JIS 63K Weld Neck Flange — Dimensions, Weights & Drilling

It is a weld neck flange made to the Japanese Industrial Standards flange system in nominal pressure class 63K. The K classes are rated in kgf/cm² — 63K corresponds to roughly 61.8 bar (about 900 psi) at room temperature — and this chart covers 3/8 to 16 inch (DN 10–400) with dimensions in millimetres. 63K is the top of the JIS K-class flange range on this site.

K classes are nominal working pressures in kgf/cm² — a basis different from both the European PN system (bar) and the ASME class system. 10K means roughly 10 kgf/cm² (9.8 bar), 30K roughly 29 bar, and 63K roughly 62 bar at room temperature, derating as temperature rises per the material tables. The common series runs 2K, 5K, 10K, 16K, 20K, 30K, 40K and 63K.

The core Japanese flange standard is JIS B 2220 (steel pipe flanges), which tabulates the 5K through 30K classes; the 40K and 63K series continue from the associated high-pressure JIS flange standards and remain widely specified on Japanese-engineered plants. We manufacture to the tabulated dimensions and certify accordingly.

Japanese practice pairs the flange construction with the duty: the lower classes (5K–20K) are normally supplied as slip-on and plate flanges, which are economical and adequate at those pressures. From 30K upward the standard provides the weld neck construction — the tapered hub and butt weld give the joint the strength and inspectability that higher-pressure service demands.

No. JIS, ASME and DIN/EN are three separate systems with different bolt circles, bolting and rating bases — a JIS 63K flange (in duty it sits between ASME Class 300 and Class 600 — closest to Class 400) will not mate with an ASME or PN flange of the same nominal size. Always match the system of the mating equipment, or use a properly engineered transition spool.

The chart runs from 3/8 inch (DN 10) to 16 inch (DN 400) — eighteen sizes, with both the inch and DN designations and the matching pipe outside diameter tabulated per row. A few of the smallest sizes carry no weld-neck data in this class, as noted under the chart.

Sizes are in inches and DN; all other values are millimetres. D is the flange outside diameter, t the thickness, f the raised face height, g the raised face diameter, C the bolt circle, Holes and h the bolt count and hole diameter, d the bore, a the weld-end diameter (matching the pipe OD), b the hub diameter and T the length through hub. The lettered drawing above the chart shows each one.

From the weight columns in our chart: a 2 in flange about 6.9 kg (15.3 lbs), a 4 in flange about 19 kg (43 lbs), a 8 in flange about 69 kg (152 lbs). These are approximate carbon-steel weights calculated from the chart's own dimensions — actual weight varies with the bore and material. Certified weights are issued on order.

The Holes and h columns give the count and hole size per DN: a 3/8 in flange takes 4 bolts in 19 mm holes and a 16 in flange 16 bolts in 46 mm holes, on bolt circle C. Metric bolting is used throughout the JIS system.

A raised face — the g and f columns give its diameter and height per size. Flat face and other facings are machined on request. Gasket contact surfaces are finished to suit the gasket specified.

Non-metallic sheet gaskets serve the lower classes; at 30K and above, spiral wound gaskets sized to the raised face are the usual choice, particularly on steam and cycling duty. Match the gasket to the class and facing of both flanges — JIS gasket dimensions follow the JIS flange series, not ASME or EN sizes.

The classic JIS assignments are SS400 and SF440A carbon steel and SUS304/SUS316 stainless — our carbon steel A105 and stainless 304/316 equivalents — alongside the full range: A350 LF2 for low temperature, 321, 310 and 347 stainless, duplex and super duplex, alloy steel F1–F91, Monel, Inconel, Hastelloy, titanium, copper nickel and clad construction, all with EN 10204 3.1 certificates.

The weld neck's tapered hub and full-penetration butt weld give the joint the strength and fatigue life of the pipe itself, and the weld can be examined by radiography. Slip-on and plate flanges are cheaper and fine at the lower K classes, but at 30K, 40K and 63K pressures the weld neck is the specified engineering choice.

63K is the top of the common JIS flange range. Plants needing more pressure typically move to the ASME class system (Class 600 and up) or to special designs. Within JIS, the classes below — 40K, 30K and the 5K–20K series — are charted on this site for the other flange types.

Every batch is dimensionally inspected against the standard, marked with size, class, material grade and heat number, and supplied with EN 10204 3.1 mill test certificates. PMI verification, ultrasonic and magnetic-particle examination, impact testing for low-temperature grades, NACE MR0175 compliance and third-party witness inspection by LR, BV, DNV, SGS or ClassNK are available on request.

Yes. Besides standard dimensions we machine special bores for any pipe wall, extended hubs, special facings and drilling, and flanges to customer drawings — including matching worn or undocumented flanges on legacy Japanese-specified plants from a sample or field measurements. Send the drawing or datasheet and we will quote to it.

Shipbuilding and marine engineering — where JIS flanges are a global default — plus power stations, chemical plants, steelworks and any plant engineered to Japanese specifications across Asia, the Middle East and beyond. Spares and tie-ins for Japanese-built vessels and plants cite JIS classes daily.

Size (inch or DN) and quantity, class (63K), type (weld neck), pipe wall or bore, facing, material grade, any impact-test or NACE requirement, and the certification and inspection you need. Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer and exporter in Mumbai, India, shipping worldwide with sea-worthy packing.