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Suspension Bridge Investigation Shows ESR's Investigative Capabilities

NCT have recently completed a large investigative programme of a suspension bridge in collaboration with the Royce Institute. The aim was to conduct an in-depth metallurgical inspection of cable wires removed from a bridge. Of interest was the existence of pre-existing cracks in the wires, and the effect of corrosion on the wires.

The wires removed were subject to a vigorous testing regime to determine their structural and chemical composition. The structural testing comprised fatigue testing (up-to 250,000 cycles), and tensile testing performed to standards ASTM E466, 586, and A370. During this stage NCT carried out nearly 1500 tensile tests over the course of two months, these were long wire tests that required specially manufactured extensometers with a gauge length of one meter.

Once fractured during structural testing the fracture faces of the wires were further examined as this provided insight into the ductility of the wire and could show what effects corrosion had on the wire.

The wires were investigated using a scanning electron microscope (SEM) to determine the morphology of the fracture faces, following this a chemical analysis was carried out using ICP analysis to determine the makeup of the wire. Some select samples were also analysed for hydrogen to examine the link between corrosion and hydrogen content.

This work highlights the need for in-service inspection and regular thorough examination of safety critical components. NCT is very familiar with material standards and regulations along with having a well-equipped laboratory that allowed us to undertake this massive task successfully.

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