Titanium immersion heaters are widely adopted in high‑temperature mineral‑leaching auxiliary heating loops, ore‑slurry pre‑heating tanks and mineral‑rich process circulation systems. The protective TiO₂ film gives titanium outstanding general‑corrosion resistance. Nevertheless, conductive metal‑oxide scales from mineral slurry continuously deposit onto sheath surfaces. These semiconducting oxide deposits form extensive conductive cathodic layers. Galvanic cells establish between conductive oxide scale and tiny film‑defect exposed titanium matrix. Accelerated local anodic dissolution occurs at defect sites. Conventional clean‑solution compatibility tests cannot simulate conductive‑scale‑driven galvanic degradation.
In mineral‑rich circulating fluid, iron‑oxide, manganese‑oxide and other semiconducting mineral particles settle and sinter onto hot titanium sheath, building continuous conductive scale layers. The thick oxide deposit acts as large‑area inert cathode. Where tiny natural defects exist in titanium passive film, bare metal substrate becomes localized anode. Cathodic oxygen reduction reaction takes place across the whole conductive‑scale surface, concentrating corrosion current onto small anodic defect zones. Deep pitting initiates at those limited defect points, even though most sheath area remains covered by intact oxide scale.
During early‑phase service, dark dense mineral‑oxide scale covers most of the heater surface. Operators may regard scale as protective barrier. In fact, severe localized pitting develops hidden beneath scale layers. With long‑time operation, pits penetrate sheath wall, leading to medium leakage and premature heater breakdown. Material‑selection manuals frequently assess solution corrosiveness without considering galvanic effect brought by semiconducting mineral‑oxide fouling.
Targeted engineering countermeasures suppress conductive‑oxide‑scale galvanic corrosion. Install pre‑filtration devices to reduce suspended mineral‑oxide particle loading. Improve flow velocity to mitigate scale sedimentation. Schedule periodic chemical cleaning to remove sintered conductive oxide deposits. Deploy local high‑magnification inspection and thickness measurement beneath scale‑covered regions during overhaul.
表格
| Heater Type | Conductive‑Oxide‑Scale‑Induced Galvanic Corrosion Risk | Core Degradation Mechanism | Early‑stage Diagnostic Feature | Key Mitigation Engineering Measure |
|---|---|---|---|---|
| Titanium | Medium‑High | Semiconducting mineral‑oxide deposits form large‑area cathodic layer; tiny passive‑film defects become concentrated anodic pitting sites | Dark compact sintered mineral‑oxide scale covering sheath exterior | Reduce suspended oxide particles; raise flow velocity; periodic chemical descaling; scale‑zone thickness detection |
| 316L Stainless Steel | High | Conductive oxide scale creates similar galvanic effect; passive‑film damage and pitting propagate rapidly | Severe mottled corrosion under adherent mineral scale | Strictly control mineral particle concentration in process fluid |
| Fused Quartz | Negligible | No electrochemical coupling reaction; only inert mineral‑oxide fouling accumulates on tube wall | Hard mineral‑oxide scale adhering to quartz surface | Mechanical or chemical cleaning workflow |
| PFA‑Jacketed | Negligible | Insulating polymer prevents galvanic coupling; mineral‑oxide only deposits on outer jacket surface | Thick mineral fouling on low‑flow jacket sections | Regular circulating flushing and descaling maintenance |
Conclusion: Clean‑medium corrosion performance cannot predict titanium heater service life in mineral‑processing circulating loops. Conductive semiconducting oxide scale establishes large‑area cathodic surfaces and concentrates corrosion current on minor film defects. Particle removal and periodic scale cleaning constitute core protective strategies.
