This is a joint industry study conducted for 18 suppliers and end-users. The study examined the performance characteristics of thirty-one (31) Tank Lining systems, which included Epoxy (Standard, Phenolic and Novolac) and Vinyl Ester coatings, all applied under the same conditions. Tests focused on performance under immersion conditions and included Soak Adhesion, Cathodic Disbondment, Standard Atlas Cell, Pressurized Atlas Cell, and Autoclave. The different tests were used to examine the effects of temperature, pressure, thermal gradient, cathodic protection, acid gases and different liquid types. The initial phase of the test program used 60°C for all tests and coatings recommended for higher temperature were examined in further tests at 85°C to 125°C. Electrochemical Impedance Spectroscopy (EIS) was also used to examine the barrier characteristics of the coatings and the feasibility of using this non-destructive test to identify degradation of the coatings.
Detailed analysis of results includes examination of variation between coating types and variations between each coating. In these categories both correlation and variations were observed. Five (5) of the thirty-one (31) coatings had good or better performance in all tests conducted at 60°C including three (3) vinyl esters and two (2) novolac epoxy coatings. Five (5) other coatings performed well in at least three (3) of the four (4) tests conducted at this temperature. There were fewer coatings that performed well at higher temperatures, indicating the need for more care in selecting coatings for use in environments that will see temperatures above 60°C. At all temperatures thermal gradient across the coating (the cold wall effect) was noted to be the most likely to result in coating degradation, especially blistering and/or adhesion loss.
Coatings used for corrosion protection of the internal of vessels and tank linings frequently have to perform under severely corrosive environments. There are many commercially available coatings that claim to be effective under a wide range of operating conditions. However, field experience indicates that while many coatings used inside oilfield vessels perform well, problems1-4 such as blistering, cracking, and delamination are not uncommon. Failures of internal coatings are expensive, hazardous and complicated to repair. It is important then, to choose the protective coating that is most likely to perform well in a given environment.
Experience demonstrates that many factors should be evaluated before qualifying coatings for internal applications (e.g., tanks, vessels and treaters). These factors include resistance to chemical attack, high temperature resistance, compatibility with cathodic protection, and resistance to cold wall effect3. Many laboratory tests are available for evaluation of tank lining performance; these tests are usually carried out under simulated or accelerated operating conditions. Accelerated exposure tests provide an estimate of long term performance of the coating in a relatively short time by indicating signs of deterioration or adhesion failure. This paper describes a study conducted on a broad range of tank lining coatings so as to provide information that would help in the selection of the most appropriate coating for a particular environment.
