# Fermentation Heating Tube Anti-Corrosion Pipeline Local Repair, Welding Construction & Post-Repair Anti-Corrosion Treatment Specification ## Preface This specification (Doc.159) is a key technical maintenance document in the anti-corrosion management system ranging from Doc.15 to Doc.158. It standardizes the whole-process control of pipeline defect positioning, construction isolation, welding process regulation, post-weld surface treatment, pressure tightness test, pickling passivation and acceptance filing for local thinning, pitting leakage, crack damage and faulty pipe fitting replacement of fermentation heating tubes. Improper welding construction will produce welding oxide layers, thermal stress zones and intergranular corrosion sensitive areas, which are the most vulnerable weak points of pipeline corrosion failure. This specification formulates unified construction and post-repair anti-corrosion standards to eliminate new corrosion hidden dangers introduced in maintenance links and ensure the consistency of the overall anti-corrosion performance of the heating loop. ## 1. Pre-Construction Defect Confirmation and Safety Isolation Measures Before carrying out any local repair or welding operation, maintenance personnel shall rely on historical ultrasonic thickness measurement data, endoscopic inspection records and on-site leakage points to accurately locate the damaged range, formulate targeted repair schemes and submit them for equipment department approval. In accordance with the safety isolation provisions of existing specifications, blind plates shall be installed for bidirectional isolation of the repaired pipeline section to thoroughly cut off the connection with the production medium and circulating water system. The pipeline must be fully emptied, repeatedly flushed and sampled to confirm no flammable, corrosive and residual fermentation materials remain, and hot work approval procedures shall be completed before construction. All isolation positions, approval numbers and risk assessment results shall be recorded in the maintenance work order. ## 2. Standard Welding Process Control for Different Metal Materials Differentiated welding technical requirements are formulated for stainless steel, titanium alloy and lined pipe heating equipment. Argon protection back welding must be adopted for stainless steel pipelines to prevent oxidation of the inner welding seam and avoid the formation of chromium-depleted layers inducing intergranular corrosion. Titanium alloy materials need high-purity argon full-range protection for both inner and outer welding surfaces to prevent high-temperature oxidation embrittlement. Welding operators must hold valid special operation qualifications as stipulated in post competency authorization specifications, and unqualified personnel are prohibited from engaging in pipeline pressure welding work. Welding current, welding speed, heat input and interlayer temperature shall be strictly controlled to reduce welding residual thermal stress. ## 3. Post-Weld Surface Treatment and Non-Destructive Inspection Acceptance After welding construction, welding spatter, oxide scale and rough burrs on the inner and outer surfaces of welding seams shall be thoroughly polished and cleaned. For pressure-bearing heating pipelines, radiographic inspection or penetrant inspection shall be carried out on all welding seams to eliminate hidden defects such as air holes, cracks and incomplete fusion. After passing non-destructive testing, a hydrostatic pressure holding test shall be implemented according to the design pressure standard, with no pressure drop, no seepage and no sweating as the qualified acceptance criterion. Any unqualified welding position must be completely cut off for re-welding; repeated repair times at the same welding point shall not exceed the specified limit to prevent material performance degradation. ## 4. Post-Repair Pickling Passivation and Passive Film Restoration After passing pressure test acceptance, the local repaired pipeline section shall be isolated for independent circulating pickling and passivation treatment. The high-temperature thermal affected zone formed by welding is extremely prone to passive film damage, so standardized passivation procedures must be implemented to reconstruct a dense protective film on the inner wall of the welding seam and adjacent base material. After passivation, purified water flushing and residual detection shall be carried out, and chemical spot tests shall be used to verify the integrity of the passive film at the welding position. The whole loop can be connected back to the original production system only after the passivation effect is qualified. ## 5. Repair File Archiving and Subsequent Enhanced Inspection Arrangement All repair-related documents including construction approval forms, welding parameter records, non-destructive test reports, pressure test acceptance sheets and passivation inspection data shall be archived into the equipment full-life management file for permanent traceability. All welding repair points shall be numbered and marked in accordance with on-site visual management specifications, listed as key enhanced inspection positions. In subsequent regular wall thickness measurement and daily patrol work, the inspection frequency of repaired sections shall be increased to monitor the corrosion development trend of welding heat-affected zones in real time. Typical cases of post-welding corrosion leakage shall be sorted into the anti-corrosion knowledge base for technical warning training for maintenance teams. ## 6. System Value This specification fills the management gap of anti-corrosion control in pipeline local maintenance and welding links, avoids introducing new high-risk corrosion weak points during equipment repair, ensures that repaired pipelines have the same anti-corrosion performance as the original design, perfects the closed-loop control from equipment damage, maintenance construction to anti-corrosion recovery, and further improves the full-lifecycle refined anti-corrosion management system of fermentation heating tubes.
