Guide to Selecting Materials for Pressure Relief Valves - LinkedIn

Pressure relief valves (PRVs) are critical components across various industries, protecting systems, equipment, and personnel from the risks of overpressure. Choosing the right materials for these valves ensures they maintain their performance, durability, and safety in different environments, from extreme temperatures to corrosive media. However, with a vast array of materials available, selecting the right one can be challenging. In this guide, we will combine key insights on material selection to help you make informed decisions.

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Importance of Selecting the Right Materials

Choosing the correct materials for pressure relief valves is essential for ensuring long-term reliability, performance, and safety:

• Safety: The right material prevents valve failure, which could lead to hazardous situations.
• Performance: Appropriate material selection optimizes valve functionality, ensuring proper flow control and pressure regulation.
• Durability: High-quality materials resist wear, prolonging the valve’s lifespan and reducing maintenance costs.

Factors to Consider When Choosing PRV Materials

When selecting materials for PRV components, multiple factors must be considered to ensure compatibility with the operating environment and system requirements. These factors include:

• Corrosion Resistance: Ensures the material can withstand exposure to corrosive media (e.g., chemicals or seawater). Materials like stainless steel, Monel, or Hastelloy excel in such environments.
• Temperature Resistance: High-temperature applications require materials that can maintain structural integrity. Inconel and titanium are ideal for extreme temperatures, while brass and bronze are better for moderate conditions.
• Pressure Handling: The material must endure system pressure without deforming or failing. Carbon steel and Monel are suited for high-pressure applications.
• Compatibility with Media: Materials must resist degradation when exposed to specific liquids or gases.
• Cost vs. Performance: Balancing the performance of high-end materials like Hastelloy or titanium with budget constraints is crucial for large-scale systems.
• Regulatory Standards: Ensure the material complies with industry regulations and safety standards (e.g., ANSI or ASME).

Common Materials Used for Pressure Relief Valve Components

Several materials are frequently used in PRV manufacturing, each with unique advantages depending on the application. Below is a breakdown of the most commonly used materials:

1. Stainless Steel Advantages: High corrosion resistance and durability, performs well under high pressure and temperature. Applications: Chemical processing, oil & gas, food & beverage industries.
2. Brass Advantages: Cost-effective, resistant to water corrosion, suitable for low- to moderate-pressure environments. Applications: HVAC systems, water systems, and low-pressure air systems.
3. Monel (Nickel-Copper Alloy) Advantages: Exceptional corrosion resistance, particularly in marine and chemical environments. Applications: Offshore oil platforms, marine environments, chemical processing.
4. Carbon Steel Advantages: High strength and durability, ideal for high-pressure environments. Applications: Oil & gas, petrochemical, high-pressure steam systems.
5. Hastelloy (Nickel-Molybdenum Alloy) Advantages: Superior corrosion resistance in highly acidic and harsh environments. Applications: Chemical processing, acid production, power generation.
6. Plastic and Composite Materials (e.g., PTFE) Advantages: Lightweight, cost-effective, and corrosion-resistant for specific applications. Applications: Low-pressure chemical systems, water treatment, and non-corrosive environments.
7. Titanium Advantages: Exceptional strength-to-weight ratio and corrosion resistance, suited for critical applications. Applications: Aerospace, desalination plants, and chemical processing.

Understanding Material Properties and Their Impact on Valve Performance

The material’s physical and chemical properties directly affect the performance of pressure relief valves. Key properties to consider include:

• Tensile Strength: Ability to withstand pressure without breaking.
• Thermal Expansion: High thermal expansion materials may deform under heat, affecting sealing performance.
• Chemical Compatibility: Ensures the material resists degradation when exposed to various chemicals.
• Fatigue Resistance: Materials must withstand repetitive stress from fluctuating pressures over time.

