# Fermentation Heating Tube Anti-Corrosion Long-Term Service Life Assessment & Scrapping Judgment Specification ## Preface This specification forms the final supporting document of the complete anti-corrosion document system ranging from Doc.33 to Doc.109. It unifies periodic inspection standards, multi-dimensional service life evaluation indicators, quantitative scrapping judgment thresholds, replacement approval workflows and post-scrapping recycling disposal rules for four types of heating tubes. It eliminates subjective arbitrary use of severely corroded equipment and avoids safety hazards and production losses caused by overdue service of heating tubes, forming a full-lifecycle closed loop covering incoming acceptance, operation monitoring, regular testing and final scrapping. The assessment cycle is defined according to equipment material characteristics. Stainless steel heating tubes shall conduct comprehensive corrosion assessment every 12 months; titanium heating tubes and PFA coated heating tubes receive full inspection every 18 months; quartz heating tubes, prone to hidden crack damage, require quarterly appearance inspection and half-year wall thickness detection. All assessment activities are incorporated into monthly maintenance work plans, and testing records are synchronously uploaded to equipment full-lifecycle archives. Five core quantitative indicators are adopted for comprehensive service life evaluation. First, residual wall thickness: compare the measured value with the original factory standard thickness, and mark tubes with wall thickness loss exceeding the safe threshold as high-risk items. Second, surface corrosion degree: record pitting density, etching depth and welding seam corrosion range via visual inspection and microscopic scanning. Third, sealing matching performance: check flange contact surface corrosion and aging of matched gaskets to judge leakage risk. Fourth, internal medium contamination risk: detect residual ion precipitation and biofilm adhesion after pickling and passivation. Fifth, historical abnormal frequency: count accumulated leakage, over-limit corrosion alarms and emergency maintenance records of the heating tube during operation. Hierarchical judgment standards divide heating tubes into three operation grades. Grade A (normal service): all indicators meet safety standards, allowed to continue operation until next assessment cycle. Grade B (limited monitoring): partial indicators slightly exceed normal range without penetration risk; the patrol frequency is doubled, and targeted enhanced pickling treatment is implemented, with reassessment arranged within three months. Grade C (mandatory scrapping): severe wall thickness thinning, penetrating pitting, coating peeling, hidden cracks or repeated leakage faults; such heating tubes must be isolated and shut down immediately, and replacement application shall be submitted within one working day. A standardized multi-level approval process is implemented for scrapping replacement. Maintenance technicians submit assessment test reports and scrapping application forms, workshop equipment supervisors verify on-site conditions, the factory equipment department reviews and approves replacement plans, and the warehouse completes new spare parts outbound procedures after approval. Disassembled scrapped heating tubes are classified for centralized disposal: metal tubes are sent for professional metal recycling, damaged quartz and failed PFA components are treated as industrial waste following environmental protection requirements, and all disposal photos and records are archived. All periodic assessment test reports, grading evaluation forms, scrapping approval documents and post-disposal recycling records are stored in dual electronic and paper archives for the whole service cycle of equipment. Long-term statistical data of heating tube service life are used as core basis for spare parts stocking adjustment, hardware transformation optimization and system quarterly review. This specification standardizes the end-of-life management of heating tube equipment, completes the full-cycle anti-corrosion control chain from commissioning to scrapping, and improves the integrity of the factory's whole-set anti-corrosion management system.
