Inadequate maintenance and unsuitable strategies repeatedly cause malfunctions, which sometimes result in significant damage and high costs. As plants are highly individual, none of the existing maintenances strategies can be implemented as is without any changes. At present, maintenance professionals rely on both deterministic and probabilistic approaches, frequently neglecting the human factor.

As well-trained and dedicated staff is crucial for qualified maintenance, internal organizations must give employees leeway to take over responsibility and make independent decisions. However, in practice, management staff and executives often give their employees too few opportunities to do so. The climate in the company should be characterized by clarity and consistency, trust and appreciation. These factors are imperative to develop and successfully implement the right maintenance strategy for process plants. However, the first step in the process should be a critical reflection on the following approaches.

Deterministics: The “if-then” Principle

Germany's technology laws are based on deterministic methods and rules that follow the “if-then” principle. Consistent compliance with the legal requirements and the technical rules and standards excludes serious risks as a result of scenarios, such as explosions. However, this requires comprehensive experience and expertise with respect to the defined safety factors, to compensate for lack of precision and uncertainties.

Preventive maintenance at fixed intervals can prevent unscheduled downtime, yet in individual cases the defined safety factors may result in excessive maintenance. If, based on deterministic methods, components and parts are replaced before they have reached the end of their service life, the costs of turnarounds and spare parts, particularly for more complex systems, will rise significantly.

Probabilistics: A Question of Time

Probabilistic strategies add the dimension of probability to the “if-then” structure of deterministic solutions. The idea behind probabilistic approaches is that technical failure is merely a question of time. This risk can be calculated by applying quantitative risk analysis (QRA) or probabilistic safety analysis (PSA). Probabilistic approaches focus on the following questions. Which parts may fail? How likely is failure and what consequences does it involve?

The approach focuses on the system rather than on individual components. It requires analysis and evaluation of the functional context of the system. By doing so, maintenance experts can determine the probability of plant failure and provide a realistic assessment of the possible consequences. Event sequences will be assessed on the basis of risk-acceptance criteria, enabling an informed prioritization of maintenance measures to be undertaken.

However, the method is generally fraught with uncertainties, as the modelling of the real-life system permits only rough approximation to real processes. In-depth and comprehensive knowledge of the plant is therefore necessary to ensure damage mechanisms and indicators of critical systems and components are correctly identified and assessed. In practice, however, many maintenance professionals lack this comprehensive and in-depth knowledge of system-related interactions.

Aligning Strategies to the Organization

Total Productive Maintenance (TPM) also pursues an integrated approach. The employees contribute their experience and knowledge of the plant's operational performance to the maintenance process, and take over maintenance and servicing tasks for their machines. However, in order to function successfully this approach requires strategic introduction within the company, as it involves a far greater number of employees than conventional maintenance solutions. Professionals must be willing to take over and delegate responsibilities. If strategies and organizations are not perfectly in step, they may lead to problems that outweigh those before the introduction of TPM.

However, successful implementation of TPM results in a continuous improvement process that eases the workload of the maintenance team. A practice-focused combination of methods and strategies enables qualified risk assessment to be made. Within the context of integrated analysis, not every fault – e.g. not every inhomogeneity or laminar material separation – needs to be repaired provided that assessment under defined service parameters has proved it to be tolerable and it is monitored in the form of periodic inspections. Dedicated analyses and optimized remediation and maintenance measures may permit even older plants to continue to run safely.

Outlook – Safety First!

Future maintenance measures will focus on plant optimization to prevent failure. Suitable strategies should consider specific plant features in their systematic assessment without neglecting safety aspects. The associated methods and their implementation in daily plant operation should be defined, taking into account business organization. In this context, buzzwords such as “TPM”, “RBI” and “value-based maintenance” are of little help.

TÜV Süd Industrie Service supports plant managers in finding and implementing the maintenance strategy that best suits their plants. System-related knowledge and pragmatic approaches are the cornerstones for optimum plant management, ensuring long-term operational safety at maximum availability.