Section 5

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Slide 1

Section 5 Galvanic and Stray Current Corrosion

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Overview Galvanic Corrosion Understanding Galvanic Corrosion Controlling Galvanic Corrosion Stray Current Corrosion Understanding Stray Current Corrosion Preventing Stray Current Corrosion Testing for Stray Current

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Galvanic Corrosion Understanding Galvanic Corrosion Causes Results Galvanic Series of Metals Additional Notes

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Causes Requires Two distinct metals (cathodes) Immersed in current-conveying arrangement (electrolyte) Interconnected by a current-conveying channel

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Old Zinc following 8 months (for 1" width shaft) Results of Galvanic Corrosion New Zinc (for 1" breadth shaft)

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Galvanic Scale of Metals What is the voltage contrast between Zinc (Zn) and Copper (Cu)? In addition respectable than Stainless Steel (Passive)? An. 0.67v An. Graphite

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Additional Notes Expect consumption with 0.25 V distinction Most negative cathodes will decay Magnesium @ - 1.50 V for freshwater Zinc @ - 1.03 V for saltwater Aluminum @ - 0.75 V will decay if neither magnesium or zinc are available Zinc (or magnesium) will secure Stainless steel shaft Bronze propeller Aluminum outdrive

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Signs of Galvanic Corrosion Blistering of paint 1 st Warning Sign Formation of fine substance second Warning Sign Pitting of metal Too late Severe Galvanic Corrosion Don't treat the indication, alter the issue

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Galvanic Corrosion Controlling Galvanic Corrosion Types of Metal Area of Metals Self-Destroying Metals Use of Sacrificial Anodes Indirect Cathodic Protection Resistance of an Electrical Path Between vessels

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Types of Metal Copper, bronze and copper-nickel are perfect Avoid bronze propeller on plain steel shaft Stainless steel shaft with bronze prop might be utilized Need zinc washer and additionally zinc prop nut Avoid graphite oil

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Area of Metal Good – applying a less honorable metal to an extensive zone Bronze through-frame on steel body Bad – applying a more respectable metal to a bigger territory Steel screws/fasteners on substantial bronze or monel plate

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Self-Destroying Metals Brass (a compound of copper and zinc) Zinc will erode away in ocean water, leaving a copper wipe Stainless steel hose clips with various metal take-up screws Stainless steel ought to be non-attractive If attractive, it will consume

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Use of Sacrificial Anodes Made from dynamic metals Magnesium, zinc or aluminum Corrosive activity happens on the extra metal anode Bolted to the metal they are to ensure Never painted Replaced when half-consumed or yearly Shaft Prop Nut Rudder

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Trim Tab 6 Zincs Powerboat Zincs

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Indirect Cathodic Protection Used when direct contact impractical Zinc dashed to outside of body Inside pontoon interface with protected AWG#8 to Rudder Post Shaft (requires shaft brush)

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Resistance of Electrical Path Fresh water is less conductive than salt water Less galvanic ebb and flow Use magnesium conciliatory anodes Salt water is more conductive than crisp water More galvanic ebb and flow Use zinc conciliatory anodes Magnesium conciliatory anodes won't last Graphite oil is a fantastic transmitter, yet is a cathode Do NOT use in stuffing boxes Do NOT use on shaft course

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Between Boats Two unique metals Aluminum versus steel (or other metal) Immersed in momentum conveying arrangement Sea water Interconnected by ebb and flow conveying channel AC ground (green) wire

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Isolation Transformer Galvanic Isolator Galvanic Isolator or Isolation Transformer Stops DC ebb and flow in AC ground wire

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Stray Current Corrosion Understanding Stray Current Corrosion Causes Results Additional Notes

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Stray Current Corrosion Requires External wellspring of power From wetted metal surface (terminals) To return circuit of lower potential (electrolyte)

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Stray versus Galvanic Current Stray ebb and flow erosion is more ruinous Hundreds of times more grounded Galvanic potential contrast 0.25 to 1.5 volts Stray ebb and flow from 12 volt battery Sources of stray ebb and flow Internal from watercraft's 12 volt battery and deficient wiring External to watercraft from another wellspring of DC

