Materials Performance

NOV 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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49 NACE INTERNATIONAL: VOL. 53, NO. 11 MATERIALS PERFORMANCE NOVEMBER 2014 Corrosion Control of the Severn Bridge Main Suspension Cables simple indicator-based test was developed that can be employed on site as part of the ongoing inspection of the main suspension cables. The system was developed by the inhibitor manufacturer and made available for site trials. In the presence of the inhibi- tor, the color of the indicator changes from blue to red and it is possible to confirm the presence of the inhibitor on the surface of the wires, even deep within the cable, by using swabs containing the indicator solu- tion (Figure 4). During the design phase of the dry air injection system, concerns were raised regarding the ability of the system to reach all parts of the cable. Site testing for the cor- rosion inhibitor found it was present at all locations tested, not just the external sur- face of the cable. In addition to the site tests, which confirmed the presence of the inhibitor across the full section of the cable, a failed corrosion probe was also retained for testing. Swab tests with the indicator confirmed the presence of inhibitor on the sensor section of the probe, which had been exposed to exhaust air from the dehumidifi- cation system. This confirmed that a suffi- cient amount of inhibitor was being intro- duced into the system for treating the full length of the suspension cable (Figure 5). Cable Monitoring It was recognized early in the assess- ment process that the future management of the bridge would be required to adhere to the principles contained in Standard BD79/13. A monitoring regime and warn- ing system were developed to provide the U.K. Highways Agency with sufficient confi- dence in the reliability of the suspension bridge cables. The monitoring system assesses the cables on a monthly basis using the follow- ing methods: • Visual obser vations: the operator, Severn River Crossing, was instructed to record any observations that may be relevant to the condition of the cable. This could include damage, e vidence of entrapm ent of wat er under the cable sleeving, and broken wrapping or main cable wire. FIGURE 4 A swab test for the presence of inhibitor was done during cable inspection. FIGURE 5 The sensor end of a corrosion probe tested positive for the inhibitor.

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