A maintenance engineer sends a list that reads “elbow 90°, 4 inch, stainless, 20 pcs; flange 4 inch, 10 pcs”. Three suppliers reply with three prices, and none of them is quoting the same thing. One has priced Schedule 10S long-radius elbows to ASME B16.9, one has priced JIS short-radius elbows, and the third has priced slip-on flanges to a Chinese national standard because nothing said otherwise.
Pipe fittings and flanges are standard parts, but only once the standard is named. A fitting is defined by five things together: the dimensional standard, the size, the wall thickness or pressure rating, the material grade, and the end or face type. Leave one out and the supplier fills the gap with whatever it stocks. This article sets out how to write those five lines for the three standard families buyers in Asia meet most often — ASME, JIS and EN — and what to check when the goods arrive.
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The five lines every fitting or flange order needs
An order line for a fitting or flange is complete only when it names the dimensional standard, the size, the wall thickness or pressure rating, the material grade and the end or face type.
The dimensional standard decides the geometry. The material grade decides the chemistry and strength. They are written separately, and a buyer who names only one has not specified the part. “ASME B16.9 elbow” says nothing about the steel; “316L elbow” says nothing about the centre-to-end dimension.
| Line | What it fixes | Example of a complete entry |
|---|---|---|
| Dimensional standard | Geometry, tolerances, marking | ASME B16.9; JIS B 2312; EN 1092-1 |
| Size | Nominal size in the system of that standard | NPS 4 (ASME), 100A (JIS), DN 100 (EN) |
| Wall or rating | Wall thickness for butt-weld fittings; pressure rating for flanges | Schedule 40S; Class 150; 10K; PN 16 |
| Material grade | Chemistry, mechanical properties, heat treatment | ASTM A403 WP316L; ASTM A105; a named EN or JIS grade |
| End or face type | How it joins the line | Butt-weld bevel; raised face; flat face; weld neck; slip-on |
Add two more lines that are not about the part but decide whether you can use it: the inspection document you require (see mill test certificates under EN 10204) and the marking you expect on each piece.
ASME fittings and flanges: B16.9, B16.11 and B16.5
For inch-based piping, butt-weld fittings are specified to ASME B16.9, small forged socket-weld and threaded fittings to ASME B16.11, and flanges up to NPS 24 to ASME B16.5.
ASME’s catalogue describes B16.9 (Factory-Made Wrought Buttwelding Fittings) as covering overall dimensions, tolerances, ratings, testing and markings for factory-made wrought butt-welding fittings from NPS 1/2 to NPS 48 (DN 15 to DN 1200). Low-pressure corrosion-resistant butt-welding fittings are excluded and sit in MSS SP-43 instead — which matters when a supplier offers thin-wall stainless fittings at an attractive price. Ask which standard they are made to. The current edition listed by ASME is B16.9-2024.
B16.11 (Forged Fittings, Socket-Welding and Threaded) covers the small-bore forged fittings used on instrument, drain and vent lines. ASME lists the 2021 edition, with a revision in progress.
B16.5 (Pipe Flanges and Flanged Fittings, NPS 1/2 Through NPS 24 Metric/Inch Standard) covers pressure-temperature ratings, materials, dimensions, tolerances, marking and testing. ASME’s catalogue lists Classes 150, 300, 400, 600, 900 and 1500 across the size range, and Class 2500 up to NPS 12. It is limited to cast or forged flanges, with blind flanges and certain reducing flanges also permitted from plate. ASME lists B16.5-2025, issued on 30 May 2025, as the most recent revision. Above NPS 24, flanges move to B16.47 (Large Diameter Steel Flanges, NPS 26 Through NPS 60), also revised in 2025.
The class number is not a pressure. A Class 150 flange has a permitted pressure that falls as temperature rises and that depends on the material group, and the table that sets it is in the standard. Do not let anyone convert a class to a bar figure in an email; ask them to state the material group and design temperature and read the rating from the current edition.
Material is named separately, usually by ASTM grade. Typical pairings in ASTM’s own titles are A105 (carbon steel forgings for piping applications) for flanges and forged fittings, A182 (forged or rolled alloy and stainless steel flanges, forged fittings and valves) for stainless and alloy forgings, A234 (wrought carbon and alloy steel piping fittings) for carbon steel butt-weld fittings, and A403 (wrought austenitic stainless steel piping fittings) for stainless butt-weld fittings. ASTM revises these often, so name the grade and let the certificate show the revision used.
