This article presents an approach for monitoring the expansion state of water walls in coal-fired power plants using a digital twin (DT) model. The monitored boiler belongs to a 1000 MW ultrasupercritical power generating unit; it has been in service for more than 14 years and has accumulated more than 100 000 hours of operation. The fracture of the water wall has become a serious problem for safe operation. The size of the water wall is huge, the structure is complex, the stress state is changeable, and the fracture treatment is difficult. Existing online monitoring systems are mainly based on wall temperature, and it is difficult to evaluate the stress state of the water wall. However, there are few technical systems that can monitor the expansion displacement and local strain/stress of water walls online. To address this problem, a DT model is built to monitor the expansion state of boiler water walls. An optical non-contact strain monitoring system (based on digital image correlation (DIC) technologies) coupled with finite element analysis is developed to measure the actual strain/stress data and generate more simulation data for improving the accuracy of the DT model. This monitoring system provides an effective way to prevent the expansion fracture of the water wall.
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