S4 · Sensitization and Chloride SCC
Stress Corrosion Cracking (316L/304 Media and Boundary List)
Lists the media, steel grades, and boundary conditions related to stress corrosion cracking: four representative components/processes, including recommended grades, specifications, failure causes, and standards.
Four Components and Material List
| Component / Part | Recommended Grade | Specification / Thickness | Surface | Excessive Delta-Ferrite in Weld | Standard |
|---|---|---|---|---|---|
| Intergranular Corrosion (Weld Heat-Affected Zone/Sensitization) | 304/304L/316L | Sensitization range 450–850°C; 316L 650–725°C × 30 min | Cr₂₃C₆ precipitates along grain boundaries → chromium depletion at Cr<12% → | Low carbon/stabilized (304L/316L/321/347); solution annealing; GB/T 4334 Method E; ASTM A262 Practice B | GB/T 4334—2020; ASTM A262 |
| Chloride Stress Corrosion Cracking (SCC) | 304L/316L | 316L SCC in dilute chloride at 95–120°C; accelerated in 40% MgCl₂ at 110°C; CO₂ 0.1 MPa, 65°C, Cl⁻ 120,000 mg/L, Iscc up to 26.8% | Reduce stress, shot peening, duplex stainless steel, high-nickel alloys | Control Cl⁻ and temperature; avoid concentrated crevices | GB/T 4334; ASTM G36/G123; NACE MR0175 |
| Alkali Stress Corrosion Cracking (Alkali Embrittlement) | 304/316L | High-concentration NaOH + high temperature + tensile stress | Selective chloride corrosion near grain boundaries + stress | Post-weld stress relief; limit alkali concentration/temperature; select duplex stainless steel or high-nickel alloy | High Delta-Ferrite in Weld |
| GB/T 4334; NACE related | 316LMaterial Selection | Material Selection | Weld Traceability | Delta-ferrite > 3% significantly degrades corrosion resistance | ASTM A249/S7; ASME BPE |
Ferrite mode, austenite retention; selective dissolution of excess austenite in corrosive mediaControl heat input/composition; maximize S7/ASTM A249 ratio to 1.25; use ≤10% austenite for crack resistance<4% for Corrosion ServiceTable: Standard Composition
Specify Service Conditions Rather Than Grade Designation
- The most common grades in this industry are 316L (4), 304 (2), and 304L (2); the numbers in parentheses indicate the number of applicable components and serve as a starting point for quotations and material ordering.
- Thickness range: 95–850 mm. Thin plate is mainly for formed parts (consider bend-back and deep-drawing cracks), while thick plate is generally for welded structures (consider heat input and sensitization).
What are the frequently asked questions?
Which stainless steel is most commonly used for the temperature-time-concentration boundaries of sensitization and chloride-ion stress corrosion cracking?
How many times are these four components counted in total?
What is the most common component type?
Which type of component has the highest failure rate?
Which type of component should use thicker gauge?
The thickness range in the list is 95–850 mm. For thin plate, consider bending and surface finish; for thick plate, consider welding and structural strength. Even at the same location, values may vary by equipment manufacturer. Reconfirm with drawings or operating conditions.
Related Materials and Adjacent Industries
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