Extreme temperatures and stresses in engineering components such as steam pipes in a power plant may cause weld cracks that may grow until the pipe breaks. However, existing creep strain measurement techniques are difficult to apply in a power plant due to oxidation at high temperature over a prolonged period of time. The lack of long-term accurate creep measurement leads to poor creep life prognosis, putting European power generation infrastructure at risk. Scientists initiated the EU-funded project 'Development of a long term creep monitoring image based technique' (CREEPIMAGE) to accurately measure creep deformation and extend component life beyond the original design limits in power stations. The project used digital images for long-term creep measurement and monitoring of pipework where direct sensor attachment and human access are difficult or dangerous. Scientists integrated a digital camera equipped with a telecentric lens into a compact prototype system that allows quick deployment on a power plant pipe. They also fabricated a protective casing for the inspection coupon and trialled it on an ex-service pipe. To produce a high-density grid pattern on the inspection coupon, scientists formulated a micro laser cladding procedure, developed integrated software that allowed the operator to acquire images and calculate strain based on digital image correlation analysis. Based on a model and surface creep strain measurements, the project developed a methodology to predict component remaining life and incorporated it in the system. Comprehensive analysis of the accelerated creep test data obtained from two different pipes showed that the CREEPIMAGE system is capable of providing highly accurate creep strain measurements.
Creep deformation, harsh conditions, power stations, strain measurement, creep monitoring, component life, pipework, telecentric lens, micro laser cladding, digital image correlation