S4 · Sensitization and Chloride SCC
Stress Corrosion Cracking (Media and Limit List for 316L/304)
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 Bill of Materials
| 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 × 30 min | Cr₂₃C₆ precipitates along the grains → chromium depletion<12% → | Low carbon/stabilized (304L/316L/321/347); solution treatment; GB/T 4334 method E; ASTM A262 method B | 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 0.1 MPa, 65 °C, Cl⁻ 120,000 mg/L, Iscc max. 26.8 % | Reduce stress, shot peening, duplex steel, high-nickel alloys | Control Cl⁻ and temperature; avoid concentrated dead corners | 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 content in welds |
| GB/T 4334; NACE related | 316LSelect Material | Material Selection | Weld Tracking | Delta-ferrite > 3% significantly reduces corrosion resistance | ASTM A249/S7; ASME BPE |
Ferritic mode, retain austenite; selectively dissolve excess austenite in corrosive mediaControl heat input/composition; maximize the S7/ASTM A249 1.25 ratio; use ≤10% austenite for cracking resistance but<4% for Corrosion ServiceTable: Standard Configuration
Specify operating conditions rather than 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 quoting and material requisition.
- Thickness range: 95–850 mm. Thin plates are usually formed parts (considering springback and deep-drawing cracking), while thick plates are usually welded structures (considering heat input and sensitization).
What are the common questions?
Which stainless steel is most used for the temperature-time-concentration limit of sensitization and chloride-ion 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 plates, consider bending and surface finish; for thick plates, welding and structural strength. Values may vary by equipment manufacturer for the same location. Re-verify with your drawing or operating conditions.
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