What Are the Considerations for Selecting Conventional and Special Valves?

For some of the precipitation or precipitate-containing media, it is inappropriate to use globe valves and gate valves, because their sealing surface is prone to precipitation or precipitate abrasion. Therefore, it should be selected ball valve or plug valve is more appropriate; can also be selected flat gate valve, but it is best to use jacketed valves.

1、 Conventional valve selection matters need attention

• Valve use requirements

     ① Ordinary gate valves, ball valves, and globe valves according to their structural characteristics are strictly prohibited from regulation. But in the process design, commonly used for mediation. As a result of the regulation of the use of valve seals for a long time in the throttling state, the impurities in the oil scour the seals and damage the sealing surface, resulting in the closure of the laxity or due to the operator the sealing surface has been damaged to achieve sealing, resulting in the valve over the over-open, over the open phenomenon.

     ②Valve installation location is not reasonable, when the use of media containing impurities, not in its front end to install filters or filters, so that impurities into the valve, resulting in damage to the sealing surface, or impurities deposited in the bottom of the valve, causing the valve to close the valve is not strict, and produce leaks.

• Considered from the perspective of process requirements

     ① For corrosive media, if the temperature and pressure are not high, you should try to use non-metallic valves, if the temperature and pressure are higher, lined valves can be used to save precious metals. The selection of non-metallic valves should still consider economic rationality; for the viscosity of the medium, the requirements of a smaller flow resistance should be used to direct flow globe valve, gate valve, ball valve, plug valve, and other flow resistance of small valves. Valves with small flow resistance, and less energy consumption; when the medium is oxygen or ammonia and other special media, the corresponding oxygen valve or ammonia valve should be used.

     ② Dual-flow pipeline should not use directional valves and should be used without directional valves. For example, after the refinery heavy oil pipeline stops running, use steam to reverse the pipeline blowing to prevent the heavy oil solidification from blocking the pipeline, it is not appropriate to use the shut-off valve, because as of the reverse inflow, easy to erode the sealing surface of the shut-off valve, but also affects the valve’s effectiveness, and should be used to select the gate valve is preferred.

     ③ For some precipitation or precipitate-containing media, should not use the globe valve and gate valve, because their sealing surface is prone to precipitation or precipitate wear. Therefore, it should be used for ball valves or plug valves are more appropriate; can also be selected flat gate valve, but it is best to use jacketed valves.

     ④ In the selection of gate valve, open rod single gate and dark rod double gate are more adaptable to corrosive media; the single gate is suitable for viscous media; wedge double gate on high temperature and the sealing surface deformation of the adaptability than the wedge single gate to be better than wedge single gate, will not appear due to temperature changes resulting in the phenomenon of jamming, in particular, more superior than the rigid single gate.

     ⑤ Valves on general water and steam pipelines can be made of cast iron valves, but if the steam pipeline is shut down outdoors, it will cause the condensate to freeze, thus freezing the valves. Therefore, in cold areas, the valve using cast steel, low-temperature steel, or effective thermal insulation measures are appropriate.

     (6) For the danger of highly toxic media or other harmful media, should be used in the bellows structure of the valve to prevent leakage of media from the packing.

     (7) Gate valve, globe valve, and ball valve are the largest use of valves, and selection should be considered. Gate valve circulation capacity, less energy consumption of the transport medium, but the installation space is larger, globe valve structure is simple and easy to maintain, but the flow resistance is larger, the ball valve has a low flow resistance, fast opening, and closing characteristics, but the use of temperature restrictions, petroleum products, and other viscous media, taking into account the strong circulation capacity of the gate valve, the majority of the gate valve; and in the water and steam pipeline, the application of the globe valve, the pressure drop is not large, so the globe valve in the water, steam, and other media pipeline applications The use of water, steam and other media pipeline applications, ball valves in the use of working conditions allow both can be.

• From the perspective of ease of operation

     ① For large diameter valves and long distance, high altitude, high temperature, high-pressure occasions, electric and pneumatic valves should be used, for flammable and explosive occasions, to use explosion-proof devices, to be safe and reliable, the application of hydraulic and pneumatic devices.

     ② The need for fast-opening, fast-closing valves, should be selected according to the need for butterfly valves, ball valves, plug valves, or fast-opening gate valves, and other valves, should not be selected from the general gate valves, or globe valves. In the operating space is restricted occasions, should not be used to open the stem gate valve, should be appropriate to use the dark stem gate valve, but the best choice of butterfly valve.