JIS flanges and fittings: B 2220, B 2311, B 2312
Japanese-built plants and Japanese machinery, including those running in Vietnam and Thailand, are typically specified with JIS flanges designated by “K” pressure classes, which do not bolt up to ASME or EN flanges.
JIS B 2220 (steel pipe flanges) is the Japanese standard most buyers meet. The most recent edition we found listed was published on 20 February 2012, covering nominal sizes 10A to 1500A and the nominal pressures 5K, 10K, 10K light type, 16K, 20K, 30K, 40K and 63K. The Japanese Standards Association’s web catalogue was under maintenance when we checked, so confirm the edition when you order.
For butt-weld fittings, Japan has two standards with different titles and uses: JIS B 2311 (steel butt-welding pipe fittings for ordinary use) and JIS B 2312 (steel butt-welding pipe fittings for piping). The second is the one to name for pressure piping. Wall thickness in JIS is expressed by schedule as well, but the pipe it mates with is a JIS pipe — JIS G 3454 for carbon steel pressure piping, JIS G 3459 for stainless steel piping — and the outside diameters of those pipes are not always the same as ASME pipe of the same nominal size. That difference is covered in JIS, ASME and EN piping standards compared.
Where a production line was designed in Japan, the spare flange, gasket and valve must follow the drawing’s JIS designation. A 10K flange ordered as “4 inch Class 150” will arrive, look similar, and not bolt on.
EN flanges: EN 1092-1 and the PN system
European equipment and EU-destined projects use EN 1092-1 steel flanges designated by PN and DN, with flange type and facing written as codes.
EN 1092-1:2018 (Flanges and their joints — Circular flanges for pipes, valves, fittings and accessories, PN designated — Part 1: Steel flanges) specifies requirements for circular steel flanges from PN 2,5 to PN 400 and DN 10 to DN 4000. It covers flange types and facings, dimensions, tolerances, threading, bolt sizes, jointing face finish, marking, materials, pressure/temperature ratings and approximate masses, and it treats lapped ends and collars as flanges. Non-gasketed pipe joints are outside its scope. The 2018 edition replaced the 2007 edition and its amendment. A draft amendment to the 2018 text (prA1) was issued for comment in 2022, and we could not confirm that it has been published as a final amendment; ask which version the supplier works to.
EN orders fail most often on the type and facing codes. A complete EN line has the shape “EN 1092-1, Type [number], Form [code], DN 100, PN 16, [material from the standard’s material tables]”. The type number identifies the flange (weld neck, slip-on, blind and so on); the form code identifies the face. Take both codes from the standard itself, not from a catalogue picture. Write both — a supplier who receives only “DN 100 PN 16” will ship whatever it holds.
💬 We source fittings and flanges to ASME, JIS and EN from manufacturers and stockists across Asia, and check the marking and documents before shipment. See pipe fittings, valves and couplings.
Face types and gaskets: where mismatches hide
The flange face and the gasket must be ordered as a pair; a raised-face flange against a flat-faced cast-iron or lined component is a known failure mode.
| Face type | Where it is used | What to write on the order |
|---|---|---|
| Raised face (RF) | Most ASME and JIS steel flanges | ”RF”, with the surface finish if your spec sets one |
| Flat face (FF) | Mating to cast iron, plastic or lined equipment | ”FF” and a full-face gasket |
| Ring-type joint (RTJ) | High-pressure and high-temperature service | ”RTJ”, and the ring gasket ordered against the same flange designation |
| EN forms (A, B1, B2 and others) | EN 1092-1 flanges | The form letter and number exactly as in the standard |
Gaskets have their own standards — on the ASME side, B16.21 (Nonmetallic Flat Gaskets for Pipe Flanges) for flat gaskets — and a gasket cut for an ASME flange does not sit correctly on a JIS or EN flange of the same nominal size. Order the gasket to the flange standard, not to the pipe size.
What to check when the goods arrive
Check the marking on the part against the order line by line, then check that the certificate’s heat or lot number matches the marking.
