Hydrogen peroxide (H2O2) is an important oxidizing agent, bleaching agent, disinfectant and dechlorination agent, which is widely used in the chemical industry, textile, military industry, electronics, medicine and other fields. With the impact of the coronavirus, the disinfection and market demand for hydrogen peroxide in the medical field are increasing especially in recent years. In the hydrogen peroxide production process, the hydrogen peroxide pipeline from raw materials to finished products is very complicated. How to ensure the safe and stable normal operation of the ball valve
in the hydrogen peroxide pipeline has become an important issue. This article mainly starts with the properties of hydrogen peroxide and the characteristics of the operating pipeline, and introduces the design optimization of the material selection, structure and technology of the ball valve in the pipeline of hydrogen peroxide transportation and storage.
2. Properties of hydrogen peroxide
The chemical name of hydrogen peroxide is hydrogen peroxide. The molecular formula is H2O2, and the molecular weight is 34.016. It is colorless, odorless and transparent liquid. Hydrogen peroxide is non-toxic, but it can bleach and burn the skin; its boiling point is higher than that of water; its density and viscosity are higher than that of water; it can be miscible with water in any ratio; it can also be dissolved in alcohol and ether.
Hydrogen peroxide is a strong oxidizing substance with weak dibasic acid properties, and hydrogen peroxide with a concentration greater than 40% is corrosive. Its chemical properties are relatively active, and it can participate in decomposition, molecular addition, substitution, redox and other reactions. Hydrogen peroxide has a certain instability due to the internal structure relationship of its molecules and the existence of impurities.
When hydrogen peroxide encounters light, heat, rough surface or is mixed with heavy metals and their salts, yeast, organic matter, alkaline substances, dust and other impurities, it will decompose into oxygen and water, and release a lot of heat, causing explosion due to severe decomposition. Although hydrogen peroxide is not flammable, the oxygen produced during decomposition can greatly support combustion, and it can cause spontaneous combustion after contact with combustibles and organic substances; there is a danger of combustion and explosion when it is impacted, rubbed and shaken. To prevent decomposition caused by direct sunlight and falling dirt, the container containing hydrogen peroxide must have vent holes.
3. Material selection and treatment of hydrogen peroxide pipeline ball valves
According to the above-mentioned chemical and physical properties of hydrogen peroxide, the reasonable selection of the main material and sealing material of the ball valve in the hydrogen peroxide pipeline, as well as the heat treatment and surface treatment of these materials, is an important basis for ensuring the reliable and safe operation of the ball valve in the hydrogen peroxide pipeline.
3.1 Material selection of hydrogen peroxide pipeline ball valves
3.1.1 Main materials
For ball valves used in high-concentration hydrogen peroxide pipelines at normal temperature and pressure, the main material should not be oxidized, rust-free, and the carbon content should be as low as possible to reduce the heat generated by friction between hydrogen peroxide and carbon in steel when hydrogen peroxide flows at high speed. Therefore, low Carbon-grade high-quality austenitic stainless steel such as ASTM A351 CF8, CF3, CF8M, CF3M or ASTM A182 F304, F304L, F316 and F316L are often selected. In general, F316L should be selected as the main material of hydrogen peroxide with a concentration of 70%; when the concentration of hydrogen peroxide is greater than 50%, it is best to choose F316L for the main material, or you can also choose F304L. When the valve is made from stainless steel castings, it must be pickled to remove the sticky sand, alkaline impurities and organic matter in the inner cavity of the valve, which can easily cause hydrogen peroxide to decompose impurities. For high concentration and high pressure (pressure greater than and equal to Class 600), the main material of the hydrogen peroxide ball valve should be a nickel-based alloy with a higher safety level.
3.1.2 Seal materials
Seal materials are generally non-metallic materials, such as flexible graphite, polytetrafluoroethylene and rubber, which are used for ball valves in normal temperature, high pressure and high concentration hydrogen peroxide pipelines. The sealing material must also meet the requirements for non-oxidation and non-dissolution. It is generally recommended to use high-purity PTFE polytetrafluoroethylene for the packing of ball valves in hydrogen peroxide pipelines; PTFE or PTFE metal wound gaskets are commonly used for the middle of ball valves; flexible graphite with metal wire can be used for the fire ring of hydrogen peroxide ball valves under the circumstance of not contacting with the medium. The performance of the metal wire should meet the requirement for not being lower than that of the main material. It is forbidden to use graphite in the part of the ball valve that can be in contact with the medium. The rubber O-ring must use at least FKM high fluorine rubber, and it is recommended to use FFKM perfluoroether rubber to ensure the sealing performance and service life.
3.2 Handling materials
3.2.1 Degreasing and oil-free
Hydrogen peroxide pipeline valves are not allowed to have oil, alkaline impurities and organic matter. Because oil, alkaline impurities and organic matter can easily cause hydrogen peroxide to decompose, oxygen and water will be generated during the decomposition, and a large amount of heat will be released. At the same time, oxygen can greatly support combustion, and it will cause an explosion after contact with combustibles and organic substances. Therefore, all parts should be degreased before valve assembly. Assembly should be carried out in a clean environment (a dust-free workshop). Clean air or nitrogen and other media should be used for Sealing inspection and pressure testing to avoid contamination of the hydrogen peroxide ball valve. There should be a dust-proof and oil-free isolation protection device at the seal of the valve stem to prevent impurities from falling, and a striking oil-free mark should be attached.
3.2.2 Internal surface treatment of ball valves
The density and viscosity of hydrogen peroxide are relatively high. there is a danger of combustion and explosion when hydrogen peroxide is hit, rubbed and vibrated in the pipeline due to its instability. Therefore, ball valves with the smallest flow resistance coefficient are preferred for hydrogen peroxide pipelines. However, when hydrogen peroxide flows, it will inevitably cause friction with the pipeline and the flow channel of the ball valve, and the friction will generate heat and static electricity. To avoid these dangers, the surface roughness of the flow channel and the inner surface of the ball valve should be controlled below Ra3.2μm. The surface of the inner cavity flow channel and flow-through components should be smooth, avoiding sharp corners, and rounding the corners of each part to avoid heat generation during high-speed flow. At the same time, when the soft-sealed ball valve is selected for the hydrogen peroxide pipeline, the structure must have an anti-static device.
Hydrogen peroxide is widely used in daily production and daily life, so the application of valves in the production, transportation and storage of hydrogen peroxide has become a new research field. New materials of the ball valve used in the hydrogen peroxide pipeline according to the working conditions of the hydrogen peroxide medium should be continuously studied, and the structure design of the ball valve should be continuously optimized to ensure the stable operation of the ball valve in the hydrogen peroxide pipeline and production system.