The power industry has seen a significant increase in failure rates in tubular air heaters where boiler operators have installed retrofit systems (such as the SCR’s) that inject nitrogen based additives into their gas streams. These create a high potential for damage caused by ammonia slip and for ammonium bisulfate (ABS) corrosion to occur in air heaters.
Because of its relatively high acid dew point, ABS corrosion may occur in hot side bundles that had previously experienced little to no corrosion damage. In tubular air heaters, ABS corrosion rapidly attacks the HAZ or seam weld of the tube. This results in intergranular corrosion which can liquefy the grain boundary at this section of the tube.
Both carbon steel and corten air heater tubing have been shown to be highly vulnerable to localized ABS corrosion in tubular air heaters. ABS corrosion typically manifests in localized failure patterns that cause intergranular corrosion failures to develop along the seam of the tubing. In many cases, this localized area will liquefy in carbon steel and even corten tubing resulting in catastrophic failures.
CR50 is an American made low carbon alloy that was designed for CMS to improve the performance and service life of tubular air heaters. This proprietary steel was created specifically to reduce the risk for localized failures caused by ABS corrosion.
The steel receives a proprietary post-weld treatment to stabilize its microstructure and reduce the potential for intergranular corrosion caused by ABS to develop. This steel also develops a highly potent oxide coating for protection from general corrosion rates.