Monel K500 Springs

Monel K-500 Custom Springs

Monel K-500 is quite similar to Monel 400 and is composed of about two-thirds nickel and one-third copper except that the addition of small amounts of aluminum and titanium transposes it to the precipitation-hardening group of alloys. It is often used in sizes larger than is customarily used for Monel 400, as it may be formed in the soft or nearby hard condition and then heat treated. It is nonmagnetic.

Monel K-500 Custom Springs FAQs

What is Monel K-500 and how is it different from Monel 400?

Monel K-500 is composed of about two thirds nickel and one third copper, the same as Monel 400, except that the addition of small amounts of aluminum and titanium transposes it into the precipitation hardening group of alloys. Published composition is nickel at 63.0 percent, aluminum 2.30 to 3.15 percent, and copper 27.0 to 33.0 percent. Because it can be formed in the soft or nearly hard condition and then heat treated, it is often used in sizes larger than are customary for Monel 400. It is nonmagnetic. Density is 0.305 lb/in³ and modulus of elasticity is 26x10^6 psi.

What applications use Monel K-500 springs?

Very low corrosion rates in high velocity seawater combined with high strength make alloy K-500 particularly suitable for marine service, including shafts, pump and valve internals, and spring hardware on offshore structures. The same combination puts it into downhole oil and gas tools, where springs see brine, hydrogen sulfide bearing fluids, and mechanical loads a solid solution alloy cannot carry. It also appears in seawater handling equipment and in instruments that require nonmagnetic behavior. Coefficient of expansion is 7.6 μin/in.-°F at 70°F worth checking against mating materials in a tightly toleranced assembly.

What aging cycle does Monel K-500 need after coiling?

CTI ages Monel K-500 springs at 1000°F (540°C) for 10 hours after spring coiling. In the spring temper plus aged condition, tensile strength runs 160 to 200 ksi. Spring temper as supplied, before aging, runs 145 to 190 ksi, and annealed material from a 1600°F (870°C) anneal runs 80 to 110 ksi. The aging cycle is not optional if you are buying the strength this grade is known for, and it produces a small dimensional change, so free length and diameter targets have to be set with the aged condition in mind rather than the as-coiled condition.

How much stronger is Monel K-500 than Monel 400?

Roughly three times the yield strength once aged, which is the entire reason the grade exists. Monel 400 takes its properties from cold work and tops out well short of what a precipitation hardened nickel copper alloy can carry. K-500 in the spring temper plus aged condition reaches 160 to 200 ksi tensile. That lets you keep the same seawater corrosion resistance while designing a smaller spring, a higher rate, or a longer working deflection. The cost is a temperature ceiling of 260°C (500°F) against 537°C (1000°F) for Monel 400, so hot service pushes you back toward 400.

What are the maximum service temperature and minimum wire size for Monel K-500 springs?

The Technical Specification table lists a Max Temp of 260°C (500°F) and a Min Size of 0.018 in (0.457 mm). The temperature limit reflects the aging response rather than corrosion, since holding a precipitation hardened alloy above its aging range gradually coarsens the strengthening phase and the spring loses load. If your application runs hotter than that, an Inconel grade is the better path. Modulus of rigidity is 9.5x10^6 psi, electrical resistivity is 370 μΩ.cm, and thermal conductivity is 121 Btu/(hr/ft²/in/°F). Give CTI the actual peak temperature rather than a nominal one, because that number decides the grade.

Can Monel K-500 springs be built to meet NACE MR0175 or ISO 15156?

Yes, as a customer requirement CTI can build and heat treat to meet. NACE MR0175 and ISO 15156 govern materials for sour service and place limits on the condition and hardness of nickel copper alloys used in hydrogen sulfide environments, which in practice constrains how far the aging response can be pushed. If your spring goes into sour downhole or wellhead service, name the standard and the environmental severity on your drawing so the aging cycle and any hardness verification are planned into the job. CTI holds ISO 9001:2015 certification and is not itself certified or accredited to NACE MR0175 or ISO 15156.

Must aging follow coiling, or can K-500 be coiled already aged?

Coil first, then age. The alloy is formed in the soft or nearly hard condition and heat treated afterward, which is exactly why it can be used in larger sizes than Monel 400. Coiling fully aged material fights the strength you paid for, risks cracking at tight index ratios, and leaves residual stress the aging cycle would otherwise have addressed. Because the aging step also shifts dimensions slightly, the coiling setup has to be developed alongside the heat treat cycle rather than after it. CTI performs both in the same facility, so that development loop stays short.

Why source Monel K-500 springs from Coiling Technologies?

Age hardenable grades live or die on heat treatment control. CTI performs heat treating and precipitation hardening in-house in Houston, alongside spring design, coiling, non-destructive testing, shot peen, and inspection, under one ISO 9001:2015 certified quality management system and without outsourcing. The aging cycle, the coiling setup, and the inspection data all sit with one supplier who can adjust one against the other. CTI has built springs since 1976 for Fortune 500 companies, the automotive aftermarket, the US Military, and other government agencies, including special Inconel springs for the deep sea research submersible ALVIN.