Socket Weld Flange Manufacturer, Supplier & Exporter
A socket weld flange (SWF) has a machined socket into which the pipe is inserted and then joined with a single fillet weld at the hub. Raaj Fittings manufactures and exports socket weld flanges to ASME B16.5 in stainless steel, duplex, nickel alloys, carbon steel and alloy steel, for small-bore piping up to NPS 3".
The socket gives a quick, self-aligning fit and leaves a smooth bore through the joint, because the socket bore is machined to match the inside diameter of the pipe. Socket weld flanges are widely used on high-pressure small-bore lines — instrument connections, hydraulic and chemical injection lines, drains and vents — where a weld neck would be heavy and costly.
Every flange is supplied with EN 10204 3.1 mill test certificates, with 3.2 certification and third-party inspection available on request.
We export socket weld flanges to EPC contractors, refineries and stockists across the Middle East and GCC, Europe and the Americas, made to the ASME, EN or DIN standard your project specifies, with PED-compliant supply for European projects on request.
Socket Weld Flange Specifications
½" NPS to 3" NPS (most classes); ½" to 2½" NPS in Class 1500
ASME Class 150, 300, 600, 900 and 1500
ASME B16.5; EN 1092-1 and other standards on request
Socket to suit the pipe OD; bore below the socket machined to the specified pipe schedule
One external fillet weld at the hub
Forged, heat treated as required, and CNC machined
EN 10204 3.1 mill test certificate as standard; EN 10204 3.2 on request
Materials & Grades
We supply socket weld flanges in the following materials and grades. All grades are supplied with EN 10204 3.1 / 3.2 Mill Test Certificates.
Stainless Steel Socket Weld Flanges
Stainless steel flanges offer excellent corrosion resistance and are essential in chemical, pharmaceutical, food processing, and marine environments.
(ASTM A182 F304 / F304L) General corrosion resistance
(ASTM A182 F316 / F316L) Superior resistance to chlorides, acids; marine & pharmaceutical service
(ASTM A182 F316H) High-temperature elevated creep strength
(ASTM A182 F321) Titanium-stabilized; suitable for sustained elevated temperatures
(ASTM A182 F347) Columbium-stabilized; used in heat exchangers and high-temperature piping
High alloy; exceptional resistance to strong acids
Duplex & Super Duplex Stainless Steel Socket Weld Flanges
Duplex and super duplex grades offer approximately twice the yield strength of standard austenitic stainless steel, combined with excellent resistance to stress corrosion cracking and pitting — making them ideal for offshore, subsea, and chemical processing.
(UNS S31803 / S32205) Used in offshore platforms and chemical processing plants
(UNS S32750) Ideal for seawater handling and desalination systems
(UNS S32760) Designed for high-chloride offshore service applications
Nickel Alloy Socket Weld Flanges
For the most aggressive corrosive environments — including concentrated acids, caustic solutions, sour gas service, and extreme temperatures — we offer flanges in a full range of nickel alloys.
(UNS N06600) High-temperature oxidation resistance
(UNS N06625) Outstanding corrosion resistance for offshore and subsea service
(UNS N08825) Excellent resistance to phosphoric and sulfuric acids
(UNS N10276) Broad-spectrum corrosion resistance in acids and chlorides
(UNS N06022) Superior resistance to oxidizing acids
(UNS N04400) Suitable for seawater, hydrofluoric acid, and marine environments
(UNS N08020) Engineered for sulfuric acid service
Exceptional corrosion resistance with low weight
(C70600 / C71500) Preferred for marine and seawater piping systems
Carbon Steel Socket Weld Flanges
Carbon steel is the standard choice for general-purpose, non-corrosive, and elevated-temperature services. The primary grade for forged carbon steel flanges is ASTM A105, and for low-temperature service, ASTM A350 LF2.
Primary grade for forged carbon steel fittings and flanges — covers ambient and elevated-temperature service in pressurised piping systems.
Low-temperature carbon steel, impact-tested for service down to -46°C (-50°F) — LNG, cold climate, and cryogenic piping applications.
Alloy Steel Socket Weld Flanges
Alloy steel flanges are specified for high-temperature, high-pressure service in power generation, petrochemical, and refinery applications.
(5% Cr, ½% Mo) Designed for elevated temperature refinery service
(9% Cr, 1% Mo) Suitable for high-temperature steam and hydrogen service
(1¼% Cr, ½% Mo) Widely used in thermal power plant piping systems
(2¼% Cr, 1% Mo) Used in high-temperature pressure vessels and reactors
(9% Cr, 1% Mo, V, Nb) Engineered for ultra-high-temperature power plant steam lines
How a Socket Weld Flange Works
The pipe end is pushed into the socket, withdrawn by about 1.6 mm (1/16") from the bottom of the socket, and then fillet-welded around the outside of the hub. The expansion gap lets the pipe grow as the weld heats and cools, preventing cracks at the root of the weld; the ASME B31 piping codes require it. Because there is no internal weld, the bore is smooth and there is no weld bead to disturb flow.
