Process Safety Valve Guide: Elements and Use Cases

Have you ever wondered how to protect process equipment from potential disasters like malfunctions, fire hazards, or explosions? The answer lies in a crucial component called the process safety valve. But what exactly is it and how does it work?

In this comprehensive guide, we will explore the elements of a process safety valve and its various use cases. We will delve into topics such as the function of safety valves, valve sizing calculation, relief valve requirements, and valve selection criteria. By the end of this guide, you will have a clear understanding of how process safety valves ensure process equipment protection and pressure safety measures.

Key Takeaways:

  • Process safety valves play a crucial role in protecting process equipment from overpressure situations.
  • They open when the system’s pressure exceeds the Maximum Allowable Working Pressure (MAWP) or the pressure for which the system is designed.
  • Safety valve selection should consider factors such as set pressure, backpressure, discharge capacity, operating temperatures, and valve material.
  • Understanding the terminology related to process safety valves is essential for proper operation and selection.
  • There are different types of safety valves, each with its own mechanism and advantages.

Important Terminology for Process Safety Valves

Understanding the important terminology related to process safety valves is essential for proper operation and selection. This section will familiarize you with key terms used in the context of safety valves.

1. Overpressure

Overpressure refers to the excess pressure that exceeds the set pressure of the safety valve. It is crucial to monitor and control overpressure to prevent equipment failure and ensure process safety.

2. Operating Pressure

Operating pressure is the pressure at which the system operates under normal conditions. It is important to consider operating pressure when determining the set pressure for a safety valve.

3. Set Pressure

Set pressure is the pressure at which the safety valve’s disc begins to lift and open. It is a predetermined value based on the design and requirements of the system. Choosing the appropriate set pressure is essential for effective pressure relief.

4. Lift

Lift is the distance the disc moves from the closed position to the position required for discharge. It is an important factor that affects the capacity and efficiency of a safety valve.

5. Backpressure

Backpressure is the pressure built upon the outlet of the safety valve during flow. It can affect the performance and reliability of the valve. Proper consideration of backpressure is necessary to ensure effective pressure relief.

6. Built-up Backpressure

Built-up backpressure occurs when the pressure downstream of the safety valve exceeds the set pressure. It can occur due to system conditions or flow restrictions. Understanding and managing built-up backpressure is crucial for maintaining proper valve performance.

7. Superimposed Backpressure

Superimposed backpressure refers to additional pressure on top of the set pressure due to factors such as elevation or fluid properties. It is important to account for superimposed backpressure when selecting and sizing safety valves.

8. Maximum Allowable Working Pressure (MAWP)

MAWP is the maximum pressure at which a pressure vessel, equipment, or system is designed to operate under normal conditions. It is an important parameter for determining the appropriate safety valve and ensuring the structural integrity of the system.

9. Blowdown

Blowdown is the difference between the pressure at which the disc lifts and the pressure at which the valve closes. It affects the capacity and efficiency of the safety valve in relieving excess pressure.

10. Blow-off Capacity

Blow-off capacity refers to the rate at which the safety valve can release excess pressure. It is a critical factor in determining the suitability of a safety valve for a specific application.

TermDefinition
OverpressureThe excess pressure that exceeds the set pressure of the safety valve
Operating PressureThe pressure at which the system operates under normal conditions
Set PressureThe pressure at which the safety valve’s disc begins to lift and open
LiftThe distance the disc moves from the closed position to the position required for discharge
BackpressureThe pressure built upon the outlet of the safety valve during flow
Built-up BackpressureBackpressure that occurs when the pressure downstream of the safety valve exceeds the set pressure
Superimposed BackpressureAdditional pressure on top of the set pressure due to factors such as elevation or fluid properties
Maximum Allowable Working Pressure (MAWP)The maximum pressure at which a pressure vessel, equipment, or system is designed to operate under normal conditions
BlowdownThe difference between the pressure at which the disc lifts and the pressure at which the valve closes
Blow-off CapacityThe rate at which the safety valve can release excess pressure

Safety Valve Types and Their Mechanisms

When it comes to ensuring the safety of industrial processes, different types of safety valves with various mechanisms and advantages come into play. Let’s explore the four main types of safety valves and their mechanisms:

1. Spring Mechanism

The spring-loaded safety valve is the most common type. It relies on a spring to maintain valve closure under normal operating conditions. When the system’s pressure exceeds the set value, the spring is compressed, causing the valve to open and release the excess pressure. This mechanism provides a reliable and responsive solution for pressure relief.

2. Balanced Bellows

The balanced bellows safety valve incorporates a bellows element that balances the pressure inside and outside the valve. This mechanism allows for a consistent set point, unaffected by changes in external pressure. When the system pressure exceeds the set value, the bellows expands, lifting the valve disc and allowing the pressure to be released.

