Technical Reports

Economic Analysis of the Use of the Electromagnetic Acoustic Transducer (EMAT) For Wheel Stress Management

  • 01
  • Jul
  • 2001
AUTHOR: Joseph Kristan, Gregory Garcia, Christopher Pinney
SUBJECT: Evaluation
KEYWORDS: Electromagnetic Acoustic Transducer (EMAT), Residual Hoop Stress, Wheel Detection Technology
ABSTRACT: Transportation Technology Center, Inc. (TTCI) has analyzed the economics of using Electromagnetic Acoustic Transducer (EMAT) technology to inspect freight car wheels. EMATs are designed to nondestructively determine the residual hoop stresses of a freight car wheel at the rim. Braking irregularities that generate heat above the upper transformation temperature of the steel causes residual hoop stresses in freight car wheels. Residual hoop stresses in freight car wheels may lead to brittle fractures of the rim, which may contribute to the propagation of cracks and potentially to wheel failure. The objective of this report is to provide technical, as well as operational information by conducting a feasibility study of the EMAT systems potential benefits and cost in today's railway operating environment. The report concludes that EMAT technology is not a fully developed wheel inspection system and it requires further testing to prove its accuracy and reliability. Accuracy and reliability drive the economics of EMATs. Under optimal conditions (1 00 percent service accuracy and reliability), and with every AAR certified wheel shop using EMATs to test for residual hoop stresses, the feasibility study shows a benefit to the railway industry. However, any deviation from these optimal conditions shows a significant loss due primarily to false positive measures, which would cause a potentially good wheel to be scrapped. Therefore, additional resources required for further development of the EMAT system must be carefully reviewed in order to justify its development for in-shop wheel inspection.