Analysis of Boiler Tube Failure at Outlet Header of Low Temperature Superheater

Abstract

This study investigates the failure of a 12Cr1MoVG boiler tube in the Low Temperature Superheater (LTSH) header outlet of a Steam Power Plant (PLTU) in East Java. The tube, which had been in service for approximately 88,000 hours, developed a leak in the confined dead zone area. Initial visual inspection revealed significant bulging and deformation at the failure site, accompanied by a measurable decrease in material hardness to below 130 Vickers (HV), indicating substantial microstructural degradation. A comprehensive Root Cause Failure Analysis (RCFA) methodology was employed to diagnose the failure mechanism. This involved detailed metallographic examination, hardness profiling, and dimensional analysis. The investigation identified two critical contributing factors: the formation of an excessively thick (220 microns) steam-side oxide scale on the tube's inner diameter, and the presence of a compromised baffle plate within the dead zone enclosure. The synergistic effect of these factors was determined to be the root cause. The internal scale acted as a thermal insulator, elevating the tube metal temperature, while the baffle plate leak allowed the ingress of higher-temperature flue gases, creating a localized over-temperature environment. This combination led to long-term overheating, resulting in creep-induced bulging, accelerated microstructural softening, and eventual rupture. To prevent recurrence, corrective and preventative actions are recommended, including the immediate repair of the dead zone baffle plate to restore proper insulation, stringent control of boiler feedwater chemistry to minimize scale formation, a feasibility study for upgrading to a superior material grade with higher creep strength, and the establishment of a periodic non-destructive testing regimen focusing on hardness measurements and visual inspections in high-risk areas.