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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48 NOVEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 11 CHEMICAL TREATMENT provided the necessary confidence to use the model to predict the future perfor- mance of the wires and the inf luence of dehumidification and corrosion inhibitors. Use of Corrosion Inhibitors To provide additional corrosion protec- tion to the wires during the initial period of moisture reduction—when corrosion rates could increase as oxygen became more available—and to provide a back-up in the event that the dehumidification system went out of service (e.g., for maintenance), FIGURE 2 Comparison between actual and predicted depth of corrosion penetration. FIGURE 3 Laboratory tests confrm compatibility of the inhibitor with the dehumidifcation system components. a vapor corrosion inhibitor (VCI) system was developed for introduction into the dry air stream. VCIs have been in use for a number of years, initially for military and aerospace applications and now for automotive, domestic, and construction uses as well. While formulations are specific to the man- ufacturers, VCIs are typically based on non- toxic volatile organic compounds that form continuous, highly adherent mono-layers on the surface of metals and effectively con- trol the processes that lead to corrosion. In industr y, VCIs are generally used with a carrier system, which may be a water or hydrocarbon solution, or a fine starch or talc powder. Because of concerns regarding the potential blocking of air voids in the cables, powder -based deliver y systems were immediately rejected as a method of introducing the inhibitor. Water-based sys- tems were also considered unsuitable, as moisture reduction was a principal aim, while solvent-based systems were found to be incompatible with the cable wrap and RH probes that formed integral parts of the dehumidification system. Laboratory Testing of Inhibitors For these reasons, an approach was developed based on the introduction of the pure inhibitor vapor using the dehumidifi- cation air stream as the carrier. The inhibi- tor is introduced into the air stream via permeable emitters with no solid or liquid material. In this manner, it is possible to ensure a sufficient level of inhibitor vapor is present within the air voids to protect exposed metal surfaces while avoiding the risks of blockage by solid or liquid material. Because the protective inhibitor layer is only one or two molecules thick, it has no influence on clearances and only a minimal effect on other physical properties. Tests confirmed this, with results showing that use of the inhibitor caused a small increase in wire-to-wire friction at low contact pres- sure and no significant frictional effect at higher load. Further tests were carried out t o c o n f i r m t h e i n h i b i t o r w o u l d n o t adversely affect other components in the system, including cable wraps, sealants, and probes. Initially, the tests were carried out in the laboratory (Figure 3). The labora- tory tests confirmed that the inhibitor had no significant effect on the characteristics of the wrap and sealant materials and did not interfere with the operation of the RH probes. Site Testing of Inhibitors Currently, exposure tests on site are ongoing to confirm no long-term influence on cable properties. To confirm the effec- tiveness of the inhibitor delivery system, a

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