How to choose the right material for valves

There are several factors to consider when choosing material for your valves. First, you need to consider what media they will handle. The material must be able to withstand the media normally present in the line as well as media that may enter the line or the external environment around the valve. 

Then you also need to consider:

• the specific requirements of your application
• process conditions
• and compatibility requirements

The material selection is critical for ensuring long-term performance, reliability, and safety.

In this article, we will highlight some of the most common media and suitable materials.

 

Chemicals

Valve materials compatibility with chemicals can vary depending on the specific chemicals involved. Some materials may corrode, i.e. rust. Which material is suitable depends on how resistant it is to corrosion caused by the liquid or gas to be handled. However, certain materials are commonly used due to their general chemical resistance properties.

We offer several valve materials for chemical applications. Here are some of them and their typical chemical compatibilities:

Stainless Steel (EN 1.4408 and 1.4409): Stainless steel is widely used due to its excellent corrosion resistance properties. It is compatible with a wide range of chemicals, including acids (such as sulfuric acid, hydrochloric acid), alkalis, organic solvents, and many corrosive fluids.

Titanium is a material that can withstand chlorides, which are found in e.g. salt water and chemicals. While titanium is a more expensive option, its light weight can bring down the cost of transport, operation and maintenance.

Steel alloys such as acid-resistant steel (EN 1.4409, EN 1.4408) are very common, but to offer higher corrosion resistance, duplex, super duplex, 904L or SMO grades such as 254 may be sufficient at lower concentration of chlorides e.g sea water at low temperatures. Carbon steel and cast iron corrode rapidly in an industrial environment, unlike the more expensive acid-resistant steels.

Hastelloy: Hastelloy alloys (such as Hastelloy C276) offer exceptional resistance to a wide range of corrosive chemicals, including strong acids, alkalis, oxidizing agents, and harsh environments. They are commonly used in demanding chemical processing applications.

 

Gas

Valve materials compatibility with gases depends on the specific gas being handled. Helium for example is a gas that is very difficult to isolate. Hydrogen atoms are forced into the material and damage the valve from the inside, a process called Hydrogene embritelment. Helium therefore requires the right material in the valve for the seals to hold.

Leakage of toxic gases or gases that have a climate impact on the atmosphere is a problem in all industries. By using valves meeting the fugitive emission standards according to ISO 15848-1 and VDI 2440 (TA-luft), the problem can be avoided or limited.

Here are some materials we use in our valves and their general compatibility with gases:

Stainless Steel (EN 1.4408 and 1.4409): Stainless steel valves are generally compatible with a wide range of gases, including inert gases, hydrocarbons, and non-corrosive gases. Stainless steel offers good resistance to corrosion and can withstand high-pressure and high-temperature gas applications. In addition, Stainless steel is highly resistant to hydrogen embrittlement, making it a safe and reliable choice for hydrogen gas applications.

Hastelloy: Hastelloy alloys, such as Hastelloy C276, are highly resistant to corrosive gases, including acidic or alkaline gases. They are commonly used in demanding gas processing applications where high corrosion resistance is required.

Duplex and Super Duplex: Duplex and super duplex materials (e.g., SAF 2205, SAF 2507) provide superior corrosion resistance in aggressive environments, making them suitable for handling corrosive gases. These materials offer excellent resistance to pitting, crevice corrosion, and stress corrosion cracking. Duplex and super duplex valves are commonly used in offshore, chemical, and oil and gas applications, where gases with high chloride content or acidic gases are encountered.

904L: 904L is a high-alloy austenitic stainless steel known for its excellent resistance to a variety of aggressive media, including sulfuric acid, phosphoric acid, and other acidic gases. It offers good strength and toughness, making it suitable for gas industry, chemical, and pulp and paper applications where corrosive gases are present.

