Review and classification of industrial boilers maintenance and a reliability-centered maintenance methodology proposal for production plants

Industrial boilers are very important equipment since they play a key role on supplying more than 65% of world energy demand and because they are essential machinery in the manufacturing processes of many of industries. Moreover, they are also highly valuable assets that require suitable maintenance plans as they represent a great investment for businesses. Their costs oscillate between hundreds of thousands and millions of dollars and it is estimated that their yearly maintenance expenditure can represent between 1% and 4% of their initial cost. Nevertheless, in spite of the big potential positive impact of industrial boilers maintenance on business, there is a lack of knowledge about the current research status on this field and the most important outcomes obtained so far. In the same way, Reliability-Centered Maintenance is one of the best known maintenance approaches focused on maximizing equipment reliability whilst minimizing life-cycle costs. According to John Moubray, a pioneer in this field, reliability-centered maintenance is capable of reducing between 20% and 70% maintenance costs in plants that already have a scheduled maintenance program. However, although this approach has been very well developed for single components, still does not exist a practical and effective reliability-centered maintenance methodology which can be applied in entire production plants. This thesis presents on its first chapter all the concepts and definitions about maintenance, from the technical foundations until the managerial issues and its intrinsic relationship with the reliability discipline, which will be needed to understand the rest of the thesis. The second chapter introduces a thorough selection of the most relevant papers related to the maintenance of industrial boilers, achieved by reading and analyzing a large amount of research material from the most important scientific databases. Then, after correlating all this information it has been proposed a suitable classification for the nineteen selected papers based on their main research topic and it has also been elaborated tables providing the most significant details per each paper. In the third chapter it has been developed a practical and effective reliability-centered maintenance methodology for whole productive plants based on a previous proposal and on a study case for a steam-process plant. Improvements have been included in this 9 proposition and also diagrams and tables with the objective of standardizing this procedure. The most important findings of this thesis are: • The main research topics on industrial boilers maintenance can be classified in five categories: Robotic Solutions, Boiler Critical Failures, Advanced Measuring Techniques, Diagnostics and Maintenance Approaches. • The presence of innovative solutions pointed to increase the safety of boilers operations, such as autonomous robots performing hazardous maintenance activities and advanced monitoring techniques aimed at ensuring an appropriate and safer combustion process. • The existence of a wide variety of diagnostics solutions capable of improving the reliability and efficiency of boilers operation. It is stated from previous research that a diagnostics system can reduce boilers operative costs by 5% whilst optimization procedures can decrease them only by 2%. • The potential benefits of implementing maintenance approaches in industrial environments. The implementation of the reliability-centered maintenance methodology in a steam-process plant reduced labor costs by 25%, whilst the application of the risk-based maintenance approach in a high press water system decreased by 70% the risk factor and the application of condition-monitoring technologies allowed to improve by 28% the sustainability performance in a central boiler room. This thesis pretends to be an important milestone in the continuous search about the most efficient maintenance practices, technologies and solutions for industrial boilers and about the most effective maintenance methodologies for entire productive plants. The contributions that are provided in this work aim to be a new starting point on these fields, helping future researchers on being aware of the current research status as well as motivating further research on these areas.