The lubricating oil system supporting the main propulsion reduction gear on the fishing trawler to which you are assigned is fitted with a sea water cooled 4-pass shell and tube lube oil cooler. The water box sacrificial zinc anodes must be inspected periodically. Which of the following listed actions correctly states maintenance criteria pertaining to scale build-up on the zincs?
• Sacrificial zinc anodes purpose and how they work in preventing galvanic corrosion • Effect of scale or marine growth on electrical contact between zinc and the surrounding seawater • Difference between removing scale and over-cleaning or replacing anodes
• Think about how sacrificial zinc anodes actually protect steel: do they need direct contact with the seawater to work effectively? • If a hard, insulating layer forms on the outside of the zinc, what happens to its ability to sacrifice itself electrically? • Would you want to throw away an anode just because it has some buildup, or would you want to maintain it so that it can keep working as long as possible?
• Verify whether scale tends to be electrically insulating or conductive in seawater environments • Consider whether the visual shininess of the zinc is a necessary condition for it to provide protection • Think about routine maintenance: is it more typical to clean and continue using sacrificial anodes, or to replace them at the first sign of scale?
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