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Results of Stray Current Corrosion

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Additional Notes Stronger than Galvanic ebb and flow 100 times more dangerous Metals can be comparable or disparate Current spill out of positive through electrolyte Positive DC terminal will erode Both AC terminals will consume Electrolyte is any damp surface Bilge water Wet wood Wet or sodden surface

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Stray Current Corrosion Preventing Stray Current Wiring Bonding Battery charger Galvanic isolators Isolation transformers

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Wiring Defective wiring is the most widely recognized cause Deteriorated protection on hot wire Always utilize marine review wires Run wires above water line Moist or wetted surfaces lead ebb and flow Moisture in free associations will bring about consumption Wires in bilge Waterproof terminals and butt flavors Heat recoil tubing is 2 nd decision Liquid electrical tape is likewise a choice Electrical tape is insufficient

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Bonding Maintain sufficient holding framework All metallic bodies and surfaces at DC negative Chapter 2 (Wiring) secured holding Propeller shaft holding Recommend by a few powers Will likewise decrease propeller "hash" (Chapter 7) Requires a pole brush

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AC Ground Isolation If your vessel has the better ground… and an adjacent vessel has stray ebb and flow Your pontoon will be harmed, unless… Stop DC ebb and flow in AC ground wire Galvanic Isolators & Isolation Transformers however Stray ebb and flow may move through your vessel In one submerged fitting Through holding framework Out another submerged fitting (recall eroded prop and shaft pictures)

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Corrosion Facts Not all consumption is electrical Seawater falls apart all metals Cavitation additionally dissolves props Stray ebb and flow erosion can be disposed of Galvanic consumption can be lessened and controlled DC ebb and flow is 100 times more terrible than AC ebb and flow

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Testing for Stray Current Measuring Stray Current Corrosion Source and Mitigation

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DC Neg AC Gnd A To Battery Negative To Shore Power ABYC Req Temporary break wire to embed Ammeter Bus Bar Bus Bar Measuring Stray Current Normally AC ground and DC negative associated With measure ebb and flow, embed ammeter in arrangement

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AC Stray Current Testing AC primary electrical switch "On" All branch circuit breakers "Off" Set multimeter to peruse AC ebb and flow Current ought to be under 1 milliampere Then specifically turn on every AC circuit If AC ebb and flow surpasses 1 mA You have stray ebb and flow in that circuit After testing Reconnect AC ground & DC negative transport bars

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DC Stray Current Testing DC principle electrical switch "On" All branch circuit breakers "Off" Set multimeter to peruse DC ebb and flow Current ought to be under 0.01 milliampere Then specifically turn on every DC circuit If DC ebb and flow surpasses 0.01 mA You have stray ebb and flow in that circuit After testing Reconnect AC ground and DC negative transport bars

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Testing with Mitigation Galvanic Isolators & Isolation Transformers Stop DC ebb and flow To check for stray ebb and flow with isolator Place ammeter between DC negative transport and green shore control wire to isolator To check for stray ebb and flow with transformer Place ammeter between DC negative transport and green shore control wire to transformer

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Internal DC Current Testing Turn off DC fundamental and all branch breakers Insert ammeter in battery negative link Hold down bilge pump coast switch So pump won't turn on Turn on DC fundamental and bilge pump breaker Measure stray ebb and flow, if any Defective wiring or pump switch Test other wiring with DC gadgets killed

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Summary 1 Types of electronic erosion Galvanic brought about by divergent metals Stray ebb and flow requires outer ebb and flow Galvanic ebb and flow Requires Different metals Immersed in ebb and flow conveying arrangement Connect together by ebb and flow conveying conduit Brass will crumble in ocean water Zincs are utilized to secure other metal parts

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Summary 2 Stray ebb and flow Requires an outside wellspring of ebb and flow Normally is created by blemished wiring Especially in/through bilge Make beyond any doubt any associations are waterproof DC is 100 times more damaging than AC Over 1 mA AC Over 0.01 mA DC

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