Stress corrosion cracking failure refers to 316 stainless steel heating tubes bearing permanent residual processing stress, assembly tensile stress and internal pressure load for a long time while being exposed to chloride-containing corrosive medium. The combined effect of tensile stress and specific corrosive environment breaks the surface passive film locally. Microcracks germinate along grain boundaries or transgranular directions, and expand rapidly under the synergistic action of stress and corrosion. Finally, penetrating through-wall cracks form and lead to sudden pipeline rupture and medium leakage. This failure features strong suddenness and hidden danger, being a major destructive failure mode of stainless steel pressure heating pipelines in halogen ion service conditions.
1. Passive Film Rupture and Crack Propagation Mechanism
Complete chromium-rich passivation film can isolate electrochemical corrosion, but tensile stress will cause tiny slip steps on the metal surface to tear the protective layer. Chloride ions preferentially adsorb at damaged positions and erode the matrix to form initial corrosion notches. Tensile stress concentrates at the notch tip to continuously pull open the crack mouth, and corrosive medium permeates the crack tip to accelerate anodic dissolution. The crack propagates alternately under mechanical stress and chemical erosion without obvious uniform wall thinning on the pipe outer surface. Unlike fatigue crack growth driven by cyclic load, stress corrosion cracking can expand under static tensile stress alone once the corrosive medium and stress conditions are met.
2. Typical Positions Prone to Stress Corrosion Damage
Cold bent pipe sections with large residual tensile stress after bending forming;
Weld seams and heat-affected zones with welding thermal stress and uneven metallographic structure;
Flange connection areas with excessive bolt pre-tightening force generating assembly tensile stress;
Horizontal pipeline bottom sediment accumulation areas where chloride ions concentrate locally;
Pipeline sections fixed by rigid supports leading to constraint stress and deformation restraint.
3. Core Inducing Factors Accelerating Cracking Failure
Process medium contains chloride ions without filtration and ion removal pretreatment;
No stress relief annealing is performed after bending, welding and pipe processing to eliminate residual stress;
Bolt fastening torque exceeds the design standard, introducing excessive assembly tensile stress;
Pipeline layout lacks expansion joints, and thermal expansion deformation is constrained to produce thermal stress;
Long-term shutdown standby leads to medium evaporation and chloride salt crystallization enrichment on the pipe inner wall.
4. Full-Link Prevention and Control Technical Measures
① Install medium filtration and dechlorination equipment at the system front end
Fundamentally reduce halogen ion concentration to cut off the corrosion medium source.
② Carry out integral stress relief heat treatment after bending and welding processing
Eliminate internal residual stress from the material processing stage.
③ Adopt torque wrench standardized fastening to control bolt pretightening force within the specified range
Avoid introducing extra assembly tensile stress.
④ Arrange expansion joints and flexible supports in the pipeline system to release thermal expansion stress
Prevent constraint stress caused by temperature deformation.
⑤ Implement regular internal cleaning and blowdown to prevent salt precipitation and ion local enrichment
Regularly conduct penetrant flaw detection on high-stress vulnerable parts to find microcracks in advance.
5. Prevention Effect Comparison Table
表格
| Processing & Operation Mode | Stress Corrosion Cracking Risk | Application Suggestion |
|---|---|---|
| High-chloride medium + no stress relief + rigid constraint installation | Sudden through-wall cracking rupture occurs during medium-term operation | Add medium purification device and retrofit stress elimination structure |
| Medium dechlorination treatment + post-processing stress relief + flexible stress release layout | Effectively suppress crack initiation and directional expansion | Standard design specification for 316 stainless steel heating pressure pipelines |
| Online chloride ion real-time monitoring + periodic non-destructive flaw detection + whole-process stress control | Extremely low sudden pipe burst and medium leakage safety risks | Preferred scheme for chemical industry long-cycle pressure-bearing heating pipe network projects |
Conclusion
316 stainless steel heating tube stress corrosion cracking is jointly induced by tensile stress and chloride corrosive medium, resulting in rapid crack penetration and pipeline fracture. Core prevention means include removing chloride ions from the medium, eliminating processing and assembly residual stress, releasing thermal expansion constraint stress, avoiding local salt enrichment and strengthening regular flaw detection of key parts. Whole-process closed-loop management of pipeline processing manufacturing, system layout design and daily operation maintenance can eliminate production shutdown and safety accidents caused by stress corrosion rupture of stainless steel heating tubes.
