|COATING ALLOWS IN-SERVICE PAINTING OF HIGH-TEMPERATURE EQUIPMENT AT AMOCO REFINERY
Painting high-temperature equip-ment in oil refineries usually poses problems for engineers and maintenance painting crews, because turnaround times must be kept to a minimum and conventional heat-resistant paints can be applied only if the equipment is down and surfaces are at ambient temperature.
At the Whiting (Indianan) refinery of Amoco Oil Company, however, these problems have been avoided by painting high-temperature equipment during operation with Thurmalox® 260 series heat-resistant coatings, which are specifically designed for application to surfaces as hot as 400°F.
Thurmalox 260 coatings are based on a co-polymerized silicone resin containing a heat-activated catalyst. Heat radiating from the hot substrate itself triggers the catalyst, cross-linking the coating and producing a “baked-on,” chemically-resistant finish similar to oven-cured factory finishes. The coatings will also air dry and can be applied to surfaces at ambient temperatures as well, curing as the equipment resumes operation and passes through the curing temperature range, 225°F to 300°F.
Amoco has been successfully applying the Thurmalox coating to hot surfaces in the refinery since 1976, the year they were introduced, says James B. Hudson, supervisor of maintenance painting at the Whiting plant.
VARIETY OF LARGE
Some of the largest units have been coated, including the #12 pipe still, the refinery’s largest; the #4 ultraformer, completed in 1972 and the largest of the refinery’s three ultraformers; and the regenerator at the huge #500 catalytic cracking unit. In addition to their use on other similar units, the Thurmalox coatings have been applied to the refinery’s prominent incinerator on the shore of Lake Michigan, and to towers, tanks, furnaces, and stacks.
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CORROSION SURVEY CONDUCTED
A corrosion survey was conducted in the dock and pier areas. While there was some evidence of corrosion in the tidal zone areas, ultrasonic testing indicated that the steelwork was still basically sound and only required minor repairs.
In the tidal zone most of the original coal tar-enamel coatings had deteriorated badly and would have to be removed and the steelwork recoated. But above the high water line, the original coatings were still in good condition and would only require cleaning, spot priming, and topcoating to provide years of additional service.
TOUGH REQUIREMENTS FOR COATINGS
In developing the coating specification many important factors were considered.
First, the coatings would have to fulfill all the stringent requirements for marine coatings, including: good adhesion in immersion, toughness, resistance to abrasion and undercutting, good corrosion inhibition, salt water and chemical resistance, humidity and weather resistance, resistance to cathodic disbonding, high film thickness, and ease of application.
Secondly, since the time available for surface preparation and application in the tidal zone would be limited by the rising tides to two hours, the coatings would have to cure sufficiently to resist immersion within this period. (Most conventional solvent-based coatings require a week to cure and to release solvents before they can be subjected to immersion service.) The coatings would also have to provide good adhesion to the original coal tar-enamel coatings.
Finally, the cost of application had to be reasonable. It would be advantageous if the coatings could be applied by an industrial painting contractor rather than by marine divers.
VARIETY OF COATINGS CONSIDERED
In reviewing the types of coatings available, New England Power ruled out hot-applied coal tar-enamel as their previous experience indicated the probability of early failure at the waterline. It would also require heating to 350°F and would be hazardous to apply without using cofferdams.
Another possibility was straight (unmodified) epoxy coatings but they were judged to be too costly.
Solvent-based coal tar-epoxy coatings were ruled out because they would not release solvents quickly enough or cure adequately before the rising tides. This could lead to blistering and disbondment of the coating due to solvent entrapment.
DAMPNEY PROVIDES COATING SYSTEM SOLUTION
To provide maximum corrosion protection in the tidal one Dampney Company recommended a two-coat system of Epodur®2755 urethane-modified epoxy primer and epodur®782 solventless coal tar-epoxy topcoat. A coating specification was prepared accordingly.
Epodur 2755 is a corrosion-inhibitive primer, which is more tolerant of surface moisture and cures at lower temperatures than conventional polyamide-epoxy primers. It provides excellent adhesion in immersion service, and resists undercutting corrosion in damaged areas.
Since it cures rapidly under highly humid conditions it was applied with assurance that it would adequately resist immersion before the rising tides.
The Epodur 782 topcoat is thixotropic, high-build coating having unique properties, which made it particularly suitable for this application. It can be applied using standard airless spray equipment with no need for special handling procedures. There was no need to preheat the components to reduce the coating to spray viscosity.
The coating could be applied in a single, high-build, non-sag coat, eliminating the need for multiple-coat application. And since it has a 2-hour pot life, there was no need to use complex plural-component spray equipment. These factors helped reduce application time and cost.
Because Epodur 782 is solventless, it eliminates potential blistering and pinholing due to solvent evolvement, thereby assuring better film integrity, and since it would not soften the existing coal tar-enamel coating it could be used to topcoat existing sound coatings.
SURACE PREPARATION AND COATING APPLICATION
First, all surfaces were washed down with fresh water to remove accumulated salts. In the tidal zone, all rust, rust scale, calcerous deposits, and foreign matter were then removed by abrasive blasting per specification SSPC-SP 10 “Near White Blast Cleaning.”
Above the high tide line, all sound existing coal tar-enamel coating was blasted per specification SSPC-SP 7 “Brush Off Blast Cleaning” to remove loose coating and contaminants and to provide and anchor pattern to improve adhesion of the topcoat.
No larger area was blasted than could be painted in one day. In the tidal zone the surfaces were primed with one coat of Epodur 2755 to a dry-film thickness of 2 mils. After the primer set dry to touch (in about 20 minutes) a single top coat of Epodur 782 was applied to a dry-film thickness of 16 mils.
Above the high water line, bare areas were spot primed with Epodur 2755 and topcoated with Epodur 782 to a dry-film thickness of 16 mils.
Extra coatings were applied to bold heads, web edges, and other areas vulnerable to corrosion. Work was conducted with the changing tides without the need for cofferdams or divers, and the coatings were immersed as the tides came in.
COMPREHENSIVE CORROSION PROTECTION ASSURED
Corrosion protection is now assured for the dock and pier area. The Epodur 2755 epoxy primer/Epodur 782 solventless tar-epoxy coating system provides long-term protection above the low waterline, and the cathodic system protects the structures elow it.
Subsequent inspections have shown excellent intercoat bond between the old coal tar-epoxy and the new 100% solids epoxy coating. The new coating system has also proven to be resistant to cathodic disbondment and to the abrasive effects of winter ice.
FOR FURTHER INFORMATION
Additional information about Epodur 2755 primer and Epodur 782 100% solids coal tar-epoxy coating may be obtained from The Dampney Company at the address below
Dampney Company, Inc.
85 Paris Street
Everett, MA 02149
Tel. (617) 389-2805
Fax (617) 389-0484