A catalogue line that reads "PN16 / 1000 WOG / Class 150" looks like three ways of saying the same thing. It is not. PN, ASME Class, and WOG are three different pressure-rating systems, used in different markets, defined against different temperatures, and not directly convertible. This guide explains each system, why a one-line conversion table will mislead you, and how to write a pressure rating that a factory can actually quote against.
1. What PN Means (EN / Metric Markets)
PN (Pressure Nominal) is the metric rating used across EN-based piping systems. The number is a nominal pressure in bar at a reference temperature near ambient — typically about 20°C. Common series: PN6, PN10, PN16, PN25, PN40, PN63, PN100.
PN is a designation, not a free pass at every temperature. Body material, flange standard (EN 1092), and the applicable pressure-temperature table still limit the allowable working pressure as temperature rises. In practice:
- PN16 ≈ 16 bar cold working pressure on the matching EN flange family.
- The same PN16 body at elevated temperature must be checked against the material-specific derating curve in the valve or flange standard.
- PN is what European, Middle Eastern, and many Asian specs put on the RFQ line.
If your project is EN 1092 flanged and the P&ID says PN16, quote PN16 — do not substitute "Class 150" without checking face-to-face, bolt circle, and the client's design code.
2. What ASME Class Means (B16.34)
ASME Class (Class 150, 300, 600, 900, 1500, 2500) is the North American and oil & gas rating system. It is not "psi divided by something simple." Class is a pressure-temperature rating family defined primarily in ASME B16.34 (valves) and related flange standards (ASME B16.5 for flanges).
Key points sourcing engineers miss:
- A Class 150 carbon-steel valve at ambient has a much higher allowable pressure than at 400°C — the Class number is a family label, not a fixed bar or psi value.
- Material group matters: the same Class 150 rating yields different bar/psi limits for WCB, CF8M, and alloy steels in the B16.34 tables.
- Class drives flange dimensions (ASME B16.5), bolt pattern, and face-to-face (ASME B16.10) — swapping Class changes the hardware, not just a stamp on the body.
Oil, gas, and petrochemical EPCs almost always specify Class. Treat ASME B16.34 as the source of truth for the pressure-temperature envelope, not a vendor's marketing "equivalent" table. For process duty context, see the Oil, Gas & Petrochemical solution.
3. What WOG Means (and Why It Is Different)
WOG (Water-Oil-Gas) is a cold, non-shock working pressure in psi, common on commercial and plumbing ball valves. A mark of 1000 WOG means the valve is rated 1000 psi cold non-shock for water, oil, or gas service — it is not a temperature-derated family like ASME Class, and it is not a PN designation.
WOG is useful for quick commercial comparison on small-bore brass or stainless ball valves, and for specs that still use imperial cold working pressure language. WOG is not enough alone for process piping, elevated temperature, steam, or PED/ASME-coded lines. If the duty leaves ambient cold water/oil/gas, demand PN or Class with a stated design temperature.
4. PN vs Class vs WOG: Comparison Table
| System | Unit / form | Temperature basis | Typical markets | Interchangeable? |
|---|---|---|---|---|
| PN (e.g. PN16, PN40) | Nominal bar | ~20°C reference; derate with temp | EN / metric, EU, ME, much of Asia | No — not equal to Class or WOG |
| ASME Class (150, 300…) | Class family per B16.34 | Full P–T tables by material group | North America, oil & gas, EPC | No — not a fixed bar/psi stamp |
| WOG (e.g. 1000 WOG) | Cold non-shock psi | Cold / ambient only | Plumbing, commercial, catalogue SKUs | No — single cold number only |
Rough cold-order-of-magnitude only (indicative, not for design):
| Cold pressure (approx.) | PN (indicative) | ASME Class (indicative) | WOG (indicative) |
|---|---|---|---|
| ~16 bar / ~230 psi | PN16 | Often paired with Class 150 hardware | ~200–300 WOG range (not a standard pair) |
| ~40 bar / ~580 psi | PN40 | Often paired with Class 300 hardware | Higher commercial ratings |
| Catalogue multi-mark SKU | PN16 | Class 150 | 1000 WOG |
That last row is the common catalogue multi-mark: three labels for three buyer questions, not a claim of mathematical equivalence. A PrimeFlow example — PF-BV-3PC-316-DN50 3-piece SS316 ball valve — is listed DN50, PN16 / 1000 WOG / Class 150, temperature envelope −20 to 180°C (PrimeFlow catalogue, indicative). Read each number against your market and design temperature; do not treat "PN16 = Class 150 = 1000 WOG" as a conversion formula. See the 3-piece SS316 ball valve detail.
