How to Select Valve Materials for Various Working Conditions

Overview

One of the key considerations in valve design and material selection is the working temperature of the valve. Industries like petrochemicals and chemical engineering, have specific requirements for the working temperature and suitable valve body materials. These provisions are based on the material properties of various types of valve steel and alloy grades. They are used in valve product design, manufacturing, and inspection. Additionally, according to technical and production management, and material procurement, it’s recommended to choose one with good comprehensive performance. Please avoid using too many steel and alloy grades to prevent confusion.

Low-Temperature Working Conditions

Ultra-Low Temperature Valve Materials

The main material of ultra-low temperature valves [-254 (liquid hydrogen)~-101℃ (ethylene)] must be austenitic stainless steel, copper alloy, or aluminum alloy with a face-centered cubic lattice. The low-temperature mechanical properties, especially low-temperature impact toughness, after heat treatment must meet the standard requirements.

The following austenitic stainless steel can be used in the manufacture of ultra-low temperature valves. It includes ASTM A351 CF8M, CF3M, CF8 and CF3, ASTM A182 F316, F316L, F304 and F304L, ASTM A433316, 316L, 304, 304L, and CF8D (designed by Lanzhou High Pressure Valve Factory, factory standard code GFQ81-93). The valve body, cover, gate, or disc of them must undergo cryogenic treatment in liquid nitrogen (-196°C) before precision machining.

Low-Temperature Valve Materials

Low-temperature valves (-100~-30°C) require specific materials, such as low-temperature austenitic stainless steel and ferritic and martensitic steel for low-temperature pressure parts.

Examples of low-temperature austenitic stainless steel include ASTM A351 CF8M, CF3M, CF8, and CF3, ASTM A182 F316, F316L, F304, and F304L, and ASTM A433316, 316L, 304, 304L, and CF8D.

Low-temperature pressure parts require the use of ferritic and martensitic steels, such as ASTM A352 LCA (-32℃), LCB, LCC (-46℃), LC1 (-59℃), LC2, LC211 (-73℃), and LC3 (-100℃).

These materials are cost-effective, but their chemical composition during smelting must meet strict internal control standards. This steel undergoes a complex heat treatment process. It involves multiple quenching and tempering treatments to meet the standard requirements for low-temperature impact toughness. The production cycle is long. If the low-temperature impact toughness does not meet the standard requirements, it cannot be used as low-temperature steel. Austenitic stainless steel is typically only used for large production batches that can be smelted in a furnace. In general, austenitic stainless steel is the preferred choice.

Non-Corrosive Working Conditions

Valves for non-corrosive substances such as water, steam, air, and oil are typically made of carbon steel. Carbon steel for valves refers to WCB, WCC cast steel, and ASTM A105 forged steel in ASTM A216 standard steel. The suitable working temperature for carbon steel valves is -29~425℃. However, considering the possibility of fluctuations in it of medium, the general working temperature of carbon steel shouldn’t exceed 400℃.

Corrosion Conditions

Chromium-Molybdenum High-Temperature Steel

It is used for the valve which mainly adopts WC6, WC9, and C5 (ZG1Cr5Mo) in ASTM A217 standard, and their corresponding rolled materials are F11, F22, and F5.

Low-Chromium Chromium-Molybdenum Steel

It includes WC6, WC9, F11, and F22, which are suitable for working media such as water, steam, and hydrogen, and are not suitable for sulfur-containing oil products. The suitable working temperature for WC6 and F11 is – 29~540℃, while for WC9 the suitable working temperature for F22 is -29~570℃.

Chromium Five Molybdenum High-Temperature Steel

Chromium five molybdenum high-temperature steel includes C5 (ZG1Cr5Mo) and F5, which are suitable for working media such as water, steam, hydrogen, and sulfur-containing oil products. If C5 (ZG1Cr5Mo) is used for steam, its maximum operating temperature is 600℃. When used for working media such as sulfur-containing oil products, its maximum working temperature is 550℃. Therefore, it is stipulated that the working temperature of C5 (ZG1Cr5Mo) is less than 550℃.

