How flanges and fittings are made, and who sells them
Flanges are forged from billet, either in closed dies or, for larger sizes, as open-die forgings or rolled rings, then machined: bore, face, raised face with its serrated finish, hub and bolt holes. Plate flanges cut from plate exist too, and a buyer who ordered forged flanges should make sure that is what arrives. Butt-weld fittings are formed from pipe or plate: elbows hot-formed over a mandrel, tees bulged or extruded, reducers pressed, caps drawn. Welded fittings carry a seam that may need radiography. Stainless fittings are solution annealed and pickled after forming.
A large share of the trade passes through stockists and traders who buy from several makers and mark and certify the goods for export. That is where most problems come from: mixed heats, re-stamped markings, and certificates issued on a trader's letterhead. EN 10204 lets an intermediary pass on the manufacturer's original document unaltered, with traceability; it does not let the trader issue its own. See mill test certificates and EN 10204.
India exported US$1,152.2 million of tube and pipe fittings of iron or steel (HS 7307) in FY2025-26, according to Department of Commerce TradeStat; the figure is provisional and includes cast fittings and other items. We name no flange cluster because we have not found an official source for one.
What we check on flanges and fittings
| Check | How it is checked | What fails |
|---|---|---|
| Flange dimensions | Outside diameter, bore, thickness, hub diameter and length, bolt circle, bolt-hole size and spacing measured against ASME B16.5, B16.47 or EN 1092-1 for the size and class | Thickness under minimum; bolt circle off so flanges will not mate |
| Facing | Raised-face height and finish checked against the ordered finish with a comparator or roughness tester; faces examined for scratches across the serrations, dents and rust | Radial scratches; smooth face where serrated was ordered |
| Fitting dimensions | Centre-to-end, outside diameter and wall thickness at the bevel, bevel angle and root face measured against ASME B16.9; forged fittings against B16.11 | Wall at the bevel below the minimum; out-of-round ends |
| Marking | Every piece read for maker's mark, material grade, size, class or schedule and heat number as MSS SP-25 and the product standard require | Missing heat number; grade marked that the certificate does not support |
| PMI | Handheld XRF analysis on stainless and alloy pieces, run by the factory or a PMI specialist in our presence, on pieces we select or on every piece if ordered | 304 found where 316 is marked; chromium or molybdenum missing in alloy grades |
| Heat traceability | Heat numbers on the pieces listed and reconciled with the EN 10204 3.1 certificates; quantities per heat checked | Heat on the part not on any certificate; more pieces than the heat could supply |
| Surface and welds | Visual check for laps, cracks, laminations and pits; pickling of stainless; radiography reports for welded fittings reviewed | Laminations at bevels; unpickled weld seams |
| Hardness | Witnessed on sampled pieces where sour service limits under NACE MR0175 / ISO 15156 apply | Hardness above the limit for sour service |
ASME, EN and material standards in the order
Dimensions. ASME B16.5 covers pipe flanges and flanged fittings from NPS ½ to NPS 24 in pressure classes 150 to 2500; the current edition is B16.5-2025. Larger flanges, NPS 26 to 60, follow ASME B16.47, which has two series that do not mate with each other. ASME B16.9 (current edition 2024) covers factory-made wrought butt-welding fittings from NPS ½ to NPS 48; ASME B16.11 covers forged socket-weld and threaded fittings. European projects often specify EN 1092-1 flanges by PN rating instead.
Materials. Common grades are ASTM A105 (carbon steel forgings for piping), A182 (alloy and stainless forged flanges and fittings, such as F304L, F316L or F11), A234 WPB (wrought carbon steel fittings) and A403 (wrought austenitic stainless fittings). Dual-certified material, for example 304/304L, must meet both grades on the certificate.
Marking. MSS SP-25 sets a marking system for valves, fittings, flanges and unions that identifies the maker, the rating, the material and any service limits. Marks should be permanent: low-stress stamping or electro-etching, not paint alone.
Certificates. Most orders call for EN 10204 3.1. If your project needs 3.2, the certificate must also be validated by your authorised representative or an inspector designated by the relevant regulation. Clear To Load checks 3.1 certificates and traceability; we do not issue or co-sign 3.2 certificates. Independent chemical, mechanical or intergranular corrosion tests go to an accredited lab through lab testing coordination.
Common defects in flanges and pipe fittings
| Defect | Why it matters | Class |
|---|---|---|
| Wrong grade (PMI does not match marking) | Corrosion or failure in service; lost traceability | Critical |
| Heat number not traceable to a certificate, or re-stamped | Material cannot be accepted on a regulated or project line | Critical |
| Flange thickness or fitting wall under the minimum | Lower pressure rating than marked | Critical |
| Cracks or laminations | Leak or rupture under pressure | Critical |
| Radial scratches or dents on the gasket face | Joint will leak | Major |
| Bolt circle or hole positions off | Flanges will not bolt up | Major |
| Bevel angle or root face wrong | Poor weld fit-up | Major |
| Light surface rust on carbon steel, faint paint marks | Appearance; easily corrected | Minor |
Packing, transit and your purchase order
Gasket faces need protection: plastic or wooden face covers on flanges and plastic caps on bevel ends. Carbon steel parts are varnished or oiled against rust. Stainless parts must be packed apart from carbon steel and not handled with carbon steel slings, to avoid iron contamination that later rusts. Crates should be ISPM 15 treated, marked with heat numbers and sizes, and strong enough for heavy flanges. The inspector checks covers, segregation, crate marks and weights before loading.
Under EU CBAM, heading 7307 is on the Annex I list and the definitive regime has applied since 1 January 2026; the EU importer will need embedded-emissions data from the producer.
Put these in your purchase order:
- Standard, size, pressure class or PN, facing type and finish, bore or schedule.
- Material standard and grade, any dual certification, and heat treatment.
- Forged, not cut from plate, where that matters; seamless or welded for fittings.
- Marking to MSS SP-25 by stamping or etching, including heat number.
- EN 10204 certificate type; manufacturer's certificate, not a trader's.
- PMI extent, hardness limits for sour service, and any lab tests.
- Face protection, segregation of stainless, crate marking.
Pipe is covered on steel pipes and tubes. Book an inspection anywhere in India.
Sources
- ASME B16.5-2025, Pipe Flanges and Flanged Fittings: NPS ½ through NPS 24
- ASME B16.9-2024, Factory-Made Wrought Buttwelding Fittings
- MSS SP-25, Standard Marking System for Valves, Fittings, Flanges and Unions (Standard Norge listing)
- Regulation (EU) 2023/956 establishing a carbon border adjustment mechanism (EUR-Lex)
- Department of Commerce, TradeStat: commodity-wise exports (HS 7307, FY2025-26 provisional)