Galvanic corrosion occurs when titanium heating tubes are electrically connected to dissimilar metals with different electrode potentials and immersed in conductive electrolyte medium. A primary galvanic cell is formed spontaneously. The metal with lower potential serves as the anode and dissolves rapidly, while titanium with stable passivation film acts as the cathode and is protected. In actual assembly, when titanium is in contact with carbon steel, copper, aluminum and ordinary stainless steel fittings, severe localized corrosion will appear on the matched metal parts, and the edge of titanium passivation film will be damaged to produce pitting leakage. This corrosion concentrates sharply on contact interfaces and causes equipment failure far faster than uniform corrosion.
1. Electrochemical Galvanic Corrosion Mechanism
Titanium has an extremely positive corrosion potential in most corrosive environments and forms a dense inert titanium dioxide passivation layer on its surface. When it makes direct metal contact with metals such as iron, aluminum and copper with more negative potentials, an electron transfer loop is built under the action of electrolyte. The dissimilar metal anode continuously loses electrons and ionizes into the medium for corrosion consumption; titanium surface captures electrons to complete cathodic oxygen reduction reaction, and its passivation film is intact in most areas. However, at the tiny gap of the contact boundary, halogen ions in the medium gather and break the local TiO₂ film, inducing pinpoint pitting on the titanium substrate. The larger the cathode-anode area ratio, the more violent the anodic corrosion rate, and the titanium contact edge is more prone to localized perforation.
2. Typical Positions Susceptible to Galvanic Corrosion
Contact parts between titanium pipes and carbon steel supports, pipe clamps and fixed brackets;
Flange assembly positions matched with brass, galvanized iron and aluminum alloy bolts;
Welding joints between titanium main pipe and non-titanium auxiliary connecting parts;
Threaded connection interfaces with ordinary steel pipe fittings and transition joints;
Splash and wet areas where titanium components touch other metal structures.
3. Core Inducing Factors Accelerating Galvanic Corrosion
Excessive potential difference between paired heterogeneous metal materials;
Titanium as large-area cathode matched with small-area anode accessories, amplifying corrosion current density;
Medium containing chloride and fluoride ions improving conductivity and destroying passivation film;
Condensed liquid and process medium seeping into assembly gaps to form closed electrolyte environment;
No insulating isolation measures leading to direct electrical conduction between two metals.
4. Multi-dimensional Whole-Link Preventive Control Measures
① Adopt homogeneous material matching principle
Unify brackets, clamps and fasteners to pure titanium or titanium alloy to eliminate potential difference fundamentally.
② Add insulating isolation gaskets between dissimilar metals
Lay PTFE, rubber or ceramic insulation pads to cut off conductive circuit and block galvanic cell formation.
③ Optimize cathode and anode area proportion
If different metals must be used, ensure the easily corroded anode part has a larger surface area to reduce unit corrosion load.
④ Seal assembly gaps to prevent liquid infiltration
Apply anti-corrosion sealing glue on flange and threaded joints to avoid electrolyte entering contact interface.
⑤ Configure sacrificial anode protection for unavoidable mixed structures
Install low-potential sacrificial metal blocks to preferentially corrode and protect titanium heating tubes.
5. Prevention Effect Comparison Table
表格
| Assembly Matching Mode | Galvanic Corrosion Risk | Application Suggestion |
|---|---|---|
| Direct contact between carbon steel accessories and bare titanium surface | Rapid corrosion of fittings and edge pitting on titanium | Add insulation or replace with titanium parts immediately |
| Full titanium matching + gap sealing treatment | Basically eliminate galvanic corrosion hidden danger | Standard installation specification for titanium equipment |
| Insulation isolation + sacrificial anode auxiliary protection | Long-term stable anti-galvanic corrosion performance | Mixed metal design mandatory supporting scheme |
Conclusion
Galvanic corrosion of titanium heating tubes is driven by potential difference between heterogeneous metals and conductive electrolyte loop. The core prevention strategies include material homogenization selection, physical insulation to disconnect conduction path, gap sealing to isolate corrosive liquid and auxiliary sacrificial anode protection. Strict standardized incoming material inspection and assembly process management can thoroughly avoid premature leakage failure caused by galvanic cell corrosion at the connection positions of titanium heating tubes.
