Long-Term Performance Attenuation Trend Prediction Model of Four Anti-Corrosion Heating Tubes in Fermentation Environment

# Model for Predicting the Long-Term Performance Attenuation Trend of Four Anti-Corrosion Heating Tubes in Fermentation Environment ## Model for Predicting Attenuation in 316L Stainless Steel Heating Tubes Factors that drive core attenuation: Chloride ion concentration in the medium, maximum temperature of alkaline cleaning fluid, annual continuous operation hours, thickness of accumulated organic scale, and wall thickness loss caused by weld pitting corrosion. Model calculation logic: The primary weighting coefficients are the medium chloride content and alkali washing temperature. The annual wall thickness attenuation rate increases exponentially when the alkali temperature exceeds 60℃ or the chloride concentration exceeds 50ppm. The ageing degree of passive film is determined by the cumulative pickling and passivation times for each year, and the thermal resistance growth value is derived from the real-time heating power deviation to evaluate the thickness of scale accumulation. Law of performance attenuation on a stage-by-stage basis 1. Initial stage (0–12 months): A uniform, intact passive film, a stable heat transfer efficiency, no apparent rust spots, and minor power fluctuations within 5%. 2. Medium ageing stage (12–24 months): Local shallow pitting is observed at welds, the passive film is partially damaged, the heating power increases by 10%–18%, and there is a slight risk of rust shedding during CIP flushing. 3. Failure early warning stage (24–36 months): The risk of leakage reaches a critical level, deep penetrating pitting expands, wall thickness attenuation exceeds 15%, thermal resistance surges, and frequent rust block shedding. This necessitates planned replacement. Key early warning thresholds include a wall thickness attenuation ratio of ≥10%, a heating power increase of ≥15%, and an average medium chloride concentration of over 50 ppm for three consecutive batches. ## Model for Predicting Attenuation in Pure Titanium Heating Tubes Factors that drive core attenuation: Trace fluoride residue in the medium, cumulative scratch coverage area on the tube surface, dissolved oxygen content of the cleaning circulating water, galvanic corrosion sediment deposition time, and annual total operation duration. Model calculation logic: The absolute risk weight is determined by the fluoride ion content. The thinning of the uniform tube wall will be significantly accelerated by the presence of any detectable fluoride. The annual attenuation coefficient is increased by 2–3 times when the dissolved oxygen in cleaning water is minimal, and the surface potential value is employed to quantify the integrity of the passivation film. The ion precipitation risk coefficient is directly influenced by the scratch area ratio. Law of performance attenuation on a stage-by-stage basis 1. Stable operation stage (0–36 months): A complete compact TiO₂ passivation film, a stable heat transfer efficiency, no translucent white etching traces, and a heating power fluctuation of less than 6%. 2. Slow ageing stage (36–60 months): Minor scratch accumulation, slight potential decrease, minor heating efficiency decline of less than 10%, but aeration cleaning can still restore passivation film performance. 3. Replacement reminder stage (over 60 months): The passivation film's self-repair ability is lost, leading to uniform wall thinning, and large-area deep scratches or long-term fluoride contact result in irreversible potential reduction. Batch replacement is highly recommended. Key early warning thresholds include a scratch coverage area of at least 20%, a tube surface electrochemical potential that is consistently below the standard range, and the presence of detectable fluoride ions in the feeding medium. ## Model for Predicting Attenuation in Quartz Anti-Corrosion Heating Tubes Factors that drive core attenuation: The annual light transmission crack expansion speed, cumulative thermal shock frequency, vibration intensity of tube bundle support, temperature rise rate during startup, and times of inadvertent alkali liquor contact. Model calculation logic: The permanent surface frosting loss coefficient is generated by each alkali contact event. The expansion of microcracks is linearly accelerated by a temperature rise speed exceeding 0.5℃/min and strong vibration. The overall structural attenuation degree is determined by integrating the coating coverage ratio and microcrack length. Law of performance attenuation on a stage-by-stage basis 1. New stable stage (0–6 months): A fully transparent, smooth surface with no internal microcracks, a stable low-power heating output, and no anomalous vibration response. 