• Consideration of the accuracy of regulating flow

The need to accurately regulate the flow should be used to control the valve, when the need to regulate the accuracy of the small flow, should be used needle valve or throttle valve. Need to reduce the pressure after the valve, should be used to reduce pressure, to maintain the stability of the pressure after the valve, should be used to stabilize the valve.

• Consideration of the temperature and pressure resistance

     High-temperature and high-pressure media often use castings of chromium-molybdenum steel and chromium-molybdenum-vanadium steel, ultra-high-temperature and high-pressure media should be considered to choosing the corresponding castings, forgings are better than the comprehensive performance of the castings, temperature and pressure resistance than the casting capacity is also superior.

• Consideration of the cleanliness

      Food and bio-engineering production and transportation, process pipeline requirements for the valve need to consider the cleanliness of the medium, the general gate valve and globe valve can not be guaranteed. From the consideration of cleanliness, there is no other kind of valve that can be compared with the diaphragm valve.

     ①Diaphragm valve structure is simple, the valve body and diaphragm materials are varied and can be widely used in the field of food and biological engineering, but also for some difficult-to-transport and dangerous media.

a. Only the valve body and diaphragm contact with the logistics, other parts of the isolation of all, the valve can be thoroughly sterilized by steam.

b. With its ability to drain.

c. Online maintenance. Therefore, the diaphragm valve has become the most widely used valve in the field of food and biological engineering.

     ② Bottom valve.

In the case of strict requirements for sterilization, the bottom of the tank discharge valve has little choice. The bottom valve in the manufacture of equipment is directly welded to the bottom of the tank head, and usually used in the bottom of the tank to do a pipe mouth, and then connected to the valve on the pipe mouth of the practice has a big difference, the valve is closed, the spool and the inner bottom of the tank is flat, so it effectively gets along with the dead space in the tank, so that all the liquids in the tank in the process of fermentation can be fully mixed, coupled with the unique steam sealing system, greatly reduces the product bacterial bacteria Possibility.

2、Specialized valves should pay attention to the selection of matters

     Specialized valves need to pay attention to the application of most of the fluid media in the processing industry involves different corrosive levels of oil and gas flow. These flow conditions including media flow are considered either clean, dirty, or abrasive (slurry conditions), the difference lies mainly in the number and type of suspended solids particles that lead to valve clogging or corrosion damage. In addition to this, media streams containing sulfur and other mixtures will contribute to a corrosive environment when combined with high temperatures. Such media streams require a careful selection of materials to maintain adequate valve life.Corrosion engineers are constantly researching and developing materials to solve these problems.

• Specialized Valves for Refinery Hydro cracking and Coking Units

      Refining delayed coking unit is the process of generating gas, light distillate, and coke by deep thermal cracking of depressurized slag oil, which is an important means for refineries are used to increase light oil production and to produce petroleum coke. The procedure is broken down into two parts: coking and decoking. Coking is a continuous production while decoking is an intermittent production. The inlet and outlet of the heating furnace and coke tower are connected by four-way valves. The four-way valve is an important channel to switch the heating furnace into the coke tower. It belongs to the special valves, used in high-temperature occasions, its quality directly affects the production capacity of the device, whether the domestic new design or the old device is mostly used in the imported four-way plug valve, but the price is expensive. Domestic four-way valves, on the other hand, are generally characterized by unreasonable structure, unstable quality, and easy failure.

     Refinery hydrocracking is one of the main crude oil refining processes. Since the hydrocracking unit operates at high temperatures and high pressure, and the medium is flammable and explosive hydrogen and hydrocarbons, the working conditions are special, so the sealing must be reliable. Therefore, the design and structure of the valves put forward high requirements. At present, most of the domestic selections of stainless steel chisel gate valves and DC globe valves.

• Oil and gas valve

     To realize the control of oil and gas flow, oil and gas valves should have the following basic performance: sealing, pressure strength, safety, adjust ability, fluid flow, and switching flexibility. For high-pressure, flammable, explosive oil and gas media, first of all, to solve the sealing, consider the special working conditions of oil and gas valve requirements:

① In the wet natural gas containing hydrogen sulfide and carbon dioxide gas, the valve body material puts forward special requirements; ② In the wellhead device and the gathering device, the valve body material puts forward special requirements.

② In the wellhead device and gathering and transportation system in the presence of brine, residual acid, and other corrosive media, the choice of valve body materials and corrosion requirements.

③ Dust and solid particles accelerate the valve closure parts of the scouring, wear, and tear. So that the sealing vice soon failed; ④ in the highlands, deserts, and other areas of the valve.

④In the plateau, desert, and cold regions outdoors, the valve material for low-temperature embitterment, bending deformation, etc.; ⑤ for long-distance transportation pipelines, the valve body material selection and anti-corrosion requirements.

