Plant Maintenance Activity Modelling for Life Cycle Costs Estimation

The present condition of competitive business environment demands production facilities to be managed effectively. The site management thus has considered its expenditure on plant maintenance as tangible information in the production planning. Consequently, engineering practice has begun life cycle costs analyses in order to provide a lifetime profitable production process by taking into account the life cycle costs of operation and maintenance. This is important in the economic evaluation of design alternatives or trade-off study. However, the engineering must first find a way to integrate maintenance with design. In addition, the estimation of the life cycle costs of maintenance faces some concerns. Firstly, maintenance continually reacts to the changes in operating requirements throughout the plant life. Secondly, plant equipment and machinery degrade and fail at any time during the operation. Thirdly, maintenance tasks are managed and planned according to the adopted policies and procedures for all installed equipment and machinery. For this purpose, this thesis proposes a maintenance activity model for evaluating the life cycle costs of maintenance activities.

The maintenance activity model has been developed through the analyses of life cycle activities in the production site. It represents the hierarchical relations among management, planning, design, operation and maintenance, and resource provision. Considering the interactions of life cycle activities, the modelling technique of IDEF0 is used in this research. Based on this model, the flows of maintenance activities can be simulated to compute the occurring costs of activities. Thus, the IDEF0 models are translated into a workflow model, and cost arguments are defined for the simulation. Model inputs include an operating scenario such as production plan and operating conditions, and equipment specifications such as construction materials, degradation models and maintenance policy or procedures. Maintenance policy or procedures are translated into simulation logic or rules. Such a modelling method allows life cycle costing for the design evaluation, and according to which maintenance requirements can be incorporated in the design specifications.

For the life cycle costs analysis, the activity model represents the actual maintenance work performed during the operation at site. To illustrate the effectiveness of the activity model and its simulation for life cycle costing, an example of a design case of process equipment in a refinery is given. The example uses actual cost data and maintenance procedures of the equipment. From the results of the simulation, the behaviour and occurrences of the maintenance workflow are practically close to those actual work carried out at site. Most importantly, it has been demonstrated that through the simulation of the activity model maintenance can be evaluated for the given operating, design and maintenance requirements, which method differs from the conventional maintenance estimations.