S4 · Sensitization and Chloride Stress Corrosion Cracking
Stress Corrosion Cracking (316L/304 Media List and Limits)
List the media, temperatures and boundary conditions related to stress corrosion cracking: 4 typical components/processes, including recommended grades, specifications, failure causes and standards.
Four Components and Material List
| Part / Component | Recommended Grade | Specification / Thickness | Surface | Excess 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 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 |
| 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 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; selective dissolution of excess austenite 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 components each applies to, as a starting point for quotation and material requisition.
- Thickness range: 95–850 mm. Thin plates are often formed parts (consider reverse bending and deep-drawing cracks), while thick plates are typically welded structures (consider heat input and sensitization).
What are the frequently asked questions?
What is the most commonly used stainless steel for the temperature-time-concentration limits of sensitization and chloride stress corrosion cracking?
How many times are these four components counted in total?
Which type of component is the most common?
Which type of component has the highest failure rate?
For which type of component 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, consider welding and structural strength. Values may vary by equipment manufacturer for the same location. Re-check against your drawing or operating conditions.
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