Flange Face Types — The Complete Guide to ASME B16.5 & EN 1092-1 Facings
The facing is the machined sealing surface where a flange meets its gasket — and choosing it is choosing how the joint seals. This guide covers every standard facing with sectional diagrams: the six ASME B16.5 types — raised face (RF), flat face (FF), ring type joint (RTJ), tongue & groove (T&G), male & female (M&F) and the lap joint arrangement — and the eight EN 1092-1 forms, Type A through Type H, including the B1/B2 finish distinction and the O-ring pairs. With it: which gasket goes with which face, the surface-finish rules (AARH), the RF-to-FF warning every cast-iron pump manual repeats, and exactly how to write the facing on an order. Every facing here is machined at our Mumbai works on every flange type and every material family this site carries — see the RF, FF and RTJ long weld neck pages for facing-specific product detail, and the RTJ ring size chart for ring numbers.
6 ASME B16.5 Face Types8 EN 1092-1 Forms — Type A to HSectional Diagrams for Every FacingGasket Pairings & Surface Finish RulesRF · FF · RTJ · T&G · M&F · Lap JointB1 / B2 Finish ExplainedAll Facings Machined In-HouseEN 10204 3.1 / 3.2 · ISO 9001:2015
Direct answer: ASME B16.5 recognises six standard flange facing types — raised face (RF), the world default; flat face (FF) for brittle and lined mates; ring type joint (RTJ) for high pressure and temperature; the matched pairs tongue & groove (T&G) and male & female (M&F); and the lap joint arrangement, where the stub end carries the face. The European standard EN 1092-1 defines eight forms, Type A to Type H: A (flat), B (raised, finishes B1/B2), C/D (tongue/groove), E/F (spigot/recess) and G/H (O-ring spigot/groove). The facing decides the gasket; the gasket decides the finish — and paired facings must always be ordered as matched sets.
The Six ASME B16.5 Flange Face Types
Raised Face (RF)The world default — gasket on a raised platformFlat Face (FF)Full-face gasket — protects brittle matesRing Type Joint (RTJ)Metal ring in machined grooves — high P&TTongue & Groove (T&G)Matched pair — gasket fully confinedMale & Female (M&F)Matched pair — gasket retained in the recessLap JointThe stub end seals — the flange just bolts
The one warning every pump manual repeats: never bolt a raised face steel flange directly against a brittle flat-faced component — cast iron, GRP, glass-lined. The bolt load levers the unsupported rim over the raise's edge until the casting cracks. Specify the steel flange flat-faced with a full-face gasket, or machine the raise off before assembly. The facing decision belongs to the joint, not to one flange alone.
The Eight EN 1092-1 Face Types — Type A to Type H
European flange orders specify the face by letter. Types C/D, E/F and G/H are mating pairs — one flange carries the projection, its partner the matching depression — and must always be ordered as sets:
Type A — Flat FaceFull-face gasket formType B — Raised FaceThe European workhorse (forms B1 & B2)Type C — TongueMates with Type DType D — GrooveMates with Type CType E — SpigotMates with Type FType F — RecessMates with Type EType G — O-Ring SpigotMates with Type HType H — O-Ring GrooveMates with Type G
EN Type
Name
Mates With
Sealing Element
ASME Nearest Equivalent
Type A
Flat face
Type A
Full-face gasket
Flat Face (FF)
Type B (B1/B2)
Raised face
Type B
Sheet / spiral wound / kammprofile
Raised Face (RF)
Type C
Tongue
Type D
Flat ring in groove
Tongue (of T&G)
Type D
Groove
Type C
Flat ring in groove
Groove (of T&G)
Type E
Spigot
Type F
Flat ring on recess floor
Male (of M&F)
Type F
Recess
Type E
Flat ring on recess floor
Female (of M&F)
Type G
O-ring spigot
Type H
Elastomer O-ring
— (EN-specific)
Type H
O-ring groove
Type G
Elastomer O-ring
— (EN-specific)
Form B1 vs B2 — the finish question: both are the same Type B raised face; B1 is the standard (coarser) finish for soft and fibre sheet gaskets (commonly Ra 3.2–12.5 µm), B2 the smooth finish for spiral wound, kammprofile and metal-faced gaskets (commonly Ra 0.8–3.2 µm). A European enquiry saying just “Type B” usually means B1 — but where the piping class gaskets are spiral wound, B2 belongs on the order line.
