Flange types

• Weld neck flanges – a long tapered hub butt-welded to the pipe; preferred for high pressure, high temperature and cyclic loading.
• Slip-on flanges – slide over the pipe and are fillet-welded inside and outside; easy to align for lower-pressure lines.
• Blind flanges – solid plates that close the end of a line, nozzle or valve.
• Socket weld flanges – the pipe fits into a socket and is fillet-welded; used on small-bore, high-pressure lines.
• Threaded flanges – screwed on to threaded pipe where welding is not allowed.
• Lap joint flanges – a loose backing flange used with a stub end, useful for alloy lines and frequent dismantling.
• Long weld neck, orifice and reducing flanges for nozzles, flow metering and size changes.
• Spectacle blinds, spades and spacers to ASME B16.48 for positive isolation.

Standards, sizes and pressure classes

Under ASME B16.5 the allowable pressure of a flange depends on its class, its material group and the design temperature, as given in the standard's pressure-temperature rating tables. Flanges to drawings, special bores and non-standard drillings are supplied to order. Dimensions by size and class are listed in our flange dimensions chart.

Facings and finishes

• Raised face (RF) – the most common facing, with a serrated finish for spiral wound and other flat gaskets.
• Flat face (FF) – used against cast iron or non-metallic flanges and full-face gaskets.
• Ring type joint (RTJ) – a machined groove for a metal ring gasket in high-pressure and high-temperature service.
• Tongue and groove, and male and female facings on request.

Bores are machined to match the pipe schedule. Carbon steel flanges can be supplied with rust-preventive oil, paint or galvanising as ordered.

The gasket must suit the facing. Raised face flanges normally take spiral wound gaskets with inner and outer rings or compressed fibre gaskets; flat face flanges take full-face gaskets that cover the whole face out to the bolt holes; RTJ flanges take an oval or octagonal metal ring sized to the groove. State the gasket type with the flange order so the facing finish is matched to it.

Materials and grades

Popular grades have their own pages, including ASTM A105 flanges and SS 316 flanges.

Manufacturing and inspection

Flanges are made from forgings or forged bar to the material specification, heat treated where the specification requires, then machined for bore, face, facing finish and bolt holes. Each flange is checked for dimensions against the ordered standard and marked with the manufacturer's identification, material grade, size, class, schedule and heat number.

Flanges are supplied with mill test certificates (MTC) for the material. Third-party inspection is available on request, and material can be supplied to NACE MR0175 / ISO 15156 on request for sour service. Faces are protected and flanges are packed in wooden cases or pallets for transport.

What to include in a flange enquiry

• Flange type – weld neck, slip-on, blind, socket weld, threaded or lap joint.
• Standard and size – for example ASME B16.5 NPS 6 or EN 1092-1 DN 150.
• Pressure class or PN rating.
• Facing – RF, FF or RTJ – and any special finish.
• Bore or pipe schedule for weld neck and socket weld flanges.
• Material grade, such as A105, A182 F316L or B564 N06625.
• Quantity, documents, inspection and any NACE MR0175 / ISO 15156 requirement.

Flanged joints also need stud bolts and nuts of a matching grade and a gasket suited to the facing; we can quote the bolting with the flanges.

Applications

Our flanges are used in refineries, petrochemical and chemical plants, oil and gas production, power stations, fertiliser plants, water treatment, shipbuilding and general engineering. They are usually ordered together with pipe fittings, seamless pipes and stud bolts and nuts in a matching material, so one supplier can cover the complete flanged joint. See the full range on the products page.