Rating is not a synonym table
A similar number can start the conversation, but approval depends on the product standard, material, size and temperature.
How to communicate PN, ASME Class, JIS K, nominal size, flange dimensions, and substitution boundaries in one technical RFQ.
No. PN10, Class 150 and JIS 10K are not automatic substitutes. Similar numbers can support initial communication, but approval requires the governing product standard, pressure-temperature basis, material group, size, connection details and written certificate or project approval.
A similar number can start the conversation, but approval depends on the product standard, material, size and temperature.
Allowable pressure can fall as temperature rises, so a nominal class alone does not define steam or hot-oil service.
Flange drilling, facing, wall thickness and face-to-face dimensions must match the piping system as well as the pressure class.
Marine requisitions often mix PN, Class and K because ship specifications, class rules and spare-part lists use different systems. The safe approach is to keep the original designation and add design pressure, temperature, material and connection details.
| Designation | Where it is commonly used | What to state with it |
|---|---|---|
| PN | ISO, DIN and Chinese product families, such as PN1.0, PN1.6 or PN2.5 MPa in the catalog | Product standard, valve type, size, body type, material, temperature and medium |
| ASME Class | ANSI/API-linked valve and flange references, such as Class 150 or Class 300 | Class number, applicable ANSI/API standards, NPS, material group, flange facing and temperature |
| JIS K | Japanese marine standards, such as 5K, 10K or 16K | JIS product standard, size callout, material, design pressure, temperature and flange details |
The table below is only for initial communication when a drawing or requisition uses another rating system. It is not an approval table and must not replace the governing product standard, class rule, pressure-temperature table or project drawing.
| Buyer designation | Common communication reference | Still confirm before substitution |
|---|---|---|
| JIS 5K | About 0.5 MPa / PN5 | Product standard, material, size, temperature and flange drilling |
| JIS 10K | About 1.0 MPa / PN10 | Pressure-temperature basis, seat material, facing and structure length |
| JIS 16K | About 1.6 MPa / PN16 | Body type, material and applicable JIS product scope |
| Class 150 | Often referenced as about PN20 | ASME pressure-temperature table, material group and end-connection standard |
| Class 300 | Often referenced as about PN50 | Whether the valve body, seat, actuator and flange all meet the same duty |
These examples show why the product page and certificate scope must be read together rather than relying only on a rating label.
| Reference | Rating information published | Procurement point |
|---|---|---|
| GB/T 587 bronze stop valve | 0.6 / 1.6 / 2.5 MPa | Size coverage changes with pressure rating |
| GB/T 590 cast-iron stop valve | 0.6 / 1.6 MPa | Steam service is limited to 220 °C in the catalog data |
| GB/T 584 cast-steel stop valve | 1.0 / 1.6 / 2.5 / 4.0 / 6.4 MPa | DN range and steam limit vary by pressure class |
| Class product-certificate scope | Confirmed by product and order | A certificate has a specific product scope; it does not transfer to every butterfly valve |
For replacement parts, measuring the existing mating flange is often faster than debating standard names. Record the values below and mark any item that cannot be measured on board or in the warehouse.
| Item | What to measure or state | Common mismatch risk |
|---|---|---|
| Nominal size | DN, NPS or JIS A/B callout | Same nominal size does not guarantee the same mating flange |
| Flange OD | Outside diameter across the flange | Interference with insulation, bracket or adjacent piping |
| Bolt-circle diameter | Center-to-center diameter of the bolt-hole circle | Bolt holes do not line up |
| Bolt holes | Number of holes and hole diameter | Wrong bolt size or number of studs |
| Hole orientation | Whether holes are aligned across the centerline or offset | Flange cannot be rotated into position |
| Flange thickness | Thickness at the rim | Stud length or spacer requirements change |
| Facing | Flat face, raised face or project-specified finish | Gasket seating area and sealing performance differ |
| Face-to-face | End-to-end or face-to-face dimension of the valve | Pipe span does not fit, especially in repair work |
| Bore and pipe connection | Pipe OD, schedule or bore where relevant | Flow area or welding fit does not match |
A photograph helps identify the valve family, but dimensions are still required before quotation. If possible, place a ruler or calipers across the flange and photograph the face square-on. Add the bolt count and any visible nameplate, casting or standard marking. For critical replacements, a hand sketch with measured OD, bolt circle, hole diameter, thickness and face-to-face length is more dependable than a photo alone.
