CableScan - Cable Inspection for Bridges

CableScan is a cable inspection service that utilizes the magnetostrictive sensing method (MsS) developed and patented by Southwest Research Institute (SwRI). MsS represents a major breakthrough in bridge inspection technology.

Literature

Corrosion of cables or ropes is not always evident from visual inspection, as corrosion often originates in the interior of the cable. Other non-destructive techniques have been used for bridge cables, such as magnetic flux leakage, dynamic analysis, or X-ray inspection. However, all of these techniques rely on bulky equipment or provide inconclusive results. CableScan is the only technique currently available that is capable of detecting and reporting the location of corrosion damage with equipment that is light and easy to use in the field.

CableScan can identify anomalies in bridge cables from a single location on each cable. This means that engineers and bridge owners can now undertake fast, accurate non-destructive evaluation of cables without the need for heavy equipment or complicated access requirements. A 300-foot-long suspender rope can be inspected in as little as 15 minutes, depending on access. The system can detect and locate broken wires and loss of cross-section along the full free length of a cable. It also provides a baseline of cable condition for comparison with future inspections.

Advantages of Cable Scan

  • Locate broken wires and loss of cross-section
  • Full cable length inspection
  • Lightweight equipment
  • Ease of use
  • Fast inspection time
  • Detailed reporting
  • Industry proven technology

How it Works

MsS technology uses structure-borne elastic waves, called guided waves, which propagate along the structure confined and guided by its geometric boundaries. Guided waves in relatively low frequencies (under 200 kHz) can propagate a long distance along the structure at speeds of more than three miles per second. A good example of this is the sound of the train wheels we can hear from miles away by pressing our ears against a railroad track.

The MsS is a device that generates and detects guided waves electromagnetically in ferromagnetic materials.

With MsS, a pulse of relatively low-frequency guided waves is launched along a structure from a fixed test location. When the propagating guided-wave pulse encounters defects, such as corrosion or fatigue damage, a portion of the waves is reflected back to the original test location, where it can be detected by the same sensor and analyzed for evidence of structural anomalies. Because these guided waves propagate at a high speed, MsS technology can rapidly inspect multiple ropes on a structure from the bridge deck and provide comprehensive structural condition information.

The CableScan Process

Step 1

Guided waves are generated using Magnetostrictive technique from a single location on the wire rope

Step 2

Defects and changes in cross-section cause reflected pulses detectable by MsS sensor

Step 3

Comprehensive report includes quantification and location of individual defects

Reporting

The CableScan report presents a comprehensive and useful summary of cable condition. An estimate of cross-sectional loss is indicated at all locations along the free length of the rope or cable. The condition of each cable is ranked, and the locations of defects are identified. A preliminary report is usually provided prior to demobilization, so that cables can be selected for close-up visual inspection, removal, load testing and/or forensic analysis.

Proven Technology

Under the SwRI internal research program, the application of magnetostrictive sensors was first proven in 1992 in an effort to find an efficient method for inspecting steel cables in highway suspension bridges.

In 1998, with support from more than 10 industrial companies in the United States and abroad, staff in the Sensor Systems and Nondestructive Evaluation Technology Department at SwRI Applied Physics Division, developed a field-ready MsS system for piping inspection. The system received an R&D 100 award from R&D Magazine for being one of the most significant technical accomplishments of 1998.

In cooperation with the Federal Highway Administration and the Port Authority of New York and New Jersey, SwRI scientists used MsS to inspect the suspenders on the George Washington Bridge (GWB). The GWB is a major suspension bridge and it was particularly difficult to obtain a reliable assessment of the suspender ropes. The initial testing found that the MsS technology identified the level of corrosion damage better than any other techniques identified by the Port Authority. Following these results, the Port Authority conducted a large-scale testing program of the ropes on the GWB, and on a tied arch bridge - the Bayonne Bridge.

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