Inspectioneering
Inspectioneering Journal

Inspection of Wire Ropes and Strand Guyed and Supported Structures Flare Stacks - Pipeline Spans Using Electromagnetics

Pipeline Spans Using Electromagnetics

By David R. Hall at Longview Inspection. This article appears in the May/June 2003 issue of Inspectioneering Journal

Many of the guyed flare stacks and wire rope or strand supported structures in use in U.S. and overseas refineries, pipelines and chemical plants were erected in the 1950’s, 60’s and 70’s. Some were built even earlier. While many of the components of these structures have been routinely inspected by various methods of testing, the wire rope and strand that support and hold these structures in position have, typically, been taken for granted and only elementary visual inspections have been performed. Wire rope and strands in sedentary environments deteriorate and lose their working capability due to many factors. These factors exist both internally and externally.

The continuing deterioration of aging wire rope supported structures, including the corrosion and degradation in the wire rope and strands used on guyed stacks and pipeline span crossings is a problem of great importance that should be addressed. The so called dressing and/or paint used in the past, on some of these wire ropes and strands is a simple, external, preservative and has no inhibiting affect on internal corrosion or abrasive wear. Old technology greases and dressings that were used to coat the external wires of the rope or strand structure had no penetrating properties that protect the wires inside the structure. Consequently, the structural integrity of these tendons may be compromised.

Electromagnetic inspection can assist in locating loss of cross sectional area, due to corrosion in wire rope and strands. Broken wires, both internal and external can be detected along with localized areas of damage cause by abrasion and wear. Wire rope and strands are manufactured with wires that have been drawn to diameters with tolerances of .0005 of an inch4. These tolerances are closer than those called for in turbine designs. When corrosion and/or damage occur, these “high tolerance” wires cannot slide easily and adequately within the rope structure. This phenomenon causes the rope structure to deteriorate at an accelerated rate.

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