3. Pilot-operated Safety Valve

Pilot-operated safety valves use a pilot valve to control the opening and closing of the main valve. When the system pressure surpasses the set value, the pilot valve opens, allowing pressure from the inlet to act on the main valve. The main valve then opens, releasing the excess pressure. This type of safety valve provides precise control and is often used in applications with fluctuating operating conditions.

4. Dead Weight Safety Valve

The simplest type of safety valve, the dead weight safety valve, relies on the gravitational force exerted by weights on the valve disc. These weights are carefully calibrated to exert the necessary force to keep the valve closed below the set pressure. Once the system pressure exceeds the set value, the weights are lifted, allowing the valve to open and release the excess pressure.

To further understand the differences between these safety valve types, refer to the table below:

Safety Valve TypeMechanismAdvantages
Spring MechanismSpring-controlled valve openingReliable and responsive
Balanced BellowsPressure-balanced bellowsConsistent set point
Pilot-operated Safety ValveControlled by a pilot valvePrecise control for varying conditions
Dead Weight Safety ValveWeight-loaded valve openingSimple and reliable

Understanding the various safety valve types and their mechanisms is crucial for selecting the most suitable valve for a specific application. Each type offers distinct advantages, ensuring efficient and effective pressure relief in different scenarios.

Selection Criteria for Process Safety Valves

When selecting a process safety valve, several criteria need to be considered. These criteria play a crucial role in ensuring the valve’s effectiveness in protecting equipment and maintaining safe operating conditions. The following factors should be taken into account:

1. Set Pressure

The set pressure is a critical parameter that determines the point at which the safety valve opens to release excess pressure. It is essential to select a valve with an appropriate set pressure that aligns with the system’s maximum allowable working pressure (MAWP) to prevent overpressure situations.

2. Backpressure

Backpressure refers to the pressure built upon the outlet of the safety valve during flow. It is important to consider the expected backpressure to ensure proper valve performance and prevent any restrictions that may hinder the valve’s ability to relieve pressure effectively.

3. Discharge Capacity

The discharge capacity of a safety valve refers to its ability to release excess pressure at a specific rate. It is crucial to select a valve with sufficient discharge capacity to handle the potential pressure relief requirements of the system and prevent excessive pressure build-up.

4. Operating Temperatures

Operating temperatures play a significant role in determining the suitable valve material and sealing material for a given application. Different materials have different temperature limitations, and it is essential to select a valve that can withstand and operate effectively within the required temperature range.

5. Valve and Sealing Material

The choice of valve and sealing material is vital to ensure compatibility with the process fluid and the surrounding environment. Proper material selection can prevent corrosion, ensure optimal sealing, and extend the valve’s lifespan. Factors such as chemical compatibility, temperature resistance, and pressure rating should be considered when choosing the appropriate valve and sealing material.

By carefully considering these selection criteria, operators and engineers can choose process safety valves that meet the specific requirements of their systems, ensuring reliable and effective pressure relief capabilities.

Conclusion

Process safety valves are crucial components in ensuring the safety of process equipment. These valves play a vital role in protecting against overpressure situations that can lead to malfunctions, fire hazards, or explosions. By understanding the elements and selection criteria of process safety valves, we can ensure proper operation and equipment protection.

When selecting a process safety valve, various factors must be considered. The set pressure determines at what point the valve opens to relieve excess pressure. Backpressure, discharge capacity, operating temperatures, and valve material are all important considerations. By carefully evaluating these criteria, the right safety valve can be chosen for each specific application.

Process safety valves are essential in maintaining pressure safety measures and preventing potential hazards in various industries. With their ability to quickly respond to pressure increases, these valves safeguard process equipment and contribute to overall safety in the workplace.

FAQ

What is the function of a process safety valve?

A process safety valve protects equipment from overpressure situations by opening when the system’s pressure exceeds the maximum allowable working pressure (MAWP) or the pressure for which the system is designed.

What are the important terminologies related to process safety valves?

The important terminologies related to process safety valves include overpressure, operating pressure, set pressure, lift, backpressure, built-up backpressure, superimposed backpressure, MAWP, blowdown, and blow-off capacity.

What are the different types of safety valves?

The different types of safety valves are spring-loaded safety valves, balanced bellows safety valves, pilot-operated safety valves, and dead weight safety valves.

What criteria should be considered when selecting a process safety valve?

The criteria to consider when selecting a process safety valve include set pressure, backpressure, discharge capacity, operating temperatures, and valve and sealing material.

What is the role of process safety valves in equipment protection?

Process safety valves play a vital role in ensuring the safety of process equipment by protecting against overpressure situations that can lead to malfunctions, fire hazards, or explosions.

Enjoyed the article? 

You can find more great content here:

About the Author Walid Ben

Walid Ben. is a seasoned process engineer with 12 years of diverse experience, from operations support to leading roles in mega projects, commissioning, and startups. Driven by an entrepreneurial spirit, I founded Induskills.com an educational platform that offers hands-on tutorials and courses, cutting through theory to provide practical skills.