Valve Classes & Ratings FAQ

Valve class ratings indicate the maximum pressure a valve can handle at specific temperatures, as defined by ASME B16.34 and ASME B16.5 standards.

Common Class Ratings:

• Class 150: Up to 19.6 bar (285 psi) at 38°C
• Class 300: Up to 51 bar (740 psi) at 38°C
• Class 600: Up to 102 bar (1480 psi) at 38°C
• Class 900: Up to 153 bar (2220 psi) at 38°C
• Class 1500: Up to 255 bar (3705 psi) at 38°C
• Class 2500: Up to 425 bar (6170 psi) at 38°C

Important: Pressure ratings decrease as temperature increases. Always refer to pressure-temperature (P-T) rating charts for your specific material.

PN (Pressure Nominal) is a European designation (EN/DIN standards), while Class is an American designation (ASME/ANSI standards).

Approximate Conversions:

• PN 10 ≈ Class 150
• PN 16 ≈ Class 150
• PN 25 ≈ Class 150/300
• PN 40 ≈ Class 300
• PN 63 ≈ Class 600
• PN 100 ≈ Class 900

Note: These are approximate conversions. PN ratings represent nominal pressure in bars at 20°C, while Class ratings vary with temperature.

To select the correct valve class, consider:

• Design Pressure: Maximum operating pressure of your system
• Design Temperature: Maximum operating temperature
• Safety Factor: Typically 1.5x to 2x operating pressure
• Material: Different materials have different P-T ratings
• Code Requirements: ASME, API, or other applicable codes
• Future Expansion: Consider potential pressure increases

Example: For a system operating at 40 bar and 200°C with carbon steel valves, Class 300 would be appropriate (provides adequate safety margin).

ANSI Valves (now ASME) are general-purpose valves for industrial applications, designed per ASME B16.34 standard.

API Valves are specifically designed for oil & gas industry applications per API 600, API 602, API 6D, and API 6A standards.

Key Differences:

• Design Standards: API has more stringent requirements
• Testing: API requires more extensive testing (shell test, seat test, backseat test)
• Materials: API specifies tighter material tolerances
• Documentation: API requires comprehensive material traceability
• Cost: API valves are typically 20-40% more expensive

When to use API: Oil & gas production, refining, petrochemical plants, and critical service applications.

Fire-safe valves are designed to maintain their sealing integrity during and after exposure to fire conditions, as per API 607 or API 6FA standards.

Key Features:

• Secondary metal-to-metal sealing when soft seats burn away
• Fire-resistant stem packing
• Blow-out proof stem design
• Tested at 750°C (1382°F) for 30 minutes

Applications: Mandatory in oil & gas facilities, refineries, petrochemical plants, and offshore platforms.

1. Flanged: Most common for DN 50+, easy maintenance, ASME B16.5/B16.47 standards.

2. Threaded (NPT/BSP): For small sizes (DN 50 and below), low-pressure applications.

3. Welded (Butt-weld/Socket-weld): Permanent connection, high-pressure, leak-proof applications.

4. Wafer: Between flanges, compact, typically for butterfly/check valves.

5. Lug: Independent flange connection, can be used as end-of-line valve.

6. Tri-clamp: Sanitary applications, easy disassembly, food/pharmaceutical industries.

Cryogenic valves are designed for extremely low temperatures (-196°C to -269°C) handling LNG, liquid nitrogen, liquid oxygen, and liquid hydrogen.

Special Features:

• Extended bonnet design to prevent freezing of packing
• Special low-temperature materials (SS316, Inconel, Monel)
• No thermal shock to packing area
• Special seat materials that remain flexible at cryogenic temperatures

Blow-out proof stem design prevents the valve stem from being ejected from the body under pressure.

Features: Stem shoulder or collar that prevents stem ejection, secondary stem seal, required by API standards.

Importance: Critical safety feature preventing catastrophic failure and personnel injury in high-pressure applications.

Rising Stem: Stem moves up/down as valve opens/closes. Visual indication of valve position, easier maintenance, requires more vertical space. Common in gate and globe valves.

Non-Rising Stem: Stem rotates but doesn't move vertically. Compact design, less vertical space, no visual position indication. Common in underground applications.

Backseat is a feature where the stem seals against the bonnet when the valve is fully open, allowing packing replacement under pressure.

Benefits: Enables live maintenance, prevents stem leakage when fully open, required by API 600 standard.

Applications: Critical in oil & gas where shutdowns are costly.

Full Port (Full Bore): Internal diameter equals pipe diameter. Minimal pressure drop, suitable for pigging operations, higher cost.

Reduced Port (Standard Port): Internal diameter is smaller than pipe diameter. Higher pressure drop, lower cost, lighter weight, adequate for most applications.

Selection: Use full port for pigging, minimal pressure drop requirements, or high-viscosity fluids.

Fugitive emissions are unintended leaks of gases or vapors from pressurized equipment.

Testing Standards: API 622 (packing), API 624 (gaskets), ISO 15848, TA-Luft.

Requirements: Valves must demonstrate leak rates below specified limits (typically 100 ppm) over multiple thermal and mechanical cycles.

Applications: Mandatory in refineries, chemical plants, and environmentally sensitive areas.