Complete maintenance cycle management system for pure titanium heating tubes in continuous fermentation workshops

Title: Comprehensive maintenance cycle management system for pure titanium heating tubing in continuous fermentation workshops The long-term stability of titanium heating tubes is contingent upon standardised periodic maintenance, rather than passive post-failure repair. This system divides maintenance into daily on-site inspection, monthly routine maintenance, quarterly comprehensive detection, semi-annual overhaul, and 3–5 year full-life assessment. It clarifies inspection items, operation standards, judgement thresholds, and abnormal disposal plans for each cycle to eliminate hidden corrosion risks in advance and extend the full service life of heating assemblies. ## 1. Daily visual patrol maintenance (5–10 minutes per tank, every shift) ### Contents of the Inspection 1. Tank liquid level interlock linkage test: Verify that the heating power is automatically shut off when the liquid level falls below the top of the heating tube, thereby preventing dry-out bubble corrosion. 2. Observation of the flange sealing surface: Inspect the gasket gaps for liquid seepage, dripping, and white/gray corrosion sediment. 3. The tube surface is visible through the tank sight glass, and there are no substantial black carbon coking or dark pitting patches that are concentrated on the weld areas. 4. Operation of the circulation pump and aeration equipment: Ensure that the circulating flow and aeration volume comply with the established standards, and prevent bubble stagnation that is a result of low flow velocity. ### Disposal standard that is abnormal - Minor gasket seepage: During monthly shutdown maintenance, mark the position and arrange for a replacement. - Monthly online cleaning schedule for thick surface carbon scale; - Immediate adjustment of equipment parameters is necessary to re-establish the rated flow in the event of abnormally low aeration/circulation flow. ## 2. Monthly routine maintenance (planned brief shutdown, full tank CIP cleaning, and surface passivation repair) ### Fundamental operational components 1. Completely graded CIP acid-base alternating cleansing Adopt the standard 3%–5% dilute alkali + citric acid descaling process, adhere to the temperature and soaking time specifications outlined in Article 66, and eliminate inorganic mineral scale and organic carbon deposits. 2. Passivation of warm aerated deionised water circulation After cleaning, circulate warm water that is rich in oxygen (40–50℃) for 2 hours. Subsequently, maintain a static tank fill for 12–24 hours to repair the thinned passive film. 3. Inspection of flange accessories during disassembly Assess the ageing, swelling, and deformation of PTFE gaskets; examine the PTFE insulation sleeves of fasteners for cracks; promptly replace any damaged isolation accessories. 4. Surface spot inspection following tank draining Utilise a high-brightness LED lamp to inspect welds and support contact areas for shallow scratches and early pitting. Record anomalous thinning positions in the wall thickness to facilitate quarterly focus detection. ### Recording requirements Record the concentration of cleaning fluid, the temperature, the duration of the cleaning, the quantity of gasket replacements, and any anomalous surface defects in the monthly maintenance log. 3. Quarterly comprehensive non-destructive testing (major detection cycle) ### Judgement thresholds and detection initiatives 1. Ultrasonic wall thickness measurement Critical indicators: The middle section of the tube body, all weld heat-affected zones, the support contact areas, and the bubble-prone upper tube arc. Safety threshold: The remaining wall thickness must exceed the original thickness by 70%. If the value is less than this, the tube should be marked as high-risk and the inspection cycle should be shortened to monthly. 2. Passive film potential electrochemical measurement Standard qualified potential is ≥ +150mV in comparison to a saturated calomel electrode, with a surface potential difference of ≤30mV. Abnormal treatment: Integral hydrogen peroxide chemical re-passivation treatment is initiated when the potential is less than +120mV. 3. Weld eddy current penetrant flaw detection Screen internal microcracks and pore defects at welds necessitate local polishing repair and secondary passivation. Additionally, any linear defect that exceeds 0.3mm necessitates secondary passivation. 