Special valve selection matters needing attention

Most of the fluid media used in the process industry involve oil and gas streams of different corrosive grades. These flow conditions, including medium flow, are considered to be either clean, dirty, or worn (mud conditions), and the difference lies mainly in the number and type of solid suspended particles that cause valve blockage or corrosion damage. In addition, media streams containing sulfur and other mixtures will contribute to the formation of a corrosive environment when combined with high temperatures. For such a medium flow, it is necessary to carefully select the material to maintain the valve with sufficient service life. Corrosion engineers continue to research and develop materials to address these issues.
Special valve for 1. refinery hydrocracking and coking unit
Refining delayed coking device is the processing process of deep thermal cracking of vacuum residue to produce gas, light distillate oil and coke, and is an important means for refineries to improve 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, used for high temperature occasions, its quality directly affects the production capacity of the device, whether the new design or the old device mostly imported four-way plug valve, but the price is expensive. The domestic four-way valve generally has the problems of unreasonable structure, unstable quality, and prone to failure.
Refinery hydrocracking is one of the major crude oil refining processes. Because 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 seal must be reliable. Therefore, the design and structure of the valve put forward higher requirements. At present, most of the domestic selection of stainless steel wedge gate valve and DC cut-off valve.
2. oil and gas special valve
In order to achieve the control of oil and gas flow, oil and gas special valve should have the following basic performance: sealing, pressure strength, safety, adjustability, fluid flow and switch flexibility. For high-pressure, flammable, explosive oil and gas media, we must first solve the sealing, to consider the special conditions of oil and gas special valve requirements:
① In the wet natural gas containing hydrogen sulfide and carbon dioxide gas, special requirements are put forward for the valve body material;
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;
Dust and solid particles to speed up the valve to close the parts of the erosion, wear, so that the seal will soon fail;
④ in the plateau, desert and alpine regions of the outdoor, the valve material of low temperature embrittlement, bending deformation;
⑤ For long-distance transmission pipeline oil and gas special valve, the requirements of the same life and pipeline, decades without change.
All these show that the oil and gas special valve is different from the ordinary valve, in the harsh conditions to have high reliability, to meet the requirements of high strength and no leakage.
3. chlorine condition
The selection of chlorine-containing valves should refer to the "Dry Chlorine Piping System" prepared by the American Chlorine Society.
The working condition containing chlorine gas or liquid chlorine is a highly corrosive working condition, especially the working condition containing water. HCl (hydrochloric acid) formed by chlorine mixed with water will corrode the valve body and internals. Due to the high thermal expansion coefficient of chlorine, if liquid chlorine is sealed in the valve cavity, it will cause the pressure in the valve cavity to increase at a high speed. The valve used in this condition should have a reliable pressure relief function in the middle chamber.
4. freezing (low temperature) condition
Although the valves used for low temperature conditions are based on ASME B16.34 and API standards, these valves also have other design features to ensure reliable operation in low temperature conditions. Such a valve may also include a bonnet extension design that extends the distance of the packing and operating mechanism from the cryogenic fluid, thereby allowing the stem packing to be operated at a higher temperature and ensuring that the valve operating device does not freeze during use. The MSS SP-134 provides some details of the design that contains the bonnet extension.
5. conditions containing hydrofluoric acid
Valves for use in hydrofluoric acid conditions should be limited to those types that have been demonstrated in service or successfully tested to handle such conditions. A valve that usually does not provide an opportunity for the accumulation of solid materials is the choice of valve type. The hydrofluoric acid treatment operation shall be carried out by qualified technicians who strictly control the valves on the market. The details of the design and material requirements and internal geometry of these valves (typical carbon steel valves with special Monel internals or solid Monel internals) are very detailed. This valve should be designed to have a special structure that is resistant to hydrofluoric acid corrosion. Valves shall be inspected and tested above the standard used for typical process valves in hydrofluoric acid conditions.
6. hydrogen condition
The valve used in this condition is often specified as having a very high casting quality compared to regular casting supplies. Because hydrogen is a very permeable fluid, a welded connection valve with a pressure rating of 600 pounds or more reduces a potential source of leakage during use.
The API 941 covers the selection and use of materials in the hydrogen regime.
7. oxygen condition
Valves used in oxygenated conditions shall comply with Compressed Gas Association Standard CGA G4.4-2003, Oxygen Piping Systems, when applicable. Valves used in this condition should be completely degreased, clean and installed under clean conditions and properly packed and sealed, because oil and grease are highly flammable in the presence of oxygen. The relevant guidelines are given in CGA G4.1 Oxygen Condition Cleaning Equipment. Proper handling and storage is necessary prior to installation.
Bronze or Monel valve body and trim materials suitable for oxygen-containing conditions are often used to prevent sparks and fires due to high-energy mechanical collisions. There are specially formulated silicon-based greases for oxygen-containing conditions, because standard hydrocarbon lubricants should not be used in the presence of oxygen.
8. pulsating or unsteady flow
Check valves used in pulsating or unstable flows, which require special consideration, such as check valves used in reciprocating compressors, may open and close quickly with changes in flow, which may cause hammering and valve damage. There may be different opinions about the type of valve used in pulsating and unsteady flow, but generally butterfly check valves, swash check valves, and axial flow check valves are recommend for pulsating or unsteady flow.
9. acid condition (wet H2S condition)
The use of valve materials in acid conditions should comply with NACE MR0103. 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-bearing parts (including valve stems); and places special requirements on bolted connections, welded valves, etc.
Attention should be paid to the responsibility of the user in NACE MR0103, which stipulates that the user should specify whether the bolt is exposed to H2S containing environment. Unless specified by the user, bolts that are not inside the valve, such as bonnet attachment bolts, are often subject to product standards, and sulfur-containing conditions are not included in this standard. The body-bonnet bolting does not need to meet NACE requirements if the material used for the bolting does not directly receive the process fluid. Bolted connections shall comply with NACE standards if any sulfur leakage from the oil containing sulfur cannot be eliminated or evaporated (e. g. to block off valves).
Special attention should be given to bolting materials where NACE permitted materials are considered undesirable. This imposed hardness requirement will result in a reduction in strength. The reduced strength of the bonnet attachment bolts may not be suitable for the same design conditions as standard bolting materials.
10. viscosity or curing conditions
Valves used in viscous or solidifying fluid conditions, such as liquid sulfur or heavy oil, often require steam tracing or steam jackets to maintain adequate operating temperatures for valve operability. Special attention should be paid to the hysteretic reaction of the check valve because it can cause operational problems.