S4 · Sensitization and Chloride SCC
Stress Corrosion Cracking (Environments and Boundary Conditions for 316L/304)
List the environments, 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 Weld Seams | Standards |
|---|---|---|---|---|---|
| Intergranular Corrosion (Weld Heat-Affected Zone / Sensitization) | 304/304L/316L | Sensitization range 450–850°C; 316L 650–725°C × 30 min | Cr₂₃C₆ precipitation at grain boundaries → chromium depletion (Cr)<12% → | Low-carbon/stabilized grades (304L/316L/321/347); heat treatment; Method E per GB/T 4334; Method B per ASTM A262 | GB/T 4334—2020; ASTM A262 |
| Stress Corrosion Cracking in Chloride Environments (SCC) | 304L/316L | SCC of 316L in dilute chlorides at 95–120°C; accelerated testing in 40% MgCl₂, 110°C; CO₂ 0.1 MPa, 65°C, Cl⁻ 120,000 mg/L, Iscc max. 26.8% | Stress reduction, shot peening, duplex steel, high-nickel alloys | Control Cl⁻ and temperature; avoid concentrated stagnant zones | GB/T 4334; ASTM G36/G123; NACE MR0175 |
| Stress Corrosion Cracking in Alkaline Environments (Caustic Embrittlement) | 304/316L | High NaOH concentration + high temperature + tensile stress | Selective intergranular corrosion near chlorides + stress | Post-weld stress relief; limit alkali concentration/temperature; select duplex or high-nickel steel | High Delta Ferrite Content in Weld Seams |
| GB/T 4334; NACE-related | 316LMaterial Selection | Material Selection | Weld Tracking | Delta ferrite > 3% significantly reduces corrosion resistance | ASTM A249/S7; ASME BPE |
Ferrite mode, austenite retention; selective dissolution of excess austenite in corrosive environmentsControl heat input/composition; maximize S7/ASTM A249 ratio 1.25; use ≤10% austenite for cracking resistance, but<4% for Corrosion ServiceTable: Standard Configuration
Specify Operating Conditions Instead of 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, serving as a starting point for cost estimation and material ordering.
- Thickness range: 95–850 mm. Thin sheets are often formed parts (accounting for springback during bending and cracking during deep drawing), while thick plates are typically welded structures (accounting for heat input and sensitization).
What Are the Common Questions?
Which stainless steel is most commonly used for the sensitization temperature–time–concentration boundary and chloride-induced stress corrosion cracking?
How many times are these 4 parts counted in total?
Which part type appears most frequently?
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, consider welding and structural strength. Values may vary among equipment manufacturers for the same location. Confirm with your drawing or operating conditions.
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