S4 · Sensitization and Chloride SCC
Stress Corrosion Cracking (316L/304 Media and Limit Reference)
Compile a reference of media, grades, and limit conditions related to stress corrosion cracking: 4 typical components/processes, including recommended grades, specifications, failure causes, and standards.
Four Parts and Material Reference
| Part / Component | Recommended Grade | Specification / Thickness | Surface | Excessive Delta-Ferrite in Weld | Standard |
|---|---|---|---|---|---|
| Intergranular Corrosion (Weld HAZ/Sensitization) | 304/304L/316L | Sensitization range 450–850°C; 316L 650–725°C × 30 min | Precipitates with Cr₂₃C₆ particles → chromium depletion at Cr<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 | 316L SCC in dilute chloride at 95–120°C; 40% MgCl₂, accelerated at 110°C; 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 corners | GB/T 4334; ASTM G36/G123; NACE MR0175 |
| Alkali Stress Corrosion Cracking (Caustic Embrittlement) | 304/316L | High-concentration NaOH + high temperature + tensile stress | Chloride selective corrosion near grain boundaries + stress | Post-weld stress relief; limit alkali concentration/temperature; select duplex steel or high-nickel | High delta-ferrite in weld |
| GB/T 4334; NACE related | 316LSelect Material | Material Selection | Track Welding | 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/structure; keep S7/ASTM A249 ratio at 1.25 max; use ≤10% austenite for crack resistance but<4% for Corrosion ServiceTable: Standard Configuration
Specify service conditions rather than specifying grade
- 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 quotations and material ordering.
- Thickness range: 95–850 mm. Thin plates are often fabricated items (considering bend-back 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 used for the temperature–time–concentration limits 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 greater thickness?
The thickness range in the list is 95–850 mm. For thin plates, consider bending and surface finishing; for thick plates, consider welding and structural strength. Values may vary by equipment manufacturer for the same location. Recheck against your drawings or operating conditions.
Related Materials and Adjacent Industries
304Materials and Specifications304LMaterials and Specifications316LMaterials and SpecificationsStainless Fasteners: A2-70/A4-70/A4-80/D Series and Latest StandardsStainless FastenersCarbon Steel Flanges for Seawater Desalination: 2205/2507 Pressure–Temperature–Corrosion LimitsDuplex Flanges and DesalinationSanitary Diaphragm Valves/Sanitary Valves: ASME BPE, Ra, and Temperature LimitsSanitary Valves