Improvements in the inspection of rail tank cars using ACFM

M Smith1, H Sadek2 and C Meeker3
1Eddyfi Technologies – TSC, UK Email:
2Eddyfi Technologies – TSC, USA Email:
3Union Tank Car Company, USA Email: 

Tank cars are widely used on freight rail networks to transport liquid and gas commodities and products. These specialist transport vehicles, typically consisting of a cylindrical liquid or gas-tight vessel welded to a rail bogie frame, require inspection and maintenance, also called qualification, at maximum intervals of ten years.

The Union Tank Car Company (UTLX) founded 1886, and Procor LLC, manufacture, lease and maintain a fleet of approximately 133,000 tank cars in the USA, which require inspection of the mostly carbon-steel welds for fatigue cracking during qualification and maintenance. Conventional visual testing, penetrant testing and magnetic particle testing techniques entailed a significant amount of time in the removal and reapplication of the multiple coat primer and epoxy coating systems subject corrosion, weathering and other issues.

This article describes how UTLX/Procor focused on alternating current field measurement (ACFM) as a technology to detect and size fatigue cracks at the welds without the removal of the protective paint coating and includes results from lab-based probability of detection (POD) tests as well as extensive comparative field trials. Testing this NDT method at multiple locations around North America on multiple designs consistently demonstrated a noticeable improvement in:
  • Efficiency
  • False call rates
  • Detectability
  • Sensitivity.

In conclusion, the application of ACFM for tank qualification of DOT-specification tank cars was found to improve the probability of detection of fatigue cracks that could lead to catastrophic failure in hazardous material service without the need for hours of surface preparation time required by traditional techniques. Improved detectability, in theory, will lead to safer transportation of hazardous materials by rail.