Titanium materials have extremely high hydrogen absorption sensitivity. Hydrogen atoms generated from pickling, welding, cathodic protection and acidic medium corrosion will penetrate into the titanium matrix. Hydrogen accumulates at dislocations, grain boundaries and internal defects to form hydride brittle phases, drastically reducing the ductility and toughness of titanium tubes. Under working stress, microcracks germinate and expand rapidly, leading to brittle cracking and sudden rupture of the heating tube without obvious plastic deformation. Hydrogen embrittlement is one of the most destructive hidden failure modes for titanium heat exchange components.
1. Core Hydrogen Embrittlement Micro-Mechanism
Nascent hydrogen atoms produced in corrosive environments can easily pass through the titanium dioxide passivation film and diffuse into the metal lattice. When hydrogen concentration exceeds the solid solubility limit of titanium, titanium hydride with hard and brittle properties precipitates along grain boundaries. Hydride phases have poor coordination with the titanium matrix, creating severe internal stress at phase interfaces. Under thermal cycling, assembly stress and medium pressure, tiny cracks initiate at hydride precipitation sites. These cracks propagate along hydride distribution paths at an extremely fast rate, eventually penetrating the pipe wall and causing fracture leakage. Unlike stainless steel hydrogen induced cracking, titanium embrittlement is dominated by hydride precipitation and phase brittleness.
2. Typical Working Links Where Hydrogen Infiltration Occurs
Acid pickling descaling without hydrogen inhibitor, causing massive hydrogen permeation during oxide removal;
Unprotected welding with moisture decomposition generating hydrogen that invades weld metal;
Excessive negative potential in cathodic protection system triggering violent hydrogen evolution reaction;
Long-term immersion in hydrofluoric acid, fluoride-containing wastewater and acidic corrosive media;
Residual water vapor inside the tube during sealed storage decomposing into hydrogen under heating conditions.
3. Key Factors Aggravating Titanium Hydrogen Embrittlement
Lack of degassing baking treatment after hydrogen absorption procedures such as pickling and welding;
Low operating temperature which reduces hydrogen escape efficiency and accelerates hydride precipitation;
High tensile residual stress from bending and forming lowering the critical threshold for cracking;
Surface scratches and inclusions serving as preferential gathering positions for hydrogen;
Direct contact with dissimilar metals inducing galvanic corrosion and additional hydrogen generation.
4. Systematic Full-Process Prevention Measures
① Add hydrogen absorption inhibitor during pickling process
Specially formulated pickling additives suppress hydrogen ion reduction reaction; strictly control pickling duration to avoid over-corrosion.
② Implement strict argon shielding welding specification
Adopt double-sided full argon protection to isolate air and moisture; thoroughly dry welding filler rods before use.
③ Calibrate cathodic protection potential range
Prohibit overprotection with overly negative potential to cut off hydrogen evolution reaction at the source.
④ Carry out low-temperature dehydrogenation baking
Heat treated workpieces to 200~300℃ for long-time heat preservation to drive dissolved hydrogen out of the matrix.
⑤ Optimize medium environment and regular inspection
Reduce fluoride and strong acid concentration in process fluid; regularly conduct ultrasonic testing to detect internal hydride crack defects.
5. Prevention Effect Comparison Table
表格
| Processing & Service Mode | Hydrogen Embrittlement Risk | Application Suggestion |
|---|---|---|
| Pickling without inhibitor + no dehydrogenation baking | Extremely high brittle fracture risk | Immediately rectify process and perform hydrogen removal |
| Inhibitor addition + post-process baking dehydrogenation | Basically eliminate hydrogen enrichment hazard | Mandatory standard process for titanium workpiece |
| Complete gas shielding welding + medium composition control | Long-term stable anti-embrittlement performance | Fluoride-containing harsh working condition priority scheme |
Conclusion
Titanium heating tube hydrogen embrittlement originates from hydrogen permeation, hydride phase precipitation and interface stress cracking. The core control methods include restraining hydrogen generation channels in production processes, forcing hydrogen escape via heat treatment, eliminating structural tensile stress and improving medium corrosion environment. Closed-loop management of processing, welding, anti-corrosion protection and daily inspection can effectively eliminate sudden brittle rupture accidents caused by hydrogen embrittlement of titanium heating equipment.
