Slip On Flange Manufacturer, Supplier & Exporter
A slip on flange (SOF) slides over the outside of the pipe and is attached with two fillet welds — one at the hub and one inside the bore. Raaj Fittings manufactures and exports slip on flanges in stainless steel, duplex, nickel alloys, carbon steel and alloy steel to ASME B16.5, EN 1092-1, DIN and other international standards, in hubbed and plate patterns.
Because the pipe simply slides into the flange, cutting the pipe to length and lining up the bolt holes is easier than with a weld neck flange, and no weld bevel or bore matching is needed. This makes the slip on flange an economical choice for low- and medium-pressure process lines, cooling water, fire water and utility piping.
Slip on flanges are supplied with EN 10204 3.1 mill test certificates as standard, with 3.2 certification and third-party inspection available on request.
We export slip on 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.
Slip On Flange Specifications
½" NPS to 24" NPS to ASME B16.5; larger sizes to EN 1092-1 / customer drawings on request
ASME Class 150, 300, 600, 900 and 1500; PN 6 to PN 100 to EN 1092-1 / DIN
Raised Face (RF), Flat Face (FF); Ring Type Joint (RTJ) on request
Slightly larger than the pipe outside diameter so the pipe slides through
Two fillet welds — outside at the hub and inside at the flange face
Forged (hubbed pattern) or cut from plate (plate pattern), then CNC machined
EN 10204 3.1 mill test certificate as standard; EN 10204 3.2 on request
Materials & Grades
We supply slip on flanges in the following materials and grades. All grades are supplied with EN 10204 3.1 / 3.2 Mill Test Certificates.
Stainless Steel Slip On 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 Slip On 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 Slip On 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 Slip On 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 Slip On 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 Slip On Flange Is Fitted
The pipe is pushed through the flange until its end sits just back from the flange face — normally by about the pipe wall thickness plus 3 mm — so that the inside fillet weld does not damage the gasket surface. The flange is then fillet-welded at the hub on the outside and at the pipe end on the inside. The two welds share the load and seal the joint.
- Easy alignment — the flange can be rotated on the pipe to line up bolt holes before welding.
- Lower cost — less forging weight than a weld neck and no bore matching or weld bevel.
- Tolerant of pipe length — small errors in cut length can be absorbed by the slip-in depth.
- Two weld options — a hubbed slip on (ASME B16.5, EN 1092-1 Type 12) for process service, or a flat plate flange (EN 1092-1 Type 01) for low-pressure utility lines.
Slip On or Weld Neck?
The fillet-welded slip on flange has lower strength and fatigue resistance than a weld neck flange. As a guide, its calculated strength under internal pressure is about two-thirds that of a weld neck, and its fatigue life about one-third. Piping codes such as ASME B31.3 restrict slip on flanges in severe cyclic service, so they are normally used for Class 150 and 300 process lines, utilities and non-critical services, while weld neck flanges are used for high-pressure, high-temperature and hazardous lines.
Small-Bore Alternatives
For pipe of 2" and below, a socket weld flange gives a similar easy-fit joint with a single fillet weld and a smooth bore. Where welding is not permitted, a threaded flange can be used instead.
Applications & Industries
- Cooling water, fire water and service water systems
- Low- and medium-pressure process piping in chemical and petrochemical plants
- Utility air, nitrogen and inert gas lines
- Water treatment, desalination and pumping stations
- Low-pressure steam and condensate return lines
- Food, beverage and pharmaceutical utility piping in stainless steel
- Shipbuilding and marine systems in copper-nickel and duplex stainless steel
See all flange types we manufacture.
Testing, Inspection, Marking & Packing
Slip on 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 by the grade, with pickling and passivation for stainless steels
- Dimensional inspection of outside diameter, bolt circle, bolt holes, bore and facing finish
- Marking with grade, size, pressure class, standard and heat number for traceability
Flanges are 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 Slip On 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 — Slip on 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.
Slip On Flanges — FAQs
A slip on flange is a pipe flange with a bore slightly larger than the pipe outside diameter. The pipe slides through it and is attached with a fillet weld on the outside at the hub and another on the inside at the face.
Use slip on flanges for low- and medium-pressure, non-cyclic service such as cooling water, utilities and Class 150 or 300 process lines, where lower cost and easier alignment matter. For high pressure, high temperature, cyclic loading or hazardous fluids, a weld neck flange is the better choice.
The pipe end is normally set back by about the pipe wall thickness plus 3 mm (1/8"), so that the internal fillet weld can be made without the weld metal reaching the gasket face.
To ASME B16.5, slip on flanges are supplied in Class 150, 300, 600, 900 and 1500. To EN 1092-1 and DIN they are supplied from PN 6 upwards, in plate (Type 01) and hubbed (Type 12) patterns.
A hubbed slip on flange has a short raised hub that adds strength and provides the outer weld location; it is used for process piping. A plate flange is a flat disc with no hub and is used for low-pressure utility service such as water and air.
Yes. We supply slip on 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.