Surface Finish — The Part of the Facing You Can't See in a Drawing
The finish is chosen for the gasket, not for looks. The default on RF and FF faces is the serrated “stock finish” — a continuous spiral or concentric-circle pattern at roughly 125–250 µin AARH (Ra 3.2–6.3 µm) — whose controlled roughness grips sheet gaskets and gives spiral wounds traction. Smooth finishes serve metal-contact gaskets, and the RTJ groove is finished to 63 µin AARH or better, because there the seal is metal flowing against metal. A perfect face with the wrong finish leaks as surely as a damaged one — state the gasket type where it is unusual, and the finish follows.
How to Specify a Facing on an Order
ASME language: the abbreviation rides with the flange type and class — “6″ Class 300 WNRF”, “SORF”, “BLRF”, “WNRTJ with R37 ring” (ring number mandatory — see the RTJ size chart), “SOFF” — and for T&G / M&F pairs, state which flange carries the tongue or male face. EN language: DN, PN and the type letter — “DN150 PN40 Type B1”, “Type B2” for the smooth finish, paired letters ordered together. Add material grade and bore as usual; where the mate is brittle or lined, say so. Every facing on this page is machined in-house on weld neck, slip-on, blind, socket weld, threaded, lap joint and long weld neck flanges, in every material family on this site.
Flange Face Types — Frequently Asked Questions
What are the types of flange faces?
ASME B16.5 recognises six standard flange facing types: raised face (RF) — the industry default; flat face (FF); ring type joint (RTJ); tongue and groove (T&G); male and female (M&F); and the lap joint arrangement, where the sealing face belongs to the stub end rather than the flange. The European standard EN 1092-1 defines eight facing forms designated Type A to Type H: A (flat face), B (raised face, in surface-finish forms B1 and B2), C (tongue), D (groove), E (spigot), F (recess), G (O-ring spigot) and H (O-ring groove). RF and Type B raised faces dominate world piping; the paired facings — T&G, M&F, C/D, E/F, G/H — always mate a projecting face on one flange with its matching depression on the other.
What is a raised face (RF) flange — and why is it the default?
A raised face flange carries a machined circular platform, raised above the bolt-circle plane, on which the gasket seats. Under ASME B16.5 the raise is 1/16" (about 2 mm) for Classes 150 and 300 and 1/4" (about 6.4 mm) for Class 400 and above. Concentrating the bolt load onto the smaller raised area multiplies the gasket seating stress compared with a full flat face — which is precisely why RF became the world's default: it seals reliably with everything from sheet gaskets to spiral wounds and kammprofiles, mates identically with any other RF flange of the same class, and needs no matched partner. Unless a specification says otherwise, a flange order means raised face — and every grade page on this site treats RF as the assumed facing.
What is a flat face (FF) flange — and when must it be used?
A flat face flange is machined over its full contact surface in one plane, with the gasket — normally a full-face sheet with bolt holes — covering the entire face. Its purpose is bending protection: when a steel flange bolts to a brittle or low-strength mate — cast iron pump and valve bodies, GRP/FRP piping, glass-lined equipment — a raised face would concentrate the bolt load and lever the brittle flange over the raise's edge until it cracks. Flat facing spreads the clamping force across the whole surface, keeping bending out of the fragile component. The rule of practice: FF is chosen by the weaker mate, not by the steel flange — and a raised face should never be bolted directly to a brittle flat-faced component.
What is a ring type joint (RTJ) facing?
An RTJ facing replaces the gasket-on-face principle entirely: a precisely machined groove is cut into each flange face, and a solid metal ring — oval or octagonal cross-section, designated by R-numbers under ASME B16.20 — seats in the opposing grooves. As the bolts tighten, the ring plastically deforms against the groove flanks, creating a metal-to-metal pressure-energised seal that tightens further as internal pressure rises. RTJ is the facing of high pressure and high temperature: wellheads, hydrogen service, Classes 900-2500, and hot hydrocarbon duty where soft gaskets retire. The groove demands a smooth finish (63 µin AARH or better), the ring must be softer than the flange, and each size-class combination has its designated ring number — this site's RTJ gasket size chart lists them all.
