Most fluid media used in the processing industry involve oil streams of varying degrees of corrosivity. These flow conditions, including media flow, are considered to be either clean, dirty, or worn (in mud conditions), the difference being mainly in the amount of solid suspended particles that cause valve blockage or corrosion damage. Types of. In addition, media streams containing sulfur and other mixtures will help to form a corrosive environment when combined with high temperatures. For such media flow, careful selection of materials is required to maintain a sufficient service life of the valve. Corrosion engineers continue to research and develop materials to solve these problems.
(1) Special valves for refining hydrocracking and coking units
The refining delayed coking unit is a processing process for deep vacuum cracking of vacuum residue to form gas, light distillate and coke, and is an important means for refineries to improve light oil yield 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 drum are connected by a four-way valve. The four-way valve is an important passage for switching the heating furnace into the coke drum. It belongs to special valve and is used in high temperature applications. Its quality directly affects the production capacity of the device. Domestically, both new designs and old devices use imported four-way plug valves, but they are expensive. The domestic four-way valve generally has the problem of unreasonable structure, unstable quality, and easy failure.
Hydrorefining in refineries is one of the major crude oil refining processes. Since the hydrocracking unit is operated under high temperature and high pressure, the medium is flammable and explosive hydrogen and hydrocarbons, and the working condition is special, so the sealing must be reliable. Therefore, high requirements are placed on the design and structure of the valve. At present, most of the domestic use stainless steel smash gate valve and DC type globe valve.
(2) Oil and gas special valve
In order to achieve control of the oil flow, the oil and gas special valve should have the following basic properties: sealing, pressure strength, safety, adjustability, fluid flow and switching flexibility. For high-pressure, flammable, and explosive oil and gas media, first of all, to solve the sealing, it is necessary to consider the special working conditions of oil and gas special valves:
1 In wet natural gas containing hydrogen sulfide and carbon dioxide gas, special requirements are imposed on the valve body material;
2 There are brine, residual acid and other corrosive media in the wellhead and gathering system, the selection of valve body materials and anti-corrosion requirements;
3 Dust and solid particles accelerate the erosion and wear of the valve closure. Quickly invalidate the seal pair;
4 In the outdoor areas of the plateau, desert and alpine regions, the low temperature embrittlement, bending deformation, etc. of the valve material;
5 For oil and gas special valves on long-distance pipelines, it is required to have the same life as pipelines and will not be replaced for decades.
All of these indicate that the oil and gas special valve is different from the ordinary valve and has high reliability under severe conditions to meet the requirements of high strength and no leakage.
(3) Chlorine conditions
The selection of valves containing chlorine should refer to the Dry Chlorine Piping System prepared by the American Chlorine Institute.
The conditions of chlorine or liquid chlorine are highly corrosive, especially in this case. HCI (hydrochloric acid) formed by mixing chlorine with water will corrode the valve body and internals. Since chlorine has a high coefficient of thermal expansion, if liquid chlorine is sealed in the valve cavity, the pressure in the chamber in the valve will increase rapidly. Valves used in this condition should have a reliable mid-pressure relief function.
(4) Freezing (low temperature) conditions
Although valves for low temperature applications are based on ASME B16.34 and API standards, these valves also have other design features to ensure reliable operation in low temperature applications. Such valves may also include a bonnet extension design that extends the distance between the packing and the operating mechanism from the cryogenic fluid, allowing the stem packing to be operated at a higher temperature and ensuring that the valve operating device is not frozen during use. . The MISS SP-134 provides some details including a bonnet extension design.
(5) Hydrofluoric acid containing conditions
Valves used in hydrofluoric acid applications should be limited to valve types that have been demonstrated in use or that can successfully handle such conditions during testing. Valves that do not normally provide opportunities for solid material accumulation are the preferred type of valve. The hydrofluoric acid treatment should be carried out by a qualified technician, who strictly controls the valves on the market. The design and material requirements and details of the internal geometry for these (typically carbon steel valves with special Monel or solid Monel internals) are very detailed and should be designed to be resistant to hydrofluoric acid. Special structure for corrosion. In the case of hydrofluoric acid containing, the inspection and testing of the valve should be higher than the standard used for typical process valves.
(6) Hydrogen-containing conditions
Valves used in such conditions tend to have a very high casting quality compared to conventional castings. Because hydrogen is a highly permeable fluid, welded joint valves with pressure ratings greater than or equal to 600 pounds reduce potential sources of leakage during use. API 941 contains the selection and use of materials in hydrogen service conditions.
(7) Oxygen service conditions
Valves used in oxygenated applications should comply with the American Compressed Gas Association Standard CGA G4.4-2003 Oxygen Piping Systems when applicable. Valves used in such applications should be completely degreased, clean and installed under clean conditions and properly packaged and sealed, as oil and grease are extremely flammable in the presence of oxygen. The relevant guidelines are given in the CGA G4.1 Oxygen Conditioning Equipment. Proper handling and storage are necessary prior to installation.
Bronze or Monel body and trim materials for oxygen-containing conditions are often used to prevent sparks and fires due to high-energy mechanical collisions. Specially formulated silicone-based greases are used in oxygen-containing applications because standard hydrocarbon lubricants should not be used in the presence of oxygen.
(8) Pulsating or unstable flow
Check valves for pulsating or unstable flow are subject to special considerations, such as check valves used in reciprocating compressors, which may be quickly opened and closed as flow changes, which may result in Hammering and damage to the valve. There may be different opinions regarding the type of valve used in pulsating and unstable flow, but butterfly check valves, swash plate check valves and axial flow check valves are generally recommended for pulsating or unstable flow.
(9) Acid-containing working conditions (wet H2S working condition)
The use of valve materials in acid-containing conditions should be in accordance with the NACEMR0103 standard. This standard for the downstream hydrocarbon processing industry limits the hardness of all steels; requires austenitic steels for solid solution annealing; prohibits the use of certain materials for pressure-bearing parts (including valve stems); and specializes for bolted joints, welded valves, etc. Claim.
Attention should be paid to the user's responsibility in NACE MR0103, which stipulates that the user should specify whether to expose the bolt to an H2S-containing environment. Unless otherwise specified by the user, bolts that are not inside the valve, such as bonnet connection bolts, are subject to product standards, and sulfur-containing conditions do not include such standards. If the bolting material does not directly withstand the process fluid, the body-bonnet bolting does not need to meet NACE requirements. If any sulfur leaks from sulfur-containing oils cannot be removed or evaporated (eg, the valve is blocked), the bolted connections should be subject to the NACE standard.
If the material allowed by NACE is considered to be unnecessary, then the bolted material should be of particular concern. This imposed hardness requirement will result in a reduction in strength. The strength of the bonnet attachment bolts will be reduced by the same design conditions that may not be suitable for standard bolting materials.
(10) Viscosity or curing conditions
Valves used in viscous or curing conditions, such as liquid sulfur or heavy oil, often require steam tracing or steam casing to maintain adequate operating temperatures in order to make the valve operational. Because the hysteresis response of the check valve can cause operational problems, special attention should be given to it. - Welcome to visit Sanjing Valve
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