Tryksikkerhedsventil: Præcisionsstøbegods & Tilpasset OEM-løsning

1. Indledning

Pressure safety valve is an engineered devices that protect pressure equipment, rør, and people by opening automatically to relieve excess pressure when a system exceeds a pre-defined safe limit.

They are the final, passive line of defense in process safety architectures: when instruments, control systems, alarms and operators either cannot or do not prevent an overpressure event, the pressure safety valve must act reliably and predictably.

2. What Is a Pressure Safety Valve?

EN tryk safety valve is a self-acting mechanical device designed to automatically release excess pressure from equipment or piping systems when internal pressure exceeds a predetermined safe limit.

Once the overpressure is relieved, the valve re-closes and restores the system to safe operating conditions.

Unlike control valves or operator actions, it functions independently of external power or signals, making it the final safeguard against catastrophic equipment failure.

Typical installations include boilers, Trykfartøjer, Varmevekslere, Opbevaringstanke, rørledninger, and compressors—anywhere an unexpected pressure rise could cause damage to equipment or pose risks to people and the environment.

Nøglefunktioner

• Automatic Activation: Triggers without human intervention when pressure reaches set pressure (typically 100–110% of MAWP), ensuring rapid response to upsets.
• Reseating Capability: Closes automatically once pressure drops to reseat pressure (5–15% below set pressure), eliminating the need for system shutdown in non-catastrophic events.
• Fail-Safe Design: No electrical, hydraulisk, or pneumatic power required—functions even during power outages or control system failures.
• Flow Capacity: Engineered to discharge fluid at a rate sufficient to prevent pressure from rising above a safe limit (accumulation), typically ≤10% of set pressure for gases and ≤20% for liquids (API 520).

Fundamental Principles of Operation

The basic operating principle is a balance of forces:

• Closing force: provided by a spring or pilot system, holding the valve shut under normal conditions.
• Opening force: generated by system pressure acting on the valve disc or seat area.

When the system pressure reaches the set pressure, the opening force exceeds the spring force, causing the valve to lift.

The valve then discharges fluid until the system pressure falls back below the reseat (blowdown) tryk, at which point the spring force pushes the disc back onto the seat, sealing the valve again.

3. Types of Pressure Safety Valves and How They Differ

Pressure safety valves can be broadly categorized by their actuation mechanism, response behavior, og service egnethed.

Different types address different operational risks—from sudden gas overpressure to gradual liquid buildup—so correct selection is critical for safety and reliability.

4. Materials and Construction

A pressure safety valve’s effectiveness depends not only on its design but also on the choice of materials and construction integrity.

Common Materials and Their Suitability

The material selection is guided by fluid type, temperatur, tryk, and corrosive exposure.

Industry note: In power generation, stainless steels and Cr-Mo alloys dominate high-pressure steam service, while offshore industries increasingly use nickel-based alloys despite higher cost, due to longevity and safety.

Construction Elements

A pressure safety valve typically includes the following engineered parts:

• Legeme: Provides structural strength; rollebesætning, forged, or precision-machined depending on rating.
• Seat and Disc: Precision-ground for tight sealing; often hardened stainless steel or stellite-coated for erosion resistance.
• Spring or Pilot Assembly: Determines set pressure; made of high-strength steel with corrosion protection.
• Bellows (if applicable): Thin-walled alloy structure to isolate backpressure.
• Motorhjelm: Houses spring and guides disc movement; designed for easy maintenance access.

5. Common Manufacturing Processes of Pressure Safety Valves

The manufacturing of pressure safety valves is a high-precision, safety-critical process, combining robust material handling, Præcisionsbearbejdning, and rigorous testing.

Body Fabrication of Pressure Safety Valves

De valve body is the core pressure-containing component of a pressure safety valve, and its fabrication is critical to ensure mechanical strength, Dimensionel nøjagtighed, og langvarig pålidelighed.

Depending on the size, pressure rating, and material, different fabrication methods are employed.

Common Casting Processes

Smedning

• Beskrivelse: A solid billet of metal is mechanically compressed and shaped under high pressure to form the valve body.
• Fordele:

• • Produces high-strength, dense components with fewer internal defects than casting.
  • Ideal for high-pressure and high-temperature applications.

• Typiske materialer: Kulstofstål, lavlegeret stål.
• Overvejelser: Forged bodies may require machining of ports, Tråde, and sealing surfaces after shaping.

Bearbejdning

• Beskrivelse: CNC or conventional machining is used to refine valve ports, Tråde, og kritiske tætningsoverflader.
• Fordele:

• • Ensures precise dimensions and smooth surfaces for proper disc-seat sealing.
  • Allows customization of body features and attachment points.

• Materialer: Applied to cast or forged bodies; compatible with carbon steel, Rustfrit stål, and alloys.
• Overvejelser: Machining tolerances are critical for valve performance, particularly seat alignment and spring assembly fit.

Internal Components

• Disc and Seat: Precision-ground for leak-tight closure; often hardfaced with stjerner eller tungsten carbide to resist erosion and high-velocity fluid damage.
• Springs: Cold-formed and heat-treated to maintain consistent set pressure under repeated cycles. Alloy selection (chrome-silicon, Inkonel) depends on operating temperature.
• Guides & Motorhjelm: Machined to tight tolerances to ensure stable disc movement and proper spring alignment.
• Bellows (if applicable): Rolled or welded from thin-walled alloy tubing; stress-relieved to resist fatigue and maintain spring isolation.

