As long as the temperature and pressure of the valve meet the requirements of non-metallic materials, it can not only solve the corrosion problem, but also save precious metals. Valve body, bonnet, lining, sealing surface and other common non-metallic materials, as for gasket, packing is mainly made of non-metallic materials. The valve lining is made of polytetrafluoroethylene, chlorinated polyether and other plastics, as well as natural rubber, neoprene, Buna rubber and other rubber. The main body of valve body and valve cover is made of general cast iron and carbon steel. It not only ensures the strength of the valve, but also ensures that the valve is not corroded. Pinch valve is also designed according to the excellent corrosion resistance and denaturability of rubber. Now more and more plastics such as nylon and polytetrafluoroethylene are used, and natural rubber and synthetic rubber are used to make all kinds of sealing surfaces and rings for various valves. These non-metallic materials used as sealing surface not only have good corrosion resistance, but also good sealing performance, especially suitable for use in the medium with particles. Of course, their strength and heat resistance are low, and their application range is limited. The appearance of flexible graphite makes non-metal enter the field of high temperature, which solves the long-term problem of packing and gasket leakage, and is a good high temperature lubricant.

3. Metal surface treatment

Valve connecting bolts are usually treated by galvanizing, chrome plating and oxidation (bluing) to improve their resistance to atmospheric and medium corrosion. Other fasteners are treated by phosphating and other surface treatments in addition to the above methods.

(2) Sealing surface and sealing parts with small diameter

The surface technology such as nitriding and boronizing is often used to improve its corrosion resistance and wear resistance. The valve disc made of 38CrMoAlA has a nitriding layer ≥ 0.4mm.

(3) Stem corrosion protection

Widely used nitriding, boronizing, chrome plating, nickel plating and other surface treatment processes to improve its corrosion resistance, corrosion resistance and abrasion resistance. Different surface treatment shall be suitable for different valve stem materials and working environment. For the valve stem in contact with asbestos packing in atmosphere and water vapor medium, hard chromium plating and gas nitriding process can be used (ion nitriding process is not suitable for stainless steel); for the valve in hydrogen sulfide atmosphere, ion nitriding process can be used Electroplated high phosphorus nickel coating has better protective performance; 38CrMoAlA is corrosion resistant by ion and gas nitriding, but hard chromium coating is not suitable; 2Cr13 can resist ammonia corrosion after tempering, carbon steel can resist ammonia corrosion by gas nitriding, and all phosphorus nickel coating can not resist ammonia corrosion; 38CrMoAlA material after gas nitriding has It has excellent corrosion resistance and comprehensive performance, and is widely used to make valve stems.

(4) Small bore valve body and handwheel

It is often chrome plated to improve its corrosion resistance and decorate the valve.

Thermal spraying is a kind of process block for coating preparation, which has become one of the new technologies for material surface protection. Most metals and their alloys, metal oxide ceramics, metal ceramic composites and hard metal compounds can be coated on metal or non-metal substrates by one or several thermal spraying methods. Thermal spraying can improve the corrosion resistance, wear resistance and high temperature resistance of its surface, and prolong its service life. Thermal spraying special functional coating, with heat insulation, insulation (or different electricity), grindable sealing, self lubrication, thermal radiation, electromagnetic shielding and other special properties, the use of thermal spraying can repair parts.

The corrosion control mechanism of corrosion inhibitor is that it promotes the polarization of battery. The inhibitor is mainly used at the medium and filler. The corrosion of equipment and valves can be slowed down by adding corrosion inhibitors in the medium. For example, chromium nickel stainless steel can be cremated in a large range of solubility in sulfuric acid without oxygen, and the corrosion is serious. However, adding a small amount of oxidants such as copper sulfate or nitric acid can make stainless steel blunt and form a layer on the surface In hydrochloric acid, if a small amount of oxidant is added, the corrosion of titanium can be reduced. Water is often used as the medium of valve pressure test, which is easy to cause valve corrosion. Adding a small amount of sodium nitrite in the water can prevent water from corroding the valve.

The operator shall clean and purge the valve regularly and add oil regularly according to the regulations in the operation regulations, which is an effective measure to control environmental corrosion. Installation of protective cover for valve rod, setting of ground valve well, painting of valve surface, etc. are all methods to prevent corrosive substances from eroding the valve.

The anti-corrosion protection of valve is considered from the design. A valve product with reasonable structure design and correct process method will undoubtedly have a good effect on reducing the corrosion of valve. Therefore, the design and manufacturing departments should improve the parts with unreasonable structure design, incorrect process method and easy to cause corrosion, so that they can meet the requirements of different working conditions.