High-strength titanium heating pressure components widely used in high-pressure hydrogenation, pressurized fine chemical and sealed energy storage reaction devices often face combined risks of seawater salt fog corrosion, chloride medium pitting and crevice corrosion. Impressed current cathodic protection is frequently adopted as an auxiliary anti-corrosion measure to restrain local passive film breakdown of titanium structures. However, unreasonable protection potential setting, excessive current output and inaccurate reference electrode positioning easily lead to over-protection phenomena. Excessively negative cathode potential will drive massive electrolytic hydrogen evolution on titanium surfaces, allowing hydrogen atoms to permeate into the metal matrix, aggregate at grain boundaries and stress-concentrated welding and bending areas, forming brittle titanium hydride phases. Such metallurgical defects drastically reduce the tensile strength, fatigue resistance and stress corrosion resistance of titanium pressure heating parts, easily triggering brittle cracking and sudden pressure leakage accidents under cyclic thermal and pressure loads. Establishing standardized selective cathodic protection parameter calibration specifications can lock the potential within the safe protection interval, inhibit localized corrosion while avoiding hydrogen evolution over-protection, and realize safe and long-term anti-corrosion operation of high-strength titanium heating pressure assemblies in harsh pressurized corrosive service environments.
Determining the critical protection potential range through laboratory polarization curve testing is the core premise of parameter calibration. Before formally putting the cathodic protection system into operation, potentiodynamic polarization tests should be carried out on titanium base materials under simulated on-site temperature, pressure and medium salinity conditions to draw accurate polarization characteristic curves. The lower limit of the safe protection potential is set slightly negative to the pitting corrosion potential of titanium, which can passivate local active corrosion points and prevent passive film breakdown; the upper limit must be controlled above the hydrogen evolution potential of the medium to avoid electrolytic hydrogen precipitation on the titanium surface. For high-strength titanium heating components sensitive to hydrogen embrittlement, the potential safety window is relatively narrow, and a buffer interval of at least 50 mV should be reserved between the set protection potential and the hydrogen evolution threshold to resist transient potential fluctuation caused by medium flow velocity change, temperature drift and anode aging. Blindly referring to carbon steel protection parameters will inevitably cause over-protection and induce irreversible hydrogen embrittlement damage to titanium substrates.
Multi-point distributed reference electrode layout paired with real-time potential closed-loop adjustment avoids local over-protection dead zones. Single reference electrode measurement can only reflect the potential state of a small regional heating component, while pipeline bent sections, flange crevices and fluid stagnant zones often bear higher cathode current density, resulting in local potential exceeding the safe negative limit even if the main measuring point is within the standard range. Reference electrodes need to be arranged at high-risk positions such as liquid level fluctuation areas, heating coil welding seams and pipeline low-flow dead zones to collect multi-dimensional potential data. The control system adopts average potential feedback to dynamically adjust the output current of the impressed current anode, so that all monitoring points are stably maintained within the calibrated safe potential interval. Regular electrode potential calibration and anti-fouling cleaning of reference probes prevent measurement drift from leading to continuous over-protection operation, which is particularly critical for large-scale pressurized titanium heating network systems with complex fluid flow fields.
Regular hydrogen embrittlement performance inspection matched with seasonal parameter recalibration forms a closed-loop safeguard mechanism. Long-term service will cause anode consumption, medium water quality seasonal fluctuation and equipment operating parameter adjustment, which may gradually shift the actual potential of titanium heating components to the over-protection range. Quarterly potential spot verification and annual full-system parameter recalibration are required to recheck the polarization curve under the latest on-site working conditions and fine-tune the protection potential upper and lower limits. Meanwhile, hardness testing, ultrasonic metallographic inspection and slow strain rate tensile tests are implemented on representative high-stress titanium heating parts to detect hydride precipitation, grain boundary hydrogen enrichment and material ductility attenuation signals. Once hydrogen embrittlement signs are found, the protection potential must be positively shifted upward immediately, combined with vacuum dehydrogenation heat treatment for defective components to eliminate brittle hydride phases and restore the intrinsic mechanical and anti-corrosion properties of titanium substrates.
The following table presents classified cathodic protection calibration schemes for different high-strength titanium heating pressure service scenarios:
表格
| Pressurized Titanium Heating Service Scenario | Recommended Cathodic Protection Calibration & Auxiliary Scheme | Core Anti-Overprotection Hydrogen Embrittlement Value |
|---|---|---|
| High-pressure high-chloride hydrogenation reactor titanium heating coil | Laboratory polarization curve safe potential window setting + multi-point reference electrode closed-loop regulation + annual metallographic hydrogen embrittlement inspection | Prevents local high current density hydrogen evolution and restrains hydride-induced stress corrosion cracking under high pressure |
| Medium-pressure coastal seawater circulating heating pressure vessel assembly | 50 mV hydrogen evolution potential safety buffer + quarterly electrode calibration + real-time potential high-limit interlock | Avoids salt water high conductivity induced over-protection and delays titanium material ductility degradation |
| Sealed batch pressurized fine chemical heating unit | Single main measuring point potential control + regular on-site polarization verification + seasonal parameter recalibration | Balances anti-pitting protection effect and effectively controls hydrogen permeation risk within a narrow safe potential range |
| Low-pressure high-strength titanium jacket heating equipment | Sacrificial anode material potential matching selection + initial pre-operation polarization parameter calibration | Realizes low-cost passive cathodic protection and eliminates artificial over-protection parameter setting errors |
Selective cathodic protection parameter calibration balances the dual demands of localized corrosion suppression and hydrogen embrittlement prevention for high-strength titanium heating pressure components. Titanium's excellent corrosion resistance cannot offset irreversible material brittle damage caused by electrolytic hydrogen permeation under over-protection conditions. Scientific polarization testing, distributed potential monitoring and periodic parameter recalibration lock the operating state within the safe protection interval, avoid human-induced hydrogen embrittlement failure, reduce pressurized equipment safety hazards, and realize full-lifecycle reliable anti-corrosion operation of high-strength titanium heating facilities in complex pressurized corrosive industrial environments.
