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. For most types of valves, the valve disc is commonly referred to as the closing element. But there are exceptions; 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. Table 1 Commonly used materials for valve trim and their operating temperature ranges
Lower limit of operating temperature /°C (°F) Upper limit of operating temperature /°C (°F)
304 stainless steel –268 (–450) 316 (600)
440 stainless steel –29 (–20) 427 (800)
316 stainless steel –268 (–450) 316 (600)
60RC –29 (–20) 427 (800)
Bronze –273 (–460) 232 (450)
17–4PH –40 (–40) 816 (1500)
Inconel –240 (–400) 649 (1200)
Alloy No. 6 (Co–Cr) –273 (–460) 427 (800)
Monel K –240 (–400) 482 (900)
Electroless nickel plating –268 (–450) 316 (600)
Monel –240 (–400) 482 (900)
Aluminum coating –273 (–460) 93 (200)
Hastelloy B –240 (–400) 371 (600)
Nitrile rubber –40 (–40) 204 (400)
Hastelloy C –198 (–325) 538 (1000)
Fluororubber –23 (–10) 232 (450)
Titanium alloy –198 (–325) 316 (600)
Polytetrafluoroethylene –268 (–450) 93 (200)
Nickel-based alloy –29 (–20) 316 (600)
Nylon –73 (–100) 93 (200)
Alloy No. 20 –198 (–325) 316 (600)
Polyethylene –73 (–100) 93 (200)
416 stainless steel –46 (–50) 316 (600)
Neoprene –40 (–40) 82 (180)
60RC –29 (–20) 427 (800)

Table 2 Commonly used materials for valve sealing surfaces and applicable media
Material code Common applications Suitable valve types PN/Mpa/°C
Rubber X ≤0.1 ≤60 Globe valves, diaphragm valves, butterfly valves, check valves, etc.
Nylon N ≤32.0 ≤80 Ball valves, globe valves, etc.
Polytetrafluoroethylene F ≤6.3 ≤150 Globe valves, diaphragm valves, butterfly valves, check valves, etc.
Babbitt metal B ≤2.5 -70 to 150 Ammonia service globe valves
Ceramic G ≤1.6 ≤150 Ball valves, plug valves
Enamel C ≤1.0 ≤80 Globe valves, diaphragm valves, check valves, discharge valves
Copper alloys QSn6-6-3, HMn58-2-2T ≤1.6 ≤200 Gate valves, globe valves, check valves, plug valves, etc.
Stainless steel 2Cr13, 3Cr13, TDCr-2, TDCrMnH ≤3.2 ≤450 Medium- and high-pressure valves
Nitriding steel 38CrMoAlA DP54 1040 Power plant gate valves; general applications
Hard alloys WC, TiCY Determined based on valve body material High-temperature and ultra-high-pressure valves
TDCoCr-1, TDCoCr-2 High-pressure and ultra-high-pressure valves; high- and low-temperature valves
Cast iron W ≤1.6 ≤100 Gate valves and globe valves for gases and oils
High-quality carbon steel ≤4.0 ≤200 Valves for oil service
1Cr18Ni9Ti, Cr18Ni12Mo2Ti ≤32.0 ≤450 Valves for corrosive media such as acids
Monel K, Monel SM Determined based on valve body material Petrochemical valves, cryogenic valves, nuclear valves
Hastelloy B, Hastelloy C Petrochemical valves, corrosion-resistant valves, power plant valves
Alloy No. 20 Petrochemical valves, corrosion-resistant valves, nuclear valves

The above lists the materials most frequently used for valve trim, based on a brief survey. 1. Bronze: The maximum operating temperature for the most widely used bronze valves, cast iron valves, and steel valves is around 280°C. Applicable media include steam, water, oil, air, and natural gas 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 nitrogen. Brass without zinc is usually aluminum brass. It is also often applied in specific situations. 2. Iron: Except for the stem which is made of steel, 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: This material is widely used in valve stems, valve seat seals, and valve discs. It is used in media containing a certain proportion of lubricant, and possesses 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 for many years in oil and steam pipelines at operating temperatures of up to 600°C. 4. Nickel alloys: Nickel alloys (referring here to combinations of nickel, copper, and tin) are used to make valve seat rings ； Using chromium 13 stainless steel for the valve disc makes it particularly suitable for gas and liquid media that are free of 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°C, while for other media it is limited to below 260°C. 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 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 internals. It is suitable for media under conditions of extreme corrosion or very high temperatures, or both strong corrosion and high temperatures. 6. Special stainless steels: These ‘20’ alloys, ‘heat-resistant nickel-chromium-iron alloy 825’, and ‘Carpenter 20cb3’ are often used to make 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 for valve internals, and it is mostly applied in iron and steel valves. Its medium is mostly seawater, salt solutions, or steam. 8. Hastelloy alloys ‘B’ and ‘C’: These materials are not frequently used for valve trim, but are commonly applied throughout the entire valve. However, when the medium is sulfuric acid or dilute hydrochloric acid, Hastelloy ‘B’ is sometimes used as the material for valve trim; meanwhile, the typical applications of Hastelloy ‘C’ are in specialized ammonia valves and valve trim for mixed acid media. 9. Cemented carbide: A layer of hard cemented carbide is surfaced on the valve disc and the valve body seat, thereby endowing the sealing surface with excellent wear resistance and anti-scuffing properties. This material is particularly suitable for applications with elevated medium temperatures and dry conditions. The material for the sealing surface is usually selected from cobalt-based and nickel-based alloys; the mating surface is typically plated with a similar material, but with a difference in hardness, so as to minimize scuffing during operation. However, the matching two surfaces are not always welded by surfacing; the type 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. When selecting materials, many evaluation factors must be considered. An important factor is that the material provided must be able to adhere easily to 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 as a valve seat in ball valves and butterfly valves, and as the diaphragm surface in diaphragm valves. In many types of valves, polytetrafluoroethylene is used as the stem packing material. As a material for valve seats and seals, polytetrafluoroethylene is the best ； It can be used with almost all media, has excellent wear resistance, and can operate at temperatures up to 250°C. 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 membrane 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. 11. “O”-rings are widely used in valve stem sealing, with nitrile rubber being the most common material. Cryofluorocarbon 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 following are the most commonly used synthetic rubbers. (1) Natural rubber (2) Butyl rubber (3) Ethylene propylene rubber (4) Neoprene (5) Nitrile rubber (6) Styrene-butadiene rubber. The advantage of using plastics and synthetic rubbers as materials for valve internals is their excellent corrosion and erosion resistance, as well as their 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.