FAILURE ANALYSIS OF A REPORTED GRADE 304 STAINLESS STEEL COCONUT FLOWER VINEGAR BOILER USING A DIRECT FLAME HEATING SYSTEM: AN SME CASE STUDY

Abstract

          This study investigates premature pitting failure at the bottom of a coconut flower vinegar boiling/pasteurization tank used in an SME food processing facility. The tank was heated by a direct flame system using LPG and developed leakage after approximately four months of operation. Failure analysis was conducted through visual inspection, pit distribution evaluation according to ASTM G46, morphological examination, and SEM-EDS analysis. The results revealed a dense distribution of pitting corrosion at the tank bottom, particularly in the area associated with direct flame exposure. Large pits greater than 3.0 mm were observed, indicating severe localized corrosion. SEM-EDS results showed that the measured nickel (Ni) content in the analyzed area was approximately 6.49–6.84 wt.%, which is lower than the compositional range specified for Type 304 stainless steel in ASTM A240/A240M. Overall, the available evidence supports the hypothesis that the failure resulted from a synergistic mechanism involving direct flame heating, residual fluid hold-up due to the absence of a bottom drain, localized concentration of acidic solution, and possible lower-than-expected corrosion resistance of the material. After the failure analysis and engineering improvement, the factory replaced the material with Type 316L stainless steel while continuing to use the direct flame heating system due to practical constraints in the SME production environment. Field follow-up for approximately one year showed no recurrence of leakage or similar damage. The findings suggest that material upgrading, improved bottom drainage, reduction of residual hold-up, and material verification before fabrication or service are practical corrective measures for reducing the risk of repeated pitting failure. The proposed root cause is based on available evidence and field follow-up information and still requires further experimental validation.