Why is my 316L mesh pitting in brine or chloride service?

The symptom

Pinhole perforations and rust-brown spots on stainless mesh or elements, often within months in warm chloride streams. Failures cluster at crevices, clamped edges and welds; the bulk material still looks bright.

Root causes

1. 01 Chlorides above what 316L tolerates: pitting resistance is finite, and rising temperature lowers the threshold sharply.
2. 02 Crevice corrosion at overlaps, gaskets and clamped edges: the crevice concentrates chlorides and depletes oxygen, so attack starts where you cannot see it.
3. 03 Weld zones without proper post-treatment: heat tint and local sensitisation make the weld the weakest point in an otherwise adequate alloy.
4. 04 Stagnant conditions during standstill: chloride-bearing liquid left in the system during shutdowns does more damage than weeks of operation.

The mesh solution

• ▸ Move up the alloy ladder deliberately: Duplex™ where strength and chloride resistance meet, Monel™ for brine and seawater atmospheres, Hastelloy™ where aggressive chemistry stacks on top.
• ▸ Design out the crevices: continuous welds instead of overlaps, edge finishing and gasket choices that leave no stagnant gap.
• ▸ Specify weld treatment (pickling/passivation) as part of the fabrication, with material certificates documenting it.
• ▸ Where the alloy jump is too expensive plant-wide, upgrade only the wetted, hot or crevice-prone components; mixed-material design is normal practice.

Prevention

• ⊕ State chloride level, temperature and pH in the RFQ; a material choice without those three numbers is a guess.
• ⊕ Flush and drain chloride-bearing systems before standstill; stagnant shutdown weeks are the hidden killer.
• ⊕ Inspect crevice locations and welds first at every turnaround: that is where the next failure already lives.