Inconel Fasteners
Giriraj Impex is a manufacturer, stockist, supplier and exporter of Inconel fasteners in alloys 600, 625 and 718. We manufacture Inconel stud bolts, hex bolts, heavy hex nuts, washers, screws and threaded rods from ASTM B166 (alloy 600), ASTM B446 (alloy 625) and ASTM B637 (alloy 718) bar, in imperial and metric sizes, with mill test certificates.
Inconel fasteners are used where bolting must keep its strength at high temperatures or resist corrosive media – in furnaces and heat-treatment equipment, gas turbines, exhaust and flare systems, chemical plants, and offshore and subsea installations exposed to seawater and sour fluids.
Specifications
| Item | Details |
|---|---|
| Material | Inconel 600 (N06600) – ASTM B166; Inconel 625 (N06625) – ASTM B446; Inconel 718 (N07718) – ASTM B637 |
| Products | Stud bolts, threaded rods, hex bolts, heavy hex bolts, heavy hex nuts, hex nuts, washers, screws |
| Dimensions | ASME B18.2.1, B18.2.2, B16.5 stud lengths; ISO and DIN for metric fasteners |
| Threads | UNC, UNF and 8UN (imperial); ISO metric coarse and fine |
| Condition | 600 and 625 annealed; 718 solution treated and precipitation hardened |
| Finish | Plain, bright; anti-galling lubricant or coating on request |
| Documents | Mill test certificate (MTC); third-party inspection on request |
Chemical composition – Inconel 600 and 625
| Alloy | Ni | Cr | Fe | Mo | Nb + Ta | C | Mn | Si | S | Other elements |
|---|---|---|---|---|---|---|---|---|---|---|
| 600 (N06600) | 72.0 min | 14.0–17.0 | 6.0–10.0 | – | – | 0.15 | 1.00 | 0.50 | 0.015 | Cu 0.50 |
| 625 (N06625) | 58.0 min | 20.0–23.0 | 5.0 | 8.0–10.0 | 3.15–4.15 | 0.10 | 0.50 | 0.50 | 0.015 | P 0.015, Al 0.40, Ti 0.40, Co 1.0 |
Nickel includes cobalt where stated in the standard. Footnotes as given in each ASTM specification.
Inconel 718 is a precipitation-hardening nickel-chromium-iron alloy containing niobium, molybdenum, titanium and aluminium; its composition and properties are given in ASTM B637. Background on all the alloys is on the Inconel page.
Choosing the alloy
Inconel 600 fasteners are used for furnace fixtures, heat-treatment baskets and muffles, and chemical equipment where resistance to oxidation, carburisation and chloride stress corrosion cracking matters more than high strength. Inconel 625, with molybdenum and niobium, combines higher strength with outstanding resistance to pitting, crevice corrosion and seawater, and is used for offshore, subsea, marine and chemical bolting. Inconel 718 is precipitation hardened to a tensile strength far higher than 600 or 625, and keeps that strength up to about 650 °C. It is used for high-strength bolting in gas turbines, aero engines, high-temperature valves and pressure equipment, and in oil and gas wellhead and subsea connectors.
High-temperature bolting
At high temperatures, alloy and stainless steel bolts relax and lose preload, oxidise, and can creep. Nickel alloy bolting keeps its strength and resists oxidation at much higher temperatures. For flanged joints in hot service, the bolt material should also have a coefficient of thermal expansion compatible with the flange, so that the joint does not lose load as it heats up. Inconel 718 is widely used for such joints because of its high strength and resistance to relaxation, and A453 Grade 660 is an iron-based alternative for moderate temperatures.
Sour and seawater service
In offshore and subsea service, bolting can be exposed to seawater, cathodic protection and sour fluids. Inconel 625 and 718 resist pitting and stress corrosion cracking in these conditions. For sour service, the hardness and heat-treatment limits of NACE MR0175 / ISO 15156 apply to the alloy and condition, and fasteners can be supplied to the standard on request. Please state the service conditions with the enquiry.
How we manufacture Inconel fasteners
We manufacture Inconel fasteners from certified bar. Studs are cut to length and threaded by rolling or cutting; rolled threads are preferred for fatigue strength. Bolts are hot forged or machined, and nuts are machined from bar. Inconel 718 fasteners are machined in the solution-treated condition and then aged, or machined after ageing where the order requires it. Nickel alloys work-harden quickly, so rigid set-ups and sharp tools are used. Each fastener is marked with grade and heat number, thread gauged and inspected, and supplied with the mill test certificate.
Galling and installation
Inconel threads can gall under load. Use an anti-seize compound suitable for the service temperature and process, tighten at a steady speed, and calculate torque from the actual lubricant and material rather than carbon steel tables. For high-temperature joints, check the lubricant's temperature limit and whether it may react with the process.
Applications and related products
Inconel fasteners are used in furnaces and heat-treatment equipment, gas turbines, exhaust and flare systems, chemical and petrochemical plants, offshore and subsea equipment, marine engineering and pollution control. Matching products include Inconel flanges, Inconel pipe fittings, Inconel pipes and tubes, Inconel sheets and plates, Inconel round bars and Inconel wires. Fasteners in other materials are on the fasteners page.
Frequently Asked Questions
Inconel 718 is used for high-strength bolting because it is precipitation hardened to a much higher strength than alloys 600 and 625, and keeps that strength up to about 650 °C.
Inconel 625 bar is covered by ASTM B446. Alloy 600 bar is covered by ASTM B166 and alloy 718 by ASTM B637.
Inconel 625 resists pitting, crevice corrosion and stress corrosion cracking in seawater and many sour environments, so it is widely used for offshore and subsea bolting.
Yes. Inconel fasteners can be supplied to NACE MR0175 / ISO 15156 on request, with the hardness and condition limits the standard sets for each alloy.
They can. Using a suitable anti-seize compound, rolled threads and steady tightening reduces the risk of galling.
Yes. Inconel fasteners are supplied in imperial and ISO metric sizes to ASME, ISO and DIN dimensions.
Request a Quote for Inconel Fasteners
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Inconel® is a trademark of Special Metals Corporation.