# Fermentation Heating Tube Anti-Corrosion High Chloride Medium Production Anti-Corrosion Special Control Specification ## Preface This specification (Doc.161) is a special technical control document supplementary to the overall anti-corrosion management system from Doc.15 to Doc.160. It targets fermentation processes with high chloride ion content in raw materials, culture media and auxiliary feed liquids. Chloride ions have strong penetrability to metal passive films, which can easily trigger local pitting corrosion, crevice corrosion and stress corrosion cracking of stainless steel heating pipelines, leading to hidden leakage risks that are difficult to detect in conventional daily inspections. This specification formulates full-chain special prevention, real-time monitoring, process limitation and targeted protective measures for high-chloride working conditions, blocking the rapid destruction of passive films by chloride ions from the source, and making up for the general anti-corrosion control deficiencies under special corrosive medium environments. ## 1. High-Chloride Working Condition Identification and Risk Grading Confirmation The laboratory shall regularly test the chloride ion concentration of each batch of fermentation medium, raw materials and process water. According to the measured concentration value, working conditions are divided into three risk grades: low chloride warning grade, medium high-risk grade and severe extreme risk grade. Once the medium chloride index exceeds the internal warning threshold, the production line shall be marked as a high-chloride risk working condition, and the equipment department shall record it in the equipment risk ledger. For production processes that continuously adopt high-chloride raw materials for a long time, the heating loop shall be defined as a permanent high-corrosion-risk area, and all conventional inspection, cleaning and maintenance cycles shall be adjusted to enhanced frequency standards. ## 2. Source Control of Raw Material Chloride Ion Input The procurement department shall require all raw material suppliers to provide chloride ion detection reports for each batch of fermentation raw materials, and raw materials exceeding the agreed chloride limit shall be rejected for incoming use. The laboratory sets sampling inspection frequency for each batch of culture medium preparation, and prohibits the use of unqualified high-chloride feed liquid for fermentation production. When process adjustment must use high-chloride auxiliary materials, a special risk approval application shall be submitted in advance, and targeted anti-corrosion protective schemes shall be formulated before feeding. Random mixing of different batches of raw materials with large differences in chloride content is forbidden to avoid sudden sharp fluctuations in medium corrosivity. ## 3. Enhanced On-Line Monitoring and Off-Line Sampling Inspection Mechanism For high-chloride risk production lines, online chloride ion monitoring sensors shall be installed at the inlet and outlet of the heating circulation pipeline to realize real-time continuous data uploading to the digital management platform. Offline manual sampling and laboratory titration testing shall be carried out every production batch to calibrate the accuracy of online instruments. Once the chloride concentration continuously exceeds the warning value for multiple batches, the equipment team shall immediately increase the frequency of ultrasonic wall thickness measurement and pipeline endoscopic inspection, focusing on checking welding seams, bent pipes, low-flow stagnant areas and flange crevice positions prone to chloride enrichment. ## 4. Optimized Cleaning, Passivation and Circulating Water Anti-Corrosion Protection Scheme Under high-chloride operating conditions, the regular deep pickling and passivation cycle of heating pipelines shall be shortened appropriately. After each batch of high-chloride fermentation is completed, enhanced alkaline cleaning shall be implemented to thoroughly eliminate residual chloride-containing medium attached to the tube wall and prevent local chloride enrichment under dirt deposits. The formula of circulating water corrosion inhibitor shall be optimized to adopt chloride-resistant special inhibitors to improve the stability of the metal passive film. Long-term static standby of pipelines filled with high-chloride residual medium is strictly prohibited; if production needs to be suspended temporarily, full-loop purified water replacement flushing must be completed first. ## 5. Material Risk Early Warning and Targeted Maintenance Upgrade Measures For heating pipelines operating under high-chloride conditions for a long time, the equipment department shall dynamically track the annual average corrosion rate. When the corrosion rate approaches the critical early warning threshold, technical demonstration shall be organized to evaluate the feasibility of upgrading corrosion-resistant materials such as titanium alloy or PFA lining. All maintenance, welding and local repair operations on high-chloride risk pipelines must implement full argon protection welding and post-repair enhanced passivation treatment. Repaired pipe sections shall be listed as key monitoring points, and the inspection frequency shall be doubled to prevent stress corrosion cracking induced by chloride ions in welding heat-affected zones. ## 6. System Value This specification constructs a special anti-corrosion defense mechanism for high-chloride harsh working conditions, effectively avoids typical local corrosion failures induced by chloride ions which are difficult to prevent by conventional management measures, forms differentiated refined risk control for different medium corrosive environments, complements the general anti-corrosion system clauses, and further improves the full-scenario, graded and targeted closed-loop anti-corrosion management system of fermentation heating tubes.
