Validation and Optimization of ARCMAC and Strain Mapping Systems for Creep Measurement

Research is ongoing to validate and optimize the E.ON UK auto-reference creep management and control (ARCMAC) system for high temperature piping creep measurement. In conjunction with the ARCMAC system, research is also being undertaken to incorporate digital image correlation (DIC) into creep strain evaluation, via a rugged high temperature pattern. The aim is to have comprehensive monitoring of creep strain in high temperature steam pipes including bends, joints, welds and other pipe structural features. This paper firstly presents work done into the determination of the best method to capture and process ARCMAC images. It was found that a bi-cubic interpolation resizing function with a combined high light intensity image gives the best results with respect to accuracy and repeatability of image acquisition. Also presented was the testing of a modified (prototype) ARCMAC camera with modified (prototype) ARCMAC gauges. The prototype ARCMAC camera, based on a DSLR camera, is approaching the accuracy of the conventional ARCMAC but an improved lens system would be desirable. For the prototype gauge, it was found that the edge-finding technique using the knife-edge was just as accurate as using the target ball reflection for strain analysis. Both techniques can be used independently to evaluate creep strain. Finally, preliminary high temperature testing results for both the ARMCAC and DIC technique are presented. For the ARCMAC gauge and the DIC high temperature pattern, small changes in strains were observed over time that were not due to sample deformation. Reasons for these small changes in strain were identified and solutions arrived at. All results are very promising and it is foreseen that a combined ARCMAC/DIC tested technique will be applied to plant piping components soon.