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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50 NOVEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 11 CHEMICAL TREATMENT FIGURE 6 Results from acoustic monitoring of the cables. • Dry air injection system: At the air inlet and exhaust locations along the length of th e cables, sensors are located to provide information on the condition of the voids within the cable. These sensors measure relative and absolute humidity, temperature, flow, pressure, and corrosion. • Traffic loading: Traffic is the domi- nant live load on the bridge and rep- resents 20% of the maximum load c a r r i e d b y t h e c a b l e s . We i g h t - in-motion sens ors have b e en in- stal l ed on al l ro ad ac cess to th e bridge since 2005, w hich enables bridge-specific assessment live load- ing to be undertaken in accordance w ith th e U.K. Hig hway s Agency 's Standard BD 50/92. 5 • Acoustic emi ssion monitoring: A partial monitoring system for the main cables was installed on the bridge in 2006, with a full system operating since 2008. Any acoustic events detected are reviewed by the sp e ci ali st sy st em suppli ers, w h o determine a confirmed wire break based on the characteristics of wire break acoustic signatures. Figure 6 presents the results from the acoustic emission monitoring. They show that: • Acoustic emissions before installa- tion of the dry air injection system represented 0.4% of the total number of wires in the cables. • Acoustic emissions during the cable dr yin g out p erio d were reduced , indicating ~15 breaks per year or 0.1% per year. • The level of acoustic emissions after drying out was <10% of the level of acoustic emissions before installa- tion of the dry air injection system. The large increase in wire breaks during 2010 can be attributed to the removal of the wrapping wire and wedging operation that took place during the second intrusive inspection. Conclusions The installation of a dry air injection syst em and th e introduction of a VC I appear to have stabilized the condition of the cable. This has been demonstrated with the reduction in the RH within the cable sheaths and low levels of acoustic emissions since the dr ying process was established. The site testing for the corrosion inhibi- tors during the second intrusive inspection demonstrated the ability and effectiveness of the dry air injection system to reach all parts of the cable.

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