S4 · Chloride-Induced Sensitization and SCC
Stress Corrosion Cracking (Medium and Envelope Reference for 316L/304)
Identify the medium, grade, and boundary conditions relevant to stress corrosion cracking: 4 common components/processes, including recommended grades, specifications, damage causes, and standards
Four Sections and Material List
| Part / Component | 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 at grain boundaries → chromium depletion (Cr)<12% → | Low carbon/stabilized (304L/316L/321/347); solution annealing; Method E per GB/T 4334; Method B per ASTM A262 | GB/T 4334—2020; ASTM A262 |
| Chloride Stress Corrosion Cracking (SCC) | 304L/316L | 316L SCC in dilute chlorides 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 crevices where concentration can build up | GB/T 4334; ASTM G36/G123; NACE MR0175 |
| Alkali Stress Corrosion Cracking (Caustic 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 or high-nickel steel | High Delta Ferrite in Weld |
| GB/T 4334; NACE-related | 316LMaterial Selection | Material Selection | Welding Traceability | Delta ferrite > 3% significantly reduces corrosion resistance | ASTM A249/S7; ASME BPE |
Ferrite mode retains austenite; selectively dissolves excess austenite in corrosive mediaControl heat input/composition; increase S7/ASTM A249 ratio up to 1.25; use ≤10% austenite to resist cracking but<4% for Corrosion ServiceTable: Standard Configuration
Specify operating conditions instead of specifying grade
- The most common grades in this industry are 316L (4), 304 (2), and 304L (2) — numbers in parentheses indicate the number of parts in use; a starting point for quotation and material ordering
- Thickness range: 95–850 mm. Thin sheets are typically formed parts (consider springback and cracking from deep cold forming); thick plates are typically welded structures (consider heat input and sensitization)
What are the frequently asked questions?
Which stainless steel grade is most commonly used for the temperature–time–concentration envelope of sensitization and chloride-induced stress corrosion cracking?
How many times are these 4 parts counted in total?
Which part type is most common?
Which part type has the highest failure rate?
Which part type should I choose a thicker specification for?
The thickness range in the list is 95–850 mm. For thin sheets, consider bending and surface finishing; for thick plates, consider welding and structural strength. Values may vary by equipment manufacturer for the same location; verify again against your drawing or operating conditions
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