Types of PRV Components and Their Material Requirements

Different components within PRVs have specific material requirements to ensure optimal performance:

• Valve Body: Made from metals like stainless steel or carbon steel for strength and corrosion resistance.
• Spring: Constructed from high-strength metals like Inconel to handle repeated use and high pressure.
• Disc/Seat: Often made from softer materials like PTFE for improved sealing performance.
• Bellows: Typically made from corrosion-resistant materials like Monel for valves exposed to corrosive media.

Testing and Certification of PRV Materials

Testing and certification are essential to ensure PRV materials meet industry standards. Critical tests include:

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• Corrosion Testing: Verifies the material’s resistance to degradation in corrosive environments.
• Fatigue Testing: Ensures the material can handle cyclic loads.
• ANSI and ASME Certifications: Validate the material’s ability to withstand intended pressures and temperatures.

Best Practices for Selecting PRV Components

To ensure long-term performance, safety, and cost-efficiency, follow these best practices:

• Conduct Material Suitability Analysis: Evaluate the operating conditions, such as temperature, pressure, and media.
• Choose Certified Materials: Always use materials that meet industry standards and certifications.
• Consider Long-Term Costs: High-performance materials may come with higher upfront costs but offer long-term savings by reducing maintenance and replacement needs.

Case Studies: Successful Material Selection for PRVs

• Chemical Processing Plant: Switching to Hastelloy PRVs improved valve life by 200% and reduced maintenance in highly corrosive environments.
• Offshore Oil Platform: Using Monel valves reduced corrosion failures in harsh marine conditions, extending operational life by five years.
• Water Treatment Facility: Stainless steel PRVs ensured consistent performance and fewer breakdowns under varying pressures.

Conclusion: Ensuring Safety and Performance

Selecting the right materials for pressure relief valve components is essential for safety, performance, and long-term reliability. With a broad array of materials available, each offering unique advantages, it’s vital to match the material properties with the specific operational conditions. By carefully evaluating factors like corrosion resistance, temperature tolerance, and pressure handling, you can ensure your PRV system operates efficiently and safely for years to come.

Spring-loaded pressure relief valves are made up of a bonnet, a nozzle or inlet, a disc that prevents flow under normal system pressure and a spring that keeps the disc closed. The spring load can be tweaked to change the set pressure that will cause the valve to open. As such, the disc only opens if the pressure within a system increases past a certain level and keeps increasing. Most spring-loaded pressure relief valves feature a control chamber, which fills with fluid once the disc starts to lift. This, in turn, exposes more of the disc to system pressure causing it to pop open. The valve remains open until system pressure decreases to a certain level.

While both pressure relief valves and pressure safety valves protect systems from over-pressurisation, they are slightly different. While pressure relief valves are designed to maintain system pressure between preset limits, pressure safety valves are designed as a last resort measure in cases of complete system failures (this includes the failure of other valves including pressure relief valves). 

In terms of their operations, pressure relief valves open when pressure within a system reaches a certain preset level. They also open proportionally to the increase in pressure within a system. Meanwhile, pressure safety valves start opening before the preset pressure limit is reached and pop open at a set point to protect the entire system. Pressure relief valves are typically used for media such as water and oils. Pressure safety valves, on the other hand, are normally used for compressed air or steam. 

Pressure reducing valves and pressure safety valves also have different setpoints or pressure points that need to be reached before they start to open. Setpoints are normally higher than working pressure levels and lower than what are considered to be overpressure conditions. While pressure relief valves begin opening at the setpoint, pressure safety valves start to open before the setpoint and open fully once the setpoint is reached.

Since pressure reducing valves only operate in over-pressurised conditions, they are not as prone to wear and tear as other valves. As such, they do not normally require to be made from highly resistant materials. The exception to the rule is when they come in contact with corrosive fluids and are used for cryogenic applications. Another exception involves situations where fluid contamination is undesirable.

The various components of pressure relief valves are often made from the following materials.

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• Bronze (for up to 15 bars of pressure).
• Cast iron (for up to 17 bars of pressure).
• Spheroidal graphite (SG) iron (for up to 25 bars of pressure).
• Cast steel (for up to 40 bars of pressure).
• Austenitic stainless steel (for pharmaceuticals, food and clean steam).