Fluid handling – Processes
Patent
1995-03-13
1996-03-26
Rivell, John
Fluid handling
Processes
137511, 137539, F16K 1504
Patent
active
055012426
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a pressure relief valve particularly, but not exclusively, for use with pipelines carrying fluid at a predetermined pressure above which the fluid requires to be vented so as to reduce pressure in the system to a level beneath the predetermined threshold. In particular, the pressure relief valve is for use in hydrocarbon production exploration industries and similar pressurised fluid environments.
Hydrocarbon fluid in a well test or well production environment is maintained initially at pressure substantially higher than atmosphere. The pipeline containing the pressurised hydrocarbon fluid usually contains a piece of equipment, such as a safety valve, such that if an over-pressure situation occurs the well fluid is vented to atmosphere via a oil rig pressure relief burner boom. Such pressure relief valves have been available for many years and one common type is a flanged pressure relief valve which is spring-loaded and which is coupled to the hydrocarbon pipeline. In the event of an over-pressure situation arising, a valve closure member is forced from a valve seat, against a spring force to open the valve, whereby pressurised fluid is allowed to flow through a valve outlet. A typical type of prior art valve is a Crosby spring-loaded flanged pressure relief valve style JOS and JBS. Although these types of valve are common in the industry, they suffer from a number of disadvantages. One significant disadvantage of this type of valve is that a back-pressure at the valve outlet of approximately 10% of the inlet pressure is sufficient to act together with a spring force to close the valve leading to a potentially hazardous situation. In addition, the top housing which contains the spring element is rated at 120 p.s.i. which is believed insufficient to use with a large range of pressures commonly encountered in hydrocarbon process equipment. In order for the valve to be used such that the outlet pressure is less than 10% of the inlet pressure large diameter piping is required at the outlet. This piping is not only heavy, but is also relatively expensive. A further consequence of the weight of the piping is that in the production and exploration structure at least 9 times the amount of piping weight requires to be added for structural considerations. Therefore, where considerable amount of piping is required, as is common in oil exploration and production platforms, this can result in a significant add-on cost in terms of weight and overall structural costs as a consequence of having to use large diameter piping to reduce the pressure relief valve back-pressure. A further disadvantage of the aforementioned prior art valves is that most of the valve closure elements are of the plate type which can result in hydrate formation as the gas expands and cools in the nozzle because of the throttling effect. If this happens and venting does not occur, the line pressure is retained and the well test equipment is likely to fail at the next weakest point which is probably the piece of equipment which the valve is intended to protect.
A further disadvantage of existing prior art relief valves is that it is not possible to test the valve in situ. The system requires to be closed down, the valve physically removed and tested and then re-inserted into the process equipment. It will be appreciated that this is an extremely time-consuming and expensive operation, especially on exploration and production rigs, which add significantly to the cost of operating the rig. Yet another disadvantage of the prior art pressure relief valves is that with a plate valve fluid impinges on the valve nozzle and the valve plate, with the result that the nozzle and the plate can wear, thus rendering the valve susceptible to leakage in the absence of an over-pressure situation which is, of course, undesirable.
Another type of pressure relief valve is a balanced bellows type valve which is used to isolate the back pressure from the top of the disc with the effective area of the bellows being equal to the seat area. T
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patent: 4248265 (1981-02-01), Freeman, Jr.
patent: 4262693 (1981-04-01), Giebeler
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patent: 4565213 (1986-01-01), Giebeler
patent: 4930553 (1990-06-01), Grillo
Coutts Graeme F.
Edwards Jeffrey C.
Expro North Sea Limited
Rivell John
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