Failure Analysis of a Waste Heat Boiler of a Sulfur-Burning Sulfuric Acid Plant

Abstract The waste heat boiler in a sulfur-burning sulfuric acid plant experienced failures, specifically furnace tube bursting and tube sheet leakage. Samples were extracted from the front tube sheet and the tubes that had failed, located where the waste heat boiler had developed leaks. The compositions, microstructures, mechanical properties, and crack morphology of the tube sheet and the tubes were analyzed. There were many small cracks in the tube-sheet joints, and Na was detected in the cracks. Na was also found in the expanded connection area between the tubes and the tube sheet. The inner wall of the tubes near the tube burst area was severely corroded. The amount of S on the inner walls of the tubes near the tube burst area was significantly higher than that on the outer walls of the tubes. Through relevant analyses, the following conclusions were obtained: the alkali stress corrosion cracks widely appeared in the tube-sheet joint. The sulfuric acid formed by the mixture of leaked water and high-temperature flue gas flowed into the tubes, and relevant tubes were seriously corroded and eventually burst.