S4 · Sensitization and Chloride SCC
Stress Corrosion Cracking (316L/304 Media and Boundary List)
List the media, grades, and limiting conditions related to 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 HAZ / sensitization) | 304/304L/316L | Sensitization range 450–850°C; 316L 650–725°C ×30min | Precipitation of Cr₂₃C₆ along grain boundaries → chromium depletion<12% → | Low carbon/stabilized (304L/316L/321/347); solution annealing; Method E GB/T 4334; Method B 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% | Reduce stress, shot peening, duplex steel, high-nickel alloys | Control Cl⁻ and temperature; avoid concentrated dead zones | 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 or high-nickel steel | High delta-ferrite in welds |
| GB/T 4334; related NACE | 316LSelect Material | Material Selection | Trace the Weld | Delta ferrite > 3% significantly reduces corrosion resistance | ASTM A249/S7; ASME BPE |
Ferrite mode, retain austenite; selectively dissolve excess austenite in corrosive mediaControl heat input/composition; maximize the S7/ASTM A249 ratio of 1.25; use ≤10% austenite for crack resistance but<4% for Corrosion ServiceTable: Standard Configuration
Specify Service Conditions Instead of Grades
- The most common grades in this sector 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 sheets are often formed parts (considering springback and deep-drawing cracking), while thick plates are typically welded structures (considering heat input and sensitization).
What Are the Common Questions?
Which stainless steel is most commonly used for the temperature-time-concentration boundary of sensitization and chloride stress corrosion cracking?
How many times are these 4 parts counted in total?
Which type of part is the most common?
Which type of part has the highest failure rate?
For which type of part should I choose a greater thickness?
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 by equipment manufacturer for the same position. Recheck against your own drawing or operating conditions.
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