What is the difference between Alloy 625 and Alloy 718 (to the API 6A CRA specification). Both alloys are corrosion resistant, however they have extremely different properties, making each one better suited for particular applications. Here is our quick guide to the differences between them:
Composition Of The Alloys
Both 625 and 718 are nickel alloys, but their composition varies. Alloy 718 contains molybdenum, niobium and tantalum, aluminium and titanium. These are combined to create a strong, hardenable metal with a particularly high yield. By contrast, Alloy 625 combines nickel, chromium and molybdenum. Here, the emphasis is more on resistance to oxidation. This allows Alloy 625 to withstand environments that other alloys cannot. Both alloys are strong: Alloy 625 has a tensile strength of at least 120 KSI, while Alloy 718 offers minimum 150 KSI.
Applications And Environments
As the two alloys are corrosion resistant materials, both can be used in oil, gas, marine and aerospace applications. That being said, Alloy 625 has a greater resistance to oxidation, which is commonly caused by sea water and harsh chemicals. This makes it more suitable for applications in environments where these are a factor – such as offshore, marine, and coastal applications. Alloy 625 is commonly used for jet engine parts, pressure valves, flare stacks, heat exchangers and turbine shroud rings.
Alloy 718 is better suited to the oil industry. Our supplies of Alloy 718 are treated for strength, weldability, and the ability to withstand stress corrosion cracking. This alloy can withstand creep rupture at temperatures up to 700°C, and generally meets the standards required for successful use within the oil industry. Within the oil, gas and aerospace industries, Alloy 718 is used for gate valves, oil tools, choke stems, fasteners, turbines and engine parts.
Shapes And Sizes
Most of our Alloy 625 stock is sold in round bar form, but rings and bored bars are also available. Stock sizes start at 6mm diameter and our range goes up to 101.6mm, with 25 different size gradients between the largest and smallest, with larger sizes available on request. Alloy 718 is also available in round bar, but we offer other forms, too, including rings, blocks, discs, pre-machined bars, and black forgings. Round bar stock sizes start at 12.7mm, with sizes up to 177.8mm diameter.
Generally, we keep a large amount of both Alloy 625 and Alloy 718 in stock. . There are exceptions if you are looking for unusual or non-standard sizes; but most orders will be quickly and easily fulfilled, without an extensive waiting period. Please get in touch with one of our technical sales team if you would like to learn more about either of these alloys, to discuss your particular needs and how best to fulfil them, or to make an order.