S4 · Sensitization and Chloride Stress Corrosion Cracking
Stress Corrosion Cracking (Medium and Limit Checklist for 316L/304)
List the media, temperatures and limiting conditions relevant to stress corrosion cracking: 4 typical components/processes, including recommended grades, specifications, failure causes and standards.
The Four Parts and Material List
| Part / Component | Recommended Grade | Specification / Thickness | Surface | Delta-Ferrite Excess in Welds | Standards |
|---|---|---|---|---|---|
| Intergranular Corrosion (Weld HAZ / Sensitization) | 304/304L/316L | Sensitization range 450–850°C; 316L 650–725°C × 30 min | Cr₂₃C₆ precipitation along grain boundaries → chromium depletion (Cr)<12% → | Low-carbon/stabilized (304L/316L/321/347); solution treatment; GB/T 4334 Method E; ASTM A262 Practice B | 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 0.1 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 zones | GB/T 4334; ASTM G36/G123; NACE MR0175 |
| Alkaline 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 caustic concentration/temperature; select duplex or high-nickel steel | High delta-ferrite in welds |
| GB/T 4334; NACE-related | 316LMaterial Selection | Material Selection | Weld Tracking | Delta ferrite > 3% significantly reduces corrosion resistance | ASTM A249/S7; ASME BPE |
Ferrite mode, austenite retention; excess austenite selectively dissolved in corrosive mediaControl heat input/composition; maximize S7/ASTM A249 ratio to 1.25; use ≤10% austenite for crack resistance but<4% for Corrosion ServiceTable: Standard Configuration
Define service conditions rather than specifying grades
- The most common grades in this industry are 316L (4), 304 (2) and 304L (2) — the numbers in parentheses indicate the number of parts they apply to, as a starting point for pricing and material sourcing.
- Thickness range: 95–850 mm. Thin sheets are often formed parts (consider reverse bending and deep-drawing cracks), while thick plates are usually welded structures (consider heat input and sensitization).
What are the frequently asked questions?
Which stainless steel is most commonly used for the temperature-time-concentration limits of sensitization and chloride stress corrosion cracking?
How many times are these four parts counted in total?
Which type of part is 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 application. Re-check against your drawing or operating conditions.
Related Materials and Adjacent Industries
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