Inspecting On-Stream Process Piping at Support Areas Using EMAT Ultrasound

This article describes a new inspection technology for rapid, on-stream, quantitative examinations of piping under support areas. This portable production system has been in commercial operation in the major U.S. Gulf Coast refineries for the past two years.

The amount of installed process piping operating in the petroleum and chemical industries is vast, and represents one of the country’s largest reported potential industrial risks and the oldest existing industrial infrastructures.To date, there has been no satisfactory method that can determine the remaining wall thickness of on-stream piping at its most critical point - the pipe support location, short of removing the support or lifting the pipe.

The Support Inspection® technology has been providing the first quantitative inspection of pipe support locations on live, in-situ process piping. By monitoring ultrasonic Lamb wave mode and velocity changes, the system performs both defect detection and sizing at support locations. The technology generates Lamb waves using EMAT (Electro Magnetic Acoustic Transduction) sensors, which are non-contact, couplant free, ultrasonic transducers that use magnetic waves and high current tonebursts to generate specialized ultrasonic waves. The technology allows inspectors to determine the remaining wall of on-stream process piping in previously uninspectable locations (i.e., underneath pipe supports).

Support Inspection® operates by generating plate waves, known as Lamb waves, which propagate circumferentially around the pipe (see Figure 1). The EMAT transducers are housed in a scanner assembly that moves axially along the length of the pipe. Mode and velocity changes of the Lamb waves are measured and converted into direct readings of remaining wall/wall loss over the entire test area of the pipe support location. This procedure represents one of the first quantitative applications of EMAT ultrasonic wave theory under which wall loss severity is evaluated without direct access to either surface of the material. The Support Inspection® technique depends heavily on the properties of Lamb waves. An example of the dispersion curves for Lamb waves is seen in Figure 2. This graph is a result of the current research, and was generated by means of the WIS Lamb Wave Solver Software.