2. Stage of hidden danger accumulation (6–18 months): The heating efficiency decreases moderately due to surface dirt adhesion, and tiny invisible microcracks appear at thread joints. If misoperated with alkali, minor frosting may occur. 3. Critical failure stage (over 18 months): Microcracks develop into penetrating cracks, frosting covers over 30% of the surface, and tube rupture is easily triggered by thermal shock or slight vibration, resulting in irreversible batch pollution loss. Key early warning thresholds include the detection of visible microcracks through light transmission, frosting coverage of at least 30%, and the occurrence of more than one alkali liquor misoperation within a six-month period. ## Model for Predicting Attenuation in PFA-Coated Heaters Factors that drive core attenuation: The duration of annual cumulative over-temperature operation, the concentration of hard abrasive particles in the medium, the frequency of high-concentration oxidant disinfection, the times of rapid cold-hot alternation after cleaning, and the coating blister expansion area. Model calculation logic: The probability of scratch penetration is determined by the hard particle scouring depth, while the exponential ageing coefficient for the fluoroplastic coating is formed when the operating temperature exceeds 95℃. The internal coating stress is increased and blister peeling is accelerated with each rapid cooling cycle. Law of performance attenuation on a stage-by-stage basis 1. The initial stable stage (0–9 months) is characterised by a uniform, intact coating that is free of blisters, a fixed thermal resistance that results in a stable extra power consumption of 10%–20%, and no surface yellowing. 2. The ageing stage of the coating (9–18 months) is characterised by the appearance of localised, small blisters and shallow scratches, as well as a partial yellow ageing discolouration. The heating power increases by over 20%, and there is a minor risk of fluorine-containing fine powder shedding. 3. Complete failure stage (over 18 months): The carbon steel substrate is exposed by penetrating scratches, the large-area coating peels, the internal substrate rust blocks break off, and the medium is polluted by plastic micro-particles. In this stage, all components must be replaced without any repair value. Key early warning thresholds include a blister and scratch damage area that is ≥5% of the total coating surface, a continuous long-term operation temperature exceeding 95℃, and an evident yellow brittleness of the coating surface. ## General Application Rules of the Attenuation Prediction Model 1. Data input source: The authenticity and traceability of the predictions are guarantyd by the use of real-time data from the online monitoring system, daily surveillance records, and periodic offline inspection reports to derive all model driving parameters. 2. Dynamic parameter adjustment: To enhance the accuracy of predictions, the attenuation weighting coefficient is adjusted quarterly in accordance with the actual medium formula, production load, and cleaning process changes. 3. Equipment maintenance linkage: In accordance with the results of the model attenuation stage, automatically push targeted maintenance tasks; increase the frequency of inspections for equipment that enters the medium ageing stage; and develop replacement plans in advance for units that reach early warning thresholds. 4. Production optimisation guidance: Utilise long-term attenuation prediction curves to optimise operation parameters, including chloride control, alkali temperature limit, heating rate, and cleansing cooling program, in order to reduce performance ageing and extend service life. ## Executive Summary The core attenuation mechanisms and performance change cycles of the four types of heating tubes are entirely distinct and are influenced by the inherent properties of the material. The attenuation of stainless steel is primarily caused by chloride pitting and high-temperature alkali damage, with a failure cycle of 2–3 years. Pure titanium, on the other hand, achieves a 4–5 year service life with slow attenuation by relying on a stable passivation film under fluoride-free conditions. Quartz glass accumulates microcracks and frosting damage as a result of thermal shock and alkali misoperation, with a short safe operation period of less than 18 months. PFA coatings are subject to abrasive scratch damage and irreversible high-temperature ageing.