Acid-Resistant Stainless Steel

Acid-resistant stainless steel refers to chromium-nickel or chromium-nickel-molybdenum acid-resistant stainless steel. It’s used in petrochemical, chemical, and fertilizer industries to resist the corrosion of nitric acid, sulfuric acid, acetic acid, and organic acids. The acid-resistant stainless steel cast steel mainly use CF8, CF8M, CF3, CF3M, CF8C, CD-4MCu, and CN7M in ASTMA743 or ASTMA744 standards, and their corresponding rolling materials are F304, F316, F304L, F316L, F347, F53 in ASTMA182 standards and UNS N08020 in the United States.

Cr-Ni Stainless Steel

Cr-Ni acid-resistant stainless steel includes CF8, CF3, F304, F304L, CF8C, and F347, which are suitable for nitric acid and other oxidizing acids. Its maximum working temperature is less than 200℃.

Cr-Ni-Mo Stainless Steel

Cr-Ni-Mo acid-resistant stainless steel includes CF8M, CF3M, F316, and F316L, which are suitable for acetic acid and other reducing acids.

CF8M, CF3M can replace CF8 and CF3, but CF8, CF3 can not replace CF8M and CF3M. Thus, the United States and other countries mainly use CF8M and CF3M for acid-resistant stainless steel valves, with a maximum working temperature of ≤ 200℃.

CN7M Alloy

CN7M alloy has good comprehensive corrosion resistance and is widely used in harsh corrosion conditions, including sulfuric acid, nitric acid, hydrofluoric acid, dilute hydrochloric acid, caustic soda, seawater, and hot chloride salt solutions, especially in sulfuric acid with various concentrations and temperatures ≤ 70℃. The usage temperature of CN7M and UNS N08020 alloy is -29~450℃.

Duplex Stainless Steel

Duplex corrosion-resistant stainless steel is a type of precipitation-hardening stainless steel. It contains 35% to 40% austenite in a ferrite matrix. Its yield strength is approximately twice that of 19Cr-9Ni austenitic stainless steel. Additionally, it has high hardness, good plasticity, and impact toughness. This material is ideal for use in corrosive working conditions that involve both abrasion and erosion. It is commonly used in strong acid conditions of oxidation and reduction. Besides, it has excellent resistance to stress corrosion cracking in environments with chlorine. CD-4MCu, CD3MN, CE3MN, and F53 duplex stainless steel can be used at temperatures ranging from -29 to 316℃.

Corrosion-Resistant Nickel-Based Alloy

Corrosion-resistant nickel-based alloy valves are mainly selected cast Monel alloy (M35-1), cast nickel alloy (CZ-100), Inconel alloy (CY-40), Hastelloy B (N-12MV, N-7M), and Hastelloy C (N-12MV, N-7M). Monel alloy (CY-40), Hastelloy B (N-12MV, N-7M) and Hastelloy C (CW-12MW, CW-7M, CW-6MC, CW-2M) from the ASTMA494 standard. The Monel alloy rolled materials used for corrosion-resistant Monel alloy valves are mainly UNS N04400 (Monel 400) and UNS N05500 (MonelK500). There is no corresponding rolled material for cast nickel alloys, and the rolled materials for Inconel alloys are Inconel 600 and Inconel 625.

Monel Alloy

Monel alloy is known for its high strength and toughness. It also has excellent resistance to corrosion in reducing acids, strong alkaline media, and seawater. Equipment and valves that are commonly used for manufacturing and transporting media, such as hydrofluoric acid, saltwater, neutral media, alkali salts, and reducing acids, are also suitable for dry chlorine gas, hydrogen chloride, 425℃ high-temperature chlorine gas, and 450℃ high-temperature hydrogen chloride. However, they aren’t resistant to corrosion from sulfur-containing media and oxidizing media, such as nitric acid and high oxygen-containing media. Valves made of Monel alloy are identified by the material code MM. However, the internal components are identified as Monel alloy valves. The valve material code is C/M when the shell is made of carbon steel, P/M when the shell is made of CF8, and R/M when the shell is made of CF8M. Monel alloy M35-1, Monel 400, and Monel K500 alloys are suitable for working temperatures ranging from -29 to 480℃.

