How to carry out daily patrol inspection for anti-corrosion status of titanium heating tubes

# Methods for conducting daily patrol inspections of titanium heating ducts to assess their anti-corrosion status Grade 2 titanium heating tubes are frequently employed in high-chloride fermentation workshops, where they are dependent on a self-repairing TiO₂ passivation film. However, there are no apparent indicators of early fluoride corrosion or film damage. Standardised daily patrols can detect abnormal signals during the initial stages of corrosion, thereby preventing sudden leakage failures and uniform wall thinning. Patrol work is a combination of visual observation, equipment operation data recording, and simple auxiliary detection. The table below organises patrol items, judgement standards, and disposal measures. | Patrol Inspection Item | Normal Standard State | Abnormal Risk Signal | Corrosion Hazard Level | On-site Disposal Operation | | ---- | ---- | ---- | ---- | ---- | | Tube surface visual observation | Uniform silvery matte surface, no milky white etching spots | Local milky white foggy discoloration, scratch deepening | Medium risk | Increase aeration, arrange quarterly potential scanning in advance | | CIP dissolved oxygen reading | Stable 8–12 mg/L throughout cleaning cycle | Continuous reading below 6 mg/L even with full aeration | High risk | Check aeration pump and pipeline blockage immediately | | Online fluoride detector data | Zero fluoride alarm, real-time value ≤0.1 ppb | Intermittent fluoride spike alarm | Extreme risk | Stop feeding and flush whole circulation loop thoroughly | | Pipeline elbow and support contact position | No obvious abrasion marks, complete PTFE isolation sleeve | Sleeve wear, direct metal contact with titanium tube | Medium risk | Replace isolation sleeve during next maintenance window | | Real-time electrochemical potential record | Steady high potential with small fluctuation range | Sustained sharp drop of potential value | High hidden corrosion risk | Arrange full tube potential scanning within 3 working days | Visual inspection is the most basic patrol step for titanium tubes. Titanium passivation film that is intact exhibits a uniform, delicate silver lustre. Before the wall thinning becomes apparent, the surface will exhibit faint milky white foggy etching layers as trace fluoride infiltrates the conduit. Subtle white discolouration is frequently misinterpreted as typical water stains by operators, who neglect concealed corrosion. In reality, milky substances are soluble titanium fluoride residues that remain after the film dissolves, indicating that the self-repair barrier has been partially compromised. It is also important to pay close attention to scratches that are caused by solid particulates. Shallow scratches can be repaired with an adequate amount of dissolved oxygen, but deep and dense scratches will develop into concentrated corrosion areas if aeration is insufficient. Monitoring dissolved oxygen levels during daily patrols is a cost-effective and efficient approach. The basic material for the self-repair reaction of titanium dioxide film is dissolved oxygen at a concentration of 8 mg/L or higher. If the circulating water oxygen content remains low despite the operation of aeration equipment at full capacity, it suggests that the tube surface film is being continuously consumed by invisible corrosive substances. Currently, maintenance personnel are required to inspect the aeration nozzle blockage, pump pressure, and pipeline air leakage points in order to restore the oxygen supply standard. Failure to do so will result in the damaged passivation film being unable to regenerate, and corrosion will continue to progress. The primary early warning link for titanium equipment is fluoride online monitoring. The titanium tube wall will be irreparably damaged by even transient fluoride surges that are the result of raw material cross-contamination. To eliminate residual fluoride sources, the tank and all pipelines must be repeatedly flushed with oxygen-rich purified water and the feeding and heating circulation systems must be promptly shut down upon the alarm being triggered. After flushing, maintain surveillance observation for one week to verify that no fluoride intrusion has occurred on a subsequent occasion. PTFE isolation sleeves are also included in fixed patrol positions at carbon steel support contact points. Galvanic cells will be formed as a result of direct contact between titanium and carbon steel, which will accelerate the loss of local film. Patrol personnel inspect the isolation sleeve for signs of ageing, such as cracking or detachment. If damage is detected, the location is marked and the accessories are replaced during scheduled shutdown maintenance to prevent galvanic corrosion cycles. Every shift, electrochemical potential records must be archived. The most accurate early indicator of passivation film degradation is the continuous decline of potential value, which is evident much earlier than milky white surface discolouration. Immediately implement a 30-minute oxygen-rich water circulation to temporarily aid in film repair before conducting formal offline maintenance, and organise full-tube scanning to identify all damaged areas when abnormal potential data is captured. Standardised patrol protocols for titanium heating tubes must be developed by enterprises, necessitating that shift staff complete surface appearance, dissolved oxygen, fluoride, and potential data records on a daily basis. To prevent uniform etching damage in a large area, isolate the heating loop in advance when multiple anomalous signals appear simultaneously. Form a closed-loop anti-corrosion monitoring system that combines daily inspection and quarterly professional testing by incorporating daily patrol records into equipment full-life-cycle archives. This system is designed to optimise the service life of titanium heating tubes in high-chloride fermentation production.