The choice of oxygen valve in the inspection

[Abstract] Since oxygen is a combustion-supporting medium, if the pressure in the pipeline is too high and the flow velocity is too large, the turbulent impact effect of the entrained particles may cause excitation energy or frictional static caused by non-metal and metal particles. In addition, there may be flammable substances such as grease, and the combustion-supporting property is likely to cause and accelerate the explosion accident. Material selection should be strictly controlled during oxygen valve selection. It should be strictly controlled in the inspection.
[Key words] oxygen valve selection CLC number: G712 Document code: A Article ID: 1009-914X(2019)01-0176-01
Many valves have pipe orientation and medium flow requirements, such as shut-off valves, throttle valves, pressure reducing valves, check valves, etc., if installed reversed, it will affect the effect and life (such as throttle), or not at all It works (such as a pressure relief valve) and even creates a hazard (such as a check valve). Generally, the valve has a direction mark on the valve body. When installing, the direction mark should be consistent with the flow direction of the medium; if it is not, it should be correctly identified according to the working principle of the valve.
Oxygen is colorless and odorless, and oxygen is the most common elemental form. Melting point -218.4 ° C, boiling point -183 ° C. It is not easily soluble in water, and dissolves about 30 mL of oxygen in 1 L of water. Oxygen accounts for about 21% of the air. Liquid oxygen is sky blue. The oxygen fixation is a blue crystal. Not very lively at room temperature, and many substances are not easy to work. However, it is very active at high temperatures and can be directly combined with various elements, which is related to the electronegativity of oxygen atoms, which is second only to fluorine. With the development of industry, the role of oxygen in production is getting larger and larger, and the requirements are getting higher and higher. Whether in industrial production and use, oxygen pipelines as the center of oxygen, should be controlled in all aspects of material selection and installation, otherwise it will have an immeasurable impact. As the middle valve, it seems to be important in the selection and installation process. The following focuses on the requirements of the oxygen valve from the "oxygen station design specification" and "oxygen valve technical conditions".
First, the design pressure on the oxygen valve material restrictions (a) "Oxygen station design specifications" (GB 50030-2013) on the oxygen valve form, material and pressure requirements are as follows:
1. Gate valves shall not be used on oxygen pipelines with a design pressure greater than 0.1 MPa;
2. A manual valve on an oxygen pipeline with a design pressure greater than or equal to 1.0 MPa and a nominal diameter greater than or equal to 150 mm shall be provided with a bypass valve;
3. For valves that are designed to operate on an oxygen pipeline with a design pressure greater than 1.0 MPa and a nominal diameter greater than or equal to 150 mm, pneumatic valves are preferred;
4. The selection of valve materials should meet the following requirements.
(1) Design pressure (2) Design pressure is 0.6-10 MPa, using all stainless steel, copper-based alloy or combination of stainless steel and copper-based alloy, nickel and nickel-based alloy.
(3) Design pressure >10MPa, using copper-based alloy, nickel and nickel-based alloy Note: 1 Design pressure or greater than or equal to 0.1MPa pipe pressure or flow regulating valve material, should be stainless steel or copper-based alloy or above Combination of materials.
2 The sealing packing of the valve should be made of Teflon or flexible graphite.
(2) The requirements for the material and pressure of the oxygen valve in the Technical Conditions for Valves for Oxygen (JB/T 12955-2016) are as follows:
1. The highest working pressure is p≤0.1, the shell material is carbon steel and stainless steel, and the valve inner material is stainless steel.
2, the highest working pressure 0.1