| Too brief | Stronger RFQ wording | Why it matters |
|---|---|---|
| Need a 10K butterfly valve | JIS 10K, DN/NPS, wafer or flanged, body and seat material, design pressure and temperature, medium, quantity | Prevents seat, end-connection and certificate mismatches |
| PN16 globe valve | PN1.6 MPa, governing GB/T / DIN / project standard, valve type and body type, DN, material list, temperature | PN alone does not define trim, flange drilling or temperature capability |
| Class 150 valve | Class 150, applicable ANSI/API standards, NPS, material group, flange facing, design pressure and temperature | Class is a designation, not a fixed working pressure |
Subject: Marine valve RFQ - pressure class confirmation Valve type: IMPA code / model / drawing reference: Original rating on requisition: PN / Class / JIS K Governing product standard: Size: DN / NPS / A-B Design pressure: Maximum and minimum temperature: Medium and application system: Body / bonnet / disc / seat / stem / seal materials: Flange standard and edition, if known: Flange facing: FF / RF / other: Flange OD and bolt-circle diameter: Number and diameter of bolt holes: Flange thickness: Face-to-face or end-to-end dimension: Certificate or inspection requirement: Quantity and destination port:
| Question | Answer |
|---|---|
| Are PN, ASME Class, and JIS K automatically equivalent? | No. PN, Class, and JIS K are different rating systems. They may be used as communication references, but substitution must be checked against the governing standard, material group, size, temperature, pressure-temperature table, and connection detail. Read the pressure-rating guide. |
| How do I specify a JIS 5K or 10K marine valve flange? | State the JIS product standard, K rating, size as A/B or DN/NPS, body and trim materials, flange standard, facing, drilling, thickness, and face-to-face length. "JIS 10K" alone does not define the full product or connection. |
| What flange details must be confirmed before quotation? | Confirm flange standard and edition, nominal size, pressure class, facing, outer diameter, bolt-circle diameter, number and diameter of holes, flange thickness, face-to-face dimension, and material. A drawing or matched counterpart flange removes uncertainty. Use the flange checklist. |
| Can GB/T, DIN/EN, and ASME flanges be interchanged? | Not automatically. Drilling, facing, thickness, pressure-temperature basis, and structure length can differ. Interchangeability must be approved through a dimensional and service review, and the project drawing or class requirement may govern. |
| What is the difference between nominal size DN and NPS? | DN is a metric nominal-size designation and NPS is an inch-based nominal pipe size. JIS marine valves may also use A or B size callouts. These designations are cross-referenced, but actual dimensions and flange drilling still follow the governing standard. |
| Can PN10, Class 150, and JIS 10K marine valves be automatically substituted? | No. PN10, Class 150 and JIS 10K are not automatic substitutes. Similar numbers can support initial communication, but approval requires the governing product standard, pressure-temperature basis, material group, size, connection details and written certificate or project approval. |
| Is JIS 10K the same as PN10? | They are often used as communication references for about 1.0 MPa, but they are not automatically interchangeable. The product standard, material, temperature, size and flange details must be checked. |
| Is Class 150 the same as PN20? | PN20 is only a common communication reference. Class 150 ratings follow their own standards and pressure-temperature tables, so it must not be treated as a direct substitution. |
| Does the PN number equal maximum working pressure? | No. It is a designation; allowable pressure depends on the product standard, material, size and temperature. |
| Can a higher nominal rating replace a lower rating? | Not by itself. Dimensions, seat material, operating torque, face-to-face length and class-society scope may still be incompatible. |
| Can JIS 10K be replaced by PN10 or Class 150? | Not automatically. These are different standard systems, so flange drilling, facing, material and pressure-temperature basis must all be checked. |
| Does the same DN or NPS mean the same flange? | No. Nominal size is only a callout. The governing flange standard and dimensions decide whether the mating parts match. |
| Is a photo of the old flange enough? | It helps, but critical dimensions are still required. A square-on photo with a ruler plus bolt count is a practical minimum. |
| Why does face-to-face length matter? | For repairs, the replacement must fit the existing pipe span. A correct flange with the wrong face-to-face length can still require rework. |
This guide supports procurement communication and does not replace JIS, ASME, ISO, DIN, GB/T, CB/T, classification-society rules, the ship specification or the approved project drawing.
Send the original rating callout with design pressure, temperature, material and connection details. We will check catalog coverage and document scope before quoting.