Common materials for valve internals and sealing surfaces

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Valve internals generally refer to the valve disc, valve seat, and valve stem, but in some cases they also include other components such as bushings, bolts, and nuts. The term “valve disc” is commonly referred to as the closing element for most types of valves. But there are exceptions as well; for example, in the case of a plug valve, the closing element is called a plug). The sealing surface of a valve refers mainly to the contact surface between the valve disc and the valve seat. The commonly used materials for internal components and their operating temperatures are shown in Table 2-22. The common materials for valve sealing surfaces and the media they are suitable for are listed in Table 2-23. (1) The highest operating temperature for bronze valves, cast iron valves, and steel valves – the most commonly used types of bronze valves – is around 280°. Applicable media include steam, water, oil, air, and natural gas transmission pipelines. The valve disc and seat can also be made of bronze of appropriate grade (with the valve stem made of stainless steel), allowing them to be used with media at extremely low temperatures, such as liquefied gas, liquid oxygen, and liquid ammonia. Zinc-free bronzes, usually aluminum bronzes, are also commonly used in specific situations. (2) The iron removal valve stem is made of steel, while all other parts of the valve are made of iron (“all-iron”). Typically, both the valve disc and the valve body have integral sealing surfaces. “\"Quan Tie\" valves represent a cost-effective choice for mixed acid media consisting of concentrated sulfuric acid and hydrocarbons, and they also perform satisfactorily in handling many other industrially relevant chemical liquids such as brine, ammonia water, alcohol, cleaning solutions, and chloride solutions. (3) Chromium 13 stainless steel is widely used in valve stems, valve seat seals, and valve discs. It is used in media containing a certain proportion of lubricant, and boasts excellent properties such as high wear resistance, scratch resistance, corrosion resistance, and erosion resistance. It also has strong antioxidant properties and the ability to resist corrosion by heat-sulfurized lubricants. This material has been successfully used in oil and steam pipelines at operating temperatures of up to 600°C for over 4 years. (4) Nickel alloys: Valve seat rings are made from nickel alloys (referring here to combinations of nickel, copper, and tin) ； Valve discs made of chromium 13 stainless steel are particularly suitable for gas and liquid media that lack lubricants and have relatively low corrosivity. Other suitable media include superheated steam and saturated steam, natural gas, fuel oil, gasoline, and low-viscosity oils. For steam, the working medium is limited to below 450°, while for other media it is limited to below 260°. Using composite nickel alloys for the valve seat and valve disc is also suitable for use with steam, water, and other media. (5) Austenitic stainless steel: Austenitic stainless steel has been discussed earlier in the context of valve body materials; it is a steel alloy based on 18-8 chromium-nickel and is widely used in the manufacture of valve components. It is suitable for media under conditions of severe corrosion, extremely high temperatures, or both severe corrosion and high temperatures. (6) Special stainless steels such as these 20 alloys, Incoloy 825, and Carpenter 20cb3 are often used to manufacture valve internals. These special stainless steel internals are often used in ordinary stainless steel valves, and sometimes only in iron and steel valves. _ (7) Monel alloy: This alloy is used to manufacture valve internals, and it is mostly applied in iron and steel valves. Its medium is mostly seawater, salt solutions, or steam. (8) Materials such as Hastelloy B and C are not often used in valve internals, but are frequently applied to the entire valve. However, when the medium is sulfuric acid or dilute hydrochloric acid, Hastelloy B is sometimes used as the material for valve internals, while Hastelloy C is typically used in specialized ammonia valves and valve internals for mixed acid media. (9) A layer of hard cemented carbide is welded onto the valve disc and the valve body seat, which enables the sealing surface to possess high wear resistance and resistance to scuffing. This material is particularly suitable for applications with elevated medium temperatures and in dry conditions. The material for the sealing surface is usually selected from cobalt-based and nickel-based alloys, and the surface that mates with it is typically plated with a similar material, but with a difference in hardness to reduce wear during operation. However, the matching two surfaces are not always formed by surfacing; the method used depends on the properties of the cemented carbide employed. Similar performance specifications for cobalt-based and nickel-based cemented carbides can be obtained from some valve manufacturers. Many evaluation factors must be considered when selecting materials. An important factor is that the material provided must be able to adhere easily to the specific parts. (10) Plastics and synthetic rubbers: Plastics and synthetic rubbers are used in the sealing surfaces and valve seats of many different types of valves, arranged in one form or another. The most widely used plastic material is polytetrafluoroethylene (PTEF). It is used to manufacture valve seats in ball valves and butterfly valves, and to create the diaphragm surface in diaphragm valves. In many types of valves, polytetrafluoroethylene is used as the seal packing for the valve stem. Polytetrafluoroethylene is the best material for valve seats and seals. It can be used with almost all media, has excellent wear resistance, and can operate at temperatures up to 250°. Pure polytetrafluoroethylene is often used, but in many cases, to improve its resistance to compressive set, some chemically inert fillers such as glass can be added. The chemical resistance of polytetrafluoroethylene makes it an ideal diaphragm material. Its stiffness and fatigue resistance are also useful properties. In most valves that use diaphragms, a thin layer of polytetrafluoroethylene is used in combination with a synthetic rubber substrate; the polytetrafluoroethylene and the synthetic rubber can be separate or bonded together. Synthetic rubber is mostly used in valve internals as O-rings, gaskets, valve seats and seat bushings, diaphragms, and bushings for butterfly valves. O-rings are widely used in valve stem sealing, with nitrile rubber being the most common material. Carbon-fluorine compound rubber, ethylene propylene rubber, and silicone rubber are particularly suitable for use at high temperatures. A variety of synthetic rubbers are widely used in valve seats, bushings, diaphragms, and guides. The combination of basic polymers can yield a wider range of physical and chemical properties. The most commonly used synthetic rubbers are: natural rubber, butyl rubber, ethylene propylene rubber, neoprene, nitrile rubber, and styrene-butadiene rubber. The advantage of using plastics and synthetic rubbers as materials for valve internals is their excellent corrosion resistance and erosion resistance, as well as the ability to achieve leak-free sealing. The drawback of these materials is that the operating temperature during use is limited by the materials used. Furthermore, whether the given material is suitable also depends on several factors. Disclaimer: The content contained in this article is intended solely for technical exchange and reference purposes only, and does not constitute any form of professional engineering advice, design basis, or operational guidance.