Abstract
Sampling of engineering components to produce mechanical test specimens has recently been used increasingly for post exposure stress rupture testing. In order to obtain a sufficiently large test piece, it is often necessary to remove so much material that the excavated component requires a weld repair before continuing service. Such a repair can necessitate post weld heat treatment, which may be too time consuming for critical plant. A requirement was to design and produce a method of taking small samples, without the need for weld repair of the component, by appropriate consideration of design and stress analysis criteria.
This paper reviews some current sampling methods for producing multiple specimens. Large samples can conveniently be taken by trepanning a full thickness plug, followed by a weld repair. Small samples can be obtained by a new jig, using the chain drilling principle, by joining a series of 3 mm diameter holes, leaving a small excavation requiring only blending out. Various jigs are available to produce samples for gauge diameters up to 15 mm. Very small samples can also be obtained by small, hand held cutting wheels, but these are only adequate to provide metallographic specimens.
Maximum benefit can be gained from the small samples by using them to produce specimen gauge diameters by welding on specimens’ ends. A procedure using electron beam welding has been developed and its initial application to stress rupture of test specimens is reported.
The overall procedure from initial sampling to a post exposure stress rupture programme is outlined and typical current costs are given. Total site and testing cost can be below £5000 and it offers a cost effective route to quantify an extended creep life beyond the design minimum.
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