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Tubestress: measures residual stresses in hard to reach areas

Back to Pre-1998 Articles Adhesive technology demonstration centre Aged samples lend added credence to safety codes Arc welding Demonstration Centre shows best practice in action Boiler takes the heat in comfort Conductive adhesive for ultrasound catheter cracking-risk-in-steel-pipelines-from-external-hard-zones Engineering critical assessment of pipeline welds Far East fitness-for-purpose check First UK Research Council contract for TWI Friction stir welding of titanium Help with adhesives training Joining demonstration centres in industry Joining Forces success in Belfast Joints take 10 seconds in the microwave LIVEMAN - Advanced joining processes for lightweight vehicle manufacture Making calculations easier 'Mildly sour' environment project saves half a million pounds New standard for weld fracture toughness testing Novel method joins plastic pipes Plastics fume - new findings released Project saves time and money for Amerada Hess Small firms seize no-cost reviews and low-cost trials South East Asia ACFM course Space Shuttle technology transferred to power generation industry Spot the evidence Structural integrity assured for Liverpool Bay Supporting technology on the Indian sub-continent Technology demonstrators show best practice in action Thermomechanical material processing by friction [friction pillar processing] 'Tubestress' measures residual stresses in parts that other equipment cannot reach TWI enhances on-stream inspection service Underwater welding work expands at TWI North Wider recognition for welding inspectors
 

Connect, no.79, September 1996

Specialised equipment for measuring residual stresses using the centre hole strain gauge method has solved the problem of locations with restricted access. Conventional centre hole equipment requires headroom of at least 200mm and clearance of about 30mm from internal corners. TWI's Structural Integrity Department has developed Tubestress for measuring residual stresses inside 70mm diameter tubes, and Cornerstress for measurement locations at 11mm from an internal corner.

Both sets of equipment have a borescope for viewing the centre hole gauge and a tungsten carbide nozzle for machining the centre hole - typically 2mm deep, 2mm diameter - using a jet of abrasive powder.

The borescope and nozzle are mounted on micrometer controlled, three-axis slides. The slides are used in conjunction with the borescope for initial alignment of the equipment with the strain gauge, moving from the viewing position to the machining position and measuring the diameter and position of the hole. Accurate alignment of the hole with the centre of the gauge is critical: the tolerance on hole eccentricity is 20 microns.

TWI Tubestress and Cornerstress equipment has been used in major projects for clients in power generation, defence and nuclear waste disposal applications. The equipment can be customised for measurements in other locations with limited access.

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