Specifications

Chemical composition and mechanical properties

Alloy 800HT also requires Al + Ti 0.85–1.20%. Alloys 800H and 800HT have grain size and heat-treatment requirements for elevated-temperature service, as given in the standards.

Values common to ASTM B407, B409 and B408 (alloy 800 family), B423, B424 and B425 (alloy 825) and B564 forgings; check the standard for the product form and size.

Fasteners keep the composition and properties of the bar from which they are made. Background is on the Incoloy page.

800H or 825 fasteners?

Incoloy 800, 800H and 800HT fasteners are used where bolting runs hot: furnace and kiln fixtures, heat-treatment baskets and supports, reformer and cracker internals, flue and exhaust systems, and flanged joints in 800H piping. They resist oxidation, carburisation and scaling, and 800H and 800HT keep their creep strength above about 600 °C. Incoloy 825 fasteners are used where corrosion rather than temperature is the main concern – in sulphuric and phosphoric acid plants, pickling lines, seawater-cooled equipment, pollution-control scrubbers and sour oil and gas service – to match 825 equipment and piping.

Strength and joint design

Annealed Incoloy alloys have a yield strength far below that of B7 alloy steel bolting, so a joint bolted with Incoloy studs cannot be tightened to the same preload. Where Incoloy is chosen for corrosion or oxidation resistance, the joint is designed for the lower bolt stress, with more or larger bolts where needed. For high-strength bolting in hot service, nickel alloys such as Inconel 718 or alloy steel B16 are used instead, if the environment allows. Please give the design temperature and joint loads so the right material can be confirmed.

How we manufacture Incoloy fasteners

We manufacture Incoloy fasteners from certified bar. Studs and threaded rods are cut to length and threaded by rolling or cutting; rolled threads give better fatigue strength and resistance to galling. Bolts are hot forged or machined from bar, and nuts are machined from hexagonal or round bar. Incoloy work-hardens during machining, so rigid set-ups and sharp tools are used. Each fastener is marked with alloy and heat number, thread gauged and inspected, and supplied with the mill test certificate of the bar.

Galling and high-temperature installation

Incoloy threads can gall when tightened under load. Use an anti-seize compound suited to the service temperature and process – for hot service, a nickel-based or high-temperature compound – and tighten at a steady speed. In high-temperature joints, consider thermal expansion of the bolts relative to the flanges and whether re-tightening after the first heat cycle is needed. Torque values should be calculated for the alloy and lubricant, not taken from carbon steel tables.

Ordering Incoloy fasteners

Please give the alloy, fastener type, diameter and thread, length, number of nuts per stud, washers, quantity, service temperature and any testing or inspection requirement. For flange bolting, give the flange size, class and facing and we can calculate stud lengths. Incoloy 825 fasteners can be supplied to NACE MR0175 / ISO 15156 on request.

Applications and related products

Incoloy fasteners are used in furnaces and heat-treatment equipment, hydrogen reformers and ethylene crackers, flue-gas and exhaust systems, sulphuric and phosphoric acid plants, seawater-cooled equipment, pollution control and sour gas service. Matching products include Incoloy flanges, Incoloy pipe fittings, Incoloy pipes and tubes, Incoloy sheets and plates and Incoloy round bars. Fasteners in other materials are on the fasteners page.