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

J Fail. Anal. and Preven. https://doi.org/10.1007/s11668-026-02473-y CASE HISTORY—PEER-REVIEWED 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 Cassius O. F. Terra Ruchert . Márcio Corrêa Carvalho Submitted: 2 May 2026 / in revised form: 20 May 2026 / Accepted: 22 May 2026  The Author(s) 2026 Abstract 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/cm2, 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/ cm2, 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 lowcarbon 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. C. O. F. T. Ruchert (&) Department of Materials Engineering, University of São Paulo, Lorena, São Paulo, Brazil e-mail: M. C. Carvalho Federal University of Southern and Southeastern Pará, Marabá, Pará, Brazil No evidence of metallurgical defects or manufacturingrelated 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. Keywords Boiler tubes
ASTM A178 Grade A
Failure analysis
Erosion–corrosion
Steam jet impingement
Decarburization Introduction Boiler tubes in power generation and cogeneration units operate under complex combinations of mechanical loading, thermal gradients, and chemically aggressive environments that may lead to premature failures and unscheduled shutdowns if not properly controlled [1–3]. This issue is particularly critical in boilers fired with solid fuels such as sugarcane bagasse, where combustion gases frequently contain significant amounts of entrained solid particles, promoting synergistic mechanisms of erosion and corrosion on external tube surfaces [4–6]. In addition to external damage, internal degradation mechanisms associated with inadequate water chemistry—such as scaling, under-deposit corrosion, and localized overheating—may further compromise the structural integrity of boiler components [2, 3]. Consequently, systematic failure analysis of boiler tubes is a key tool for improving reliability, optimizing maintenance strategies, and ensuring safe long-term operation [1–3]. Low-carbon steels manufactured in accordance with ASTM A178 Grade A are widely employed for water and 123 J Fail. Anal. and Preven. steam tubes in boilers operating at moderate pressures and temperatures due to their good formability, weldability, and adequate mechanical properties [7, 8]. The performance of these steels in service is strongly influenced by their chemical composition, microstructure, wall thickness, and the presence of surface layers such as decarburized zones formed during tube manufacturing [8, 9]. Although internal decarburization and grain coarsening near the bore can modify local mechanical properties to some extent, service failures in boiler tubes are more frequently associated with external or internal wall thinning processes, thermal overstress, or fabrication defects than with intrinsic shortcomings of the steel grade itself [1, 3, 8]. Among the external degradation mechanisms observed in biomass-fired and other solid-fuel boilers, solid particle erosion, erosion–corrosion, and fluid jet impingement are frequently reported as critical damage processes [4–6, 10]. Solid particles entrained in the combustion gases can impact tube surfaces at high velocities and oblique angles, causing material removal by micro-cutting, plowing, and near-surface fatigue, especially at bends or regions with complex flow patterns [4, 10]. When erosive attack occurs in the presence of corrosive species (e.g., alkali salts, chlorides, and SOx), the combined action of mechanical and electrochemical processes may result in accelerated wall loss, commonly referred to as erosion–corrosion [5, 6, 11]. In addition, localized jets of high-velocity steam or gas can cause severe impingement erosion on tube surfaces, resulting in characteristic flow lines and highly localized thinning [11, 12]. If the local wall thickness is reduced below the minimum required to withstand the internal pressure, catastrophic rupture may occur during normal operation or even under hydrostatic testing conditions [1–3]. On the internal side, scaling, deposition, and corrosion associated with inadequate boiler water treatment remain important causes of tube failures [2, 3]. Deposits of salts and corrosion products can increase the thermal resistance at the metal–water interface, leading to local overheating, loss of strength, and creep damage, particularly at higher operating temperatures [2, 3]. Microstructural indicators of such overheating include spheroidization of pearlite, grain coarsening beyond the manufacturing condition, and, in extreme cases, partial melting or ‘‘burning’’ of the steel [8, 9]. When careful metallographic examination does not reveal these features, and no internal deposits are found, overheating due to water-side problems becomes less likely as a primary failure mechanism, shifting the focus toward gas side degradation processes such as erosion, erosion– corrosion, and steam jet impingement [1, 3–6]. The literature on failures in tube bundles shows that damage often concentrates in regions with unfavorable flow patterns, such as banks near headers, turning zones in 123 the gas stream, and the last rows of tubes, where particle trajectories may deviate from simple intuition [4, 10, 13, 14]. In these regions, the combination of solid particle impingement, gas side corrosion, and, in some cases, steam leakage through small defects can produce highly localized wall loss (...truncated)