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Contract Number:
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Design Number:
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| Library File Number: | Submitted Date: 01/24/2012 |
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SR/Terminal/Vessel: M/V Chetzemoka |
Region: WSF |
| Contract Title: M/V Chetzemoka Keel Cooler Leak, Port Townsend, Washington on August 6, 2011 | |
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EXPERIENCE: Describe the particular situation or event. The Chetzemoka’s No. 2 ship service diesel generator developed a hole in the charge air keel cooler. The keel cooler is attached to the outside of the hull and this multi pass tubular cooler allows heat to exchange between the engine coolant water and the sea water circulating around the cooler. This hole in the cooler caused the engine to lose coolant water and rendered the machine inoperable. The US Coast Guard was notified and a repair plan was developed. The vessel was removed from service for two days to affect the required repairs, to investigate the cause of the failure, and to make improvements in the keel cooler bonding scheme. Several corrosion experts were employed to give opinions on the cause of the failure. The builder was notified of the failure and they were given an opportunity to inspect the cooler while the vessel was on dock. The failed cooler and several bonding straps were sent for a forensic analysis. Findings indicate that the bonding strap protecting the keel cooler had failed due to ‘reversed bending fatigue’ and was progressive in nature and most likely due to vibrational forces. There was no indication of metallurgical abnormalities. |
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LESSON: Describe what knowledge was gained from the experience. Once the bonding strap failed, the cooler was no longer electrically protected and the cooler itself became the sacrificial anode instead of the zinc anodes provided for that purpose. According to the corrosion experts' report, corrosion progressed uninhibited. As the corrosion scale progressed, it continually sloughed off from erosion, which in turn exposed fresh metal. This cycle repeated itself until the cooler thickness was perforated and failed. The vessel’s construction technical specification was referenced to determine the requirements with regard to the installation and bonding of the vessels keel coolers. The specifications called for two anodes to be affixed to each keel cooler guard and each of the anodes should be electrically bonded to the keel cooler with a hard copper bar bonding strap. The keel coolers were all found to be bonded on only one end and with a solid copper wire, not a hard copper bar as specified. The failure of the lone copper wire was the root cause for the keel cooler failure. The contractor's failure to use specified material and not adhering to the installation specifications attributed to the failure. |
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RECOMMENDATION: Describe how the knowledge gained can be used. WSF undertook immediate improvements in the bonding strap material employing a solid copper bar bonding strap. The quantity of bonding straps were doubled, as per the construction specifications, replicating the successful application of bonding straps on WSF’s Issaquah Class ferries which also have keel coolers. On subsequent occasions, these improvements were carried out on the MV Salish and the MV Kennewick. |
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Project Delivery Method: Design-Bid-Build Design-Bid-Build Phase: Operations |
Categories: Restrooms/Sewage/Water Systems |
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