Pipe fittings, valves and flanges: how to read JIS, DIN/EN and ANSI notation

What do JIS 5K, 10K and 16K mean on a marine valve or flange?

JIS marine valves and flanges carry a K-number, such as 5K, 10K or 16K, as their pressure designation. Marine valves are covered by the JIS F series (shipbuilding) and their flanges by JIS B 2220, with the K-class set by the valve series. A higher K-number means a higher pressure class, not a pressure in bar.

The K-numbers trace back to pressure expressed in kgf/cm², so they are labels, not bar values. The titles in the JIS F list mix materials and classes: bronze and cast iron valves at 5K and 10K, cast steel up to 40K, and so on. The JIS F title tells you the valve type, material and class together, so quote the full number (for example "JIS F 7301 5K") rather than "JIS valve". JIS is mainly used in Japan, Korea and Southeast Asia.

What do DN, PN, NPS and Class mean?

DN is a metric nominal size (ISO 6708) and NPS is its North American counterpart in inches; they map one to one, so NPS 4 is DN 100. Both are labels, not measurements: an NPS 4 pipe has an outside diameter of 4.500 in (114.30 mm), not 100 mm.

PN (EN 1333) is a reference designation such as PN 16, not a pressure value. According to BSI's summary of the standard, the allowable pressure depends on the PN, the material and design, and the maximum allowable temperature. ASME Class (150, 300 and so on) works the same way: Class 150 does not mean 150 psi. The allowable pressure is read from a table for the material group and the temperature. Always check the manufacturer's pressure-temperature data for your actual service.

Is DIN the same as EN 1092-1?

DIN flange standards have largely been replaced by EN 1092-1, the current European standard for steel flanges. Older ship drawings and parts lists may still say "DIN PN 16", but a new order should name EN 1092-1, the DN, the PN and the facing type.

Why can flanges not be mated across standards, even at the same DN?

Flanges from ASME, EN and JIS are drilled to different bolt circles, bolt counts and bolt-hole or thread systems, so they usually cannot be bolted together. A DN 150 / NPS 6 example shows the problem: ASME Class 150 has eight 3/4 in UNC bolts on a 241.3 mm bolt circle, while EN PN 16 has eight M20 bolts on a 240 mm bolt circle. The circles look close, but the bolting differs, and mixing standards in one joint is best avoided; where two systems meet, a transition spool is the usual answer.

Do not rely on a near match at one size. Hole number, spacing and shape vary between standards at other sizes as well. Check the standard's drawing or the manufacturer's data sheet before you accept a substitute.

How do the standards compare?

The regions are tendencies reported by a trade reference, not rules. A ship's own piping drawings decide which standard applies.

What about threads: BSP and NPT?

Threaded valves and fittings use BSP outside North America and NPT in North America, and they are different thread systems. BSP follows the Whitworth form with a 55 degree angle between flanks; NPT has a 60 degree angle and a taper of 3/4 inch per foot. BSP comes as parallel (BSPP, ISO 228) and taper (BSPT, ISO 7) versions, so say which you need. A parallel thread seals with a washer or O-ring, a tapered one seals on the thread. Do not assume BSP and NPT will screw together.

What should you state when ordering valves?

State the valve type, nominal size, standard and pressure rating, body material, end connection, medium and design temperature. Broad types: gate valves for full-open or full-closed isolation, globe valves for throttling (with higher pressure drop), ball valves for quarter-turn shut-off, butterfly valves for compact large-bore service, check valves to stop backflow, and plug valves or cocks for quarter-turn shut-off. End connections are flanged, threaded, butt-weld or socket-weld (and wafer or lug for butterfly types).

Body material codes such as bronze, cast iron, WCB cast steel or CF8M stainless change both price and suitability, so give them explicitly. For gaskets, name the flange face (raised or flat), the pressure class and the medium: soft sheet, spiral wound and ring-joint gaskets are different types, and ring-joint gaskets need matching grooved flanges. For stem packing, give the valve make and model and the medium.

Where do these items sit in the IMPA catalogue?

ShipsBay lists these under Pipes & Tubes (IMPA section 71), Pipe & Tube Fittings (73), Valves & Cocks (75) and Packing & Jointing (81). If you cannot find the flange you need, search by name or state the size, standard and pressure rating in your RFQ. See what an IMPA code is and how to prepare an RFQ, and for unit conventions units of measure.

You can search for gate valves or gaskets, or add lines to the RFQ cart with the standard and rating in the line note.