Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering Transport Technology
H. van Doesburg The implementation of maintenance and repair programmes for a backhoe into an on-line management system. Masters thesis (2nd part), Report 97.3.GV.4848, Dredging Engineering.
Skanska Dredging AB, located in Göteborg, Sweden, is currently renewing its maintenance planning and routines to improve reliability and availability of their dredgers. A well thought maintenance concept is needed for that purpose. To develop a suitable maintenance concept the present maintenance situation, the failure behaviour of components and the effectivity of the dredger must be established first.
In chapter 3, 'Statistics on Storken' a statistical analysis of the backhoe Storken is carried out. This analysis was carried out with help of a functional decomposition of Storken, which enables to assign failures to the components responsible. The statistical information available is however limited to the daily reports of 1996 and the journals of hydraulic cylinders and hydraulic main pumps. The analysis of Storken's effectivity of 1996 showed that this effectivity is about 55%, which is considered to be quite low. The main reason for this low effectivity is that 24% of System Duty Time (SDT) was spent on carrying out repair activities, which is, even for a twelve year old backhoe dredger, too much. Reasons for this are (ranked):
1. Age of the machine
2. Too low level of Preventive Maintenance (PM) 3. Excavator operation
Reason 2 is subject of this report. Increasing the level (its frequency) of PM may give possibilities to improve the reliability and availability of Storken. Increasing this level is however not always effective and depends on the failure behaviour of the components analysed.
To help selecting effective maintenance policies a Repair and Maintenance System (RMS) (chapter 6) is developed. The RMS developed helps defining effective maintenance policies on basis of a significance and risk analysis of failure consequences and their rate of occurrence (imported from the database) or by simulating this rate. The RMS consists of a number of modules with different functions. These modules are linked, except for the economic analysis module that can be operated independently. The theories used in this RMS are inspired on the MA-CAD method by Vucinic. Results of the RMS can be exported to the database that stores information about components, maintenance planning and cost.
The RMS is applied on the excavator attachment and the hydraulic system. The excavator attachment, which is responsible for 35% of down-time of 'normal' failure behaviour, has to be inspected every week for initial cracking in the boom, the stick and the bucket. Cracks, if any, can be discovered and preparations for repair activities (Corrective Maintenance or CM) can be taken. The condition of the bushings has to be checked as well. The cost of these inspections (OCPM activities) will be calculated in the evaluation of this report.
The hydraulic system (chapter 5) accounting for 20% of 'normal' failure behaviour is studied more accurately. The functional decomposition is made to the level of component types for this hydraulic system, Together with the RMS, this results in a set of maintenance activities to be carried out, like weekly inspections to determine the state of various items of the hydraulic system. Amongst others the hydraulic pressure hoses, their fittings, filters and the oil must be inspected. PPM can be applied to pumps, filters, hydraulic cylinders and hydraulic pressure hoses. For hydraulic pumps and cylinders overhaul intervals already exist, but these proved out to be too long. An economic analysis of these activities, including spare parts cost will be carried out in an evaluation in accordance with the last assignment.
Skanska has purchased AMOS (chapter 9), to register and plan maintenance. The potential of this system is big as it controls spare part administration, purchase orders, maintenance planning and supports failure registration and RMS Outputs. It also enables a detailed failure registration. The success of the system depends however amongst others on the input of the system (maintenance plans) and the motivation of the crew to work with it. Due to
programming errors the system is not fully operational right now, so a fair judgement about this system can not be made at this moment. Reports on Transport Engineering and Logistics (in Dutch)
