Failure mode
Stress-Corrosion Cracking
A load-bearing stainless part in chloride service develops fine branching cracks — not pitting, not general thinning — and fails suddenly, often at a fraction of its rated load. The surface may look almost clean right up to the crack.
At a glance
| Grades affected | 304 · 316L · 2205 |
|---|---|
| Where it shows up | Stainless Steel Sheet & Plate · Stainless Steel Tube & Pipe |
| Measured by | There is no quick acceptance test for SCC; it is avoided by material and design choice. |
| Write into the order | Identify hot + stressed + chloride · Choose duplex for the combination · Control residual stress |
Mechanism
Why it happens
Four causes account for most of it. They are not equally common, and they are not equally within the mill's control.
Tensile stress + chloride + temperature
SCC needs all three: a tensile stress (residual or applied), a chloride environment, and temperature above roughly 60 °C. Remove any one and the cracking stops.
Austenitic susceptibility
304 and 316L are austenitic and are the most SCC-prone family. The same chloride level that merely pits a cold part can crack a hot, stressed one.
Residual stress
Welding and cold forming leave residual tensile stress that acts like an applied load. This is why SCC often starts at a weld.
Concentrated chloride
Evaporation can concentrate chlorides under insulation or in a splash zone far above the bulk concentration, driving SCC where the nominal environment looked mild.
Verification
How it is measured
There is no quick acceptance test for SCC; it is avoided by material and design choice. The decision rule is the environment: hot, stressed and chloride-exposed points to a duplex (2205) or ferritic grade rather than an austenitic one. Duplex alloys resist SCC that will crack 316L.
Specification
How to specify around it
Most of these cost nothing to write into an order and are difficult to enforce afterwards. This is the part worth copying into your next RFQ.
1
Identify hot + stressed + chloride
If all three are present, austenitic stainless is the wrong family. Say the design temperature and the stress, not just "stainless".
2
Choose duplex for the combination
2205 resists SCC that cracks 304 and 316L, and doubles the yield strength at the same time.
3
Control residual stress
Solution-anneal after welding, or design the joint so residual stress is relieved, if the part must stay austenitic.
4
Watch under-insulation chloride
Where insulation can trap and concentrate chloride, the material decision has to assume a harsher environment than the bulk chemistry suggests.
On enquiries that combine load, temperature and chloride, we ask the design temperature before quoting and flag it if an austenitic grade is under-specified. Where 2205 is the right call, we say so rather than quote 316L into a known SCC risk.
We do not claim this never happens. Metal is rolled, shipped across an ocean and unloaded by someone else. What we do is ask the question before the order runs, put the answer in writing, and be the single party that answers for it afterwards.