Failure of Large Tantalum Heat Exchanger During Transportation to Site

A steam heated exchanger was designed for concentrating sulfuric acid. Tantalum was selected for the tubing and the tube sheet liner because of its outstanding corrosion resistance. However, although the exchanger passed a searching shop inspection, it leaked during site testing. Considerable argument ensued about whether the cracking observed was due to poor welding during fabrication, or through abuse during handling on site. An SEM examination of the fractures revealed high cycle, low amplitude fatigue, and the problem was traced to vibration during road transport. Further failures were avoided by improved design and packing. This paper illustrated the value of SEM fractography when a rapid investigation is needed under the pressures of a fast moving project.