Each of these standards sets a marking requirement, and the marking is the cheapest inspection you will ever do. Before the goods arrive, read the marking clause of the edition you ordered to and list what each piece should carry; the content differs between ASME, JIS and EN. At the least, the marking should let you tie the piece to the standard, the size and rating, the material grade and a heat or lot number.
| Check | How | Why it matters |
|---|---|---|
| Marking vs order | Read every piece in a sample; all pieces for small lots | Catches the wrong standard before it reaches the line |
| Heat number vs certificate | Match the marking to the certificate’s heat or lot field | A certificate that cannot be linked to the part proves nothing |
| Dimensions | Outside diameter, wall thickness at the bevel, bolt circle, bolt holes | Confirms JIS vs ASME vs EN |
| Material identity | Positive material identification on stainless and alloy parts | Catches substituted grades |
| Face finish and damage | Visual check of sealing faces and bevels | Damage here leaks regardless of grade |
API RP 578 (Material Verification Program for New and Existing Assets, 4th edition, February 2023 in API’s catalogue) describes how owners use positive material identification to confirm that installed components match the specified material. Even if your plant does not run a formal programme, a handheld check on a sample of stainless fittings is a reasonable condition to write into the order. Sampling and acceptance are covered in pre-shipment inspection and AQL.
Pressure-equipment rules in the country of use
Fittings and flanges become part of pressure equipment, so the rules of the country where the line operates apply in addition to the product standard.
In the EU, Directive 2014/68/EU covers the design, manufacture and conformity assessment of stationary pressure equipment with a maximum allowable pressure greater than 0,5 bar, according to the European Commission. How it applies to a given flange or fitting depends on the fluid, the pressure and the size, and on whether the item is supplied on its own or as part of an assembly. For Vietnam, we found no line for pipe fittings, flanges or valves (HS 7307, 8481) in the product lists of Circular 16/2026/TT-BNV (Ministry of Home Affairs) or Circular 33/2026/TT-BCT (Ministry of Industry and Trade), both read in the original. Press reports say the medium-risk list of the Ministry of Science and Technology (Circular 36/2026/TT-BKHCN, applied from 1 July 2026) includes stainless steel; we have not read the original or its HS codes, so check with your customs broker whether stainless fittings are caught. For other countries, including Japan, confirm the current rule in the country of use before you order, and ask the end user which documents its inspector expects. We do not state a conclusion here that only the authority or the notified body can give.
💬 Need fittings, flanges and gaskets consolidated with other plant spares from several Asian suppliers? Tell us what the line needs, and see also consolidating Asian suppliers into one shipment.
Frequently asked questions
1. Can I order “4 inch” and let the supplier choose the standard?
No. A 4-inch ASME part, a 100A JIS part and a DN 100 EN part are different parts. Name the dimensional standard on every line.
2. Is Class 150 the same as 10K or PN 16?
No. They are pressure designations in three different systems with different dimensions and rating tables. Read the rating from the standard for your material and temperature, and do not mix flanges across systems.
3. Do I need to name both the dimensional standard and the material grade?
Yes. ASME B16.9 sets geometry; a grade such as ASTM A403 WP316L sets the material. One without the other leaves the part undefined.
4. What is MSS SP-43 and why does it matter?
It is the standard for low-pressure corrosion-resistant butt-welding fittings, which ASME B16.9 excludes. If a stainless fitting is offered to SP-43, it is not a B16.9 fitting; check that your line allows it.
5. Which edition of the standard should I write on the order?
Write the edition your design or your customer’s specification names. Where it names none, ask the supplier which edition it manufactures to and record it on the purchase order.
Sources: ASME catalogue pages for B16.9 and B16.5, and ASME’s B16 revision list (B16.5-2025, B16.9-2024, B16.11-2021, B16.21-2021, B16.47-2025); EN 1092-1:2018 as listed by SIS (Swedish Institute for Standards); JIS B 2220, JIS B 2311, JIS B 2312, JIS G 3454 and JIS G 3459 titles from the JISC database, JIS B 2220:2012 edition data from the JSA listing; ASTM titles for A105, A182, A234 and A403; API 2025 Publications Catalog (RP 578); European Commission page on Directive 2014/68/EU. Checked on 27 October 2026.