Under Deposit Corrosion | Materials And Corrosion Control
| Damage Mechanism | Under Deposit Corrosion (Cl) |
Damage Description |
A localized corrosion attack that occurs under any build up of debris/sand, adherent corrosion/scale deposits, or scratches/failures in coatings. |
Affected Materials |
Most common materials of construction including carbon and low alloy steels, 300 Series SS and 400 Series SS, aluminum, copper and some nickel base alloys. |
Control Methodology |
· Systems that contain water (cooling water, storage tanks, etc.) should be treated with biocides such as chlorine, bromine, ozone, ultraviolet light or proprietary compounds.
· Proper application of biocides will control but not eliminate microbes so that continued treatment is necessary. · Maintain flow velocities above minimum levels. Minimize low flow or stagnant zones. · Systems that are not designed or intended for water containment should be kept clean and dry. · Empty hydrotest water as soon as possible. Blow dry and prevent moisture intrusion. · Wrapping and catholically protecting underground structures have been effective in preventing MIC. · Effective mitigation of established organisms requires complete removal of deposits and organisms using a combination of pigging, blasting, chemical cleaning and biocide treatment. · Maintain coatings on the interior of storage tanks. |
Monitoring Techniques |
· In cooling water systems, effectiveness of treatment is monitored by measuring biocide residual, microbe counts and visual appearance. · Special probes have been designed to monitor for evidence of fouling which may precede or coincide with MIC damage. · An increase in the loss of duty of a heat exchanger may be indicative of fouling and potential MIC damage. · Foul smelling water may be a sign of trouble. · Conduct UT and/or RT as part of the OSI program. · Perform Internal visual inspection during T&I. |
Inspection Frequency |
· Field sampling of the free water phase on a periodic basis · UT and RT per OSI output. |
KPIs |
· Solids limit exceedance
· Microbe counts level exceedances · Number of failures caused by Under deposit corrosion |
Reference Resources (Standards/GIs/BPs) |
· API RP 571 (DM #51) |
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