Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Submerging – raising – or manipulating line of pipe or cable...
Reexamination Certificate
1997-12-23
2001-11-13
Bagnell, David (Department: 3673)
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Submerging, raising, or manipulating line of pipe or cable...
C405S154100, C405S169000, C405S170000, C138S033000, C166S248000, C166S265000, C392S304000, C392S321000
Reexamination Certificate
active
06315497
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a heated flowline isolation joint. More particularly, the present invention relates to a joint for a pipe-in-pipe flowline in which electrical current is introduced to the inner pipe at the joint.
One important and representative application for such a joint is in providing direct electric heating along the length of an extended subsea pipeline. The heating provided by the electricity introduced is a result of a combination of electrical resistance and magnetic eddy current effects associated with transmission of an alternating current through the pipeline.
Offshore hydrocarbon recovery operations are increasingly pressing into deeper water and more remote locations. Here it is very expensive to provide surface facilities and it is desirable to minimize these requirements. Often satellite wells are completed subsea and are tied to remote platforms through extended subsea pipelines as a means to reduce the production cost. Even these platforms serving as central hubs in the offshore infrastructure are provided only the minimal facilities required for collecting and partially treating the well fluids before exporting them toward onshore facilities through yet more subsea pipelines. However the subsea pipelines crucial to this infrastructure prove a weak link as they are subject to plugging with hydrates or with paraffin deposition. Both hydrates and paraffins are of limited trouble at the pressures and temperatures experienced at the producing well, but can cause serious plugging problems when cooled to lower temperatures during pipeline transport.
Hydrates are the product of complicated chemistry in which water and certain hydrocarbon components of the produced well fluids combine to form ice-like crystals in pipelines as the temperature decreases during transport. The resulting hydrate crystals can suddenly solidify and plug the bore of the subsea pipeline. Paraffins are also a product of temperature in the pipeline and come out of suspension and deposit on the pipeline walls when the well fluids are below the “cloud point” which may be as high as 100-120 degrees Fahrenheit. Eventually this waxy buildup can completely seal off a pipeline.
These difficulties are combated between the satellite subsea wells and platform hubs by insulating the pipelines and moving the produced well fluids as quickly as possible to minimize temperature loss. However, the long length of such pipelines renders passive insulation ineffective and it is often necessary to resort to large amounts of chemical inhibitors or to mechanical clearing operations to maintain the pipeline free of plugs.
In conventional practice, removal of a hydrate plug requires reducing the fluid pressure on both sides of the plug and applying chemical agents to the plug. Paraffin buildup is most often remedied by frequent routine pigging to scrape away the deposits fouling the bore of the pipeline. Before entering the pipelines between the platform and the onshore facilities, the fluids may be dewatered, separated into oil and gas, and treated with additives or other refined products. Again, it is often necessary to supplement this platform processing with routine pigging operation, even in these export pipelines.
Pipelines that are shut-in during workover of the wells or during work on the platform facilities are particularly susceptible to hydrate and paraffin problems as the hydrocarbon temperature drops toward the ambient seawater temperature. Thus, in present practice it is sometimes necessary to displace the hydrocarbons throughout an entire subsea pipeline with fluids that protect the pipeline during such operations. Further, it is then necessary to purge such fluids before production can resume. This is not an insignificant expense in both time and materials when considering pipelines whose lengths are measured in miles and tens of miles.
A suitable heated flowline electrical isolation joint is a critical aspect to providing the benefits of direct electrical heating to pipe-in-pipe subsea pipelines. Thus there is a clear need for a reliable joint that can withstand the pressure and voltage requirements of such applications.
SUMMARY OF THE INVENTION
Toward providing these and other advantages, the present invention is a a heated flowline electrical isolation joint for introducing current into a pipe-in-pipe system having an outer and an inner pipe. A hub presents a load flange having tension and compression load shoulders on its terminal end and connects to the inner pipe on its other end. An end flange presents an end flange load shoulder on one end and a high strength, highly electrically insulative first ring separates the compression load shoulder from the end flange load shoulder which engage therethrough in a load bearing relationship. A plurality of o-ring seals secure the compression load shoulder-to-first ring-to-end flange load shoulder interfaces. A retainer flange connects to the end flange on one end and to the outer pipe on the other end, encircling the hub and presenting a retainer flange load shoulder. A second high strength, highly electrically insulative ring separates the tension load shoulder of the hub from the retainer flange load shoulder which engage therethrough in a load bearing relationship. A plurality of o-ring seals securing the tension load shoulder-to-second ring-to-flange load shoulder interfaces. An electrical feedthrough tube receives an electrical penetrator which reaches through the retainer flange to electrical connection with the hub. An electrically insulative material in the annulus between the hub and the retainer flange and between the electrical penetrator and the electrical feedthrough tube secures electrical isolation across non-load bearing areas.
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patent
Bass Ronald Marshall
Langner Carl Gottlieb
Wittman Robert Henry
Bagnell David
Mayo Tara L.
Shell Oil Company
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