Failure Analysis of ASTM A178 Grade A Boiler Tubes in a Sugarcane Bagasse-Fired Boiler: Combined Effects of External Erosion–Corrosion and Steam Jet Impingement

This work presents the failure analysis of carbon steel boiler tubes manufactured from ASTM A178 Grade A, installed in the tubular bundle connecting the upper and lower drums of a 42 kgf/cm 2 , 100 t/h steam boiler operating at approximately 420 °C. During a hydrostatic test at room temperature, conducted at 1.5 times the working pressure, two tubes ruptured at 53 kgf/cm 2 , with no evidence of internal scaling or generalized wall thinning. The investigation comprised macrographic examination, stereomicroscopy, optical metallography, and chemical analysis by optical emission spectroscopy. The chemical composition was found to be in full agreement with the requirements of ASTM A178 Grade A. The microstructure of both tubes consisted of a typical low-carbon steel, with equiaxed ferrite grains and small fractions of pearlite, and intense decarburization at the inner surface associated with the tube manufacturing process. Macro- and stereoscopic examinations revealed severe localized wall loss on the external surface, corrosion pits and generalized corrosion, and clear erosive flow marks in one of the tubes, consistent with high-velocity steam jet impingement. The first tube failed due to localized loss of wall thickness from external abrasive/corrosive action by solid particles. The second tube exhibited a combination of external solid particle erosion and wear from high-temperature steam jet impingement, resulting in extensive wall thinning and subsequent rupture under internal pressure. No evidence of metallurgical defects or manufacturing-related anomalies was observed. The root cause of failure is therefore associated with service conditions, especially external erosion–corrosion by solid particles and steam flow, rather than material nonconformity or deficiencies in water treatment.