"It corroded" is a description, not an explanation. Steel in service corrodes for specific reasons, in specific patterns, at rates set by specific conditions — and a corrosion failure investigation exists to name those specifics, because only the specifics tell you what to change.
Step 1: Read the morphology
The shape of the attack is the first witness:
- General wall loss — broadly uniform thinning suggests the whole surface saw an aggressive environment.
- Pitting — discrete deep holes point to local breakdown of a protective film or deposit, typically chloride-driven in stainless alloys. More →
- Attack concentrated at crevices, supports or the 6 o'clock position — geometry and water are choosing the site.
- Grooving at welds — galvanic or microstructural preference along the weld or its heat-affected zone.
- Scalloped, directional loss — flow-assisted attack or erosion-corrosion.
Step 2: Interrogate the deposits
Corrosion products and deposits carry the chemistry of the crime. Analysing them — done through the specialist partner methods each case needs — identifies the aggressive species (chlorides, sulphur species, acids), distinguishes microbiological involvement, and separates original cause from later contamination. This is why deposits must never be cleaned off before investigation.
Step 3: Reconstruct the environment
The nominal process conditions are the starting point, not the answer. What did the surface actually see? Condensation and wet-dry cycling under insulation; oxygen ingress during shutdowns; a dosing pump that drifted; deposits creating their own micro-environment. Most corrosion failures happen because the local environment departed from the nominal one — the investigation's job is to prove where and why.
Step 4: Name the mechanism, then the cause
Mechanism and cause are different layers. "Chloride pitting of 316 stainless" is a mechanism; "insulation soaked by a failed weather jacket concentrated chlorides against a surface designed for dry service" is a cause. The corrective action lives at the cause layer: change the material, the design detail, the coating, the chemistry control or the inspection plan — chosen against the mechanism actually operating, not the one everyone assumed.
What you get at the end
A defensible statement of the damage mechanism and its evidence; the local conditions that drove it; whether other locations on the asset share those conditions (usually the most valuable output); and practical recommendations — materials, design, operating or inspection changes. Our Corrosion & Integrity service →
When to contact MTIS
When inspection finds unexpected loss and the run-repair-replace decision needs a mechanism, not a guess; when a corrosion-control measure has stopped working; or when the same location keeps corroding after every repair. Preserve samples and deposits uncleaned (how →) and start a job request.