Recent Developments and Applications of the ACFM Inspection Method and ACSM Stress Measurement Method
Alternating Current Field Measurement (ACFM) is an electromagnetic inspection method which is now widely accepted as an alternative to magnetic particle inspection in the Oil and Gas Industry, both above and below water. Although developed initially for routine inspection of structural welds, the technique has now been developed to cover broader applications across a range of industries. Increases in inspection speeds, application to non-planar crack morphologies and extension of sizing models to accommodate different crack types have all been achieved. These have required developments in both hardware and software and generally utilise array technology. This paper will describe how the use of the ACFM technique has been extended over the past few years, including examples of specific developments in a range of industries including power generation, railways and shipping. The paper will also consider one of the spin-off technologies now being developed, known as the Alternating Current Stress Measurement (ACSM) technique. ACSM is an electromagnetic method for non-contacting stress and load measurement. Examples will be given of early applications of the technique, including offshore mooring load measurement and tunnel lining stress monitoring. The Alternating Current Field Measurement (ACFM) technique is an electromagnetic inspection method for surface crack detection and sizing. The technique does not require coating removal and was originally developed in the late 1980s for use in the Oil Industry, where there was a requirement for improving the reliability and sizing capability of subsea inspection. The ACFM technique differs significantly from conventional eddy currents in using a locally uni-directional and constant electric field in the sample, which provides a number of benefits including the ability to mathematically model the perturbations in this field produced by a simple defect. The technique therefore allows crack depth sizing to be carried out by comparing measured field disturbances to predicted disturbances around pre-defined defects. The technique was originally developed for the detection and sizing of fatigue cracks, which tend to be single planar defects compatible with the model. When used to inspect more complex cracking, e.g. Stress Corrosion Cracking (SCC), the modelling becomes complex. Defect detection is not generally affected but the ability to determine the depth of complex cracks is limited by the theoretical modelling constraints. It has been found however that in certain situations, where the cracking is of a specific nature, the modelling of simple cracks can be extended empirically to provide reasonable estimates of crack severity. ECNDT 2006 - Tu.3.6.5
The detection of pipeline SCC flaws using the ACFM technique : NDT in oil & gas industries
Whilst pigging techniques are being developed to locate and size Stress Corrosion Cracking (SCC) in pipelines, the industry still relies heavily on manual inspection ofthe pipe at discrete locations to identify cracking. This normally entails excavating sections of the pipeline, removing the protective coatings and inspecting with magnetic particle testing to locate and assess the SCC area, then using incremental grinding to determine the depth. Alternating Current Field Measurement (ACFM) testing is a non-contacting electromagnetic technique normally used for detecting and sizing flaws in welds but has also been found to be able to detect clusters of SCC through coatings. The technique can operate through coatings and provide an estimate of defect depth. Sample sections recovered from pipelines containing SCC were examined using an ACFMT array probe and provided good correlation in identifying and localising the SCC indications. The equipment was then taken out to dig sites in Canada where it was used alongside MT on exposed sections of pipeline both through coating and on bare metal. The correlation with MT results was excellent and the equipment proved robust in field use. To date, models for crack depth sizing on SCC are in their infancy and more work is planned to evaluate the depth sizing predicted by ACFM.
Persius and the Programmatic Satire: A Study in Form and Imagery
Introduction 1. Style and expression in Persius' fifth satire 2. The programmatic satire and the method of Persius I 3. The nature and sources of Persius' imagery 4. Persius' first satire: analysis 5. Grandeur and humility: Juvenal and the high style Appendixes Text Translation Index of modern authors Index locorum potiorum Index of images, topics and words.