Technical Note｜PN vs Class Pressure Ratings — Differences & Professional Valve Selection Guidelines

PN and ASME Class are two dominant pressure‑rating systems for industrial valves across global piping projects. Misunderstanding between these two specifications frequently results in flange mismatch, on‑site assembly failure, insufficient pressure resistance and costly rework for EPC contractors and overseas buyers. JOLA Valve clarifies their technical features, application markets and selection tips to support accurate valve specification and reduce project risks.

1. PN Pressure System (Metric Standard for Eurasia & Russia)
PN stands for Nominal Pressure with bar as its reference unit. It is adopted by GB, DIN, GOST and EN standards, widely specified in municipal and industrial projects throughout Central Asia, Russia, Eastern Europe and Africa.

Common PN ratings cover PN10, PN16, PN25, PN40, PN63 and PN100. Higher PN value means thicker valve body and greater pressure‑bearing capacity.

- PN10 and PN16 are general‑purpose low‑pressure grades for water supply, wastewater treatment, cooling water and HVAC pipelines.
- PN25 and PN40 serve medium‑pressure applications such as steam, gas and moderate chemical service.
- PN63 and above are high‑pressure options for power plants and heavy‑duty chemical installations.

PN‑rated flanges follow metric European dimensions including outer diameter, bolt circle and gasket face. They are completely non‑interchangeable with ASME Class flanges

2. ASME Class Pressure System (US Standard for Oil & Gas Industry)
ASME Class is an imperial‑based rating without simple fixed bar conversion. It is the preferred specification for API oil‑gas, petrochemical and international projects in Middle East, Europe and North America. Widely‑used classes include Class150, Class300, Class600, Class900 and Class1500.

Unlike PN which is defined at ambient temperature, ASME Class is a comprehensive system integrating pressure, temperature, material and flange construction. Its allowable working pressure varies with operating temperature while maintaining reliable performance under high‑temperature service.

- Class150 applies to general chemical, water and low‑pressure oil pipelines.
- Class300 and higher classes are widely specified for natural gas, crude oil, high‑temperature steam and corrosive process media in oilfield, LNG and petrochemical plants.

3. Key Technical Differences for Project Engineering
• Standard framework: PN for metric GOST / DIN / GB / EN; Class for ASME / API imperial specification.
• Flange compatibility: Non‑interchangeable in outer diameter, bolt circle, sealing face and face‑to‑face dimension.
• Pressure principle: PN defines nominal pressure at room temperature; Class follows temperature‑pressure curve for high‑temperature working conditions.
• Target markets: PN for water‑heat projects in Central Asia and Russia; Class for oil‑gas and heavy‑industry global projects.

4. JOLA Professional Selection Support
JOLA supplies industrial valves complying with GOST, DIN, ANSI and API standards. Our engineering team provides one‑to‑one technical recommendations based on clients’ piping specification, process medium, operating temperature, working pressure and site conditions. We help avoid flange mismatch and under‑specification risks, delivering dependable fluid‑control solutions for overseas EPC contractors, trade distributors and end‑user plants.