S4 · Sensitization & Chloride SCC
Stress Corrosion Cracking (316L/304 Media and Boundary List)
List the media, grades and boundary conditions associated with stress corrosion cracking: 4 typical components/processes, including recommended grades, specifications, failure causes and standards.
Four Parts and Material List
| Part / Component | Recommended Grade | Specification / Thickness | Surface | Excessive Delta Ferrite in Welds | Standards |
|---|---|---|---|---|---|
| Intergranular Corrosion (Weld SWC/Sensitization) | 304/304L/316L | Sensitization range 450–850°C; 316L 650–725°C ×30min | Cr₂₃C₆ precipitation along grain boundaries → chromium depletion<12% → | Low carbon content/stabilization (304L/316L/321/347); solution treatment; Method E per GB/T 4334; Method B per ASTM A262 | GB/T 4334—2020; ASTM A262 |
| Chloride Stress Corrosion Cracking (SCC) | 304L/316L | SCC of 316L in dilute chlorides at 95–120°C; 40% MgCl₂, 110°C accelerated; CO₂ 0.1MPa, 65°C, Cl⁻ 120,000mg/L, Iscc max 26.8% | Stress reduction, shot peening, duplex steel, high-nickel alloys | Control Cl⁻ and temperature; avoid concentrated dead zones | GB/T 4334; ASTM G36/G123; NACE MR0175 |
| Alkaline 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 Content in Welds |
| GB/T 4334; NACE-related | 316LSelect Material | Material Selection | Welding Traceability | Delta ferrite > 3% significantly reduces corrosion resistance | ASTM A249/S7; ASME BPE |
Ferrite mode, retain austenite; selectively dissolve excess austenite in corrosive environmentControl heat input/composition; maximize S7/ASTM A249 ratio 1.25; use ≤10% austenite for cracking resistance, but<4% for Corrosion ServiceTable: Standard Configuration
Determine operating conditions instead of specifying grades
- The most common grades in this industry are 316L (4), 304 (2) and 304L (2) — the numbers in parentheses indicate how many parts they apply to, as a starting point for quotation and material ordering.
- Thickness range: 95–850 mm. Thin plates are often formed components (considering springback cracking and deep drawing), while thick plates are typically welded structures (considering heat input and sensitization).
What are the frequently asked questions?
Which stainless steel is most commonly used for the sensitization temperature-time-stress boundary and chloride-ion-induced stress corrosion cracking?
How many times are these 4 parts counted in total?
Which part type is the most common?
Which part type has the highest failure rate?
For which part type should a greater thickness be selected?
The thickness range in the list is 95–850 mm. For thin sheets, consider bending and surface finish; for thick plates, welding and structural strength. Values may vary by equipment manufacturer for the same location. Recheck against the drawing or operating conditions.
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