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Brief analysis of valve selection in ten common working conditions

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1. Special valves for refining hydrocracking and coking units

Refining delayed coking unit is a processing process for deep thermal cracking of vacuum residue to generate gas, light distillate oil and coke. It is an important means for refineries to increase the yield of light oil and produce petroleum coke. The process is divided into two parts: coking and decoking. Coking is continuous production, and decoking is intermittent production. The inlet and outlet of the heating furnace and the coke tower are connected by a four-way valve. The four-way valve is an important channel for switching the heating furnace into the coke drum. It is a special valve and is used in high temperature occasions. Its quality directly affects the production capacity of the device. Most of the domestic new design or old devices use imported four-way plug valves, but the price is expensive. However, the domestic four-way valve generally has the problems of unreasonable structure, unstable quality and prone to failure.

Refinery hydrocracking is one of the main crude oil refining processes. Since the hydrocracking unit operates under high temperature and high pressure, the medium is flammable and explosive hydrogen and hydrocarbons, and the working conditions are special, so the sealing must be reliable. Therefore, higher requirements are put forward for the design and structure of the valve. At present, most of the domestic stainless steel wedge gate valves and straight-line globe valves are used.
Brief analysis of valve selection in ten common working conditions

2. Special valve for oil and gas

In order to realize the control of oil and gas flow, the oil and gas special valve should have the following basic properties: sealing, compressive strength, safety, adjustability, fluid flow and switching flexibility. For high-pressure, flammable and explosive oil and gas media, the sealing must be solved first, and the special working condition requirements of oil and gas special valves must be considered:

① In the wet natural gas containing hydrogen sulfide and carbon dioxide gas, special requirements are put forward for the material of the valve body;

② There are brine, residual acid and other corrosive media in the wellhead device and gathering and transportation system, so the selection of valve body materials and anti-corrosion requirements;

③ Dust and solid particles accelerate the erosion and wear of valve closing parts. Make the sealing pair fail quickly;

④ Outdoors in plateaus, deserts and alpine regions, low-temperature embrittlement and bending deformation of valve materials;

⑤ Special valves for oil and gas used on long-distance pipelines require the same lifespan as the pipelines and should not be replaced for decades.

All these show that oil and gas special valves are different from ordinary valves. They must have high reliability under harsh conditions and meet the requirements of high strength and no leakage.

3. Working conditions containing chlorine

The selection of valves for chlorine-containing conditions should refer to the “Dry Chlorine Piping System” written by the American Chlorine Society.

Conditions containing chlorine gas or liquid chlorine are highly corrosive conditions, especially if water is present in such conditions. HCI (hydrochloric acid) formed by chlorine mixed with water will corrode the valve body and internal parts. Because chlorine has a high coefficient of thermal expansion, if liquid chlorine is sealed in the valve cavity, the pressure in the valve cavity will increase rapidly. The valve used in this working condition should have a reliable cavity pressure relief function.

4. Freezing (low temperature) working condition

Although valves for cryogenic service are based on ASME B16.34 and API standards, these valves also have other design features to ensure certain reliable operation in cryogenic service. Such valves may also include a bonnet extension designed to extend the distance between the packing and operating mechanism and the cryogenic fluid, thereby allowing the stem packing to operate at a higher temperature and ensuring that the valve operating device will not freeze during use. . MISS SP-134 provides some details including the design of the bonnet extension.

5. Conditions containing hydrofluoric acid

Valves used in hydrofluoric acid service should be limited to valve types that have been demonstrated in service or tested to handle this service successfully. Valves that generally do not provide the opportunity for solid matter to build up are the preferred valve type. Hydrofluoric acid treatment operations should be performed by qualified technicians with strict control over the valves listed. For these (typical carbon steel valves with special monel trim or solid monel trim) the design and material requirements and details of the internal geometry are very detailed and such valves should be designed to be resistant to hydrofluoric acid Corroded special structure. In hydrofluoric acid service, valve inspection and testing should be higher than that used for typical process valves.

6. Hydrogen-containing working conditions

Valves used in this service are often specified to have a very high casting quality compared to conventional casting supplies. Because hydrogen is an extremely permeable fluid, welded connection valves with pressure ratings greater than or equal to Class 600 reduce potential leak sources in use. API941 includes the selection and application range of materials in hydrogen working conditions.

7. Oxygen-containing conditions

Valves used in oxygen-containing service conditions should follow the American Compressed Gas Association standard CGA G4.4-2003 “Oxygen Piping System” when applicable. Valves used in this service should be completely degreased, clean and installed in clean conditions and properly packed and sealed, as oils and greases are extremely flammable in the presence of oxygen. Relevant guidelines are given in CGA G4.1 Cleaning Equipment for Oxygen Service. Proper handling and storage is necessary prior to installation.

Bronze or Monel valve body and trim materials suitable for oxygen service are often used to prevent sparks and ignition due to high energy mechanical impact. There are specially formulated silicon-based greases for use in oxygen-containing service, since standard hydrocarbon lubricating oils should not be used in the presence of oxygen.

8. Pulsating or unstable flow

Special consideration should be given to the selection of check valves used in pulsating or unsteady flows, such as check valves used in reciprocating compressors, which may be opened and closed rapidly with changes in flow, which may cause Hammering and valve damage. Opinions may vary regarding the type of valve used in pulsating and unsteady flow, but generally butterfly check valves, swash plate check valves, and axial flow check valves are recommended for pulsating or unsteady flow.

9. Acid-containing working condition (wet H2S working condition)

The use of valve materials in acid-containing conditions should comply with the NACEMR0103 standard. This standard for the downstream hydrocarbon processing industry limits the hardness of all steels; requires solution annealing of austenitic steels; prohibits the use of certain materials for pressure-containing parts (including valve stems); Require.

Attention should be paid to the responsibility of the user in NACE MR0103, which stipulates that the user should specify in detail whether the bolt is exposed to the environment containing H2S. Unless specified by the user, bolts that are not inside the valve, such as bonnet connection bolts, are often subject to product standards, and sulfur service conditions are not included in such standards. Body-bonnet bolting does not need to meet NACE requirements if the material used for the bolting is not directly subject to the process fluid. If any sulfur leakage from sulfur containing oil cannot be removed or evaporated (eg block valves), then the bolted connection should be subject to NACE standards.

If NACE-approved materials are deemed unnecessary, special attention should be paid to bolted joint materials. This imposed hardness requirement will result in a reduction in strength. Bonnet connection bolts will have reduced strength and may not be suitable for the same design conditions as standard bolting materials.

10. Viscous or curing conditions

Valves used in viscous or solidified services, such as liquid sulfur or heavy oil, often require steam tracing or steam jacketing to maintain adequate operating temperatures in order for the valve to be operable. Special attention should be paid to check valves because hysteresis response can cause operational problems.

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