The development of the Udang "B" project in the Indonesian Natuna Sea required the installation of two insulated submarine pipelines in nearly 300 feet of water. These pipelines carry 100 degrees F pourpoint crude, water, gas from the recently installed Udang "B" platform to the Udang "A" platform. At the Udang "A" platform, the produced fluids are processed. platform. At the Udang "A" platform, the produced fluids are processed. The crude oil is then transported to a permanently moored storage tanker through two other insulated submarine pipelines.
The Udang "B" pipelines have a 12 ¾ inch inner pipe with an 18 inch outer pipe. The annulus between the two pipes is filled with a polyurethane pipe. The annulus between the two pipes is filled with a polyurethane insulating foam. That annular cavity is then sealed with a steel washer plate at either end of the insulated pipe joint. The pipeline system is plate at either end of the insulated pipe joint. The pipeline system is designed to withstand at 190 degrees F operating temperature and to comply fully with applicable pipeline codes. The pipeline is designed so that the polyurethane insulating foam is protected from the 140 psi external polyurethane insulating foam is protected from the 140 psi external hydrostatic pressure.
The pipelines were installed offshore using a lay barge with innovative methods used at the field joints to insure the uniform structural integrity of the pipeline and the continuity of the insulation system. The risers were also insulated and installed in one piece with a flanged connection completed on the seafloor to connect the riser with pipeline. Third party underwater inspection of the jacket, riser, and pipeline connections was provided by a remote controlled vehicle (RCV). provided by a remote controlled vehicle (RCV). This paper discusses the insulated pipeline system as it evolved through the design, onshore pipe insulation and joint fabrication, and offshore construction. The paper reviews the design and construction techniques used successfully for these offshore insulated pipelines. These techniques could be applicable for other similar deep water insulated pipeline applications.
The Continental Oil Company of Indonesia as operator for itself Java Gulf Limited, Getty Oil International (Indonesia) Ltd and Inpex Natuna Limited operates the Udang production facility under a production sharing contract with Pertamina. This facility is located in 300 feet of water in the Indonesian Natuna Sea about 750 air statute miles north of Jakarta and 50 miles north of the Anambas Islands, the nearest landfall. Two combination drilling and production platforms am in operation in conjunction with a moored production platforms am in operation in conjunction with a moored storage tanker and export facility. The two platforms and the tanker are linked by dual subsea insulated pipelines.
The Udang 'A' facility, installed in 1978, utilizes a 14 slot, 8 pile, 2300 ton jacket, with attendant flam structure. Three stage separation and treating facilities are on the platform as well as emergency accommodations. The storage tanker, the "Udang Natuna", is permanently moored approximately 6,100 feet southeast of the Udang 'A' platform. Two insulated subsea pipelines connect the Udang 'A' platform with a PLEM (pipeline and manifold) beneath the loading buoy on the seafloor. These pipelines are a 8 5/8 inch pipe inside of a 12 ¾ inch pipe with insulating foam in the annulus.
The Udang 'B' facility, installed in 1980, is located, 12,500 feet to the southwest of the Udang 'A' platform. The Udang 'B' jacket, also located in 300 feet of water, is a 15 well, 8 pile 2,160 ton jacket with emergency living quarters and well test separation. The crude oil, associated gas, and produced water flow through dual subsea insulated pipelines from the 'B' facility to the 'A' facility for further processing. These two pipelines have a 12 ¾ inch inner pipe and an processing. These two pipelines have a 12 ¾ inch inner pipe and an 18" outer pipe with insulating polyurethane foam in the annulus.
The Udang crude has an API gravity of 40 degrees but its pourpoint is 100 degrees F. Consequently in order to flow it must be maintained at an elevated temperature. The maximum anticipated crude temperature is 190 degrees F. A minimum temperature of 150 degrees F is maintained in the storage tanker by heating the storage tanks. Because of the high crude pourpoint and the necessity of maintaining the crude at an elevated temperature, all Udang subsea pipeline systems have a redundant pipeline installed. This dual pipeline systems have a redundant pipeline installed. This dual pipeline system allows the pipeline contents to be circulated in the event pipeline system allows the pipeline contents to be circulated in the event of equipment failure or scheduled maintenance. this circulation, in conjunction with the addition of heat as the pipeline circulates through the "A" facility, will prevent the formation of gels which could plug the pipeline. The pipeline insulation also increases the allowable pipeline shut-in time before circulation and heat imput are required.
The pipeline and risers designed to be in compliance with the det Norske Veritas (DNV) pipeline code. Because of the high crude temperature and the need for insulating the pipeline, the design of the pipeline system had to accomodate some interesting features.
The thermal insulation system, which was developed by Conoco during 1975 – 1971 for use on the Udang 'A' project, was used on the Udang 'B' pipelines. The design utilizes a closed cell polyrethane insulating foam with a heat transfer coefficient of 0.15 BTU-IN/ deg. F-F+ 2 hour or less. The foam weighed 3.2 pounds per cubic foot. A minimum foam thickness of 1.375 inches was required for the Udang 'B' pipelines. Because the Udang pipelines are in 300 feet of water the polyurethane foam must be completely protected from the external hydrostatic head. The head pressure in 300 feet of water is sufficient to cause seawater to infiltrate the foam causing it to lose its insulating capability. To eliminate this problem, the insulated 12 inch pipe joint was encapulsated within an 18 inch pipe. Only the ends of the 12 inch pipe joint extended past the end of the 18 inch outer pipe with the two pipes joined by a steel end washer or disc.
The design of the pipeline and riser system to withstand the thermal expansion forces was a major consideration in the design effort. For design purposes, 190 degrees F was selected as the maximum pipeline temperature and 62 degrees F was selected as the sea bottom water temperature. This differential temperature of 128 degrees F was accommodated in the design. The pipeline and riser system design was analyzed using a conventional analytical technique modified slightly to reflect the use of an outer and inner pipe. The resistance of the sea bottom to the pipelines' axial expansion was considered.