4. Examination of the support bracket Inspect the steel supports for peeling PTFE coating and pointed burrs that are scratching the tube surface. Replace any damaged supports. ## 4. Semi-annual thorough overhaul (long tank shutdown, complete disassembly inspection, and partial repair) 1. Complete disassembly of the titanium heating tube assembly Remove the tube bundle to conduct a comprehensive external surface inspection. Utilise fluoride-free ultra-fine polishing paste to polish local pitting, deep scars, and weld discolouration. 2. Complete chemical re-passivation of the entire tube To reconstruct a uniform, compact TiO₂ passive film, allow the entire heating tube to soak in a 2% dilute hydrogen peroxide solution for six hours. 3. Complete replacement of auxiliary components that are susceptible to damage To eliminate the concealed hazards of galvanic corrosion that are the result of ageing isolation materials, all PTFE gaskets, bolt insulation sleeves, and aged PTFE soft supports are replaced uniformly. 4. Retest for hydraulic pressure tightness The qualification process involves testing the pressure at 1.5 times the rated working pressure, maintaining the pressure for 30 minutes, and ensuring that there is no pressure decline or leakage. Leaking tubes are repaired using argon welding and subsequently retested. 5. Examination of power circuits Test the insulation resistance of the internal heating wires and eliminate the danger of electric leakage that is a result of the long-term ageing phenomenon at high temperatures. ## 5. Assessment of the complete life cycle and decision to replace within the next 3–5 years In conjunction with cumulative wall thickness loss, frequent passive film failure, and repeated weld repair records, it is necessary to determine whether to scrap and replace: ### Standards for mandatory replacement 1. The residual corrosion allowance requirement cannot be met due to the local remaining wall thickness being less than 50% of the original design thickness. 2. Despite the completion of numerous weld pitting restorations, new corrosion pits continue to emerge following each maintenance cycle. 3. The passive film's self-repair capability is completely lost due to the long-term low surface potential that results from repetitive integral re-passivation. 4. Repeated flange leakage following multiple gasket replacements, severe pitting deformation of the flange sealing surface, and inability to be polished for recovery. ### Cost recommendation After 4–5 years of complete maintenance, unified batch replacement is required for conventional TA2 titanium tubes. High-end TA1 pharmaceutical equipment can be extended to 5 years with strict quarterly detection. ## 6. Maintenance cycle management control table | Maintenance Cycle | Core Work Content | Qualified Standard | Abnormal Disposal Measure | | ---- | ---- | ---- | ---- | | Daily shift patrol | Liquid level interlock test, flange leakage, circulation & aeration check | No seepage, normal flow, no thick scale | Record defects, adjust operation parameters on site | | Monthly routine maintenance | Standard CIP cleaning + water passivation, partial gasket inspection | Complete scale removal, intact isolation accessories | Replace damaged gaskets, advance cleaning cycle | | Quarterly NDT detection | Wall thickness measurement, film potential test, weld flaw detection | Residual wall ≥70% original thickness, potential ≥+150mV | Chemical re-passivation, shorten thickness detection cycle | | Semi-annual deep overhaul | Tube disassembly polishing, full re-passivation, all vulnerable parts replacement, hydraulic test | Smooth scratch-free surface, pressure holding no leakage | Local welding repair for weld defects, replace severely corroded accessories | | 3–5 year full-life assessment | Comprehensive corrosion loss statistical evaluation | Wall thickness retention ≥50%, stable passive film | Scrap and replace if reaching any mandatory replacement standard | Brief Summary Establish a layered cyclic maintenance system for titanium heating tubes, which includes a daily patrol, monthly cleaning passivation, quarterly non-destructive testing, semi-annual disassembly overhaul, and multi-year life assessment. Transition from passive emergency repair to proactive regular maintenance, continuously eliminate scale accumulation, passive film damage, galvanic corrosion, and wall thinning hidden dangers, maximise the full service cycle of titanium heating tubes, and reduce unplanned production shutdown losses of fermentation workshops.