Cast Nickel Alloy

The chemical composition of cast nickel alloy (CZ-100) is 95% Ni and 1.00% C, and there is no corresponding rolled material. When CZ-100 is used in high-temperature, high-concentration, or nonaqueous alkaline solutions, it exhibits excellent corrosion resistance. CZ-100 is commonly used in chlor alkali production with high corrosion concentration (including molten anhydrous caustic soda) and in situations where metal-contaminated products such as copper and iron cannot be present. The material code for the cast nickel alloy CZ-100 valve is Ni. The suitable working temperature for CZ-100 alloy is -29~316℃.

Inconel Alloy

Inconel alloy CY-40 and Inconel 600 (ASTM B564 N06600) are mainly used for stress corrosion resistance, especially suitable for high-concentration chloride media. When the Ni content is ≥ 45%, they have an “immune” effect on chloride stress corrosion. In addition, it can also resist the corrosion of boiling concentrated nitric acid, fuming nitric acid, high-temperature gases containing sulfur and vanadium, and combustion materials.

Inconel alloy has been widely used in the manufacturing of components for boiler feedwater systems in nuclear power plants because it is safer than stainless steel. At the same time, it is also suitable for industrial production that requires high strength, high-pressure sealing, high corrosion resistance, and resistance to mechanical wear and oxidation at high temperatures. For example, large fertilizer plants use Inconel 600 or Inconel 625 alloy (the rolled material grade of Hastelloy CW-6MC) to manufacture high-pressure (600-1500 LB) high-concentration oxygen valves. The material code for CY-40 and Inconel 600 alloy valves is In. The suitable working temperature is -29~650℃.

Hastelloy Alloy

Hastelloy is a commercial name that includes a series of alloy grades. The main types used for corrosion-resistant valves are Hastelloy B and Hastelloy C. Hastelloy B has two casting alloy grades:

N-12MV (N-12M-1) and N-7M (also known as Chloromet2 alloy) in the ASTMA494 standard, and its rolled material grade is UNS N10665 in the ASTMA435 standard. Hastelloy B is resistant to hydrochloric acid at various concentrations, as well as non-oxidizing salts and acids. For corrosion-resistant valves made of Hastelloy B, it is recommended to consider low-carbon Hastelloy B (N-7M) due to its corrosion and intergranular corrosion resistance. The valve industry does not have regulations regarding the material code of Hastelloy alloy. The casting alloy grade directly represents the material code of the Hastelloy B valve. Hastelloy B has a suitable working temperature range of -29℃~425℃.

Hastelloy C has several cast alloy grades, including CW-12MW (also known as CW-12M-1) and CW-7M (also known as Chloromet3 alloy), as well as Hastelloy C-276 alloy. The cast alloy grades for Hastelloy C-4 alloy and CW-6MC are also available, along with CW-2M. The corresponding rolled grades for casting Hastelloy CW-7M, CW-12MW, CW-6MC, and CW-2M are UNS N10001, UNS N10003, UNS N10276, and UNS N06455, respectively. Hastelloy C is resistant to corrosion from oxidizing solvents, low concentrations of hydrochloric acid at room temperature, and nitric acid.

The first generation of Hastelloy C (OCr16Ni60Mo16W4) has excellent corrosion resistance in highly corrosive oxidizing and reducing acid media. However, the high nickel content of this austenitic corrosion-resistant alloy reduces the solid solubility of carbon in austenite, among other factors. Both Ni Mo Hastelloy B and Ni Mo Cr Hastelloy C alloys are highly susceptible to intergranular corrosion, which can result in stress corrosion and crevice corrosion at high temperatures. To prevent intergranular corrosion, the second generation of Hastelloy C-276 (with a reduced C content from 0.03% to 0.02%) and the third generation of Hastelloy C-4 were developed. These alloys have low Si content (Si ≤ 0.08%) and ultra-fine C content (C ≤ 0.015%), as well as reduced Fe and W content. Additionally, stabilized alloying elements like Ti were added.

To ensure corrosion resistance and inter-granular corrosion resistance in valves made of Hastelloy C, it is recommended to select either Hastelloy C-276 (CW-6MC) or Hastelloy C-4 (CW-2M).

