Gate Valve Technology: Designs for the Times

ABSTRACT The end users of gate valves for onshore and offshore applications rarely understand the design process related to gate valves. The gate valve manufacturing industry has products that have gone through a technical evolution during the past fifty years to meet the service demands of the petroleum and chemical proms industry. The gate valve has traditionally been an after thought for the design and process engineer. Gate valves are often the first point of fluid control, and they deserve to be understood by design engineers, field engineers, and maintenance personnel. INTRODUCTION Gate valve technology since the early decades of this century has gone through an evolution of design characteristics and materials usage in order to withstand the critical service in today's petroleum production, petrochemical processing and power generation applications. The gate valve, although simple in concept compared to downhole drilling tools, high technology chemical processes and power generating equipment may well be the component that receives the least attention. Contrastingly, it may well be the most important component in well completions, production control systems and facility and personnel safety. The gate valve usually provides the first point of shutoff capability for almost all wells drilled for a variety of applications and uses. The wells are drilled for specific purposes. They produce oil, natural gas, minerals, water and steam with each having difficult chemical compositions, dissolved solids content and particulate matter. These flow characteristics coupled with temperature and pressure variations create very hostile environments. Gate valves are expected to operate freely over extended time periods with little or no maintenance in these harsh conditions. Valves do not get the priority of design engineers' time or understanding when projects are defined. Specifications for gate valves are as important as specifications for drilling rigs, turbines and process equipment. After all, if a valve should become inoperative or leak beyond an acceptable limit, an entire revenue producing operation may be forced to cease operations while a single valve is repaired or replaced. Reviewing the valve design, materials of construction and intended application may save thousands or millions of dollars and prevent environmental and personnel safety hazards. DESIGNS FOR THE TIMES Gate valves are intended to provide positive shutoff for a multitude of flowing products. The flow can be gases, liquids, slurries, or a two phase mixture of vapor and liquid. The conditions of the flowing medium range across a very wide spectrum of chemical compositions and solids content, creating varying degrees of erosive and corrosive environments. Gate valves are typically designed to handle a specific set of conditions and generally purchased to a tight specification. Unfortunately, gate valves purchased for specific conditions and according to tight specifications can end up in an entirely different application from that which the specifications were intended. It is these facts that make the evolutionary design of gate valves such an important aspect in the engineering, construction and operation of any fluid handling system. Gate valves were probably among the first valves to be built and used.