Overfladebehandlinger

• Passivering: Stainless steel components are chemically treated to remove surface impurities and enhance corrosion resistance.
• Hardfacing: Seats and discs receive stellite or similar coatings to resist erosion and extend service life.
• Protective coatings: Exterior surfaces may receive paints, epoxies, or plating to prevent corrosion in harsh environments.

Forsamling

1. Undersamling: Disk, sæde, spring, and guide components are pre-assembled in a controlled environment.
2. Final Assembly: The body, motorhjelm, and sub-assemblies are joined; fasteners are torqued to specification.
3. Calibration: Spring compression or pilot valve settings are adjusted to ensure correct set pressure.

Testning & Kvalitetssikring

• Set Pressure Verification: Each valve is tested on a calibrated test bench to confirm lift occurs at the specified set pressure.
• Leakage Testing: Seat tightness is checked per API 527 or equivalent standard.
• Capacity Testing: Til kritiske applikationer, valves are tested to ensure they can relieve the required maximum flow.
• Ikke-destruktiv test (Ndt): Radiografi, ultralyd, or dye penetrant inspections detect internal flaws in castings or welds.

6. Key Standards and Codes of Pressure Safety Valves

Pressure safety valves are safety-critical devices, and strict standards and codes govern their design, manufacture, testning, and installation to ensure reliable performance under overpressure conditions.

7. Common failure modes and root-cause mitigation

Understanding failure mechanisms helps prioritize mitigation:

• Leakage (seat leakage): caused by seat erosion, foreign debris, or soft seat deterioration. Afbødning: filtrering, teflon or metallic seat selection per service, scheduled bench tests.
• Set drift / spring creep: springs lose preload with time and temperature. Afbødning: periodic recalibration, use of high-temperature spring materials, pilot systems for better stability.
• Sticking (stuck valve): due to corrosion, deposits, or mechanical binding. Afbødning: beskyttelsesbelægninger, regular cycling, use of blowdown devices to keep stem free.
• Chattering / instability: caused by inadequate flow path, improper sizing, or excessive backpressure. Afbødning: re-evaluate sizing, use of pilot valves, add damping orifice.
• Incorrect reseat (won’t close): caused by high backpressure, two-phase flow, or damaged seats. Afbødning: balanced valve designs, pilot control adjustments, replace seating surfaces.
• Inadequate capacity: due to wrong sizing assumptions (F.eks., neglecting flashing or unexpected failure mode). Afbødning: conservative relief case definition and independent sizing verification.

8. Industry Applications of Pressure Safety Valves

Pressure safety valves are ubiquitous across sectors. Typical examples:

• Olie & gas and petrochemicals: protection for separators, Opbevaringstanke, kompressorer, and flare knock-out drums; valves often must handle two-phase flows, sour service chemistries and fire case scenarios.
• Kraftproduktion (boilers and turbines): steam relief on boilers and turbines with high temperature duty requires metal seats and high-temperature spring materials; inspection regimes are tightly defined by boiler codes.
• Chemical and process plants: corrosive chemicals and special fluids require specialty materials (Duplex, Nikkellegeringer) and strict documentation.
• Marine and offshore: space and weight constraints plus saline corrosion drive selection of corrosion-resistant alloys and compact designs.
• Pharmaceutical and food: sanitary valves with hygienic design and soft seats where tight shutoff and cleanliness are paramount.

9. Comparison with Other Valves

Pressure safety valves and safety pressure relief valves are specialized safety devices, but industrial systems also use other types of valves, such as gate, globus, and control valves, for flow regulation and isolation.

Understanding the differences helps engineers and procurement managers select the right valve for both operation and safety.

Sammenlignende tabel

Nøgleindsigter

• Critical Safety Role: Both pressure safety valves and safety pressure relief valves are fail-safe devices; port, globus, and control valves serve operational or flow-control purposes rather than overpressure protection.
• Automatic vs. Manuel: Safety devices operate automatically and independently of operators, ensuring immediate protection.
• Precision and Capacity: Safety pressure relief valves often include pilot or balanced designs for higher set-pressure accuracy and capacity, especially under variable backpressure conditions.
• Integration with Other Valves: Safety devices are installed alongside control and isolation valves, allowing normal process operation while maintaining emergency protection.

10. Konklusion

Pressure safety valves are simple in mechanical concept but central to process safety.

Proper selection requires understanding the protected equipment, credible relief scenarios, fluid properties and the relevant codes.

Good practice couples conservative engineering assumptions, rigorous materials and manufacturing standards, correct installation and risk-informed testing intervals.

Digital technologies are making valve health more visible and manageable, enabling condition-based maintenance that reduces both risk and cost.

FAQS

How often should a PSV be tested?

Test frequency depends on criticality and service. Many organizations perform annual bench testing for critical valves and visual checks quarterly; lower-criticality valves may have longer intervals. Use a risk-based approach.

Can I use the same PSV for gas and liquid service?

Not without careful evaluation. Liquid relief often involves two-phase conditions and higher volumetric flows—valves and inlets must be designed accordingly.

What’s the difference between a PSV and a relief valve?

Terms vary by region; broadly, a PSV is used for gas/vapor and a relief valve for liquids.

In practice the term “safety valve” often implies fast pop action used for steam; “relief valve” implies proportional opening. Always define by function in specifications.

Are pilot-operated valves always better?

Not always. Pilots offer precise control and high capacity for gases/steam but are more complex and costlier. For small or simple duties, direct spring valves can be the better choice.