# Fermentation Heating Tube Anti-Corrosion Low-Flow & Static Standby Protection Specification ## Preface This specification is a supporting document of the complete anti-corrosion document system from Doc.33 to Doc.115. It standardizes protective operation procedures, parameter control standards, regular maintenance and risk early warning rules for heating tube loops under low-flow operation, intermittent production shutdown, long-term static standby and idle line standby conditions. It solves prominent corrosion problems such as medium stagnation, biofilm accumulation, ion concentration enrichment and localized pitting caused by insufficient fluid scouring, and fills the anti-corrosion management gap in non-continuous production states. Three operating states with differentiated protection schemes are clearly classified. The first category is low-flow continuous operation, referring to circulation flow far below the standard design rate during low-load fermentation. Slow flow leads to long medium residence time inside the tube, and corrosive substances easily deposit on the inner wall. The second category is short-term static standby, including daily shift shutdown, batch interval pause with standby time less than 24 hours. The third category is long-term idle standby, such as production line halt for maintenance, seasonal shutdown and new equipment idle storage exceeding 72 hours, which faces the highest risk of severe local corrosion. Unified protection operation standards for low-flow working conditions are formulated. When the flow rate drops below the safe threshold, the patrol frequency of heating tube inlet and outlet monitoring points is doubled, and online chloride and pH data are recorded every 30 minutes. Regular forced high-flow flushing is added every 4 hours to wash away sediment and attached microorganisms on the tube wall. The pickling cycle is shortened by half compared with normal full-flow operation, and mild neutral circulation cleaning is supplemented between pickling cycles to reduce biofilm accumulation. Complete graded static standby protection workflows are implemented. 1. Short-term standby (≤24h): After stopping circulation, drain excess redundant medium, inject sterile pure water to fill the entire heating tube loop, maintain slight micro-circulation at fixed intervals, and record standby start time to strictly control the stagnation duration not to exceed the upper limit specified in the red-line operation standard. 2. Long-term idle standby (>72h): Fully drain all culture medium and flushing liquid inside the pipeline, conduct full pickling passivation treatment, then dry the inner wall with sterile hot air, and fill the closed loop with inert protective gas for sealing isolation. All inlet and outlet valves are closed and locked with blind plates installed to prevent air, moisture and external pollutants from entering the tube. Weekly appearance inspection of pipeline outer walls and regular internal re-drying treatment are required during idle storage. Special risk identification and early warning mechanisms are established. Key warning signals include abnormal pH drift during standby, continuous upward trend of chloride concentration, fogging and spot etching on tube inner walls after liquid drainage, and sticky biofilm residue found during routine opening inspection. Once early warning signals appear, forced full-loop flushing and enhanced cleaning shall be carried out immediately, and the standby duration limit of the production line shall be temporarily reduced to avoid concentrated ion corrosion. All low-flow operation parameter logs, static standby start/end registration forms, forced flushing execution records, idle pipeline maintenance checklists and standby abnormal disposal files adopt dual electronic and paper archiving. Monthly data trend analysis counts the corrosion failure frequency of equipment under static and low-flow states; if repeated stagnation corrosion occurs in certain workshops, the production batch interval planning and standby protection operation clauses will be revised in the quarterly system review. This specification covers all non-normal continuous production operating conditions of heating tubes, eliminates corrosion blind spots caused by flow reduction and long-term shutdown stagnation, and perfects the full-condition closed-loop anti-corrosion protection system of fermentation heating tubes.
