The Electric Discharge Sampling Equipment (EDSE) was developed by our UK based partner in collaboration with international partners to aid in the condition and life assessment of components. The sampling of in-service components has long been seen as an effective way of determining actual material properties and sub-surface material condition. However, many of the existing methods of sample removal require mechanical cutting which can deform the surface and usually require weld repair.
Unlike the traditional mechanical ‘boat sampler’, with EDSE, the surface damage if any is of the level of only a few microns. Our partner has recently used EDSE for the sub-surface material characterisation and quality checks of new and in-service P91 components. EDSE can also be used to cut out specimens for small punch testing and miniature creep, fatigue or tensile testing for more accurate quantitative life assessment.
The most accurate way of determining an aged material’s condition is through non-destructive, physical testing. For a large plant component, this is obviously impossible without taking a sample. Without care, this sample can leave the component damaged with stress concentrations and a reduced wall thickness, shortening the service life.
Based on the EDM process, the EDSE cuts out small, thin section of samples; leaving no sharp corners and without inflicting work hardening on the component surface. These samples can then be machined down to be used in creep, fatigue, tensile, toughness and hardness tests. The EDSE can cut out small slices between 1 to 20 mm thick and approximately 20mm2 or 40mm2 or 40mm x 120mm from thick section components for their remaining life evaluation and extension. The unique cutting process leaves behind cavities with round edges that do not require repair.
Advantages of EDSE
An advantage of the EDSE system is that the resulting cavity leaves rounded edges with a 4mm radius and no stress concentrations. The process of cutting uses a consumable electrode that removes material via electric spark erosion, with purified water to remove debris and provide a cooling medium. The cutting time for a standard specimen is about 1.5 hours and the EDSE can be used on horizontal, vertical and angled surfaces by either strapping to the component or through the use of a magnetic mount.