Why Inconel 718 Bolts Are Preferred for High-Temperature Environments

What are Inconel 718 Bolts?

Inconel 718 Bolts are high strength screws and they are made of nickel-chromium superalloy. It consists largely of Nickel (50-55%), Chromium (17-21%), Niobium(4.75-5.5%), Molybdenum(2.8-3.3%) and controlled amounts of Iron, Titanium, and Aluminum. This balanced composition gives Inconel 718 its fasteners all the high mechanical strength, oxidation resistance, and thermal stability - qualities which cannot be equated to the performance of the usual stainless steel or carbon steel bolts.

Inconel 718 Bolts are available in various forms including hex bolts, stud bolts, U-bolts, eye bolts and anchor bolts including the corresponding nuts and washers. They concur with the standards such as the ASTM B637 and AMS 5597/5596. To have a wider view of the entire scope of grades and types to be introduced, check our extensive guide on Inconel Fasteners Manufacturers.

Key Reasons Inconel 718 Bolts Are Preferred for High-Temperature Applications

Inconel 718 Bolts are preferred for high-temperature applications for the following reasons:

• Outstanding High-Temperature Strength: Inconel 718 Bolts do not lose tensile strength and structural integrity at temperatures to 704degC (1300degF). The vast majority of alloy steel or stainless steel fasteners lose much strength far below this range. This is why Inconel 718 fasteners have been used in the jet engines, gas turbines, nuclear reactors, and high-temperature process plants that require bolted joints to support thermal cycling and constant load.
• Exceptional Corrosion and Oxidation Resistance: This is due to the high Chromium content of the Inconel 718 which forms a stable self-renewing oxide layer on the bolt surface that is resistant to oxidation even at a high temperature. Molybdenum also improves pitting and crevice corrosion resistance and the Nickel base offers strong protection against chloride stress-corrosion cracking. Inconel 718 fasteners have a much longer life than the rest when it comes to oil and gas wellhead, chemical reactor or offshore platform, where fasteners are regularly exposed to acids, chlorides, and sour gas. In case of considering other corrosion-resistant alloys in the lower temperature setting, our blog on Inconel 600 Fasteners covers a widely used alternative grade.
• Superior Creep and Fatigue Resistance: Creep means deformation of metal due to continuous pressure at high temperature - is also a severe form of failure in the important bolted connections. The Inconel 718 Bolts are also tailored in order to withstand creep and stress rupture to the temperature range of that particular material. Moreover, their fatigue behaviour with cyclic loading is outstanding and hence they suit rotating equipment, vibrating structures and pressure vessels which undergo varying mechanical loads.
• Precipitation Hardening for Maximum Strength: Inconel 718, in contrast to most nickel alloys, attains high strength by precipitation hardening (age hardening) - a heat treatment method in which Niobium, Titanium and Aluminum are precipitated into microscopic hardening particles in the grain structure of the alloy. When treated, tensile strength may be greater than 1, 240 Mpa (180,000 psi). This not only renders Inconel 718 Bolts stronger than most of the competing high-temperature alloys, but also makes it retain good ductility and weldability.
• Weldability Advantage: A lot of high-strength superalloys tend to crack after welding, thus making fabrication and repair difficult. Inconel 718 was one of the materials that were created to address this drawback. Its high weldability is what enables manufacturers to make more intricate fastener assemblies and fabricated parts without the fear of cracking heat-affected zones - which is of paramount importance to a project that may need a custom or non-standard bolt design.

Industries That Rely on Inconel 718 Fasteners

Considering their unusual blend of features, Inconel 718 Bolts are used in vital areas of various industries.

• Inconel 718 Bolts have widespread applications in the Aerospace & Defence industry in jet engines, rocket motors, structural airplane joints, and spacecraft hardware. High thermal cycling and mechanical loads in these conditions require fasteners that will not lose their strength and dimensional stability at temperatures that would cause other alloys to become useless.
• Inconel 718 fasteners are the most used in the Oil & Gas industry in the down-hole tooling, wellhead assembly, subsea connector, and sour gas extraction apparatus. High-pressure conditions combined with the presence of hydrogen sulphide, chlorides and non-negotiable corrosion resistance means that Inconel 718 Bolts will continue serving long where other materials are corroded or broken.
• Inconel 718 Bolts are applied in Power Generation to fasten parts of land-based gas turbines, internals of nuclear reactors, heat exchanger bolting, and steam generation systems. They are highly resistant to creep and are also resistant to oxidation which makes them best suited to high duty continuous power plants.
• Chemical Processing reactors, pressure vessels and piping systems often use aggressive acids, chlorides and high temperature process fluids. Inconel 718 fasteners are used to ensure the structural integrity and chemical resistance of these systems to maintain the systems intact and working in a harsh processing environment.
• The Inconel 718 Bolts are also used in Automotive & High-Performance Racing in high-performance engine and exhaust assemblies in which thermal stability over extreme operating cycles is paramount. They can resist repeated heating and cooling processes without losing their clamping power and that is why they are a reliable option in performance sensitive bolted joints.

How to Select the Right Inconel 718 Bolts for Your Project

The selection of the appropriate fastener is not just a matter of selecting the appropriate grade. The most important aspects that procurement engineers and project managers must consider are the following:

• Operating Environment: Learn about the maximum operating temperature, exposure to chemical, the pressure, and the cyclic or static nature of the environment.
• Load and Joint Design: Identify the clamping force that is necessary, bolt diameter, and type of thread, as well as select stud bolts, hex bolts, or any other design.
• Standards Applicable: Make sure that the fasteners are compatible with ASTM B637 or any other AMS requirement. Incidents: Unsure of the applicable standard? Our guide on ASTM A193 vs ASTM A453 Fasteners breaks down the key differences and helps you choose the right specification.
• Fastener Type: Inconel 718 Fasteners are provided in bolts, nuts, studs, washers, and screws, each of which is designed to be used in a particular joint setup. High-pressure and load bearing joints are normally done using bolts and stud bolts.
• Supplier Qualification: Do business with an approved Inconel 718 Fasteners supplier like Unifit Metalloys Inc. whose quality control mechanisms, third party tests and export compliance can be verified to suit your target market.

Source Inconel 718 Bolts from Unifit Fastener

The increased demand of Inconel 718 Bolts in high temperature conditions is not a phenomenon but a consequence of long time test performances in the most severe conditions of industry. Their special combination of high temperature strength, corrosion resistance, fatigue performance and weldability make them the most preferred fastener by engineers who cannot afford to fail. Peace of mind is a part of the package when you settle on a competent Inconel 718 Bolts manufacturer such as the Unifit Fastener as far as proven materials, documented quality and worldwide supply can assure your peace of mind.

Unifit Metalloys is trusted Inconel 718 Bolts and Inconel 718 Fasteners suppliers, based in India which serves its customers in the UAE, USA, Europe, Southeast Asia and Middle East. Mechanical and chemical conformance Our fasteners are made to rigid dimensional specification and are tested prior to shipment. We also offer complete material traceability, mill test certificate and third party inspection support where necessary.

You need a small job lot of stud bolts, or a bulk lot of stock required to supply a critical industrial project, Unifit Fastener provides the assurance of the availability of stock, competitive lead times and technical advice to make sure that you have the right fastener for the right project.

Contact us today to request a quote or technical datasheet for Inconel 718 Bolts and fasteners.