Method and apparatus for covering a pressure vessel

Abstract

An apparatus disclosed herein relates to a pressure vessel cover comprising, a periphery of the cover, a first surface of the periphery for sealing on a first side of the cover and a second surface on a second side of the cover opposite from the first side, a third surface on the first side of the cover and located radially inwardly from the periphery, the third surface being displaced axially from the first surface in the direction of the second surface, a fourth surface on the second side of the cover radially inwardly positioned from the periphery, and a bore through the cover in fluidic communication with the third surface and the fourth surface.

Description

BACKGROUND OF THE INVENTION[0001]A chamber that contains a fluid within the chamber at higher pressures than is on an exterior of the chamber is often referred to as a “pressure vessel.” Pressure vessels may be used to house valves, which control the flow of the fluid through the pressure vessel. Such fluid flow may be for the transport of steam, for example, in the case of a steam turbine power plant. Housing the valves within the pressure vessel makes necessary a cover through which access to the valves is possible for purposes of servicing the valves, for example. The cover must form and maintain a seal to the pressure vessel under the various operating conditions that it will be subjected to, such as, elevated pressures and temperatures as well as cycles of varying pressures and temperatures.[0002]Variable flow “control valves” and only fully-opened or fully-closed “stop valves” are commonly used in steam turbine power plants. With the use of these valves it is desirable to have...

AI Technical Summary

Problems solved by technology

Covers that incorporate bores tend to be very thick heavy plates of metal.

Pressure vessels with thick flat covers with bores, however, continue to have failures due to stresses.

Such failures include LCF bolt failures that result from the cyclic application of bending stresses.

Such dishing causes a peripheral portion of the cover, through which the bolts pass, to also dish resulting in a bending stress being applied to the bolts.

Such dishing, in the opposite direction than that from the turbine start up condition, results in a bending stress, on the bolts, in an opposite direction.

Consequently, each start up cycle of the steam turbine may result in a fatigue cycle of the cover and the bolts, first in one direction and then in the opposite direction.

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