- Self-aligning fit — the socket holds the pipe square to the flange while it is welded.
- Smooth bore — the bore is machined to the pipe schedule, so flow is not restricted.
- Single fillet weld — faster to fit than a slip on flange, with no bevel preparation.
- High-pressure capability — suitable for small-bore lines in Class 600 to 1500.
Specifying the Bore
Always give the schedule of the pipe, such as SCH 80 or SCH 160. The socket is sized for the pipe outside diameter, and the bore beneath it is machined to the pipe's inside diameter so the two line up.
Limitations
The small gap between pipe and socket can trap fluid, so socket weld flanges are generally avoided in services prone to crevice corrosion and where piping codes restrict them under severe cyclic conditions. For larger or more critical lines, a weld neck flange is specified. Where welding is not allowed at all, a threaded flange is the alternative, and for low-pressure lines a slip on flange can be used.
Applications & Industries
- Small-bore process piping in refineries, petrochemical and gas plants
- Instrument, sampling, vent and drain connections
- Hydraulic, lube oil and seal oil systems
- Chemical injection and high-pressure dosing lines
- Steam tracing and condensate lines
- Offshore small-bore piping in duplex and super duplex
Pair socket weld flanges with our forged socket weld fittings for a complete small-bore system, or see all flange types.
Testing, Inspection, Marking & Packing
Socket weld flanges are produced under our quality assurance process:
- Incoming material verification with PMI testing
- Chemical and mechanical testing to the applicable ASTM material specification
- Heat treatment as required, with pickling and passivation for stainless steels
- Dimensional inspection of socket bore, socket depth, bore, bolt circle and facing
- Marking with grade, size, class, schedule and heat number
Supplied with EN 10204 3.1 mill test certificates; EN 10204 3.2 certificates and third-party inspection are available on request.
Flanges are packed for export with gasket faces protected by covers, rust-preventive coating on carbon and alloy steel, and seaworthy wooden cases; marking, tagging and packing to your specification are available on request.
Why Choose Raaj Fittings for Socket Weld Flanges?
Raaj Sagar Steels has supplied piping components since 2003 and today manufactures flanges at two plants in India for buyers in the Middle East, Europe and the Americas.
- Manufactured in-house — Socket weld flanges are made in our own plants, so material, dimensions and delivery stay under our control.
- Ready stock, short lead times — common sizes and grades are held in stock for prompt dispatch; other sizes, grades and specials are manufactured to order.
- Certified quality — ISO 9001:2015, ISO 14001:2015 and ISO 45001:2018 certified; PED 2014/68/EU and IBR supply available, and NACE MR0175 / ISO 15156 material on request.
- 100% material verification — PMI testing on incoming material and EN 10204 3.1 mill test certificates with every order; 3.2 certificates on request.
- Third-party inspection ready — we regularly work with SGS, Bureau Veritas, TÜV and DNV.
- Export documentation — MTCs, certificates of origin, packing lists and inspection reports to suit projects in the GCC, Europe and the Americas.
- Export packing — seaworthy packing with end and face protection, and packing to your specification on request.
- Fast response — our team replies to enquiries within one business day.
Socket Weld Flanges — FAQs
A socket weld flange has a counterbored socket that accepts the pipe end. The pipe is joined with a single fillet weld around the outside of the hub, leaving a smooth, full bore through the joint.
Socket weld flanges are used for small-bore piping and are supplied to ASME B16.5 from ½" up to 3" NPS, and up to 2½" NPS in Class 1500. Larger lines normally use weld neck flanges.
A gap of about 1.6 mm (1/16") allows the pipe to expand as the fillet weld is made and cools, so the weld does not crack. The ASME B31 codes require this expansion gap.
Give the size, pressure class, facing, material grade and the pipe schedule — for example 1" Class 600 RF, ASTM A182 F316L, SCH 80. The bore is machined to match the pipe schedule.
Avoid them in services prone to crevice corrosion, where the small gap between pipe and socket could trap fluid, and where the piping code restricts them under severe cyclic conditions. A weld neck flange is preferred in those cases.
Yes. We supply socket weld flanges for projects under the European Pressure Equipment Directive (PED 2014/68/EU), and with IBR certification for Indian boiler applications. NACE MR0175 / ISO 15156 compliant material is also available on request for sour service in the Middle East and the Americas.
