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Population growth in city centers has spurred the expansion and new construction of direct current (DC) powered transit systems throughout the world1. Despite stringent design criteria, quality assurance and quality control (QA/QC) monitored construction practices and ongoing track maintenance, it is a fact that DC stray current will eventually occur and negatively impact buried and/or submerged metallic structures immediately adjacent and within the transit right-of-way (ROW)2. In combination with other methods to reduce stray current such as high track-to-earth (TTE) resistance values and shorter distances between substations, transit agencies are specifying the welding of reinforced steel structures within their purview such as retaining walls and footings, approach slabs, aerial inverts, and bridge abutments to prevent stray current from reducing the design life of surrounding metallicstructures.
This paper will present field verified methods for corrosion engineers and/or technicians to accurately inspect and log structure configuration, field conditions and perform field tests to verify electrical continuity prior to concrete operations (prepour testing). Additional topics will include troubleshooting as it pertains to prepour testing and also if a structure has already been poured (postpour) whether it was previously tested or not. The concluding topic addresses the utilization of project documents such as structural and shop drawings to extract relevant reinforcing steel information used in the creation of theoretical resistance and when to use either a standard mathematical analysis or Simulation Program with Integrated Circuit Emphasis (SPICE) software to develop said theoretical resistance as a computer model.
Various austenitic stainless steels such as UNS S30409, S31609, S32109 and 34709 are widely used in complex refinery or chemical plants at temperature ranges between 550°C and 950°C. However, Stress Relaxation Cracking (SRC) in welded joints or cold deformed parts has been a serious problem during fabrication or operation. Several researches were conducted to construct SRC test methods. This included the evaluation of SRC susceptibilities among various austenitic stainless steels and to determine SRC mechanism within TNO Science and Industry or JIP1-4. It was concluded that SRC was caused by the accommodation of strain due to both carbide/nitride precipitation hardening inhibiting dislocation movement and the formation of precipitation free zone along the M23C6 carbide at grain boundary during stress relaxation process of welding residual stresses at temperatures between 550°C and 750°C.
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The corrosion of aircraft costs the U.S. Department of Defense billions of dollars annually and accounts for a significant portion of maintenance time and costs.1 Coatings are the most effective way to protect aircraft, but they have a finite lifetime and must be maintained or replaced before the underlying substrate is damaged by corrosion. Current aircraft maintenance practices call for coating inspections and maintenance based on elapsed time and not on measurements of coating health. Coating lifetime varies depending on the environmental stressors experienced in service, including temperature, humidity, and salt loading.
There are more than 47,000 publicly-owned roadway bridges in Canada.1 Over 25% of these bridges have main structural load bearing components made of structural steel (i.e., truss and steel girder bridges) based on data from the Ministry of Transportation, Ontario – MTO.2 According to Statistics Canada, the condition of approximately 40% of these bridges is rated as either very poor (unfit for sustained service), poor (increasing potential of affecting service), or fair (requires attention).3 It was reported by Koch et al.4 that corrosion is one of the main reasons that lead to structural deficiency of steel components of highway bridges. Especially in marine environments, steel bridges are at risk of high rates of corrosion, particularly beyond 15-20 years in service.5 This observation can be expanded to locations where the use of de-icing salt is common practice such as urban areas in North America. In addition, future climatic changes that are evident (i.e., change in temperature and relative humidity) may potentially affect the rate of corrosion-induced deterioration and affect the resistance of bridges against various load types throughout their life-cycle.