Custom Alloy 20 Springs

Alloy 20 Spring Manufacturer

Alloy 20 is one of the so-called "super" stainless steels that was designed for maximum resistance to acid attack. It's nickel, chromium, molybdenum and copper content contribute to its overall resistance to chloride-ion stress corrosion cracking and general pitting attack.

Alloy 20 Springs FAQs

What is Alloy 20 and what problem was it designed to solve?

Alloy 20 is one of the super stainless steels, developed for maximum resistance to acid attack. Its nickel, chromium, molybdenum, and copper content together resist chloride ion stress corrosion cracking and general pitting attack. The nominal composition on the Coiling Technologies table is chromium 19.0 to 21.0, nickel 32.0 to 38.0, molybdenum 2.0 to 3.0, and copper 3.0 to 4.0. That nickel level runs far above a conventional austenitic stainless and puts the alloy closer to the nickel alloy family in behavior, which is where much of its resistance to stress corrosion cracking originates.

Why would a buyer choose Alloy 20 over 316 stainless?

Copper. Alloy 20 carries 3.0 to 4.0 percent copper, which 316 does not have, and copper is what gives the alloy superior resistance to stress corrosion cracking in boiling 20 to 40 percent sulfuric acid. 316 is attacked in that service. The nickel content, 32.0 to 38.0 percent against roughly 10 to 14 percent in 316, adds resistance to chloride ion stress corrosion cracking, the failure mode that takes out austenitic springs in hot chloride environments. For dilute acid, mild chlorides, or general process water, 316 is adequate and cheaper. Hot sulfuric acid is where Alloy 20 earns its premium.

How does the stabilized composition resist sensitization?

Alloy 20 in the UNS N08020 chemistry carries a small niobium addition, a few tenths of a percent, which is why it is often written as 20Cb-3. Niobium has a stronger affinity for carbon than chromium does, so it ties up carbon as niobium carbide instead of letting chromium carbide precipitate along grain boundaries during welding or extended time in the sensitizing temperature range. Those boundaries would otherwise become chromium depleted and corrode preferentially. Niobium is not listed on this page's specification table, so confirm the heat chemistry against your own specification if a stabilized grade is a hard requirement.

What are the temperature and wire size limits for Alloy 20 springs?

Max Temp on the specification table is 537°C (1000°F) and Min Size is 0.018 in (0.47 mm). The temperature figure is high for a stainless family alloy and reflects the nickel content. Note the wire size floor, which is coarser than the 0.005 in (0.130 mm) available in Nitronic or in the titanium grades. If a design needs very fine wire and acid resistance at the same time, the material choice narrows, and that is worth reviewing with the engineering team before the drawing is released. Across the sizes it does cover, the alloy coils conventionally.

What design values apply when I substitute Alloy 20 into an existing stainless design?

The table gives a modulus of elasticity of 26x10^6 psi, a modulus of rigidity of 10675 ksi, and a density of 0.27 lb./in3. Spring rate follows the shear modulus, and at roughly 10.7x10^3 ksi the alloy sits within a percent or two of standard spring stainless, so an existing stainless geometry usually carries over without recalculating the rate. Allowable stress is what changes, since Alloy 20 does not reach the tensile strength of cold drawn 302. Plan on a lower design stress or heavier wire to hold the same load safely.

Which industries and spring configurations use Alloy 20?

Chemical processing is the core market, specifically pickling lines, sulfuric acid plants, heat exchangers, mixing and storage tanks, and the valve and pump internals that see acid service. Coiling Technologies builds for valves and for oil and gas and petrochemical work, all of which include acid handling equipment. On configuration, the shop coils compression, extension, and torsion springs along with disc, wave, and canted coil designs, and which of those is practical in Alloy 20 depends on the wire size and load involved. Send geometry and service conditions together so material and design get checked against each other.

Which standards might my purchase order call out for Alloy 20 springs?

Buyers commonly reference ASTM B473, the specification covering UNS N08020 bar and wire, and sour service applications may add NACE MR0175 and ISO 15156. Coiling Technologies can build and heat treat to a customer specified standard, and the company holds ISO 9001:2015 certification for its quality management system. That is the certification CTI carries. If your purchase order names a material or process standard, put it on the drawing and in the RFQ so the requirement flows into the material purchase and the inspection plan from the start rather than getting reconciled after the springs are coiled.

What information should I provide for an accurate Alloy 20 quote?

Send the load and deflection requirement or the target spring rate, the working envelope including any bore or rod the spring has to clear, free length and solid height limits, expected cycle life, and the service conditions, which for Alloy 20 means the acid, its concentration, and the operating temperature. Wire size and coil count help if you have them but are not required, since the engineering team can develop a design from performance requirements alone. A print, a specification sheet, or a physical sample all work as a start. Concentration and temperature matter as much as load, because they decide whether Alloy 20 is the right pick.