Tenaris TEMPALOY AA-1 is suitable for the construction of Ultra Super Critical boiler components such as super-heaters and re-heaters.
Advanced materials for increased steam parameters
The steam parameters in the new high efficiency fossil-fueled power plants are continuously increasing, requiring new advanced materials with enhanced creep strength able to operate in even the most severe temperature and pressure conditions.
For this purpose, we have developed TEMPALOY AA-1, a high Chromium austenitic stainless steel suitable for Ultra Super Critical boiler construction. We also supply conventional carbon-molybdenum, high-alloy and low-alloy ferritic grades for super-heaters and re-heaters.
Tubes for super-heaters and re-heaters
Steel Chemical Composition
Thanks to its alloy concept (18Cr-10Ni-3Cu-Ti-Nb-B), TEMPALOY AA-1 can be used for these applications with steam temperatures of up to 650°C (1202°F), guaranteeing extremely high creep and corrosion resistance.
The level of Chromium and Nickel gives TEMPALOY AA-1 a stable austenitic structure free from δ-ferrite, while the addition of Niobium and Titanium promotes the formation of fine MX type precipitates and the addition of Copper significantly increases the creep resistance of the steel.
TEMPALOY AA-1 has been extensively characterized regarding creep properties. Creep tests have been performed at 600, 650, 700, 750 and 800°C at different stresses with test durations lasting over 105 hours and with a database recording more than 1.5 million broken creep test hours. Not only are its creep performances outstanding, but the steel also maintains a high toughness after long exposure at service temperature.
Corrosion and Steam Oxidation Resistance
TEMPALOY AA-1 shows excellent resistance to high temperature corrosion and steam oxidation, two phenomena that are taken into account when selecting boiler materials. These results are confirmed by long-term corrosion resistance tests performed in simulated coal ash and heavy oil combustion atmospheres. Laboratory steam oxidation tests have been performed at the typical service temperatures for this steel.
Furthermore, the optional shot-blasting operation on the inner tube surface significantly increases TEMPALOY AA-1 steam oxidation resistance: the cold working caused by the shot-blasting promotes in fact a fast diffusion of Chromium towards the inside surface, increasing its concentration locally and consequently, the oxidation resistance.
Tenaris super-heaters and re-heater tubes are designed according to the most stringent quality standards (ASTM A209, ASTM A210, ASTM A213, EN10216-2, EN10216-5) and manufactured under the certified quality system (ISO 9001). Quality control procedures include statistical process controls, process and product audits as well as traceability systems covering all manufacturers involved.