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Under-deposit corrosion mechanism caused by reaction of phosphate with magnetite form maracite. Most often found in high heat areas of the boiler. Typically associated with boilers suffering phosphate hideout and using disodium phosphate or sodium hexametaphosphate.
Issue Type:Holes, Pits, Gouges » Waterside
Mechanism:Acid Phosphate Attack
Download a PDFUndercut corrosion, multi-color deposits (red, white, black). (This is a view of a tube ID following cleaning.)