5. Temperature Derating: Where Specs Fail
Pressure rating falls with temperature. Soft seats (PTFE / R-PTFE) often limit the valve before the metal body does. Practical checks:
- Design temperature on the RFQ — not just ambient or room-temperature test pressure.
- Seat limit first — a SS316 body may be fine at 250°C while a PTFE seat is not; the PF-BV-3PC-316 line's −20 to 180°C envelope is typical of PTFE/R-PTFE seat packages (indicative).
- Material group in B16.34 (for Class) or EN flange/body material tables (for PN).
- Shock, fire, and steam — WOG "non-shock" language excludes water-hammer and many steam duties; Class and PN systems still need the correct P–T table and trim.
If a supplier only quotes cold WOG and refuses a design-temperature allowable pressure, they have not sized the valve for your line.
6. How to Specify Pressure Rating on an RFQ
Write the rating the way the destination market audits it:
- EN / metric projects: DN + PN + design pressure/temperature + flange standard (e.g. EN 1092-1) + body/seat material.
- ASME / oil & gas: NPS + Class + design P/T + ASME B16.34 material group + end standard (B16.5 / B16.11) + applicable API/ISO product standard if required.
- Commercial multi-market SKUs: Accept multi-mark catalogues (PN / WOG / Class) only as a starting shortlist; confirm the governing code and derated allowable at design temperature before PO.
For a full selection path beyond pressure alone — size, seat, ends, port, actuation — see the ball valve selection guide. When isolation type is still open, compare ball valve vs gate valve.
Frequently Asked Questions
Can I convert PN16 directly to Class 150?
No. PN16 is a metric nominal bar designation near ambient; Class 150 is an ASME B16.34 pressure-temperature family with material-specific tables. Hardware, face-to-face, and allowable pressure at temperature will not match a simple bar-to-Class formula. Use them as market labels, then check the governing standard.
Is 1000 WOG the same as PN16 or Class 150?
No. 1000 WOG is a cold non-shock psi rating. PN16 and Class 150 describe different systems. Multi-mark SKUs often print all three for commercial convenience; that is indicative marketing, not a code conversion.
Which pressure rating should I use for EU export?
Prefer PN with the applicable EN flange/body standards and CE/PED documentation. Class-rated ASME valves can be used in Europe when the design code allows, but the documentation path (PED category, Notified Body if required) must be planned — do not assume a Class stamp alone satisfies PED.
Why does allowable pressure drop at higher temperature?
Metal strength and soft-seat integrity decline as temperature rises. ASME B16.34 and EN material tables publish derating curves for this reason. Always quote design temperature with design pressure.
What should I put on the RFQ line for a DN50 SS316 ball valve?
Example pattern: DN50 (or 2" NPS), PN16 or Class 150 (pick the project code), design pressure and temperature, medium, ends (threaded/flanged/weld), seat material, and certificates (e.g. EN 10204 3.1, CE/PED if EU). Reference product: 3-piece SS316 ball valve PF-BV-3PC-316-DN50 (indicative).
Next step
If your line sheet has DN (or NPS), design pressure, design temperature, and medium, that is enough to fix PN vs Class vs WOG language and raise an RFQ. Share the destination market and governing code — PrimeFlow will return a rating and certificate set against your spec, not a generic multi-mark stamp.
Request a quotation → View a 3-piece SS316 ball valve