Titanium Alloy

Titanium (Ti) is a strong and lightweight metal with good heat resistance and low-temperature toughness. It also has excellent processing and welding capabilities. In valve production, cast pure titanium and forged pure titanium ZTA2 are the main products used.

Depending on the working conditions, such as temperature, titanium can exhibit corrosion resistance, non-corrosion resistance, and even resistance to fire and explosion from corrosive media. Clear regulations should be provided for the properties of the medium used during ordering and design selection, including concentration and temperature.

Titanium valves demonstrate excellent corrosion resistance in various oxidizing, highly corrosive, and neutral media.

Additionally, titanium exhibits exceptional corrosion resistance in nitric acid below the boiling point and with a concentration of ≤ 80%. Titanium reacts with fuming nitric acid and explodes when the NO2 content exceeds 2% and the water content is insufficient. As a result, it is not typically used for high-temperature nitric acid with a content of over 80%. Titanium has moderate corrosion resistance in hydrochloric acid but is not resistant to corrosion in sulfuric acid. Industrial pure titanium is believed to be usable in hydrochloric acid at concentrations of 7.5% at room temperature, 3% at 60℃, and 0.5% at 100℃. Titanium can also be used in phosphoric acid at concentrations of 30% at 35℃, 10% at 60℃, and 3% at 100℃.

Titanium is not resistant to corrosion in hydrofluoric acid (HF) or acidic fluoride solutions. However, it is resistant to corrosion in boric and chromic acid and can be used in hydroiodic and hydrobromic acid.

Titanium can be used in various acid mixtures, including a 10% sulfuric acid and 90% nitric acid mixture at 60°C, a boiling mixture of 1% hydrochloric acid and 5% nitric acid, and room temperature aqua regia (a mixture of 3 volumes of concentrated hydrochloric acid and 1 volume of concentrated nitric acid). Titanium is highly resistant to corrosion in solutions of various concentrations of barium hydroxide, calcium hydroxide, magnesium hydroxide, sodium hydroxide, and potassium hydroxide at room temperature. However, it cannot be used in boiling solutions of sodium hydroxide and potassium hydroxide. The corrosion of titanium can be exacerbated by ammonia in alkali.

The maximum operating temperature of titanium in tap water, river water, and air is 300℃. Titanium can also be used in seawater with a maximum flow rate of 20m/s. Titanium has high corrosion resistance in seawater with a temperature of up to 120℃. Temperatures above 120℃ may cause point corrosion and crevice corrosion.

Titanium has excellent corrosion resistance to all organic acids except for formic acid, oxalic acid, and concentrated citric acid (concentration ≥ 50%). However, if the water content in organic acids is too low (less than 0.1%), titanium may be susceptible to pitting corrosion.

Titanium has excellent corrosion resistance in hydrocarbons and chlorinated hydrocarbons. It can undergo violent reactions in dry chlorine gas to generate TiCl4, and there is a risk of ignition.

However, it is stable in HCl dried at 20~160℃, but corrodes in wet hydrogen chloride.

Titanium has a higher resistance to chloride ion pitting than stainless steel, making it a popular choice for use in chloride solutions. Titanium has a higher resistance to chloride ion pitting than stainless steel, making it a popular choice for use in chloride solutions. This is due to its higher pitting potential in such solutions. Titanium has a higher resistance to chloride ion pitting than stainless steel, making it a popular choice for use in chloride solutions.

Titanium generally does not experience pitting corrosion when the temperature is below 80℃. However, it is more susceptible to pitting corrosion in high-temperature and medium-concentration chloride solutions. For example, it is prone to pitting corrosion in 25% aluminum chloride solution at 100℃, 70% calcium chloride solution at 175℃, 25% magnesium nitride solution at 200℃, and 75% zinc chloride solution at 200℃.

High-Temperature Working Conditions

High-temperature working condition valves mainly refer to high-temperature valves used in refineries.

Sub-high Temperature

Sub-high temperature refers to the working temperature of the valve in the range of 325℃~425℃. If the medium is water and steam, WCB, WCC, A105, WC6, and WC9 are mainly used. If the medium is sulfur-containing oil, C5, CF8, CF3, CF8M, and CF3M with resistance to sulfide corrosion are mainly used. Refineries mostly use them in atmospheric and vacuum distillation units and delayed coking units. At this time, valves made of CF8, CF8M, CF3, and CF3M materials are not used for acid solution corrosion resistance, but for sulfur-containing oil products and oil and gas pipelines. In this operating condition, the maximum operating temperature limit of CF8, CF8M, CF3, and CF3M is 450℃.

