Efficient maintenance of power plant components - Innovative temperature monitoring without intervention

Pressurized components in power plants are exposed to considerable stress due to frequent load changes and strong temperature fluctuations. TÜV SÜD has developed a new temperature monitoring method to detect damage at an early stage and to design maintenance plans in line with requirements - without any intervention in the components. The method improves condition analysis and allows more precise predictions to be made regarding the service life of critical system components.

Thermal power plants - especially when used as regulating power plants - work under operating conditions with frequent load changes. These lead to rapid temperature changes, causing the inner and outer walls of components to heat up and cool down unevenly. This creates mechanical stresses that accelerate material fatigue. Fittings and valves, which as central control elements in piping systems often must withstand high cyclical loads, are particularly affected. Their usually massive wall thicknesses further exacerbate the problem: the thicker the wall, the greater the temperature difference within the component during thermal load changes.

To make the operation of these components more efficient and condition-oriented, flexible monitoring and reliable forecasts of damage and remaining service life are required. However, the current practice of temperature monitoring cannot meet these requirements. In the absence of suitable alternatives, many operators continue to rely on rigid maintenance intervals - regardless of the actual condition of the components.

Reduce costs, exploit potential

Condition-based maintenance brings clear economic benefits. For example, if it is determined that a valve is only exposed to low loads and sufficient reliable data is available, the inspection interval can be extended - which enables direct savings. Particularly in dynamic regular operation, which is often associated with higher revenues, a precise assessment of the actual state of damage provides the basis for economical and safe operation, even if the components are used intensively. If, on the other hand, the interval needs to be shortened, this can be implemented in a targeted and needs-based manner using the monitoring method further developed by TÜV SÜD.

Pressure-bearing components are challenged by rapid temperature changes in dynamic power plant operation. Source: Shutterstock

Limitations of conventional methods

Conventional temperature monitoring in power plants is based on sensors that are installed in specially drilled openings within the component wall or in the flow area. This method is not only cost-intensive and time-consuming but also makes it difficult to make subsequent changes - such as adjusting the sensor position or adding new measuring points.

It is particularly problematic with complex-shaped components such as fittings and valves. Here, it is almost impossible to record the sometimes widely varying temperature curves within the material using conventional sensor arrangements. A flexible and adaptable measuring system is crucial to obtain a complete and realistic load image.

Reliable temperature monitoring - without any intervention

To meet the requirements for more precise and at the same time more economical temperature monitoring, TÜV SÜD has fundamentally developed the classic method. Instead of laboriously inserting the sensors into the component wall or mounting them inside, they are now attached to the outer wall. This is made possible by an improved calculation method that allows the internal temperature profile of the components to be reliably recalculated from the temperature curves measured on the surface. The method meets all the relevant requirements of the regulations - and does so with a high degree of accuracy.

The temperature is measured invasively with sensors or on the outer wall of the component. Source: TÜV SÜD

This form of external wall measurement has several decisive advantages: it does not require any structural interventions, which means that the sensor positions can be flexibly selected and easily changed if necessary. In addition, the system allows spontaneous, event-related recording of thermal loads - for example, when operating modes change. This allows their effects to be documented and analysed immediately.

This method creates real added value, especially for fittings and valves that are exposed to particularly frequent pressure and temperature changes. The improved knowledge of the actual loads during operation enables more precise maintenance planning, reduces unplanned downtimes and thus contributes directly to increasing operational safety.

New buildings: Gas-fired power plants as the key to the energy future

When building new modern gas-fired power plants, temperature measurement on the outer wall opens considerable opportunities to increase efficiency and reduce costs. Due to their high flexibility in operation, these plants are particularly suitable for covering the residual load. The system enables precise monitoring and control of component stress - and therefore also targeted control of material wear - particularly in the case of demanding operating requirements such as the increasing demand for fast-start capability.

In view of the gradual phase-out of fossil fuels, so-called H2-ready power plants are becoming increasingly important. These plants are already designed in such a way that they can be operated with hydrogen in the future. Reliable and adaptable monitoring of temperature loads is not only essential for current operation but also forms the basis for long-term sustainable and safe energy generation.

Comparison of the temperature curves of two start-up processes. With transient 2, the plant is started up faster and the temperature is steadily increased. Source: TÜV SÜD

TSE: Longer service life, lower costs

TSE (Temperature Stress Exhaustion) is a service package developed by TÜV SÜD that continuously evaluates and interprets temperature profiles. Instead of rigid inspection intervals, TSE analyses the actual thermal loads on components and determines the remaining service life. This allows operators to take targeted and timely action - before material fatigue leads to damage.

The intelligent combination of precise temperature monitoring and data-based service life analysis opens completely new possibilities for a predictive, economically optimized maintenance strategy.

Early detection of potential weak points

Needs-based inspection instead of rigid intervals

Reduced downtimes

Reduced maintenance costs thanks to targeted measures

Adapted operation, as critical components are continuously monitored

TSE is therefore a tool for increasing efficiency in maintenance. Operators can make well-founded decisions and optimize operating modes with a view to the service life of the components.

Offline evaluation: Deeper insight for targeted optimization

In offline evaluation, sensor data is collected over longer periods of time and then analysed in bundled form. This enables a comprehensive view of the load behaviour of components over related operating phases. In this way, complex relationships between different stresses can be systematically identified and understood.

A key advantage of this approach is the ability to run through hypothetical operating scenarios - so-called “what-if simulations”. Expert teams’ model various transient curves and analyse their influence on the component load. Particularly for systems with frequent load changes, which are typical in regular operation, this results in valuable approaches for optimizing the operating mode. The aim is to utilize the maximum dynamic potential of the system without unnecessarily impairing the service life of the components. The knowledge gained is not only incorporated into operational practice but can also contribute to the further development of the components themselves - for example in the case of planned system adaptations.

Another advantage of offline evaluation is the use of more complex calculation models, as no immediate provision of results is required. Finer calculation grids - i.e. a more precise segmentation of the component wall - make it possible to create a very accurate temperature profile. The smaller the calculation cells, the more detailed the overall picture - like a high-resolution mosaic. On this basis, specifically adapted test concepts can be developed.

The faster start-up (transient 2) is accompanied by a lower range of stresses - the material fatigues more slowly than with transient 1. The faster start-up is therefore recommended. Source: TÜV SÜD

Technical faults, such as defective sensors or transmission problems, can also be quickly identified and rectified thanks to the improved accessibility - before they affect the data quality. The result: a reliable database that can be traced at any time.

In addition, other components can also be temporarily included in the analysis if required. As a guideline, the VGB standard S-506-00-2019-02-EN recommends an annual evaluation regarding service life consumption and remaining service life - a practical basis for well-founded maintenance decisions.

Regulatory requirements and modern maintenance

When monitoring and testing power plant components, legal requirements such as the German Ordinance on Industrial Safety and Health (BetrSichV) and technical regulations such as TRBS 1201 must be observed. However, these regulations leave room for innovative maintenance strategies based on the latest technologies. By using real load data and predictive maintenance concepts, operators can not only meet the legal requirements but also make their maintenance more flexible and economical.

Future-oriented monitoring of fittings and valves

Temperature measurement on the outside of components marks a decisive advance in the maintenance of critical components - especially fittings and valves. These components are often subject to high stresses, especially with fluctuating operating conditions and large wall thicknesses. The new monitoring method provides more reliable data for well-founded decisions.

Against the backdrop of growing demands for efficiency, flexibility and security of supply, the use of such advanced technologies is becoming a key resource. They create the basis for economical, compliant and safe power plant operation - today and in the future.