What are tongue and groove (T&G) flange facings?
A matched pair: one flange carries a raised ring — the tongue — and its mate carries a corresponding recessed channel — the groove. The gasket sits inside the groove, so when the joint is assembled the gasket is completely enclosed on its inner and outer diameters: it cannot blow out, cannot be over-compressed into the bore, and presents minimal exposed area to the process fluid. The confinement allows very high gasket seating stresses on a small, precisely defined area, which suits high-pressure service, thermal cycling and applications where gasket retention matters more than assembly convenience. The price is the pairing itself: tongue must meet groove, so the two flanges are not interchangeable with the rest of the world's RF stock — T&G lives on matched equipment sets, exchanger girths and licensor-specified systems. EN 1092-1's Types C and D are the European expression of the same idea.
What are male and female (M&F) flange facings?
The second matched pair: the male flange carries a raised face extending beyond the standard raise, and the female carries a matching recess or counterbore into which the male face enters. The gasket seats on the floor of the female recess, retained on its outer diameter by the recess wall — located positively, protected from blow-out, and self-centred on assembly. M&F offers gasket retention like tongue and groove with a somewhat more forgiving geometry, and appears in heat-exchanger channels and covers, high-pressure equipment connections and services where a licensor or vessel designer wants the gasket captive. As with every paired facing, the two halves must be ordered as a set — a male face has no partner in an RF world. EN 1092-1's spigot and recess (Types E and F) are the European equivalents.
What facing does a lap joint flange use?
None of its own — and that is its defining trick. In a lap joint arrangement the pipe ends in a lap joint stub end whose flared lap carries the actual sealing face; the lap joint flange is a loose backing ring that slips over the pipe behind the lap and simply provides the bolting. The gasket seats stub-to-stub, the flange never touches the process fluid, and because the flange is free to rotate, bolt holes align at assembly no matter how the pipe was welded — the classic advantage in awkward erection and frequent-dismantling service. The economics follow: on expensive alloy systems the wetted stub end is alloy while the backing flange can be carbon steel. Our lapped joint flange pages across every material family cover the type in full.
What are the EN 1092-1 flange face types A to H?
EN 1092-1 designates eight facing forms by letter. Type A — flat face, the full-face-gasket form. Type B — raised face, the European workhorse, supplied as B1 (standard, relatively coarse finish) or B2 (smooth finish) depending on the gasket. Type C — tongue, and Type D — groove: the mating pair with the gasket confined in the groove. Type E — spigot, and Type F — recess: the male-and-female pair, spigot entering recess with the gasket on the recess floor. Type G — O-ring spigot, and Type H — O-ring groove: the elastomer-sealed pair, with the O-ring housed in the Type H groove for vacuum-tight and gas-tight duty at modest pressures. C/D, E/F and G/H must always be ordered as matched pairs; a DN and PN rating plus the type letter fully defines the face on an EN 1092-1 order.
What is the difference between EN 1092-1 Form B1 and Form B2?
Surface finish on the same raised face. Form B1 is the standard finish — a relatively coarse machined surface, roughness commonly specified around Ra 3.2 to 12.5 µm — whose peaks bite into soft and fibre sheet gaskets exactly the way ASME stock finish does. Form B2 is the smooth finish — commonly around Ra 0.8 to 3.2 µm — specified where the gasket wants a fine seating surface: spiral wound, kammprofile and metal-jacketed types, whose own sealing layers do the conforming and are damaged rather than helped by coarse serrations. The geometry is identical; only the machining changes. A European enquiry that says 'Type B' without a number usually means B1; where spiral wounds or kammprofiles are the piping-class gasket, B2 belongs on the order line — and our machine shop supplies either finish to specification.
Can you bolt a raised face flange to a flat face flange?
