Custom Nimonic 90 Springs

Nimonic 90 Spring Manufacturer

Nimonic 90 is a precipitation hard enable Nickel-Chromium-Cobalt alloy with high strength at high temperatures and is creep and oxidation resistance up to 1688°F (920°C).

Nimonic 90 Springs FAQs

What is Nimonic 90 and why is it specified for springs?

Nimonic 90 is a precipitation hardenable nickel-chromium-cobalt alloy. The nominal composition on CTI's specification table is chromium 18.0 to 21.0 percent, cobalt 15.0 to 21.0 percent, iron 3.00 percent, with nickel as the balance. Density is 0.296 lb./in3 and modulus of elasticity is 32.0x10^6 psi. Engineers specify it when a spring has to hold load at temperatures where stainless steel and carbon steel have already relaxed. The cobalt content strengthens the nickel matrix and improves hot strength, while chromium forms the oxide layer that resists high temperature oxidation and combustion gas attack.

What applications use Nimonic 90 springs?

Nimonic 90 has a long service history in gas turbine hot sections and in exhaust valve and valve train components, which is where the alloy earned its reputation. Typical spring work includes turbine and engine hot section hardware, exhaust and waste gate actuation, industrial furnace and heat treating fixtures, combustion and burner assemblies, turbocharger components, and instrumentation exposed to hot process gas. Coiling Technologies also builds Nimonic 90 springs for oil and gas and petrochemical service where a valve or actuator spring sits close to a heat source and cannot be allowed to lose load over a maintenance interval.

What is the maximum service temperature for a Nimonic 90 spring?

CTI's technical specification table lists a Max Temp of 704°C (1300°F) for Nimonic 90 spring service. Treat that as a load bearing limit rather than a survival limit. Bare oxidation resistance extends higher than the temperature at which the alloy can still carry a design stress without measurable relaxation, because a spring fails functionally as soon as creep takes free length or load out of tolerance, long before the material itself degrades. If your duty cycle sits near the top of that range, supply the actual metal temperature and dwell time so the design can be stressed conservatively.

What is the minimum wire size for Nimonic 90 springs?

The specification table lists a Min Size of 0.005 in (0.130 mm) for Nimonic 90. That figure covers fine wire instrument and sensor springs where a high temperature alloy is required at very small section. Practical minimums on a given part depend on more than wire size alone, since coil diameter, index, free length, and the number of active coils all affect whether fine wire can be coiled and heat treated to the required load without distortion. Send the load and deflection requirement along with the envelope and CTI's engineering team can confirm what section the geometry supports.

How does precipitation hardening actually strengthen Nimonic 90?

Nimonic 90 gets its high temperature strength from titanium and aluminum additions that precipitate a fine, coherent gamma prime phase inside the nickel matrix during aging. Those particles obstruct dislocation movement, and because gamma prime remains stable at service temperature, the strengthening does not disappear the way cold work does when a work hardened spring is heated. The alloy is solution treated, coiled, then aged to develop the precipitate. Aging temperature and time set the final balance of strength, ductility, and creep resistance, so the aging condition belongs on your drawing as a callout rather than being left to the supplier.

How does Nimonic 90 compare to Inconel X-750 for high temperature springs?

Both are precipitation hardened nickel-base alloys strengthened by titanium and aluminum, and both are common in hot spring work. The difference is cobalt. Nimonic 90 carries 15.0 to 21.0 percent cobalt per CTI's table, and that cobalt raises hot strength and creep rupture life at the upper end of the range, which is why the alloy is associated with turbine and exhaust valve service. Inconel X-750 has broader availability, a longer general purpose track record, and usually costs less. Choose X-750 when temperature and dwell are moderate, and Nimonic 90 when sustained load at temperature is the governing requirement.

Why does creep rupture strength matter more than tensile strength for a hot spring?

A spring is a stored energy device, so its function depends on holding a specific load at a specific deflection over time. At high temperature the governing failure mode is not fracture, it is creep relaxation, where the material slowly deforms under sustained stress and the spring loses load and free length while remaining fully intact. A room temperature tensile number tells you nothing about that behavior. Creep rupture and stress relaxation data at the actual service temperature and hold time are the properties that predict whether a Nimonic 90 spring still meets its load rating after thousands of hours.

Does Coiling Technologies perform the solution treatment and aging in house?

Yes. Heat treating is one of CTI's in-house services, performed in Houston under the same ISO 9001:2015 quality management system that covers design, coiling, finishing, and inspection. For a precipitation hardened alloy that matters more than it does for a plain carbon spring, because the aging cycle is what creates the mechanical properties, rather than only a stress relief after forming. Keeping solution treatment and aging under one roof removes the handoff to an outside heat treater, keeps the thermal history documented against the same part record, and lets the coiling and aging parameters be adjusted together when a load target needs correction.