Aea Technology Inc.

Maps Technology Limited

Esr Technology Limited

William Dalzell

David John Buttle

Peter John Thayer

Geoffrey Charles Eckold

Stephen Frank Burch

A flexible elongate structure, such as a flexible riser () for connecting oil and gas wells to floating production platforms, comprising at least one layer () of steel wires near the surface which extend at least partly along the length of the structure, can be monitored by inducing a magnetic field in the steel wires using an electromagnetic coil, and monitoring the magnetic flux density near the surface of the structure so as to detect if any wires have broken. Measurements are made at two different frequencies, the lower frequency giving an output dependent both on stresses and on the number of adjacent wires in the layer (), and the higher frequency giving an output primarily dependent on the number of these wires. By comparing these two measurements a corrected output parameter (P) may be obtained that is indicative only of stress. A break in a wire can be expected to change the stress in that and adjacent wires.

Detecting failures in flexible multistrand steel structures

A flexible elongate structure, such as a flexible riser (), comprising at least one layer () of steel wires near the surface which extend at least partly along the length of the structure, can be monitored by inducing a small, alternating magnetic field in the steel wires using an electromagnetic coil, and monitoring the magnetic flux density near the surface of the structure so as to asses the stress and hence detect if any wires have broken. By using an array of stress-measuring electromagnetic probes () around the structure some spatial resolution can be provided as to the location of any break in the wires.

Detecting failures of flexible multistrand steel structures

In a railway line, thermally-induced stresses are a factor for both rail breaks and rail buckling. These stresses are in the longitudinal direction. A nondestructive measuring technique enables the residual stress in a rail to be determined, and hence the thermally-induced stress. An electromagnetic probe is used to measure the stresses in the rail web in the vertical direction, and in the direction parallel to the longitudinal axis. The residual stress in the longitudinal direction can be deduced from the measured stress in the vertical direction; hence the thermally-induced stress can be determined.

Measurement of residual and thermally-induced stress in a rail

The onset of rolling contact fatigue in an object may be detected by measuring the residual stresses in the surface of the object, and monitoring changes in their magnitude or their direction. The values of residual stresses in the surface are those averaged over a depth that may be in the range say 0.1 mm to 8.0 mm, for example about 2.5 mm. For ferromagnetic objects such as rails, the method may utilize an electromagnetic probe. Prior to rolling contact fatigue the surface stresses are compressive, and the onset of rolling contact fatigue may be characterized by a marked decrease of the stress in the generally transverse direction.

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Winchester, United Kingdom

William Dalzell