Only when both flanges are ductile steel — and even then it is poor practice; when the flat-faced component is brittle, never. Bolting an RF steel flange against a flat-faced cast iron, GRP or glass-lined mate levers the brittle flange over the edge of the raised face: as the bolts tighten, the unsupported outer rim bends until the casting cracks — a classic and entirely avoidable failure. The correct answers are to specify the steel flange flat-faced with a full-face gasket, or to machine the raise off an existing RF flange before assembly. Between two ductile steel flanges an RF-to-FF joint can be made to seal with a suitable gasket, but the mismatch invites uneven seating and is rightly rejected by most piping specifications. The rule for the enquiry: state what the flange will bolt against, and the facing follows.
What surface finish do flange faces have?
The finish is part of the sealing system, chosen for the gasket. The default on RF and FF faces is the serrated 'stock finish' — a continuous spiral or concentric-circle groove pattern machined to roughly 125-250 µin AARH (Ra 3.2-6.3 µm) — whose controlled roughness grips soft, fibre and PTFE sheet gaskets and gives spiral wounds the traction their windings need. Smooth finishes (125 µin and finer) serve metal-faced gaskets — kammprofile, jacketed, and above all the RTJ groove, which is finished to 63 µin AARH or better because the seal is metal flowing against metal. The site-wide honesty: a perfect face with the wrong finish leaks as surely as a damaged one, so state the gasket type where it is unusual, and the facing finish follows — serrated for sheets and spirals, smooth for metal contact.
Which gasket goes with which flange face?
Face and gasket are a system. Raised face: the universal platform — compressed fibre and PTFE sheets for mild duty, spiral wound with inner ring or kammprofile for process and high-energy service. Flat face: full-face sheet gaskets with bolt holes, spreading load across the whole surface to protect brittle mates. RTJ: solid metal R-number rings, oval or octagonal, softer than the flange, per ASME B16.20 — see this site's RTJ size chart. Tongue and groove / male and female / EN Types C-D and E-F: flat ring gaskets cut to the confined seat's dimensions — the confinement itself provides the retention that RF gaskets get from friction. EN Types G-H: elastomer O-rings in the Type H groove. The piping class normally fixes both face and gasket together; where it does not, name the service and we advise the pairing.
How do I specify the flange facing on an order?
One line does it, in either standards language. ASME orders: the facing abbreviation rides with the type and class — e.g. '6" Class 300 WNRF' (weld neck, raised face), 'SORF', 'BLRF', 'WNRTJ with R37 ring number', 'SOFF' — with the RTJ ring number mandatory for ring joints and the mating arrangement stated for T&G and M&F pairs (which flange carries the tongue or male face). EN 1092-1 orders: DN, PN and the type letter — e.g. 'DN150 PN40 Type B1', 'Type B2' where the gasket wants the smooth finish, and paired letters ordered together ('Type C on the pump nozzle, Type D on the spool'). Add the material grade and schedule bore as usual — and where the mate is brittle, lined or non-standard, say so: the facing decision belongs to the joint, not to one flange alone.
Do all facing types come on all flange types and materials?
Effectively yes — facing and flange type are independent choices. Weld neck, slip-on, blind, threaded, socket weld, lap joint (via its stub end) and long weld neck flanges are all machined with raised face, flat face or RTJ facings as ordered, and the paired facings are cut on any forged type where a matched set is specified. The same independence applies to material: every grade this site manufactures — carbon and low-temperature steels, the chrome-moly ladder, every stainless family, duplex and super duplex, 904L and the nickel alloys — takes any facing, because the facing is machining, not metallurgy. The only systematic couplings are practical: RTJ concentrates in high-class carbon, alloy and duplex service; flat face follows cast iron and GRP mates; and the O-ring forms belong to EN-specified equipment.
Who manufactures flanges in all facing types in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, machining every standard facing — raised face, flat face, ring type joint with B16.20 grooves, tongue and groove, male and female, lap joint stub-end faces, and the EN 1092-1 forms Type A through Type H including B1/B2 finishes and the O-ring types — on the full range of flange types from ½" to 60" and DN15 to DN1500, in every material family this site carries: carbon, LTCS, chrome-moly, stainless, duplex, super duplex, 904L and the nickel alloys. Facings are machined to specification, surface finish verified (serrated stock finish or smooth per gasket type, RTJ grooves at 63 µin or better), and every lot ships with EN 10204 3.1/3.2 certification. Exported to more than 50 countries.
