Chloride Stress Corrosion Cracking: Why Stainless Fails Without Losing Weight

Stress corrosion cracking (SCC) produces brittle cracks in austenitic stainless steel under the combined action of tensile stress, chloride and temperature. Because there is little general corrosion, wall-thickness inspection looks normal right up to the failure. It is the most dangerous corrosion mode in hydrometallurgical plants.

The three-legged stool

Remove any one leg and SCC stops. Practical options therefore are: reduce chloride (process change or wash), reduce temperature, or reduce stress (stress relief, better support, avoid cold work). Alloy change removes the susceptibility leg.

Condition	Risk with 304/316	Mitigation
< 60 °C, < 100 ppm Cl	Low	Normal inspection
60–80 °C, 100–500 ppm Cl	Moderate	Duplex, or stress relief and coating
> 80 °C, > 500 ppm Cl	High	Titanium (oxidizing), duplex with care, or lined steel
Wet-dry cycling, deposits	Severe	Eliminate deposits and stagnant zones

Where it hides

Insulation that gets wet, crevices under gaskets, weld heat-affected zones, and cold-formed bends all concentrate stress and chloride. A pipe that runs dry and wet repeatedly is a classic location because chloride concentrates as water evaporates.

Detection

Visual inspection will not find it. Use dye penetrant on suspect welds, and consider acoustic emission or eddy current for critical lines. If a component fails by cracking rather than thinning, treat it as an SCC finding and inspect the whole similar circuit — the conditions that cracked one line exist elsewhere.

Design habits that help

Avoid dead legs and low points that accumulate chloride. Slope lines to drain. Do not insulate stainless lines that can get wet with chloride-bearing water unless a proper vapour barrier is used. Keep chloride-bearing wash water away from hot stainless surfaces.

Send the chloride range, temperature profile and a sketch of the circuit, and we will flag the SCC-prone locations and the alloy change with the least cost impact.