S4 · Chloride Sensitivity & SCC
Stress Corrosion Cracking (Tools and 316L/304 Threshold Reference)
List tools, grades, and threshold conditions relative to Stress Corrosion Cracking: 4 common components/processes, including recommended grades, specifications, failure causes, and standards.
Four Components and Material Reference
| Component / Part | Recommended Type | Feature / Risk | Surface | Excessive delta-ferrite in weld | Standards |
|---|---|---|---|---|---|
| Intergranular corrosion (Weld HAZ / sensitization) | 304/304L/316L | Sensitization range 450–850°C; 316L 650–725°C ×30min | Cr₂₃C₆ precipitates along grain boundaries → chromium depletion<12% → | Low-carbon/stabilized (304L/316L/321/347); solution treatment; GB/T 4334 E method; ASTM A262 B method | GB/T 4334—2020; ASTM A262 |
| Chloride stress corrosion cracking (SCC) | 304L/316L | 316L SCC in aerated chloride at 95–120°C; 40% MgCl₂, accelerated at 110°C; 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 sharp corners | GB/T 4334; ASTM G36/G123; NACE MR0175 |
| Alkali stress corrosion cracking (alkali embrittlement) | 304/316L | High NaOH concentration + high temperature + tensile stress | Selective chloride corrosion near grain boundaries + stress | Post-weld stress relief; control alkali concentration/temperature; choose duplex steel or high-nickel alloy | Delta-ferrite on the surface |
| GB/T 4334; NACE relevant | 316LMaterial Selection | Material Selection | Tracing the Report | Delta Ferrite > 3% significantly reduces corrosion resistance | ASTM A249/S7; ASME BPE |
Ferrite Phase, Austenite Retention; Failure via Additional Austenite Selection in Stainless VesselsHeat Input / Mixing Control; Increase S7/ASTM A249 Ratio to 1.25; Use ≤10% Austenite for Crack Resistance but<4% for Corrosion ServiceTable: Standard Configurations
Define operating conditions instead of specifying grades
- The most common grades in this sector are 316L (4), 304 (2), and 304L (2) — the numbers in parentheses indicate how many components they apply to, which is the starting point for quoting and material ordering.
- Thickness range: 95–850 mm. Thin sheets are often formed parts (focus on springback and deep-drawing cracking), while thick plates are typically welded structures (focus on heat input and sensitization).
What are the common questions?
Which stainless steel grade is most used for the temperature–time–concentration threshold of sensitization and chloride-ion stress cracking?
How many times are these 4 components counted in total?
Which component type is the most common?
Which component type has the highest failure rate?
For which component type should I choose thicker plate?
The thickness range in the list is 95–850 mm. For thin sheets, consider bending and surface quality; for thick plates, consider welding and structural strength. Specific values may vary by equipment manufacturer. Please re-verify against your own drawings or operating conditions.
Materials and Adjacent Sectors
304Materials and Properties304LMaterial and Properties316LMaterial and PropertiesStainless Steel Fasteners: A2-70/A4-70/A4-80/D Series and Latest StandardsStainless Steel FastenersSeawater Desalination Carbon Steel Flanges: Pressure–Temperature–Corrosion Thresholds for 2205/2507Duplex Steel and Seawater Desalination FlangesSanitary Diaphragm Valves/Sanitary Valves: ASME BPE, Ra and Temperature ThresholdsSanitary Valves