Riser splash zone encapsulations in fifth year of service
Stingray Pipeline Co.'s compressor platform at West Cameron 509A, located 98 miles offshore in the Gulf of Mexico, gets its share of rough weather.
Stingray Pipeline Co. has identified a field applied, composite encapsulated system that can withstand the environmental stresses placed on risers in the splash-zone of offshore drilling and production rigs. The company began looking for such a system over five years ago after one corrosion protection system, installed on several risers at the platform at West Cameron 509 A, failed and had to be removed before anything new could be applied. (Offshore - April 1995)
Stingray needed a long-term, cost-effective, corrosion protection system that could be field applied in the splash zone. Many operators in the Gulf of Mexico have experience with field-applied coatings and wrap systems. Stingray had tried several, but none provided the long-term protection needed.
Stingray learned the A-P-E Process field applied encapsulation system had been used for several years as corrosion protection on coastal structures, but had not yet been used offshore. While this system, manufactured by Master Builders, Inc. of Cleveland, Ohio, had an excellent track record onshore, Stingray was not sure it would perform as well on a platform 98 miles offshore in the Gulf of Mexico.
Severe wave action at the West Cameron 509A site had contributed to the failure of an earlier system and would present a challenge to any new system the company planned to apply. Key benefits to the new system, according to Stingray, were that it properly addressed the problems of installation and long-term durability in wave active environments. After completing an evaluation, Stingray engaged MADCON Corp., of New Orleans, to install A-P-E Process encapsulations on several risers at the West Cameron platform. This represented the systems first application in the Gulf of Mexico.
Process Described
The A-P-E Process consists of a translucent Fiberglass Reinforced Plastic (FRP) outer jacket and aggregate filled epoxy grout. The jacket and grout bond tightly with the encapsulated member to form a composite. One of the advantages of the A-P-E Process is that it can be installed in several steps. After surface preparation, the outer FRP jacket is placed around the riser and sealed. Once the jacket is securely in place, the aggregate filled epoxy grout is pumped into the jacket from the bottom up. During this separate operation, the progression of grout is monitored through the translucent jacket. This monitoring procedure helps ensure a complete, void-free encapsulation. The separate pumping step also creates a mechanical scouring effect when the aggregate filled grout is forced upward within the confines of the jacket. This scouring effect makes a significant contribution to achieving the final bond between the encapsulation materials and the riser. Aggregate filled epoxy grout, as opposed to neat epoxy, is thermally compatible with the steel riser. This compatibility minimizes the risk of delamination. Installation in separate, manageable steps also allows the installation contractor to work more effectively in the wave-active splash zone.
Typical test specimen 'divot' seen at completionof bond test.
Condition Monitored
Stingray has continuously monitored the condition of the encapsulations since the installation of this system, in 1994. The monitoring consisted of periodic visual examinations, combined with 'sounding.' Sounding involves striking the encapsulations with a hammer or other object to detect any change in sound that might indicate delamination within the encapsulations or disbondment from the risers. In addition, the encapsulations have been physically tested for bond to the risers by the Modified Elecometer test method. This test employs a hand-held device that applies a direct tensile load to a test dolly adhered to the outer surface of the encapsulation. Coring through the encapsulation, down to the riser surface isolated a 3-in. diameter section of the encapsulation. This test is considered an effective means of evaluating corrosion protection systems because it determines the actual bond at the interface between the encapsulation materials and the riser.
This procedure also produces a sample of the encapsulation materials that can be examined for signs of delamination or products of corrosion. A typical 3-in. diameter sample, called a 'divot,' is seen with the test dolly attached. At maximum test load, the aggregate filled epoxy grout typically fails adjacent to the riser interface, leaving some of the grout still adhered to the riser. When the test is complete, the test dolly is removed. The divot is coated with epoxy paste and placed back into the cored test hole to re-seal the encapsulation. The most recent series of tests, performed in late 1998 at West Cameron 509 A, indicated that the encapsulations, which were by this time more than four years old, remained tightly bonded to the risers. No signs of corrosion were found.
The encapsulations are currently in their fifth year of service, still protecting the risers in the severe environment found 100 miles offshore. There is no evidence of deterioration and, aside from a slight build-up of marine growth, the encapsulations appear as they did when first installed. They have been carefully examined for signs of delamination or disbondment, including the possibility of cathodic disbondment, and none has been found.
