Fermentation Heating Tube Anti-Corrosion Cross-Medium Switching Operation Standard Specification

# Standard Specification for Fermentation Heating Tube Anti-Corrosion Cross-Medium Switching Operation ## Preface This specification is compatible with the entire anti-corrosion document system, which spans from Doc.33 to Doc.110. It ensures that the entire set of operating procedures, cleansing verification standards, risk prevention measures, and record filing requirements are standardised when fermentation production transitions between various corrosive media. It eliminates cross-ion contamination, galvanic corrosion, and rapid tube wall etching that are caused by incomplete pipeline cleaning during medium replacement. Additionally, it addresses the management deficit of anti-corrosion control in medium conversion links. Acidic fermentation broth, alkaline culture medium, and high-chloride raw material liquid are the three corrosive categories into which media are classified for differentiated switching control. Direct switching between any two distinct categories is strictly prohibited in the absence of multi-stage rinsing and complete isolation. The primary risk associated with unstandardised switching is the formation of a corrosive composite solution within heating tube loops, which accelerates the pitting corrosion of stainless steel, the coating peeling of PFA tubes, and the surface erosion of titanium tubes in the form of residual ion mixing. The switching operation steps are uniformly formulated. Production personnel initially shut off the raw material inlet and halt the circulation of the original medium. They then completely drain all residual liquid in heating tubes, connecting pipelines, and storage tanks. Secondly, perform a preliminary water flush for a minimum of the designated duration to eliminate the majority of residual medium. Afterward, completely discharge all flushing waste liquid. Third, implement targeted pickling or alkaline neutralisation cleaning in accordance with the properties of the previous medium. Maintain the standard circulating temperature and duration to eliminate adsorbed biofilm and ion residues that are affixed to the inner walls of the tube. Fourth, perform numerous cycles of pure water replacement flushing and collect samples from the pipeline outlet for ion detection. The transition to the new medium can only be completed once the test results satisfy the safety threshold standards. Special isolation protection measures must be implemented for production lines that frequently transition between mediums. Dedicated temporary isolation blind plates are installed at shared pipeline junctions during conversion to prevent medium backflow, and independent branch pipelines are configured for different media to reduce the frequency of repeated flushing. The priority items of patrol inspection are altered within 24 hours of medium switching, with a particular emphasis on abnormal temperature fluctuations, flange liquid seepage, and tube wall fogging that are the result of residual ion corrosion. Enhanced circulation cleaning will be initiated promptly in the event that etching traces are detected. Complete real-time record filling is necessary for all transitioning activities. The ledger must document the start and end times of the switching process, the categories of original and new mediums, the duration of the flushing cycle, the concentration of the cleaning agent, the results of the ion sampling test, the on-site operator's signature, and the abnormal check results of the patrol. The secondary full pipeline cleaning process will be initiated by the detection of unqualified sampling records, and the entire repeated operation process will be recorded as key risk tracking files. The frequency of corrosion abnormalities and the fluctuations in maintenance costs of frequent medium switching workshops are analysed on a monthly basis. In the event that unreasonable switching processes result in recurrent cross-contamination risks, the corresponding process clauses will be revised during the quarterly system review meeting. All medium switching operation files, ion inspection reports, and post-switching patrol records are archived and dual-backed. This specification eliminates concealed corrosion risks caused by medium conversion, implements full-process anti-corrosion control for various production volumes, and enhances the closed-loop management system of fermentation heating tube anti-corrosion.