⑤Used in long-distance transportation pipelines on the oil and gas special valve, the requirements and pipeline life, decades without replacement.

All these show that the special valves for oil and gas are different from ordinary valves, which should have high reliability and meet the requirements of high strength and non-leakage under adverse conditions.

• Chlorine-containing conditions

     Chlorine-containing conditions should refer to the selection of valves prepared by the American Chlorine Institute, “Dry Chlorine Piping Systems”. Chlorine or liquid chlorine-containing conditions are highly corrosive conditions, especially when this condition contains water. Chlorine mixed with water to form HCI (hydrochloride acid) will corrode the valve body and internal parts. Since chlorine has a high coefficient of thermal expansion, if liquid chlorine is enclosed in the valve cavity, it will lead to a high rate of pressure increase in the valve cavity. Valves used in this condition should have a reliable center cavity pressure relief function.

• Refrigeration (Cryogenic) Conditions

     Although valves for cryogenic service are based on ASME B16.34 and API standards, these valves have additional design features to ensure reliable operation in cryogenic service. Such valves may also include bonnet extensions that extend the packing and operating mechanism away from the cryogenic fluid, allowing the stem packing to be operated at a higher temperature and ensuring that the valve operating mechanism does not freeze in service. MISS SP-134 provides details of bonnet extensions that are included.

• Hydrochloride Acid Service

     Valves for use in hydrochloride acid service should be limited to those types of valves that have been proven in service or tested to handle this service successfully. Valves that do not normally provide an opportunity for solids buildup are the preferred type of valve. Hydrofluoric acid handling operations should be performed by certified technicians who have strict control over the listed valves.

     The design and material requirements and internal geometry details for these (typically carbon steel valves with special monel internals or solid monel internals) are very detailed and such valves should be designed to have a special construction for resistance to hydrofluoric acid corrosion. In hydrofluoric acid-containing service, valves should be inspected and tested to a higher standard than those used for typical process valves.

• Hydrogen-containing service

     Valves used in oxygen-containing service should follow the American Compressed Gas Association standard CGA G4.4-2003, Oxygen Piping Systems, when applicable. Valves used in this service should be fully decreased, clean, and installed under clean conditions and properly packaged and sealed, as oil and grease are highly flammable in the presence of oxygen. Guidance on this is given in CGA G4.1 Cleaning equipment for oxygen service. Proper handling and storage are necessary before installation.

     Bronze or Monel valve bodies and internal materials suitable for oxygenated service are often used to prevent sparking and ignition due to energetic mechanical collisions. Specially formulated silicone-based greases are available for use in oxygenated service, as standard hydrocarbon lubricants should not be used in the presence of oxygen.

• Pulsating or Unsteady Flow

     Special consideration should be given to the selection of check valves for use in pulsating or unstable flows, such as those used in reciprocating compressors, which may be opened and closed rapidly in response to changes in flow rate, which may result in hammering and damage to the valve. Opinions may differ as to the type of valve to be used in pulsating and unsteady flows, but in general butterfly check valves, swash plate check valves, and axial flow check valves are recommended for pulsating or unsteady flows.

• Acid-containing conditions (wet H2S conditions)

      The use of valve materials in acid-containing service should comply with NACEMR0103. This standard for the downstream hydrocarbon processing industry limits the hardness of all steels; requires solid annealing of austenitic steels; prohibits the use of certain materials for pressurized parts, including valve stems; and imposes special requirements for bolted, welded valves.

Attention should be drawn to the user’s responsibility in NACE MR0103, which states that the user should specify whether or not the bolts are to be exposed to H2S-containing environments. Unless specified by the user, bolts not inside the valve, such as bonnet bolts, tend to be subject to product standards, and sulfur-containing conditions are not included in such standards. Body-bonnet bolting is not required to meet NACE requirements if the bolting material is not directly exposed to process fluids. If any sulfur leakage from a sulfur-containing oil cannot be eliminated or evaporated (e.g., by isolating the valve), then the bolted connection should be subject to the NACE standard.

     If NACE-permitted materials are not considered necessary, then bolted connection materials should be about special concerns. The imposed hardness requirement leads to reduced strength. The strength of the bonnet bolts will be reduced and may not be suitable for the same design conditions as the standard bolting material.

• Adhesive or curing conditions

     Valves used in viscous or curing service, such as liquid sulfur or heavy oil, often require steam tracing or steam casing to maintain adequate operating temperatures for valve operability. Special attention should be given to checking valves because of the operational problems caused by their hysteretic response.

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