An anonymised case review for reference in similar projects (no client-identifying information).

Background: stainless 316L mullions on a coastal building showed rust spots and pitting after about two years.

Investigation:

1) On site: rust concentrated at mullion bottoms and gasket contact areas — crevices and dirt traps. 2) Testing: positive blue-dot test, indicating free iron contamination on the surface. 3) Analysis: cutting and welding during installation were not followed by thorough pickling and passivation; combined with high coastal chlorides and crevice geometry, pitting and crevice corrosion developed.

Root cause: free-iron contamination + trapped water in crevices + high-chloride environment. The material itself was not the main issue — 316L is a reasonable choice for this environment.

Remediation:

• Full pickling and passivation to remove free iron and scale. • Detail redesign: improve drainage, avoid water under gaskets, reduce crevices. • Regular cleaning, especially salt deposits in coastal areas. • Grind and re-passivate pitted areas; replace severely affected parts.

Lesson: in coastal service, choosing the right grade is only the first step — surface treatment and drainage determine service life. Require pickling/passivation records and blue-dot testing at acceptance.