyclic Temperature Service”.
