The port service arm of KCI Konecranes pulled together some comments for PS from a number of their engineers, which are worth repeating. They say that external failures, which by their nature are difficult to foresee and forecast, are much more probable reasons for crane malfunction than internal failures. These might take the form of collisions with other cranes or objects, or other operational errors such as rough usage of the loading devices by the operator.
Also, says Konecranes, into the same human error category can be included maintenance and installation errors such as a wrongly adjusted mechanical component (e. g. alignment of a coupling) or a wrong setting value of an electrical one (e. g. protection fuse is set for too high a current). Continuous training, in the fields of operation, maintenance and safety, as well as motivated personnel, are critical when it comes to the prevention of external failures they say.
Internal failures, if they do arise, are likely to be during the first hours, or maximum first months, of the use of a new or electrically refurbished crane. Here, the occurrence of electrical, electronic or automation related failures is most probable, possibly due to cable or other electrical misconnections or to defective components such as faulty electronic cards. After any such teething troubles these components are likely to run for their full lifetimes from several years to decades.
Newer cranes of course are more reliable in terms of improved (computer-aided) calculation methods resulting in optimisation of selected components and materials, as well as in terms of the continuous product development of components. Also improved maintenance practices, aided by sophisticated computer programmes able to collect maintenance data, are constantly improving the reliability of the crane operation, although not the actual crane itself.
Significantly, says Konecranes: “One also has to consider tough competition amongst crane manufacturers, thus sometimes the crane manufacturer may not be able to select the better (and usually more expensive) component.” What was it the astronaut said?
On preventive maintenance, Konecranes advises: “Frequent followup (i. e. condition monitoring) of certain major components such as steel ropes and related components, as well as meggering and maintaining electrical motors, correct lubrication of the gear reducers and greasing of bearings and joints, should be the initial phases for developing sound preventive maintenance practices.”
Monitoring can take the form of frequent measuring or visual observation of certain components, in order to verify the condition and react if necessary in a corrective way including terminating operation. These practices – observations, indications and actions – should be collected and stored to a database where the information is easily available to all relevant personnel for future purposes.
“The crane’s steel structure, single machineries and single components, are usually calculated for a theoretical lifetime (20 years for example), ” says Konecranes, “which definitely does not mean any foreseeable total breakage of welded seams for instance, or a particular component, after this point in time. Usually it means the occurrence of fatigue-cracks could increase after that point, which means even more attention should be paid to preventive maintenance and inspections such as steel structure surveys.”
Konecranes has some final advice: “This theoretical lifetime is basically the function of the total duration of use (cycles and/or hours) and the load spectrum (i. e. “average” load and/or stress). These factors should be specified and understood together, before the design of the crane, by the crane manufacturer and the operator of the crane, in order to optimise the crane design for the intended use and purpose. These factors specify the classification of the crane by determining the permissible stresses on the steel structures in terms of fatigue, thus basically the more demanding the use, the lower stresses allowed. Some other characteristics will also influence the crane’s classification and design such as any special requirements of the operator, ambient environment (temperature, humidity, etc. ), and the cargo to be handled by the crane.”
E.Konecranes has a product called Crane Reliability Survey (CRS) which evaluates the remaining lifetime of the crane. In this CRS, the actual use of the crane over its accumulated past lifetime is compared with the original design lifetime and design characteristics of the crane, thus as a calculation result, the theoretical remaining lifetime of the crane, which could be say 55% meaning the crane has just entered the latter half of its remaining lifetime, can be achieved.
“Also unusual usage and various incidents must be considered in this calculation, either increasing (e. g. minor or easier use, refurbishments, etc. ) or decreasing (e. g. collisions, poor or unsuccessful repairs, demanding sea transportation, etc. ) the theoretical, remaining lifetime. The environmental study, thus considering the ambient temperature, humidity, chemical load from the environment and from the material handled, direct sunlight, wind conditions, etc. and the estimated combined influence of these on the crane structures and mechanical and electrical components, should also performed as part of the CRS.”
Konecranes stresses the need for the condition monitoring of certain components such as steel ropes. For George Deden of the Weyenberg Group, providers of electrical engineering services and the supply of crane parts and components, this is the most striking item:
reliable, high-quality ropes for main hoist and trolley motion applications.
Weyenberg represents Germany’s DIEPA in Vietnam, Sri Lanka and India and Deden explains that they are currently working on this issue:
“We compile papers showing the incredible loss of income as a result of the usage of low-quality (= cheap! ) wire ropes. We are in the middle of a test with one terminal user right now. So far they have been using Indian-made wire ropes which fail approximately two months after they are put onto the cranes. There is no point ‘comparing’ the prices of those ropes with those of our principal, but the point is that the far costlier German-made wire ropes have a much longer lifetime, in addition to the fact that they do not need to be lubricated on a regular basis. This supposedly big initial investment is a drop in the ocean compared with the yield from more boxes handled due to fewer crane downtimes. We have been attempting to do a chart on the matter, but frankly, the cost vs yield ratio is so very much higher compared to cheap wire ropes, you might think we were kidding!”
