The E.ON UK ARCMAC gauge has been developed to provide for point-to-point biaxial creep strain measurements. Research is continuing to provide for strain field mapping about the ARCMAC point-to-point monitoring system. The aim is to have comprehensive monitoring of creep strain in high temperature steam pipes including bends, joints, welds and other pipe structural features. A requirement is that all creep strain measurements made satisfy the standards of the UK National Physical Laboratory that maintain liaison with the standards authorities in other countries. Creep strain and other monitoring equipment for power-station steam pipes need to be rugged and suitable for the many different locations in which they are to be installed. Appropriate equipment is also required for capturing data at different times from the installed gauges. The use of strain mapping is particularly required when monitoring non uniform sections of pipes. Results to be presented will show the current state-of-art measurement techniques now available.
Remaining life of power station high pressure steam pipes is heavily dependant upon material creep rates. However, due to the difficulty in monitoring strain in these pipes as a result of the demanding operational conditions, a rugged optical strain gauge system has been developed. The current E.ON UK ARCMAC gauge system has been validated using the UK National Physical Laboratory standard grade extensometer and provides a strain measurement accuracy of 64 micro-strain with an error of <10%. This system uses precision optics, a CCD camera and a light source system to capture images of uniaxial and biaxial optical strain gauges on steam pipes during periodic maintenance. Further developments of the ARCMAC system have included the design, manufacture and validation of an advanced ARCMAC optical measurement system with improved sensor resolution and improved accuracy. Additionally, the methodology of image processing has been studied in order to reduce errors in both the existing and the new ARCMAC systems. Finally, Digital Image Correlation (DIC) has been used alongside ARCMAC gauges to monitor strain fields around welds and defects in steam pipes. Some of these techniques have also been used in a related study into strain monitoring in wind turbine blades.
This paper presents the experimental results obtained of flexurally loaded wind turbine blade cross section material. All material was extracted from a wind turbine blade box girder and testing was conducted in four point configuration. The aim was to gain an understanding of the structural integrity of this lightweight material as it deforms in flexure. To allow for thorough analysis, digital image correlation (DIC) was used to produce full field strain maps of the deforming specimens. Results highlight the capability of the DIC technique to identify regions of failure, as well as the aspects responsible for them. Overall, the results present a foundation for tests on larger substructure, and eventually integration into manufacturing and maintenance aspects of the industry.
Weld residual stress and fracture behavior of 316L electron beam weldments, which are of particular interest in power generation industry, were investigated in this work. Two butt‐weld joints were manufactured in stainless steel 316L plates of 6 mm and 25.4 mm thicknesses. Three complementary methods were used to measure the three orthogonal components of the residual stress in the weld coupons, and fracture tests were conducted on single edge notched bending specimens extracted from different regions of the welds and parent metals. The residual stress measurements showed a maximum value of 450 MPa in longitudinal direction, while it was less than 150 MPa in the other two orthogonal directions, revealing that in our material, and with the chosen weld parameters, the residual stresses were biaxial. The fracture resistance of the weldment and parent material was similar, with material microstructure differences being more significant than the measured residual stresses. The study suggests that 316L electron beam weldments are not susceptible to fracture failure due to their high ductility and ability to relieve residual stresses through gross plasticity. Electron beam welding may therefore be suggested as a reliable manufacturing technology for safety critical 316L components.
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