Technique Description Long Range UT using guided waves is different from conventional ultrasonic inspection. (Figure 1) Straight beam UT measures pipe thickness at a small spot under the transducer. In order to cover a large area, the transducer must be scrubbed over the pipe surface. There are automated systems that accomplish the process but they are relatively slow.  The Guided Wave system uses a transducer collar (Figure 2 & 3) that produces a 360° sound wave moving axially down the pipe. The pipe itself becomes the guide for the wave – thus “guided wave”. Guided waves propagating in the pipe wall are similar in nature to Lamb waves in plates. They are capable of propagation over hundreds of feet in plain pipe. A large number of guided wave modes are present in a GWUT shot, however the signals are simplified and only selected wave modes are utilized by the system. This is necessary for signals from anomalies and pipe features to be interpretable.			Figure 1. Comparison between traditional straight beam UT thickness measurement (top) and long range guided wave UT (bottom). Conventional UT measures a single point; GWUT covers 100% of pipe circumference up to 300 feet.
	Figure 2, The Guided Wave System consists of a laptop computer, sequencer box (left) and transducer collar as shown in Figure 3 & 4.			Figure 3, Transducer collars are of fixed sizes up to six-inch diameter pipe. Collars over six inches (Figure 4) are modular and can be assembled for pipe up to 60 inches in diameter.
LRUT technology is significant to pipeline operators at this point in time. There are over two million miles of pipelines in the United States. The Office of Pipeline Safety has stated that 30% of these lines cannot be inspected with smart pigs. With the current gas rules now pending, pipeline operators will have the option to assess the integrity of lines that are unpiggable using Direct Assessment. Guided Wave UT technology offers a cost effective method of compliance if direct assessment is elected as the inspection method. While there is no one technology that can cover all inspection situations, GWUT coupled with CIS, DCVG and other indirect assessments will be important tools in maintaining the integrity of many pipeline systems.			Figure 4, 24-inch modular collar. Modular collars use a pneumatic bladder under the metal collar to ensure that the transducers have positive contact with the pipe surface.

The proposed pipeline integrity regulations allow operators to assess unpiggable pipeline sections using “other technology”. Hydrostatic testing may be an option in these cases but can be very costly and in some cases, lines cannot be taken out of service. Clearly, “other technologies” are urgently needed for operators who will use Direct Assessment. Long-range ultrasonic inspection is available to address these needs. Long-range ultrasonic testing or guided wave ultrasonic testing was commercially introduced in early 1998 for in-service monitoring of pipes and pipelines. The oil, gas and chemical process industries now uses it for detection of corrosion and other metal loss defects and it has  acceptance as a valid means of assessing the condition of pipes and pipelines where inspection preparation or access is difficult or expensive. The rise of the technology is especially significant in view of the recent United States government emphasis on pipeline integrity assessment and the lack of a proven technique to inspect the pipelines that cannot be evaluated with “smart pigs”. The technique has now been extensively used in the field for evaluating the condition of pipes in the range of 2" to 60" in diameter and has performed well in identifying corrosion in pipes in a variety of situations including buried and aboveground pipeline sections as well as plant process piping.Low frequency, long range, guided wave ultrasonic technique has been developed for the rapid survey of pipes, for the detection of both internal and external corrosion. The principal advantage is that long lengths, i.e., 200 to 600 feet of pipe can be examined from a single test point. The benefits are:

	Reduction in the costs of gaining access to pipes for inspection, eliminating removal and reinstallation of insulation, except in the area where the transducers are mounted,
	Direct assessment of unpiggable pipeline sections in lieu of hydro testing, pig launcher-receiver installation, and/or upgrading the line.
	The ability to inspect inaccessible areas, such as under clamps, sleeves or buried pipes,
	100% of the pipe wall is tested,
	Site trials have demonstrated that this method is capable of detecting corrosion <30% through wall and <25% circumferential width.

benefit of using long range ultrasonic testing (LRUT) to obtain information on conditions in areas where access is restricted becomes obvious. The experienced gained by PetroChem Inspection Services through the use of LRUT over the last 2 and ½ years has validated he equipment as a reliable inspection technology. Applications for the technology are numerous. Industrial utilization is not limited to the oil, gas and petrochemical sector but open to any situation where metal loss in piping presents an environmental or safety concern.