In the industrial field and in many piping systems, stainless steel valves are a common equipment. However, many people have a certain misunderstanding of the name "stainless steel valve," thinking that since it is stainless steel, it will never rust. But is that really the case?
Stainless steel is an alloy, the main components include: iron, chromium, nickel and other elements. Among them, chromium is a key factor in making stainless steel corrosion resistant. Chromium forms an extremely thin and strong chromium-rich oxide film on the surface of stainless steel, which can prevent corrosive media such as oxygen and moisture from further invading the interior of stainless steel, thus playing a protective role. When this layer of oxide film is destroyed, stainless steel is likely to rust.
1. If the stainless steel valve in the high concentration of chloride ions in the environment, such as the sea water treatment system or the use of chlorine disinfectant industrial environment. Chloride ion has a strong penetration ability, which can penetrate the oxide film on the surface of stainless steel and destroy the integrity of the oxide film. Once the oxide film is broken, the iron atoms are exposed and react with oxygen and moisture from the outside world, causing rust. For example, a small seaside seawater desalting plant, the use of stainless steel valve in operation for a period of time, the valve surface appeared rust. After testing, it is due to the continuous erosion of chloride ions in the sea water valve surface, although it is stainless steel material, but it is difficult to resist the long-term role of high concentration of chloride ions. Influence of pH: Stainless steel valves may also rust in strong acidic or alkaline environments. For example, in some chemical companies, stainless steel valves are used in piping systems that handle strong acids or alkalis. Extreme pH will change the chemical state of the stainless steel surface, so that the oxide film can not be maintained normally, which in turn causes corrosion and rust. For example, a chemical company in the production process of stainless steel valves, due to exposure to strong acidic chemicals, the valve inside the sealing parts soon appeared rust phenomenon, affecting the normal sealing performance of the valve. High temperature environment: In high temperature environment, the stability of stainless steel will be affected. High temperature may lead to changes in the internal structure of stainless steel, making the distribution of chromium in stainless steel uneven, reducing the ability of chromium to form an effective oxide film. At the same time, high temperatures may also accelerate the speed of chemical reactions, making stainless steel more susceptible to reacting with the surrounding corrosive medium. There is a high temperature steam pipe system in the stainless steel valve, in a high temperature environment for a long time, the surface of the valve corrosion, because the high temperature changes the internal structure of stainless steel, reducing its corrosion resistance.
2. Material factors Types of stainless steel: Not all stainless steels have the same corrosion resistance. Common stainless steel austenitic stainless steel, martensitic stainless steel and ferritic stainless steel. Austenitic stainless steel contains a higher proportion of nickel, its corrosion resistance is relatively strong, but the price is also high. The corrosion resistance of martensitic stainless steel and ferritic stainless steel is relatively weak, and the risk of rust will increase if used in some harsh environments. If you do not choose the appropriate stainless steel type according to the actual use environment when selecting stainless steel valves, it may lead to rust problems. For example, in an ordinary industrial environment containing a certain amount of chloride ions, in order to save costs, a martensitic stainless steel valve was selected, and the valve rusted before long. Impurity content: The impurity content in stainless steel will also affect its corrosion resistance. If the stainless steel contains too much sulfur, phosphorus and other impurities, these impurities will form a local micro-battery inside the stainless steel, accelerating the corrosion process. Some low-quality stainless steel materials may be due to the production process, high impurity content, when used to manufacture the valve is easy to rust.
3. Processing and use factors surface damage: In the process of stainless steel valve processing, such as cutting, welding, grinding and other operations, if improper operation, may cause damage to the oxide film on the surface of stainless steel. For example, the high temperature generated during welding will destroy the oxide film of the welding part, and if there is no timely treatment, such as pickling and passivation, this part is easy to rust. In the process of use, by the impact of external objects or scratching, will also destroy the surface of the valve oxide film, thus creating conditions for rust. For example, when a factory installed a stainless steel valve, due to careless operation, the surface of the valve was scratched by a sharp object, and then in the process of use, the scratched part soon rusted. Stress concentration: If there is stress concentration in the stainless steel valve during installation or use, it will also affect its corrosion resistance. The distribution of element Cr in local area is changed and the corrosion resistance of these areas is decreased. For example, in the connection of the valve, if the bolt tightening force is uneven, it may cause stress concentration, which in turn causes rust.
How to prevent stainless steel valve rust 1. Choose the right stainless steel material according to the specific use of the environment to choose the appropriate stainless steel valve. If it is in the marine environment or chlorine-containing environment, the austenitic stainless steel valve with strong corrosion resistance to chloride ion is preferred, and the higher the nickel content, the stronger the corrosion resistance. For acidic or alkaline environments, choose a stainless steel type that can withstand the corresponding pH. 2. Optimization of processing and installation In the process of processing, appropriate processing technology should be adopted to minimize the damage to the oxide film on the surface of stainless steel. After welding, pickling and passivation treatment should be carried out in time to restore the corrosion resistance of the welded parts. During installation, make sure the valve is installed correctly to avoid stress concentration. For example, tighten the bolt evenly to avoid excessive tightening of the valve deformation. 3. Environmental Control For the environment in which the stainless steel valve is located, if possible, minimize the concentration of chloride ions, acid-base substances and other corrosive media. In chemical enterprises, some protective measures can be adopted, such as setting an isolation layer around the valve to prevent corrosive substances from directly contacting the valve. 4. Check and maintain the stainless steel valve regularly to find out whether there is damage or rust on the surface of the valve. If slight rust is found, suitable rust removal techniques, such as mechanical rust removal or chemical rust removal, can be applied, followed by protective treatments, such as rust preventive oil or passivation. Although the stainless steel valve has a certain corrosion resistance due to its stainless steel material, it is still likely to rust under the influence of a variety of adverse factors. Understanding the causes of rust in stainless steel valves and taking corresponding preventive measures are of great significance to ensure their normal use in various environments and prolong their service life. Whether in industrial production or daily life in the pipeline system, the correct treatment of stainless steel valve rust problem is to ensure the safe and stable operation of the system key link.
