Erosion-Corrosion
Erosion-corrosion is accelerated metal loss caused by the combined action of erosive wear (from fluid impingement, particles, or cavitation) and corrosion, typically producing smooth, grooved, or directional wall loss patterns.
Definition
Erosion-corrosion is common at pipe elbows, tees, and reducers where flow direction changes. It is detected and quantified by UT thickness grid surveys and by PAUT corrosion mapping.
How this damage forms
Mechanical removal of the protective film by flowing fluid combines with electrochemical attack of the freshly exposed metal. Neither mechanism alone accounts for the rate; the two together remove metal far faster than either would.
How it is detected
Ultrasonic thickness measurement at the locations flow dictates — outer radius of elbows, downstream of orifices and control valves, tube inlets — rather than on a uniform grid, because the damage is localised by hydrodynamics.
Why it gets missed
A grid-based thickness survey that does not include the flow-affected locations will miss it entirely while reporting a comfortable average.
What causes it, and what prevents it
The characteristic appearance is directional — grooves, waves, horseshoe-shaped pits undercut in the flow direction. Mitigation is by material selection, flow-path geometry, and velocity limits rather than by coating, which is removed by the same mechanism.
Codes that govern assessment
API 571 describes the mechanism and its typical locations; API 570 and API 574 drive the CML placement that finds it.
The common reporting error
Placing condition monitoring locations for convenience rather than for mechanism. Erosion-corrosion is precisely the damage that an accessible-locations-only survey is designed to miss.
Where Erosion-Corrosion fits in an inspection programme
A term is only useful when it connects to a decision. Erosion-Corrosion appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.
Related terms
- Pitting Corrosion — Pitting corrosion is a localized form of corrosion that produces small, deep holes (pits) in an otherwise relatively unattacked surface, especially in stainless steels and aluminum alloys exposed to chloride-containing environments.
Further reading
corrosion mapping with multiple ndt methods
More defect terms
Crack · Lack of Fusion · Lack of Penetration · Slag Inclusion · Porosity · Undercut · Overlap · Burn-Through · Weld Spatter · Lamination
Where this comes up in practice
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.