Sanicro® 31HT is an austenitic, nickel-iron-chromium stainless steel combining good resistance to high-temperature corrosion with high mechanical strength. Developed for severe, high-temperature environments, Sanicro® 31HT can be used at temperatures up to 1100°C (2010°F) in oxidizing atmospheres.
The grade performs exceptionally well in different combustion and synthesis gases and also has good resistance to carburization and isothermal and cyclic oxidation. Typical applications for Sanicro® 31HT include muffle tubes for wire annealing furnaces, furnace tubes and heat exchangers.
One of the most distinguishing characteristics of Sanicro® 31HT is its excellent resistance to nitrogen absorption at high temperatures. This is due to the relatively high chromium and nickel contents and makes this grade a recommended material for use in cracked ammonia (NH3) and hydrogen (H2). The nickel content also contributes to very good structural stability, including very good ductility and high creep strength.
A Belgian steel wire manufacturer experienced problems with nitridation attack and oxidation with their existing muffle tubes made from a high-temperature steel grade of type 21Cr11Ni. They wanted to prolong the service life of the muffle tubes to reduce costs for downtime, re-tubing and loss of production. Using cracked ammonia and hydrogen as the protective gas and a relatively high operating temperature, 1100°C (2010°F), there was a need for an alloy with improved high-temperature corrosion properties.
After discussions with Alleima engineers, the company decided to upgrade to muffle tubes in Sanicro® 31HT. The decision was based mainly on the excellent nitridation resistance of Sanicro® 31HT, but also on our documented references for similar applications and environments. Tubes in Sanicro® 31HT were installed in two furnaces and as a result, the overall service life of the muffle tubes has been increased by over 50 percent.