Galvanic Corrosion
Galvanic corrosion is the accelerated corrosion of the less-noble metal in an electrolytically connected pair of dissimilar metals exposed to an electrolyte, governed by the galvanic series and the area ratio of the two metals.
Definition
Galvanic corrosion is prevented by insulating dissimilar metals, by using sacrificial anodes, or by applying coatings to the cathode. Detection is by visual inspection and UT thickness measurement at dissimilar-metal joints.
How this damage forms
Accelerated corrosion of the less noble metal when two dissimilar metals are electrically connected in an electrolyte. The driving force is the potential difference; the damage concentrates on the anodic partner, worst where its area is small against a large cathode.
How it is detected
Visual examination finds it at the classic locations — bolted joints of mixed metallurgy, weld transitions, tube-to-tubesheet interfaces — and UT thickness quantifies the loss.
What causes it, and what prevents it
Control is by design: isolation, compatible pairings, coating the cathode (not just the anode), and attention to area ratios. An inspection programme should treat every dissimilar-metal junction as a named CML rather than hoping the grid catches it.
Codes that govern assessment
API 571 describes the mechanism; NACE/AMPP practices cover control; API 570/510 inspection planning should reflect it at junction locations.
The common reporting error
Coating only the anode. Coating defects then concentrate the whole galvanic current onto pinpoints of exposed anodic metal, and perforation is faster than with no coating at all.
Where Galvanic Corrosion fits in an inspection programme
A term is only useful when it connects to a decision. Galvanic 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.
- 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.
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.