14. starptautiskÄ konference 2012 - Latvijas JÅ«ras akadÄmija

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Proceedings of 14th International conference „Maritime Transport and Infrastructure - 2012”abFig.3. Damages suffered by the vessela – main bearing; b – crankshaftAnother example would be a rather large fishing trawler suffering damage to her gearboxwhile operating off African coast. The damage was identified when the crew heard a severe rattlecoming out of the gearbox and seen lubrication oil gushing from it. As in the previous case – thedamage was noted already too late to be prevented and the gearbox seized it’s functioning, deprivingthe vessel from her propulsion. Eventually, the vessel had to be towed a significant distance to thenearest port of refuge, where the necessary adequate repair facilities were available.Upon investigation, it became obvious that some teeth of main gearwheel of the reductiongear and those of the secondary gearwheels were broken off. Although it was initially suspected that aforeign object got in between the gearwheels and has caused the damage, it later transpired that theaccident was actually caused by the misalignment of the gearwheels, which gradually lead to grindingof the teeth and eventually to the mentioned incident and a major breakdown.The costs involved are again quite impressive. The repairs alone would have taken 3-4 monthand would have cost in between 200,000 and 350,000 Euro. In addition to that towage expenses, 3-4month being out of service, surveyor and supervision costs and so on have to be added. All in all, theowners of the vessel were facing about a half a million to a million Euros expenses in relation to thisincident.If the AE damage detection system would have been applied on this vessel, the damage couldhave been identified at a lot earlier stage and consequently easily prevented by simply fixing thealignment of the gearwheels. This, of course, would require the owners to go through certain expenses,but in comparison to the consequences of the incident – they can be considered neglectable.Third and final example is of a small elderly general cargo coaster, loaded with a consignmentof grain in bulk. This vessel, due to her age, lack of proper hull maintenance and unfavourable weatherconditions, has suffered from multiple cracks in her hull and heavy ingress of water. Initially thedamage was noted by an extraordinary change in the vessel`s angle of list and was later confirmed in amost obvious way – by actually seeing the water gushing in through fresh openings in the hull. Thevessel had to urgently proceed to the nearest port of refuge, hoping for her equipment to be sufficientto pump out the entering water and to remain afloat, which she eventually managed to do.We believe this example to be interesting not only regarding the vessel’s structural damage,but also from her P&I point of view. The ingress of salt water has penetrated into the holds anddamaged the cargo beyond the point at which it still could have been accepted by the consignee. Thelatter has arrested the vessel and presented the owners with a cargo claim for several hundreds ofthousands of euros. Apart from the cargo claim the owners were also facing the costs of repairs neededto bring the vessel back into service, which, judging the overall condition of her wasted hull and herage might have made the vessel a constructive total loss.Application of AE would have given a clear sign that the vessel`s hull is far from a perfectcondition and that a laden sea voyage is highly not recommended, due to excessive risk. Should the116
Proceedings of 14th International conference „Maritime Transport and Infrastructure - 2012”owners have wished to keep the vessel in service – the system would have indicated which hull areasare requiring immediate repairs and would have certainly alarmed the owners not to accept cargo, thusavoiding an eventual cargo claim.ConclusionsThe most important contribution of AE to industry is that AE can provide early warnings ofsevere and sudden failures, the most dangerous characteristic of which is that they usually happenwithout a warning or with very insignificant warnings. AE can be efficiently used to detect theaccumulation of microdamage inside components, especially during service, and allow for thesefailures to be identified and, possibly, prevented.The use of AE will become more prevalent because it can provide unique insights into damageprocesses. However, the AE technology is not fully developed yet and still needs some improvements,such as noise reduction, reliability, and reducing some problems with waveform analyses. Theseneeded improvements represent areas of future endeavor in AE science and technology. There is also agreat need for further research.References1. A.Nasibulins, A.Urbahs, M.Banovs. Acoustic Emission Monitoring of Fatigue Crack Origination duringTitanium Specimens Tests. Riga Technical university. 2005.2. http://www.pacndt.com/index.aspx?go=technologies&focus=acoustic%20emission.htm3. http://www.ndted.org/EducationResources/CommunityCollege/Other%20Methods/AE/AE_Intro.htm4. http://www.tms.org/pubs/journals/JOM/9811/Huang/Huang-9811.html5. http://mech.vub.ac.be/teaching/info/Damage_testing_prevention_and_detection_in_aeronautics/PDF/acoustic-emission.pdf6. https://dspace.lib.cranfield.ac.uk/bitstream/1826/1779/1/Acoustic%20emission%20activitygear%20defect%20.pdf7. http://www.hub.sciverse.com/action/search/results?st=acoustic+emission8. Damage reports, Survey reports. Transport Claims Consultants Network cvba files 2012117
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14. starptautiskÄ konference 2012 - Latvijas JÅ«ras akadÄmija