High-Temperature Level I

When the working temperature of the valve is 425~550℃, it is classified as high-temperature level I (referred to as PI level). The main material of the PI level valve is CF8, a high-quality heat-resistant steel with high temperature I grade medium carbon chromium nickel rare earth titanium, as the base shape in the ASTMA351 standard. As PI grade is a specific term, it includes the concept of high-temperature stainless steel (P). Therefore, if the working medium is water or steam, although high-temperature steel WC6 (t ≤ 540℃) or WC9 (t ≤ 570℃) can also be used, and high-temperature steel C5 (ZG1Cr5Mo) can also be used in sulfur-containing oil products, they cannot be referred to as PI grade here.

High-Temperature Level II

The working temperature of the valve is 550~650℃, designated as high-temperature level II (abbreviated as P level II). The P-II high-temperature valve is mainly used in heavy oil catalytic cracking units in refineries. It includes high-temperature lining wear-resistant gate valves used in three-way nozzles and other parts. The main material of Class II valves is CF8-based high-temperature Class II medium carbon chromium nickel rare earth titanium tantalum reinforced heat-resistant steel according to ASTM A351 standard.

High Temperature Level III

The working temperature of the valve is 650-730℃, designated as high-temperature level III (abbreviated as P III). P-III high-temperature valves are mainly used in large-scale heavy oil catalytic cracking units in refineries. The main material of the P-III high-temperature valve is CF8M, which is a high-temperature III medium carbon chromium nickel molybdenum rare earth titanium tantalum reinforced heat-resistant steel based on the ASTMA351 standard.

High Temperature Level IV

The working temperature of the valve is 730~816℃, designated as high-temperature level IV (referred to as PIV level). The upper limit of the operating temperature for PIV-level valves is set at 816℃ because the valve design uses the standard ASME B16.34 pressure-temperature rating, which provides a maximum temperature of 816℃ (1500°F). In addition, after the working temperature exceeds 816℃, the steel is close to entering the forging temperature range. At this time, the metal is in the plastic deformation range, and its plasticity is good, making it difficult to withstand high working pressure and impact force and maintain deformation. The main material of the PIV valve is CF8M in the ASTMA351 standard, which is a high-temperature grade IV medium carbon chromium nickel molybdenum rare earth titanium tantalum reinforced heat-resistant steel. Heat-resistant stainless steels such as F310 (with C content ≥ 0.050%) and F310H in CK-20 and ASTM A182 standards.

High Temperature Level V

When the valve’s working temperature exceeds 816℃, it is classified as a high-temperature V-class (PV class). High-temperature PV-class valves require special design methods such as lining insulation or water or air cooling to ensure proper operation. They are used as shut-off valves rather than regulating butterfly valves. PV-grade high-temperature valves do not have a regulated upper limit for working temperature. This is because controlling the valve’s working temperature is not solely based on materials, but also on special design methods. The principle of these design methods is the same. To meet the requirements of the valve’s working medium and pressure, reasonable materials can be chosen for PV-grade high-temperature valves using these special design methods. PV-grade high-temperature valves typically use HK-30 and HK-40 high-temperature alloys in ASTM A297 standard for the insert plate or butterfly plate of the flue plug valve or butterfly valve. These alloys can resist corrosion in oxidizing and reducing gases below 1150℃. However, they are not suitable for withstanding impact and high-pressure loads.

Conclusion

In today’s rapidly developing technology, the main materials of valves are becoming increasingly diverse and highly parameterized. The working medium corresponding to the valve is also more complex, and the working temperature requirements are higher. Understanding the properties and suitable working temperatures of various types of steel and alloys used in valves is a necessary knowledge for technology personnel and operators involved in the design, manufacturing, procurement, and use of valves. Especially, the temperature at which materials are used should not exceed their suitable working temperature, otherwise, it will cause terrible and serious accidents.

 

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