S4 · Sensitization & Chloride SCC
Stress Corrosion Cracking (316L/304 Media and Boundary List)
List the media, grades, and boundary conditions related to Stress Corrosion Cracking: 4 typical components/processes, including recommended grades, specifications, failure reasons, 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 | Cr₂₃C₆ precipitates along grains → chromium depletion Cr<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 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 concentratedDead corners | GB/T 4334；ASTM G36/G123；NACE MR0175 |
| Alkali Stress Corrosion Cracking (alkaline embrittlement) | 304/316L | High Concentration NaOH + High Temperature + Tensile Stress | Chloride selective corrosion near crystal boundaries + stress | Post-weld stress relief; limit alkali concentration/temperature; select duplex steel or high nickel | High delta-ferrite in welds |
| GB/T 4334; NACE related | 316LSelect Material | Material Selection | Track Welding | Delta Ferrite > 3% Significantly Reduces Corrosion Resistance | ASTM A249/S7；ASME BPE |
Ferrous Mode, Retain Austenite; Selectively Dissolve Excess Austenite in Corrosive MediaControl Heat Input/Composition; Maximize S7/ASTM A249 Ratio 1.25; Use ≤10% Austenite for Crack Resistance but<4% for Corrosion ServiceTable: Standard Configuration
Specify Usage Conditions Over Specifying 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 ordering.
- Thickness range: 95–850 mm. Thin plates are often formed pieces (considering bend back and deep drawing cracking), while thick plates are typically welded structures (considering heat input and sensitization).
What are common questions?
What stainless steel is used most for the temperature-time-concentration boundary of sensitization and chloride-ion stress corrosion cracking?
How many times are these 4 parts counted in total?
What 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 thicker thickness?
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. Recheck with your drawing or operating conditions.
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