RopeScan, the newest robotic nondestructive wire rope testing method by IPC is a the latest in
critical wire rope and guy wire inspections. Know when to replace your wire rope!
Wire ropes and guy wires play a major role in supporting essential infrastructures, are a critical safety and balancing component, while also being a lifeline in hostile and demanding conditions. From suspension cables on bridges to crane cables, hoists, and pulleys to guy wires holding up flare stacks, to broadcast and transmission towers, these ropes are widely used on projects involving bridges, vessels, stadiums and glass façade/membrane buildings for critical support. This makes it imperative that they are maintained properly, starting with reliable inspection.
Guy wires are normally secured radially, in trios and quads, around a structure, one end tied to the structure, and the other secured to the ground. The tension of guy-wire ropes helps the structure to withstand lateral pressure such as from strong winds.Therefore, by the very nature of the job they perform, guy wires are always under stress.The constant force put on them from holding up structures can cause the wire to fray and break over time, causing catastrophe.
Apart from bearing the brunt of tension, these wire ropes are consistently exposed to adverse weather conditions for the whole of their service life – the scorching heat of the summer sun and the bitter cold of icy winters. These extreme weather conditions also have a negative impact on the service life of wire ropes. Like everything exposed to the elements, they corrode, rust and deteriorate over time.
Furthermore, the service that guy wires provide is inextricably linked with their structural design. The structure of guy wire strands is so designed to provide little or no movement between wires, while the individual wires are covered with a hot-dipped galvanized zinc coating, to prevent corrosion. The outer wires of the strand are given extra and longer protection through thicker galvanization. However, this thicker zinc coating on the outer wires also seals in moisture, making chances greater for internal wires, which have a thinner zinc coating, to corrode faster. And, as internal wires enable greater tension than the outer wires of a guy wire strand, early detection of corrosion on the internal wires is critical for durability and longer service life of the guy wires, and the safety and stability of the structure.
If one localized area of corrosion hidden deep in a guy wire remains undetected, and subsequently leads to loss of metallic area, even if the rest of the wire is in good shape, it will fail to stabilize and secure what it upholds. This could lead to collapsing of structures, to horrific accidents, and loss of life and property.
Famed safety advisor Dr. Trevor Kletz, once said, “If you think safety is expensive, try an accident.”
Recently, a cable snapping smashed a 100-foot wide hole in Puerto Rico’s Arecibo Observatory that searches for aliens and tracks dangerous asteroids. Earlier, the accidental dropping of a module of the Petronius platform into the Gulf of Mexico when a crane load line snapped while lifting it, cost an estimated US$ 116 million. Apart from material costs, since 1999, over 60 people have been killed from wire rope breaking accidents, with over 65 injured.
The life of a wire rope is determined by various factors like wear, metal fatigue, abrasion, corrosion, kinks and improper reeving. Experts recommend guy wire rope inspections based on Occupational Safety and Health Administration (OSHA) and industry standards, every 18 to 24 months, for early detection of corrosion.
However, manually executed, visual inspection of guy wires, is only as good as the eye can see.Even a powerful scope cannot expose issues or deterioration inside wire strands.Therefore,such inspections obviously cannot provide comprehensive reports on the interior health of guy wires.
On the other hand, quantitative measurements of the wire interior are critical for estimating the remaining guy wire life, to prioritize replacements, while ensuring its stabilizing service is not impaired.
To overcome the limitations of visually inspecting wire ropes, the Infrastructure Preservation Corporation (IPC), a Florida-based robotic engineering firm,spent six years developing and perfecting the newest robotic nondestructive wire rope testing method, called RopeScan®.
Doug Thaler, President of IPC, says, “RopeScan is a remotely-operated,efficient and safe method of professionally inspecting and evaluating guy wires and just about any wire rope.”
RopeScan® is a lightweight portable, wireless robot that engages nondestructive testing (NDT) to penetrate and expose issues both on the surface and interior of the wire as well as locating loss of metallic area (LMA) inside individual wire strands,that are either exposed, or protected right through in a high-density polyethylene (HDPE) sheathing.
Since magnetic flux flows equally throughout the cross-section of the wire rope, LMA in the wire interior is just as easily measured as on the exterior. As corrosive products are non-magnetic, LMA is an optimal measurement to quantify directly, the loss of tensile strength due to corrosion.
“At the same time, it conducts visual inspection of the exterior of the cable for broken or split wires,” says Thaler.
He added that RopeScan inspection is safer than existing manual inspections, and more convenient too, as bucket trucks and man lifts are not required. It also provides asset owners more quantitative data than they have ever collected in the history of guy wire and wire rope inspections.
According to Thaler, RopeScan® is the new frontier in wire rope and guy wire inspection, as it provides exact and minute information on the health of the guy wires under inspection. Asset managers are given a clear understanding of the degree of corrosion within the wire ropes, so they can extend the service life of critical wire ropes.
Replacing corroded wires is a significant annual cost to major asset owners. Inaccurate or incomplete visual inspections often lead to replacing wires that could still be of service. RopeScan®, on the contrary, minimizes replacement with accurate and timely diagnoses, providing deterioration progression over time.
RopeScan® surpasses current manual visual inspection as it is based on technology, focused on accuracy and timely detection. Above all, accuracy builds credibility, says Thaler.
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