Case Study | Stainless Steel
AUT CORROSION MAPPING ON STAINLESS STEEL
Why Corrosion Matters?
Corrosion doesn’t announce itself. A vessel or tank shell can look sound from the outside while wall thickness quietly drops beneath the surface, often fastest at welds, nozzles and the waterline. Automated Ultrasonic Testing (AUT) turns that invisible degradation into a full thickness map of the asset, showing an inspector exactly where metal loss is occurring, how fast, and whether it’s isolated or spreading.
That matters because the alternative is guessing. Point readings from a handful of spot checks can miss a thinning patch sitting between grid lines. A full C-scan corrosion map doesn’t miss it, which is why AUT is the standard operators reach for when they need to sign off on fitness-for-service rather than just tick a compliance box.
“Stainless fails locally, through pitting and crevice corrosion, not uniform rust. Full-surface mapping catches it; spot checks don’t”
Why Stainless has been the exception?
On carbon steel tanks, automated corrosion mapping is routine: a magnetic crawler carries the UT probe up the shell, holds it to the surface, and scans line after line without anyone climbing scaffolding. That approach depends entirely on the shell being ferromagnetic.
Austenitic stainless steel isn’t. It’s non-magnetic, so the wheeled, magnet-adhered crawlers built for carbon steel simply can’t grip it. For years that left stainless assets, food and beverage vessels, pharmaceutical tanks, and process vessels in chemical plants without the automated option their carbon steel counterparts had, even though stainless corrodes too, particularly pitting under residue or at welds
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Traditional method
Manual, point by point: A technician marks a grid on the shell and takes handheld UT thickness readings at each point, one at a time.
Access-dependent: Reaching the full height of a tank or vessel means scaffolding, rope access, or a cherry picker, adding cost and time before any data is collected.
Sampling, not full coverage: Because every point is manual, coverage is a statistical sample of the surface, not a continuous map, so a defect between grid points can go undetected.
Slow to complete: Large stainless vessels can take days of manual gridding and reading, often requiring the asset to be taken out of service for access
Stainless tank – scanner coverage
Crawlers that adhere by vacuum or controlled airflow rather than magnetism don’t care whether the shell underneath is ferrous. That means the same continuous, automated scanning pattern operators already trust on carbon steel tanks, full-height, full-coverage, no scaffolding, can now run on stainless too.
The inspection itself doesn’t change: a UT probe payload scans line by line to build a complete corrosion map. What’s changed is that stainless no longer has to fall back on manual spot checks.