Fluid handling – Processes – Cleaning – repairing – or assembling
Reexamination Certificate
2001-03-08
2003-08-26
Chambers, A. Michael (Department: 3753)
Fluid handling
Processes
Cleaning, repairing, or assembling
C137S014000, C137S236100, C137S552000, C137S556000
Reexamination Certificate
active
06609533
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to gate valve actuators and, in a particular embodiment, to apparatus and methods for a fail-safe hydraulic subsea actuator that reliably operates in deep water for extended time periods.
2. Description of the Background
Remote subsea fail-safe gate valves are typically controlled with hydraulic actuators. The hydraulic actuators and often their controls are located on the ocean floor along with other equipment. Due to the cost of positioning equipment on the ocean floor, it is desirable that any equipment be as compact as possible while still affording very high reliability. Although the location, configuration and types of actuators and controls vary, their operation is subjected to ambient sea pressure whether the actuator and controls are an open or closed system. The time required for a fail-safe valve to fail-safe close is critical, and therefore a short response time is highly desirable. The more hydraulic fluid required to operate the actuator, the longer the operation time. As water depth increases, increased hydrostatic head, or ambient sea pressure, creates forces on the valves and actuators that due to a combination of conditions can unreasonably delay or preclude fail-safe operation upon loss of hydraulic control pressure. The valve size and internal valve line pressure can create additional problems under such conditions. As well, the hydraulic fluid volume and pressure may be limited due to the need to avoid multiple hydraulic lines to the surface. Moreover, it is sometimes desirable to change out hydraulic fluid to prevent contamination that might cause actuator failure. This is another reason for limiting the amount of hydraulic fluid necessary for controlling the actuator because use of a smaller volume of fluid is quicker to exchange and/or clean. Moreover, it would be desirable to avoid hydraulic fluid contact with return springs that are used in the subsea actuators because contaminants often eventually get into the hydraulic fluid and react with the return springs thereby further increasing hydraulic fluid contamination and/or damaging the return spring.
As another matter, it would be desirable to improve indicators which can be viewed by remotely operated vehicles. In some cases, such indicators require seals that may fail and cause actuator failure. Indicators may also increase the size of the actuator.
U.S. Pat. No. 6,041,804, issued Mar. 28, 2000, to V. R. Chatufale, discloses a subsea actuator and method that includes a removable monolithic cap/hydraulic chamber that seals the actuator housing top with seals placed around the monolithic cap, defines a straight hydraulic line and port for control line hydraulic fluid, and provides for fasteners to secure the top of the subsea actuator. The monolithic cap/hydraulic chamber is so limited in metal and machine time that it can be a throw away maintenance item. A preferably cup-shaped spring pusher is provided in telescoping relationship to the hydraulic chamber. Several short hydraulic fluid passageways are provided in the bottom cup portion of the spring pusher to permit assist hydraulic control fluid into the hydraulic chamber below the piston. The driving stem provides a removable connection to the hydraulic piston from the top of the actuator housing and a quick disconnect permits disconnection of the driving stem from the valve stem. The high tension spring does not need to be removed to perform maintenance, and all wear items and seals are readily accessible. Change or replacement of the stem packing is made from the top of the bonnet to avoid dissasembling the bonnet to valve body connection. The spring chamber within the actuator housing may be increased in size to accommodate a larger spring as necessary for fail-safe operation without changing the size of the hydraulic chamber. All sliding components ride on wear rings to increase the lifetime of reliable subsea operation. The moving components are mounted in a compact, concentric configuration.
While the above actuator has many advantages, the actuator uses a significant amount of hydraulic fluid which, as explained above can sometimes be problematic. Contact of the spring with hydraulic fluid can also present a long term viability problem. It would also be desirable to limit any leakage that might occur between the valve bonnet and actuator, even if packing should leak. Moreover, the above patent does not address limiting the size of the actuator with respect to manual override operators and valve status indicators.
Furthermore, subsea actuators need to be very reliable because they operate in an environment that is not readily accessible. Conventional subsea actuators often have numerous problems that limit the operational range, reliability, cost, and maintenance thereof. While there are several commercially available subsea actuators on the market with different designs, the problems tend to be related. For instance, over long periods of time packing may leak permitting flow of fluid between the actuator housing and valve bonnet. It would be desirable to eliminate such leakage. Moreover, it would be desirable to provide that any component maintenance used to limit such leakage do not require an expensive complete exchange of the bonnet or valve stem.
In another commonly used design, the spring used for fail-safe operation is located within the hydraulic cylinder. This design is likely to cause hydraulic fluid contamination and spring damage. Moreover, while this arrangement may afford sufficient spring strength for actuation to depths of 1000 feet or so, it results in numerous problems for deep water subsea actuators. In this design, the spring outer diameter is limited to the size of the hydraulic cylinder. It is generally not desirable to increase the size of the hydraulic cylinder to provide a more powerful spring because this also increases the amount of hydraulic fluid necessary for operation and may present a potential problem at significant water depths. With a limited spring size, the fail-safe operation that the spring may afford is limited because the spring size is quite limited. Furthermore, positioning of the spring within the hydraulic cylinder also has the disadvantage of increasing the likelihood of ruining the sealing surfaces of the hydraulic cylinder due to contact with the spring during operation and also during assembly or disassembly. The damage requires replacement or reworking of the entire actuator housing and is therefore quite expensive. In this design, maintenance of even a single seal necessarily requires removal of the spring, which is normally under very high spring pressure, and may be a somewhat dangerous operation without special equipment. Typically, the entire gate valve as well as the operator must be broken down when doing virtually any maintenance. Thus, even replacing a single seal is a time consuming, costly operation. Not only is extensive time required for maintenance, but parts including additional replacement seals of all stationary metal-to-metal seals are necessary even though such may have been operating fine without problem. Thus, commonly available actuators tend to have numerous limitations including highly limited operational abilities, reliability problems, and very high maintenance costs.
Consequently, there remains a need for a compact subsea valve actuator that offers dependable operation at significant water depths, reduces the size of the manual override control, reduces the need for hydraulic fluid, reduces maintenance time, provides an improved valve/actuator status indicator system, limits leakage from the actuator to valve even if the packing should leak, permits easier maintenance, all for reduced levels of capital investment. Those skilled in the art have long sought and will appreciate the present invention which provides solutions to these and other problems.
SUMMARY OF THE INVENTION
The present invention is embodied in a design for a hydraulic subsea actuator and method for a gate
Chambers A. Michael
Nash Kenneth L.
World Wide Oilfield Machine, Inc.
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