1. 316L Stainless Steel Heating Tube Common Faults
Fault 1: Tube wall scattered rust spots, heating power gradually rises
Root cause: Chloride ion erosion destroys chromium passive film; bubble stagnation at inclined upper arc causes oxygen-deficient pitting; hot alkali CIP accelerates film attenuation; thick composite scale forms thermal resistance.
Solution: Monthly citric acid deep descaling; semi-annual offline supplementary passivation; adjust installation inclination ≥12° and add exhaust valves; reduce alkali cleaning temperature below 60℃; perform wall thickness inspection, replace tubes with pit penetration.
Fault 2: Weld local leakage and medium overflow
Root cause: Weld heat-affected zone has incomplete passive film; thermal cycle stress superimposes chloride corrosion to expand penetrating pits.
Solution: Stainless steel weld corrosion cannot be repaired; directly replace the heating bundle, optimize subsequent circulating flow to reduce dirt accumulation at welds.
Fault 3: Serious biofilm residue after CIP cleaning
Root cause: Uneven weld surface forms dirt dead corners; passive film matte roughening increases organic adsorption capacity.
Solution: Extend acid circulation time; polish weld surface during overhaul; increase flow velocity to strengthen scouring effect.
2. Pure Titanium Heating Tube Common Faults
Fault 1: Local tube surface milky white matte whitening
Root cause: Trace fluoride residue in medium/cleaning liquid etches TiO₂ film; long-term bubble retention leads to slow film degradation; hard tool scratches destroy protective layer.
Solution: Completely eliminate fluoride-containing reagents; increase exhaust flow to eliminate gas film; offline enhanced passivation repair scratches; use nylon soft slings for hoisting to avoid hard friction.
Fault 2: Heating efficiency drops slightly without obvious dirt
Root cause: Persistent bubble air film forms thermal barrier on the upper arc of tube bundle.
Solution: Optimize installation angle to 8°–10°; install automatic exhaust ports at the highest point of heating assembly; increase circulating pump flow to break tiny bubbles.
Fault 3: Rust sediment adheres to titanium surface
Root cause: Carbon steel brackets without PTFE isolation produce galvanic corrosion shedding iron rust.
Solution: Add full sets of PTFE gaskets and isolation sleeves between titanium flanges and metal supports; regularly flush rust deposits on tube surface during routine maintenance.
3. Quartz Anti-Corrosion Heating Tube Common Faults
Fault 1: Glass surface foggy frosted layer, difficult to clean scale
Root cause: Hot alkaline CIP liquid reacts with silicon dioxide to form permanent rough etched layer.
Solution: Cancel all alkali-containing cleaning processes, only use citric acid and neutral disinfectant; severely frosted quartz tubes must be replaced, no recovery method available.
Fault 2: Sudden tube rupture during heating or CIP temperature switching
Root cause: Low thermal shock resistance; accumulated internal microcracks caused by collision and extrusion during installation and transportation; excessive surface power density generates huge temperature difference stress.
Solution: Control power density below 0.8 W/cm²; adopt shockproof foam packaging and rubber buffer pads during installation; avoid rapid cold water flushing on hot quartz tubes; regularly inspect invisible microcracks with strong light transmission.
Fault 3: Tiny glass fragments mixed into fermentation medium
Root cause: Microcracks expand and peel off small glass residues under long-term thermal stress vibration.
Solution: Replace cracked quartz tubes immediately; quartz is prohibited for large-scale continuous sterile fermentation lines to prevent batch pollution losses.
4. PFA Coated Heater Common Faults
Fault 1: Coating blistering, local bulging and peeling
Root cause: Long-term operating temperature exceeds 110℃; rapid cold-hot alternation expands the gap between fluoroplastic and steel substrate; corrosive medium invades the interior after minor scratches.
Solution: Strictly control medium temperature ≤100℃; prohibit sudden cold water quenching; wrap with soft cloth during disassembly to avoid sharp scratch damage.
Fault 2: Local dark spots exposing metal substrate
Root cause: Abrasion of suspended solid particles in medium; friction with metal brackets cuts through coating.
Solution: Reduce circulating flow velocity to mitigate particle scouring; add PTFE soft contact gaskets; once substrate is exposed, the whole heater must be replaced (local repair invalid).
Fault 3: Continuous high power consumption, slow temperature rise
Root cause: Inherent thermal resistance of PFA coating; aging coating roughens and accumulates thick scale, dual thermal resistance superposition.
Solution: Regular monthly water flushing to remove surface dirt; avoid long-term high-temperature operation to delay coating aging; replace with titanium tubes if energy consumption loss cannot be accepted.
General Fault Handling Principles
- Distinguish material root causes first, do not use unified maintenance schemes for four heating tubes. Stainless steel focuses on passivation and anti-chloride pitting; titanium eliminates fluoride and bubble stagnation; quartz avoids alkali and thermal shock; PFA controls temperature and anti-scratch protection.
- Prioritize preventive adjustment of process parameters (CIP temperature, flow velocity, installation angle, power density) to reduce fault recurrence rate.
- Judge repairable minor defects and irreparable complete failure separately; avoid forced use of damaged heating tubes leading to sudden leakage and batch scrap losses.
