PITA Fiscal Year 2015 Projects

Ultrasonic detection of defects in “clad steel” materials for oil and gas pressure vessels

Lead University: Carnegie Mellon University
PI: Irving J. Oppenheim, Civil and Environmental Engineering
Co-PI(s): Jose M.F. Moura, Electrical and Computer Engineering

“Clad steel” is a high-value product consisting of a thick carbon steel structural plate bonded to a somewhat thinner corrosion resistant alloy (CRA) plate, used to construct pressure vessels that are essential to the production of oil and gas, with similar applications throughout industry. The CRA resists the chemically aggressive environment on the interior of the vessel, but cannot prevent the development of corrosion losses and cracks that limit the continued safe operation of such vessels. At present there are no practical methods to detect such defects from the exposed outer surface of the thick carbon steel plate. The significance of this problem to the oil and gas industry is exemplified by the following description issued by BP: “Current NDT techniques cannot provide imaging and analysis of the inner stainless steel clad from the outside of the vessel. Therefore it is common practice to internally inspect the vessels visually, which involves isolating, cleaning, washing the vessel (that is, removing it from service), and then putting inspection engineers inside the confined space.” The proposed research will detect scatterers on the (inner) CRA layer using ultrasonic transducers applied only to the outer surface of the carbon steel layer. Complex propagation effects have prevented other researchers (both in industry and in universities) from accomplishing that goal, but the CMU research team has developed and demonstrated signal processing methods that use the wave complexity to great advantage. The proposed technical approach is centered on laboratory experimental studies to be performed on new clad steel test specimens, which are being provided by a Pennsylvania industry contributor.