Things to Consider for Valve Applications in High-Pressure Environments
Nebula Engineering
Valves / Gearbox / Compressor / Safety Equipment / Pipe & Vessel Design / Heat Exchanger / Instrumentation / Filters
(Basic of High Pressure Valve)
It goes without saying that safety is the most important criteria. However, safety is not a parameter that can be chosen but rather an outcome of other parameters when correctly done. Consequently, we will describe the five parameters essential to guarantee a safe and functional operation of a high-pressure valve.
1. Maximum Operating Pressure
The maximum operating pressure is a valve specification that defines the pressure limit beyond which proper or safe operation of the valve cannot be guaranteed by the manufacturer. All valves, including high-pressure valves, have a maximum operating pressure. The selection of a high-pressure valve is not based on just the high operating pressure of your process stream but also on the potential high-pressure limit when a pump is set at maximum head against a closed valve downstream. The worst-case operational scenario is your selection criteria for high-pressure valves.
2. Operating Temperature
It is common to have the maximum operating temperature alongside the pressure specification for high-pressure valves. Both parameters are often associated with many industrial applications. Look out for a high-pressure valve that also has a temperature limit that meets your process operating temperature.
3. Valve Material
The material for high-pressure valves and the parts determine its resistance to pressure, temperature, wear, corrosion etc. Material incompatibility between the fluid, additives and the valve must also be considered. Industrial valve manufacturers publish incompatibility charts for a detailed list of which fluids can work with a specific valve material.
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The valve body and seat can be made of ductile iron; it is cheap and can absorb shock but is not very resistant to corrosion. Brass/bronze are for better corrosion resistance but are usually not high pressure. Though more expensive than iron, brass, or bronze, 316 stainless steel offers corrosion resistance, high tensile strength at high temperature. Valve bodies can also be made of monel (an alloy of nickel and copper) or Inconel (an alloy of nickel, chromium and iron) for better corrosion resistance and corrosive fluid handling while maintaining strength at high temperature.
Other parts of the valve, such as gaskets, seals and packing, are many times made of polytetrafluoroethylene (PTFE) for low friction between moving parts at high pressure and temperature. They may also be made of polyurethane, viton or polyetheretherketone for durability, chemical resistance and corrosion resistance. When choosing the proper valve body material and seat material, it is best to consult a valve expert, especially when the process is deemed high pressure for its application.
4. Connection End Type
The type of end connection used in high-pressure applications is vital to prevent leaks. Threaded end connections are useful when the pipe diameter is small (below 2 inches). Beyond this size, it will be difficult to seal the space between the threads under high pressure. Threaded connections are useful if the valve is to be periodically maintained.
Welded connections are a more popular connection type for high-pressure applications as they guarantee zero leakages. They are also used in hazardous fluid systems. Welded end connections are permanent. There are two types of welded end connections for high-pressure valves: socket welded connections and butt-welded connections.
High-pressure valves can also be connected to pipes using flanged connections, particularly if the valve is larger than 4 inches. Flanged connections are standard in industrial applications, especially high pressure ones. They provide a good enough seal, allow easy maintenance of the valve, and are easy to install. There are multiple flanged connection types and styles under standards DIN 1092-1, ANSI/ASME B16.5 and SAE J518.
5. Leakage Tolerance
Depending on your application, there may be some leakage tolerance, especially if the process fluid is not hazardous. Determine how much leakage can be tolerated from a high-pressure valve to save unnecessary costs associated with zero tolerance valves. Valve leakage is mainly related to the end connection type, but some valves also leak through the packing seal that holds the shaft to the valve’s body.?
The amount of leakage tolerance is pressure dependent. High-pressure valve manufacturers provide such information in charts supplied with the valve. MSS standard SP-61 and ANSI standard 70-2 define allowable leakages and leakage classifications for high-pressure valves.
6. Size Availability
High-pressure processes are often operated with smaller pipe diameters. This is because of the material cost of the pipes to hold the pressure without breaking. Though not so obvious, most high-pressure valves in the industry are small. When designing your process, check that there are readily available high-pressure valves for the piping dimensions.