254SMO: 254SMO (EN 1.4547), a super-austenitic stainless steel, exhibits exceptional resistance to a wide range of corrosive gases, such as sulfuric acid, hydrochloric acid, and acetic acid. It is highly resistant to pitting, crevice corrosion, and stress corrosion cracking, even in harsh environments. 254SMO valves are commonly utilized in chemical, pulp and paper, and offshore applications.

Titanium*: Titanium is highly resistant to a wide range of corrosive gases, including wet chlorine, hydrochloric acid, and many organic compounds. It offers exceptional resistance to pitting and crevice corrosion and maintains its integrity at elevated temperatures. Titanium valves find applications in the chemical industry, petrochemical plants, and other environments where extreme corrosion resistance is required.

*There are different grades of titanium. The grades refer to different alloys or compositions of titanium and are designated by numbers or alphanumeric codes, each representing a specific composition and set of properties. Grade 5 is the most used one for valves, but also grade 2 is used. The choice of grade depends on the specific requirements of the application.

 

Slurries

A particularly challenging type of media is when there are particles in it, as they will wear the valves. Slurries, consisting of solids suspended in liquid, can be highly abrasive and corrosive, posing unique challenges to valve performance. The material of the valve must therefore be able to withstand the abrasive and erosive nature of the mixture when handling slurry. It is also important to consider the specific characteristics of the slurry, such as particle size, concentration, and velocity, when selecting the material.

Here, we will discuss two valve materials suitable for slurry applications: cast iron with natural rubber lining and stainless steel with SuperExpanite® treatment, highlighting their specific strengths and considerations.

Cast Iron with Natural Rubber Lining: Valves made from cast iron with a natural rubber lining are well-suited for handling slurries in low-pressure and low-temperature applications. The cast iron body provides structural integrity, while the natural rubber lining offers superior resilience and abrasion resistance. These valves are particularly effective in industries such as mining, steel plant, waste water, where slurries are encountered. They provide reliable sealing, minimize wear, and reduce the risk of leakage. However, it’s important to note that cast iron with natural rubber lining is not specifically designed for highly corrosive media or applications involving high pressures and temperatures.

Stainless Steel with SuperExpanite® treatment: Valves made from stainless steel, combined with the SuperExpanite® treatment, provide exceptional resistance to corrosion, and aggressive media. The SuperExpanite® treatment is a hardening process that significantly enhances the hardness and wear resistance of the base material. This treatment improves the valve’s durability and resistance to wear, and erosion. Stainless steel valves with Expanite treatment are well-suited for a wide range of applications, including mining, steel plants, pulp and paper, power plants, food and beverage processing, and the chemical industry. They excel in environments where abrasion resistance, longevity, and reliability are paramount, while being cost effective compared to other expensive solutions such as ceramic valves.

To sum up, cast iron valves with natural rubber lining are suitable for low-pressure, low-temperature applications with non-corrosive slurries. For more demanding slurry conditions involving higher pressures, temperatures, and corrosive media, stainless steel valves with SuperExpanite® treatment offer superior resistance and durability.

 

How to define the level of quality

When choosing material for your valve, it can be a challenge to define the right level of quality. Higher alloys and titanium require a large investment, while cheaper materials often need additional maintenance and/or reduced production capacity.

Avoid plastic or other composite materials, which are cheaper than standard metal valves, as one piece of advice. They have much lower pressure ratings, and because plastic is always vulnerable to UV radiation from daylight, the valve will crack under even the slightest pressure. This can cause major extra costs and even accidents.

To help you define the appropriate level of quality we’ve made a list of important factors to consider:

• Service life
• Maintenance intervals
• Spare parts requirements
• Wear and tear
• Production losses and delays
• Fluid Compatibility
• Pressure and Temperature Ratings
• Material Strength
• Corrosion Resistance
• Abrasion Resistance
• Environmental Factors
• Cost Considerations

Feel free to contact us if you need guidance in choosing the most suitable valve material for your valve. You can also book a meeting with one of our technical specialists.