3, the highest working pressure of 0.6

4, the highest working pressure 3

5, the highest working pressure 10

Second, the medium flow rate on the oxygen valve material restrictions "Oxygen station design specifications" (GB 50030-2013) on the oxygen valve material and flow rate requirements are as follows: the diameter of the oxygen pipe should be calculated according to the following conditions: 1 Calculate the flow The actual working flow rate at the lowest working pressure and maximum working temperature of the piping system shall be adopted; 2 The flow rate shall be the actual flow rate of oxygen in the pipe under working pressure, and the maximum flow rate in the oxygen piping shall not exceed the requirements.
The requirements for the oxygen valve material and flow rate in the Technical Conditions for Valves for Oxygen (JB/T 12955-2016) are as follows: The flow rate in the valve body should not be higher than the limit of the oxygen pipe flow rate, and the oxygen flow rate of different material pipes is limited. Provisions.
In the process of oxygen fluid transport, the flow of oxygen in the pipeline system will change. The standard IGC Doc 13/12E "Oxygen Pipeline and Piping Systems" developed by the European Industrial Gas Association (EIGA) divides the oxygen service into "impact occasions". "and "non-impact occasions." Also in the "Deep Freezing Process for the Production of Oxygen and Related Gas Safety Technical Regulations" (GB16912-2008) also refers to the division of EIGA. It is defined as a position that causes a sudden change in the direction of oxygen flow or a vortex to cause an impact of particles entrained in oxygen on the pipe wall. Such a position is called an "impact occasion." "Impact occasions" are prone to excitation energy, causing combustion and explosion. It is a dangerous occasion and the safety control requirements are more stringent. Oxygen valves are typical "impact scenarios."
The flow rate calculation method is given in "Technical Conditions for Valves for Oxygen" (JB/T 12955-2016): According to the working conditions of the pipeline, appropriate measures should be taken to control the flow rate in the valve flow passage. The flow rate should be actually cut in the valve. The area is calculated. For the valve with obvious throttling in the valve structure, the volume flow rate under the pre-valve pressure and the orifice area should be used as the basis for calculating the flow rate at the corresponding opening degree, and the valve inner material is selected accordingly. For the valve outlet flow rate, the volume flow rate under the throttling pressure and the valve outlet area should be used as the basis for calculating the flow rate. Since the flow rate inside the valve is higher than the flow rate of the pipe, because the cross-sectional area has changed, it is not easy to grasp according to the above Table 1. Therefore, JB/T12955-2016 supplements the relationship between the material and flow rate of the valve as follows: When the flow rate in the valve flow passage exceeds the range, the valve body should be exempted from the material under the corresponding pressure.
Third, the oil degreasing according to the "Oxygen valve technical conditions" (JB/T 12955-2016) for the definition of degreasing treatment is as follows: "Inorganic non-flammable cleaning agent, dichloroethane, trichloroethylene solvent or ultrasonic method The process of removing oil from the surface of the part." The valve body and the trim should be degreased before and after assembly to prevent iron filings, grease, dust, extremely small solid particles, etc. generated or left in the manufacturing process. Friction occurs when oxygen passes through the valve, causing dangerous consequences such as burning or explosion.
IV. Selection of oxygen valve selection test 1. Valves on the oxygen pipelines of the valve type should use special valves for oxygen. Most domestic gas pipelines use shut-off valves (optional oxygen ball valves are also available). The flow direction of ordinary valve media is downward and upward. . In the oxygen working condition, the valve flow path is different from the ordinary valve. The upper and lower parts are selected to ensure that the valve stem is well stressed and the spool is quickly closed.
2. The valve body material is recommended to use stainless steel below 3MPa; Inconel 625 or Monel 400 alloy steel is used above 3MPa.
3, valve trim material conventional oxygen valve internals only Inconel and Monel, but because Inconel 625 has advantages over Monel K500 in high temperature applications, so choose:
(1) The valve trim is treated with Inconel 625 plus surface hardening;
(2) The stem/sleeve material is selected from Inconel X-750 or Inconel 718;
(3) The valve should not be reduced in diameter and kept at the same diameter as the original pipe; and the valve seat should not be used for hard surfacing, because it is easy to produce certain unsafe factors due to the limitation of process level during surfacing.
(4) The valve sealing ring material is made of grease-free molded graphite (low carbon content);
(5) The upper bonnet is double-filled, and the packing is made of high temperature resistant grease-free graphite (resistant to 468 ° C);
(6) Because oxygen encounters burrs or grooves in the flow, it will produce high-speed friction and accumulate a large amount of heat. If the carbon compound may explode, the surface finish of the valve should meet the requirements of ISO 8051-1 Sa2.

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