Installation of Safety Valves in Steam and Pressurised Process Systems

The safety valve is one of the most important components within an industrial system, as its function is to guarantee a safe operationThe main purpose of a pressure relief valve is to protect lives, equipment and assets from the risks associated with overpressure. Its primary mission is to prevent the internal pressure of a piece of equipment, line or asset from pressure tanks exceeds the limit set by the calibration pressureThe aim is to prevent accidents and ensure compliance with regulations.

In industry, where they interact steam boilers, boiler systems, steam distribution systems, Heat exchangers, y Regulating stationsThe correct use of safety valves is essential to maintain the integrity of the equipment and the continuity of the production processes.

This article details best practices for the selection, sizing, installation and maintenance of safety valves in industrial steam systems, integrating also the requirements of international standards such as API 526, DIN standards, EN 1092-1 and the AD Merkblatt A2 standardstogether with the ASME Code Section VIII which regulates the manufacture and use of these devices.

Fundamental concepts of steam safety valves

Calibration pressure and trigger pressures

The calibration pressure is the essential parameter in any safety relief valve. It is defined as the pressure at which the internal spring allows the valve to open automatically. It is essential to respect the trigger pressures The energy release point is set by the regulations, as they determine the exact point at which the device will act to release the excess energy.

A safety valve not to be confused with a pressure regulating valve nor with a pressure relief valve. While the latter two are responsible for controlling and stabilising pressures in normal operation, the former is designed exclusively for the purpose of safety deviceThe pressure gauge is only activated when the maximum allowable pressure is exceeded.

Materials and construction

Valve body materials determine valve strength and durability. Carbon steel is commonly used in standard applications, stainless steel in corrosive or high cleanliness environments, and nodular cast iron or cast iron in low cost applications. High alloy materials such as AISI 316 are used for critical conditions, especially in contact with aggressive fluids.

The stainless steel bellows is used in valves subjected to corrosive media to protect internal parts. In addition, the use of standard materials facilitates the replacement of parts, while rugged materials and manifold materials ensure reliability under extreme pressure and temperature conditions.

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Types of safety valves

There are different typologies on the market:

• Conventional safety relief valvethe most widespread design, regulated by API 526suitable for multiple industries.
• Gas safety valveis used in compressed gas systems, where expansion conditions and flow rates are different from steam.
• T&P valvetemperature and pressure valve, common in domestic hot water systems and storage tanks.
• Diaphragm valve y automatic valves: used in auxiliary processes where automatic control and fast response are required.
• Shut-off valvesafety relief valve: this is not a safety relief valve, but is sometimes confused with one; its function is to isolate a section of the system.

Applicable rules and regulations

All valves security must comply with current codes and regulations. Among the most relevant:

• ASME Section VIIIPressure Vessel Valves: sets out the requirements for the design, testing and use of valves on pressure vessels.
• API 526International reference standard for conventional safety relief valves.
• DIN standardsEuropean level.
• EN 1092-1regulates flanges and connections such as the Flanged end of the valves.
• AD Merkblatt A2 standardsGerman technical document for pressure vessel safety.

Compliance with these standards not only ensures legal compliance, but also the industrial safety and accident risk reduction.

Sizing and selection of a safety relief valve

Capacity and flow rate

The safety relief valve must be selected according to the maximum pressure of the system and the maximum operating temperature. Consideration should be given to:

• Large Flows in processes where pressure release must be fast.
• temperature range applications such as chemicals or power generation.
• working temperature normal and Maximum temperature in extreme situations.

The orifice calculation must be based on the process data, respecting the margin between operating pressure and calibration pressure.

Material compatibility

The body material should be chosen taking into account corrosion, erosion and mechanical resistance. In food and pharmaceutical applications, priority is given to the Stainless Steelwhile for compressed air o air compressor valves are often used with a body in carbon steel or standard alloys.

Installation

Correct installation is as important as sizing. Best practices include:

• Install the valve in mechanical system clean, free of incrustations or dirt.
• Vertical positioning, with open cap in outdoor applications to avoid water accumulation.
• Respect the Input connection without using reductions that restrict passage.
• Use gas thread BSP or flanges in accordance with EN 1092-1depending on the design.
• In large diameters such as DN 200 mmIn order to support the weight of the assembly, structural reinforcements must be provided.
• Incorporate lever for manual opening on critical valves, allowing for periodic verification of correct operation.
• Never install isolation valves between the valve and the protected equipment.

The design should consider venting through sized piping, avoiding back pressure. The use of drip pan elbows is essential to divert condensate and protect the system.

Practical applications

Safety valves are used as a priority in the following scenarios in steam systems:

• Industrial steam boilersEach boiler must be equipped with at least one safety relief valve correctly dimensioned according to the calibration pressure design. These valves are the last resort to protect against a pressure surge caused by a failure of the combustion controls, feed water supply or automatic blowdown.
• Steam distribution manifoldsin systems where the steam is diverted to different process lines by means of steam distibutorsThe safety relief valves are installed to protect the main header and prevent overpressure when control valves fail or pressure backflows occur from secondary lines. You may be interested in reviewing the Design Guide for Industrial Steam Distribution Systems
• Steam heat exchangersIn heat transfer equipment, such as shell and tube heat exchangers, water heaters or process reactors, safety relief valves are installed to protect the shell from possible overpressure caused by a burst pipe, water hammer or a poorly adjusted pressure regulating valve.
• Steam regulation stationsIn pressure-reducing trains, where high-pressure steam is converted to service steam at a secondary pressure, safety valves are installed downstream of the reducing valves. This protects the low-pressure lines and equipment against a possible failure of the regulating valve which could allow steam to pass at full boiler pressure.
• Condensate recovery and return systemssafety relief valves are applied in return tanks and condensate pumping systems when there is a risk that the retreating steam will generate a pressure higher than the pressure admissible in the tank.

A real example is the use of steam safety valves of the company Spirax Sarcoinstalled in a pressure reduction station of a food plant. There, the safety valve protects the line from secondary pressure feeding the pasteurisation heat exchangers. In the event that the pressure reducing valve is locked in the open position, the safety valve opens automatically, ensuring that downstream equipment does not exceed the maximum working pressure and maintaining process safety.

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Security and operation

The essential function of the valve is to ensure a Instant total security. To achieve this:

• Periodic checks should be carried out on the calibration pressure on the test bench.
• It must be ensured that the spring and internal parts are free of corrosion, especially in chemical environments.
• Do not tamper with the seals or break the seal, as this will invalidate the certification.

The use of industrial valves in critical environments requires frequent inspections. Users must be trained in industrial pressure control and to know the limitations of the valves according to their design.

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Additional considerations

All technical documentation must include:

• Information from personal data of authorised maintainers.
• Ensure the management of information in accordance with the Privacy Policy of the company.
• Record the traceability of each valve: date of installation, set pressure, maximum operating temperatureThe calibration date, body materials, and calibration date.

Conclusion

The security valves for steam are the heart of protection in any industrial installation. Their correct selection, based on calibration pressuresuitable materials such as Stainless Steel or the carbon steelcompliance with international standards such as API 526 y ASME Section VIIIand proper installation with Flanged endensure the integrity of equipment such as Heat exchangers, boiler systems or lines of steam distributors.

Rigorous maintenance, with periodic opening tests, visual inspection of the body materialreview of shut-off valve and functional testing of the lever for manual openingare essential to maintain the safe operation of the systems.

In short, the steam safety valve is more than just an accessory: it is the last resort in the event of a system failure. Implementing these best practices ensures not only regulatory compliance, but also the protection of people, assets and critical processes in the industry.