Abstract
The telecommunication systems outside plant are made of a variety of materials, including metals, alloys, electrical contacts, polymers, concrete structure and so on. The interaction between the outside plant metal components and the environment leads to various types of corrosion. Metal-coated steel wires are widely used as supports for telecommunication cables. In coastal areas the metal-coated steel wire corrodes and even fractures in a short time. Atmospheric corrosion exposure tests were made on three classes of hot-dip galvanizing steel, and aluminum-coated steel wire strands at different environmental sites. A two-step laboratory test, salt spray after sand blast, was designed to simulate windy coastal environments and this test was adopted to evaluate the zinc- and aluminum-coated steel by studying the mutual action of sand abrasion and marine corrosion. Measurements of electrochemical impedance have also been conducted for zinc, aluminum and aluminum-zinc metallic coatings in 3% NaCl aqueous solution. Numerous lead-sheathed cables have been served as primary carriers of communication signals over twenty years at outside plants of Chunghwa Telecommunication Company (CHT) in the islands of Taiwan. Corrosion of lead-sheathed cables in aggressive flooded manhole’s environments causes a reduction of lead sleeve thickness in the cable sheaths, and when the reduction equals the extreme value of the lead sleeve thickness, failure occurs. Repair and replacement costs are expensive. At the request of CHT, a non-destructive method of applying zinc sacrificial anode cathodic protection (CP) to in-situ lead-sheathed cables has been undertaken. In addition to the reliability, such factors as the manhole’s environmental hazard of lead also analyzed. The reliability and quality of the electrical contacts and connections are very important for the telecommunication users. This investigation concerns the influence of NO2 and SO2 at low concentration levels in high humid atmospheres on the corrosion of gold, silver and nickel-coated contact materials. The major testing technique includes mixed gas corrosion tests and AC impedance measurements also known as electrochemical impedance spectroscopy (EIS). Contact resistance and corrosion characteristic for the three types of the contacts are investigated and compared. The results atmospheric corrosion test and erosive wear corrosion test showed that the aluminum-coated steel performed only 60% better than the zinc-coated steel. Also it was found that the erosive wear of zinc and aluminum-coated steels fit a ductile-cutting model. The electrochemical impedance spectroscopy of the aluminum-zinc coating revealed a characteristic Warburg impedance that was absent in compared with that of the aluminum coating. Both aluminum and aluminum-zinc coatings are found with a high charge transfer resistance that changes slightly even standing for one year’s exposure. The results of mixed-gas corrosion test show that the contact resistance was the most stable for gold-plated connector in SO2 atmosphere. But in a mixed SO2 + NO2 accelerated corrosion environments, silver-plated connectors were found to possess the best performance in the contact resistance. The atmosphere of the mixed SO2 and NO2 was found to be more corrosive than that of the single component SO2. All SEM analyses show that the pitting corrosion take place on all three types of the contacts.