SHORT BLOCK 10R9062 - Caterpillar

Table 1
Corrosion probe
Readings in Millivolts Freely Eroding Protected Over Protected
Bronze
0–600 600–700 700–1200
Steel
0–750 750–950 950–1200
Aluminum
0–800 800–1050 1050–1200 To ensure the engine and all components on the vessel in contact with sea water are bonded correctly, the technician clamps the black cable onto the engine component being tested. This component should be in contact with seawater with the engine running. The probe on the red cable is lowered into the water along the vessel. The technician plugs the cables into any multimeter that reads millivolts. Recommended voltage potential when connected to an anode should coincide with the 244-1536 Cable Group tag (200-300 mV above the noble scale value of the least noble metal you are trying to protect). Begin bonding testing with all electrical components on board switched OFF.To complete voltage potential testing, leave both leads connected to the multimeter and the red cable lowered in the water along the vessel. Move the clamp on the black cable to anode connections inside the hull and measure voltage. Move the same clamp to all metal components in contact with seawater. Ensure the voltage potential at the 1) engine bonding stud 2) the individual anodes and 3) all metal components in contact with seawater is equal. If the voltage potential between each of these components is not equal, the anode connection may be corroded or missing and needs replaced. In any case, if the voltage potential measurement between components is not equal, troubleshooting must occur and the issue(s) should be corrected. If the reading indicates metal is eroding, anodes should be added to increase the reading. If the reading indicates the metal is overprotected, anodes should be removed.Note: When the vessel is bonded correctly, the voltage potential for all components in contact with seawater will be exactly the same. After vessel bonding and anodes have been installed, the hull needs to “polarize” – a natural process that can take up to 24 hours.To investigate stray current corrosion, turn on-board electrical components “ON” one-by-one. As components are turned “ON”, watch for changes in voltage. With any voltage change on any component, this is a sign of stray current and should be corrected immediately.Results of the Test
The voltage potential must be between 600 mV and 700 mV.Note: A value near or greater than 0.0 mV is extremely corrosive.Measure the galvanic potential of the system and apply zinc or other less noble metal to divert corrosion. Contact your Cat dealer for more information.Bonding the Marine Engine
Illustration 2 g06219255
(1) Engine
(2) Propeller shaft
(3) Sea cock
(4) Vessel anode
(5) Engine bonding conductor
(6) Common bonding conductor (wire)
(7) Hull Through-boltsThe purpose of bonding is to prevent corrosion of the cathode (engine, vessel) by providing a less noble anode. The sacrificial anode corrodes instead of the protected metal. For galvanic cathodic protection to work, the anode must possess a lower more negative electrode potential than the cathode (the target structure to be protected).Three distinct methods to protect a vessel from galvanic corrosion are recognized in the industry today:
Completed circuit between any metal