SMO 254 Flanges
Giriraj Impex is a manufacturer, stockist, supplier and exporter of SMO 254 flanges to ASTM A182 / ASME SA182 grade F44 (UNS S31254). We manufacture SMO 254 flanges to ASME B16.5 from ½" to 24" NB in Class 150 to 2500, to ASME B16.47 for larger sizes and to EN 1092-1, in weld neck, slip-on, blind, socket weld, threaded and lap joint types, with mill test certificates.
SMO 254 flanges connect SMO 254 pipe and equipment in seawater, desalination, bleach-plant and chloride-bearing chemical service, where 316L flanges would suffer crevice corrosion at the gasket face.
Specifications
| Item | Details |
|---|---|
| Material | ASTM A182 / ASME SA182 F44 (UNS S31254) |
| Dimensional standards | ASME B16.5, B16.47 Series A and B, B16.36, B16.48; EN 1092-1 |
| Sizes | ½" to 24" NB (B16.5); larger to B16.47 |
| Classes | 150, 300, 600, 900, 1500, 2500 |
| Types | Weld neck, slip-on, blind, socket weld, threaded, lap joint, orifice, reducing, spectacle blind |
| Facings | RF, FF, RTJ |
| Condition | Solution annealed |
| Documents | Mill test certificate (MTC); third-party inspection on request |
Chemical composition and mechanical properties
| C | Mn | Si | P | S | Cr | Ni | Mo | N | Cu |
|---|---|---|---|---|---|---|---|---|---|
| 0.020 | 1.00 | 0.80 | 0.030 | 0.010 | 19.5–20.5 | 17.5–18.5 | 6.0–6.5 | 0.18–0.25 | 0.50–1.00 |
Limits for plate, sheet and strip to ASTM A240. Pipe (A312), tube (A249, A269) and bar (A276, A479) limits are similar.
| Tensile strength, MPa (ksi) | Yield strength 0.2%, MPa (ksi) | Elongation, % | Hardness max |
|---|---|---|---|
| 655 (95) | 310 (45) | 35 | 223 HB |
Values for plate, sheet and strip; check the standard for other product forms and thicknesses.
Actual values for each heat are reported on the mill test certificate.
Why SMO 254
SMO 254 is a 6% molybdenum super-austenitic stainless steel with a PREN of at least about 42. It is chosen for seawater, brines, chlorinated water, pulp and paper bleach liquors, flue-gas scrubber condensate and chloride-bearing acids. Compared with 316L, SMO 254 has far better resistance to pitting, crevice corrosion and chloride stress corrosion cracking and about 50% higher yield strength; compared with super duplex it is fully austenitic, easier to form and tougher at low temperatures.
How we manufacture SMO 254 flanges
SMO 254 flanges are machined from forged blanks or rings of certified F44 material, forged close to shape and solution annealed and quenched. Machining covers the bore, facing, hub, thickness and bolt holes to ASME B16.5 or the specified standard, with a serrated or smooth face finish as ordered. Every flange is marked with grade, size, class, facing and heat number, and inspected before dispatch.
Gasket faces and crevice corrosion
The gasket contact area of a flange is a natural crevice, and in seawater this is where stainless flanges most often fail. SMO 254, with its high molybdenum and nitrogen, resists crevice corrosion far better than 316L. Joint design still matters: use non-absorbent gaskets, such as PTFE-based or suitable compressed sheet, avoid graphite in seawater where galvanic attack could occur, and tighten evenly. Lap joint arrangements with SMO 254 stub ends and coated steel backing flanges reduce cost in larger sizes.
Welding and fabrication
SMO 254 is welded by TIG, MIG and manual arc processes with over-alloyed nickel-based fillers such as ERNiCrMo-3 or ERNiCrMo-4, on clean joints free of oil, paint, marking crayon, sulphur and lead, using low heat input and controlled interpass temperatures. Heat tint is removed and welds are pickled where corrosion resistance at the weld matters. Fabrication areas should be kept separate from carbon steel, and dedicated tools used to avoid iron contamination.
Testing and ordering
Common supplementary requirements are an ASTM G48 pitting test, positive material identification and third-party inspection by the buyer's nominated agency. Please give the grade and specification, product type, size, schedule or class, quantity and any testing or inspection requirement with your enquiry. Each piece is marked with grade, specification, size and heat number, packed in wooden boxes or on pallets, and traceable to its mill test certificate.
Sizes, supply and packing
Flanges are bored to match the pipe schedule for weld neck and socket weld types, with a raised face serrated to ASME B16.5 or a smooth finish for special gaskets, and RTJ grooves for high-pressure classes. Faces are protected with covers or plywood discs, and flanges are packed in wooden boxes so that faces and bevels are not damaged in transit. Non-standard flanges – long weld necks, orifice flanges, reducing flanges and flanges to customer drawings – are made on request.
Certification and traceability
SMO 254 looks identical to 304L and 316L, so mix-ups in a workshop are a real risk. Every piece carries its grade and heat number, and the mill test certificate reports chemistry – including molybdenum and nitrogen, which set the PREN – and mechanical properties. Positive material identification by portable XRF can be carried out before dispatch on request, and pitting tests to ASTM G48 can be added where the specification calls for them.
Applications and related products
SMO 254 flanges are used in seawater cooling and firewater systems, desalination plants, offshore platforms, pulp and paper bleach plants, flue-gas scrubbers and chemical plants. Matching products include SMO 254 pipes and tubes, SMO 254 sheets and plates, SMO 254 round bars and SMO 254 pipe fittings. Background on the alloy is on the SMO 254 page. Flanges in other materials are on the flanges page.
Frequently Asked Questions
SMO 254 flanges are made from forgings to ASTM A182 grade F44 (UNS S31254), with dimensions to ASME B16.5, B16.47 or EN 1092-1.
F44 is the ASTM A182 forging grade for UNS S31254, the 6Mo super-austenitic stainless steel known as SMO 254.
They resist crevice corrosion at the gasket face much better than 316L flanges.
Non-absorbent gaskets such as PTFE-based types are common; graphite should be checked for galvanic compatibility.
Class 150 to 2500 to ASME B16.5 and B16.47.
Yes. SMO 254 stub ends can be supplied with coated steel backing flanges.
Request a Quote for SMO 254 Flanges
Tell us the product, grade, size, standard, quantity and delivery location, and our sales team will reply with a quotation.
254 SMO® is a trademark of Outokumpu.