Editorial PT 7

Increasing Importance of Technical Quality Control because Conventional Power Plants Need to be More Flexible

New construction projects as well as different maintenance and optimisation projects that are being carried out at existing plants, show large quality deficits in manufacturing and assembly of power plant components. As documented by the papers published in the current issue of VGB Power Tech, unfortunately the quality level has not risen. In parallel, however, safety technical- and operational requirements continue to increase. The increasing fed-in of electricity based on volatile (renewable) energies has a particular effect on controllable (conventional) power plant operation.
The reasons for still existing quality deficits in manufacturing and assembly are largely known and communicated. The problems are mainly due to globalisation of manufacturing and assembly as well as the related increasing complexity of order structures between contractor, manufacturer and sub-supplier. Cultural issues like language and communication problems, but also different mentalities together with unsettled interfaces and vague manufacturing specifications further enlarge these problems. It seems to be nearly impossible to improve the situation of current projects because of the enormous work load of manufacturers and the obvious lack of experienced and skilled personnel. Besides, a large number of national and international rules and codes have to be taken into account and interpreted. The leading article of the issue of VGB Power Tech at hand by Dr Bauer and Dr Benesch on the subject of "Pro-quality Approach" is providing a valuable overview and shows the thread of VGB´s code system.
Apart from numerous indications from power plant new constructions, the focus is on controlling the quality of inspections and maintenance activities that are running throughout the year. This is urgently required because the control requirements to be met by controllable power plants are increasing with higher demand in flexibility. Existing generation plants were mainly designed for damage caused by cyclic fatigue and creep damage (thermal power plants). Due to higher flexibility of power plant utilisation, the number of start-ups, shutdowns and changing load enlarges and timely load ramps also change. Consequently cyclic stress increases, leading to a virtual shorter lifetime of plants because the design limit is defined as the total number of load cycles. These developments have the following consequences for quality control in order to minimise negative technical and economic effects:
- Early and comprehensive condition monitoring as well as age management for existing and new plants. One example can be an extended and adopted scope of NDT and monitoring.
- Additional measuring and evaluation of variables that can be used to calculate  more exactly creep fatigue, like e.g. force-path measurement and strain measurement with high-temperature strain gauges.
- Supplementing of common analytical calculation methods through FE modelling and -calculation of selected components by taking into account measured parameters for load and material.
- Revision and/or new approach of design principles against the background that in future a larger number of load cycles and an increasing part of creep fatigue will have to be permitted.
- Determination of necessary material characteristics for current and future materials.
- Supervision of construction and assembly inclusive of documentation, especially of cycling fatigue of highly-stressed components.
The challenges described can only be mastered through comprehensive quality control on both sides, i.e. manufacturer and operator. Furthermore, quality control has to remain in one hand in order to enable transfer of know-how from current operation into new projects and vice versa.