S4 · Sensitization & Chloride SCC
Introduction and Cracking (316L/304 Material List and Boundaries)
See the Water Level List, Product Types and Limiting Conditions by List: 4 Element/State Samples, including Carrier, Specification, Causes of Failure and Standards.
Selection List for 4 Positions
| Position / Part | Recommended Grade | Size / Thickness | Surface | Primary Failure Mode | Recommended Standard |
|---|---|---|---|---|---|
| Intergranular Corrosion (HAZ/Chromium Depletion) | 304/304L/316L | Chromium depletion interval 450–850°C; 316L 650–725°C × 30 min | Cr₂₃C₆ precipitation along grain boundaries → Chromium-depleted zone → Intergranular corrosion<12% → Màng chống oxy hóa bị phá hủy | Carbon/Chromium Depletion (304L/316L/321/347); Tempering; ASTM A262 B method; GB/T 4334 E method | GB/T 4334—2020; ASTM A262 |
| Stress Corrosion Cracking (SCC) | 304L/316L | 316L SCC at 95–120°C dilute chloride solution; 40% MgCl₂, 110°C acceleration; CO₂ 0.1MPa, 65°C, Cl⁻ 120,000mg/L with maximum Iscc of 26.8% | Cl⁻ breaks down the protective oxide film + tensile stress + temperature → cracking along grain boundaries or transgranular | Eliminate stress, use duplex stainless steel, control Cl⁻ and temperature, avoid concentrated dead corners | GB/T 4334; ASTM G36/G123; NACE MR0175 |
| Post-weld stress relief | 304/316L | NaOH liquid + high temperature + tensile strain | Limit | Select duplex stainless steel or high-nickel alloy | GB/T 4334; relevant NACE |
| Excessive ferrite in homogenization | 316LWeld seam | Corrosion resistance; select thickness; delta-ferrite ＞3% | FA solidification mode, ferrite retained; excess ferrite in corrosive environments selectively dissolves | Control heat input and composition; ASTM A249/S7 maximum ratio 1.25; ferrite 4–10% for crack resistance but corrosion service requires lower | ASTM A249/S7; ASME BPE |
In the table isStandard ConfigurationSpecify service conditions rather than designating a specific steel grade.
Selection Highlights
- Most common steel grades selected: 316L (4), 304 (2), 304L (2).
- Length from 95–850 mm: thin sheet is typically used for bent finished parts (see springback during pressing and cracking under tension) and thick plate is typically used for welded structures (see heat input and oxidation).
Frequently Asked Questions
Chloride Stress Corrosion Cracking and Sensitization: which steel grade is used most within the temperature–time–concentration range?
Overall statistics show the most common grades are 316L (4), 304 (2), 304L (2).
Where do common weaknesses occur?
According to the failure descriptions, typical is "Intergranular Corrosion (Hardenability/Chromizing)": low-carbon/stabilized (304L/316L/321/347); solution treatment; ASTM A262 B; recommended grades 304/304L/316L, chromium depletion limit 450–850°C; 316L 650–725°C × 30 min. These conditions should be clearly stated during the design phase.
What thickness should be selected for the color?
Thickness values in the list range from 95–850 mm. For thin steel consider shape and surface; for thick steel consider structural strength; values for the same position may differ between equipment manufacturers—check against your drawings or operating conditions.
Material Volume and Related Industries
304Material Volume and Specifications304LMaterial Volume and Specifications316LMaterial Volume and SpecificationsStainless Steel Fasteners: A2-70/A4-70/A4-80/D Series and Latest StandardsStainless FastenersDuplex Steel Flanges and Pure Water: Pressure–Temperature LimitsDuplex Flange & DesalinationSanitary Valves/Fittings: ASME BPE, Ra and Temperature LimitsSanitary Valves