Specifications

Composition

Phosphorus and sulphur limits as given in the standards.

C276 is the usual flange alloy for reducing acids and chlorides, and C22 for oxidising and mixed media; the flange alloy should match the pipe and equipment it connects.

Flange types

• Weld neck flanges – for pressure and cyclic service.
• Blind flanges – to close nozzles, manways and line ends.
• Slip-on flanges and socket weld flanges where permitted.
• Lap joint flanges with Hastelloy stub ends and stainless or carbon steel backing flanges.
• Orifice and reducing flanges, and spectacle blinds.

Cost-effective flange arrangements

Because Hastelloy is a high-cost alloy, piping designers often limit it to the wetted surfaces. Three common arrangements are used. Solid Hastelloy flanges give full corrosion resistance everywhere, including the outside, which matters where the external environment is also aggressive. Lap joint flanges use a Hastelloy stub end for the wetted face with a backing flange in a less expensive material, which also eases bolt-hole alignment. For large or heavy flanges on vessel nozzles, carbon steel flanges with Hastelloy weld overlay on the face and bore are used. The piping or vessel specification states which arrangement applies.

Manufacturing and inspection

Hastelloy flanges are machined from solution-annealed B564 forgings. Machining uses sharp tools and low speeds because the alloys work-harden. Each flange is dimensionally inspected and marked with the manufacturer's identification, alloy and specification, size, class, bore schedule and heat number. Ultrasonic testing, liquid penetrant examination, intergranular corrosion testing and third-party inspection can be added, and flanges can be supplied to NACE MR0175 / ISO 15156 on request.

Bolting and gaskets

In aggressive environments where process spills or vapours reach the outside of the joint, Hastelloy studs and nuts are used so that the bolting does not become the weak point; elsewhere, high-strength alloy or stainless bolting may be acceptable. PTFE-based gaskets are common for acid service, and spiral wound gaskets with alloy windings for higher temperature and pressure. See Hastelloy fasteners.

Ordering

Please state the flange type, standard, size, class, facing, bore schedule, alloy and UNS number, quantity and any supplementary tests or inspection required.

Pressure ratings and design

ASME B16.5 includes nickel-chromium-molybdenum alloy forgings such as C276 in its material groups, with pressure-temperature ratings for each class. C276 has higher strength than austenitic stainless steel, so its ratings in a given class are comparatively high at moderate temperatures. Designers should take the ratings from the B16.5 table for the actual material group and design temperature, and allow for the joint's gasket and bolting. For lined or overlaid flanges, the rating is based on the backing material, while the alloy layer provides the corrosion resistance; the flange drawing and inspection plan should show the overlay thickness and testing.

Applications and related products

Hastelloy flanges are used in chemical and pharmaceutical reactors and piping, acid and chlorine plants, pulp bleaching, flue gas desulphurisation, waste incineration and sour-gas service. They connect Hastelloy pipes and tubes and Hastelloy pipe fittings. Flanges and blinds can also be machined from Hastelloy plates and Hastelloy round bars where the specification allows. See all flange materials on the flanges page and alloy guidance on the Hastelloy page.