As there are more types of check valves, the design of the petrochemical plant pipelines, inevitably involves the selection of check valves.
Check valve type selection is reasonable, not only affects the investment in construction and normal production of the device but also affects the safety of the pipeline system and equipment. Therefore, the choice of the check valve is very important, the main factors affecting the choice of check valve type are as follows.
1. First of all, you should understand the purpose of the process and set a check valve to meet the process requirements.
When the process has special requirements for the structure of the check valve, generally should be specified in the PID (process piping instrumentation flow chart). Such as the reciprocating compressor export pipeline, the process will require the use of a non-impact check valve, the purpose is to avoid frequent fluctuations in the export pressure of the reciprocating compressor, resulting in frequent opening and impact on the valve flap, resulting in damage to the check valve. For the outlet and inlet pressure difference greater than 4.0MPa centrifugal pump, the process generally requires a different type of double check valve on the pump outlet pipeline. This is due to the pump outlet and inlet pressure difference being large, the pump suddenly stops running, and the leakage of the check valve is larger, in order to reduce the amount of leakage of the check valve, while reducing the chance of damage to the check valve failure, so the use of two different types of the check valve.
2. The requirement of pressure drop should be satisfied.
Some pipelines have particularly strict requirements for pressure drop, the check valve on these pipelines should use a low-pressure drop check valve, a commonly used double-plate check valve, etc. If necessary, simulations are required to determine whether the pressure drop meets the design requirements.
3. Operating pressure requirements.
For the operating pressure is particularly low for a large-diameter check valve, if the standard pressure level swing check valve or lift check valve is selected, it may be heavy due to the valve flap, resulting in normal operating conditions, the valve flap can not be opened. And for a high-pressure check valve with higher operating pressure, the check valve with a pressure seal bonnet can be used.
4. The impact of valve size.
In general, the nominal diameter of the check valve less than DN50 is commonly used lift check valve; a nominal diameter greater than or equal to DN50, less than DN400, can be selected swing check valve; a nominal diameter greater than DN400, less than DN600, can be selected swashplate check valve; nominal diameter greater than DN50, less than DN1200, can be selected double-plate check valve.
5. The influence of the installation direction.
Lifting check valve without spring should be installed in the horizontal pipeline; swing check valve and tilting disc check valve are generally installed in the horizontal pipeline, can also be installed in the vertical pipeline or inclined pipeline from the bottom up flow; double-plate check valve, the axial flow check valve can be installed both horizontal and vertical installation.
6. The impact of installation space.
For a larger diameter check valve, when the installation space is small, you can choose to clamp the double-plate check valve.
7. The impact on the economy.
When a variety of check valves can meet the requirements, should give priority to the simple structure, low-price check valve.
Petrochemical installations, have the largest amount of lift check valves and swing check valves. Check valve selection, can not only consider the impact of a single factor but is often the result of a combination of factors. Several commonly used check valves for the occasion are shown in the table below.
Check valve selection of other technical indicators.
Check valve selection in addition to the type of structure, but also clarify some other major technical indicators. Such as material, end connection type, pressure level, implementation standards, etc.
Check valve body, the cover material is generally consistent with the main or equivalent, when the nominal diameter is less than DN50, the valve body, the cover is generally used forgings; when the nominal diameter is greater than or equal to DN50, the valve body, the cover is generally used castings, of course, for harsh working conditions, also often use forgings. Seat sealing surface and valve sealing surface material are generally used stainless steel or carbide, when using a spring check valve, you also need to specify the spring material. Valve material chemical composition, mechanical properties, heat treatment state, grain size, non-metallic inclusions, non-destructive testing, corrosion resistance, and other indicators should be based on the use of working conditions, the design of restrictions, and additional requirements to meet the requirements of specific working conditions.
Check valve end connection types commonly used are flange connection, socket weld connection, butt weld connection, and threaded connection. For petrochemical installations, socket weld connections and threaded connections are generally only used for pipelines with nominal diameters less than DN50, and shall not be used for pipelines with crevice corrosion media. For valves with a pressure level greater than or equal to CL900, socket weld connections (nominal diameter less than DN50) and butt weld connections (nominal diameter greater than or equal to DN50) are generally used to reduce leakage points.
Check valve pressure level is generally consistent with the pressure level of the pipeline system, when using threaded or socket weld connection, the valve pressure level of CL800 is at least.
Check valves for petrochemical plants generally use American standards or British standards, commonly used standards are API602-2009 “Steel gate, globe and check valves of nominal size less than and equal to DN100 for oil and gas industry”, API594-2010 “Clamp-on, lug-on-clamp and double-flange check valves”, ASMEB16.34-2009 “Flange, threaded and welded end connection valves”. Threaded and welded end connection of the valve” and BS1868-1975 “petroleum, petrochemical and allied industrial steel check valve (with flange and butt weld end) with the specification”, etc.
In order to ensure the need for check valve design and manufacturing quality, so as to meet the requirements of the check valve on the use of working conditions, it is recommended in the petrochemical plant design process for the check valve technical specifications, and the specifications should include at least the valve structure, implementation standards, valve specifications, pressure levels, valve body material, spool material, operating temperature, operating pressure, media and media characteristics, allowable pressure drop, the installation location and special requirements of the process. The manufacturer should be based on the above conditions and requirements, the design of the check valve, if necessary, through analytical calculations, computer fluid simulation analysis or simulation test, type test, and other methods to verify the performance of the check valve to ensure that the check valve to meet the requirements of the working conditions.
TAG: Influence factors, the selection of check valves, wesdom, wesdom valve