The big advantage of guided wave testing is that the ultrasonic guided wave travels along the axial length of pipeline with low attenuation. Other NDT testing such as UT, RT, and ET is spot measurement tool with which the tested area is limited to the probe installation location. Because the  axial symmetric guided wave, torsional mode, fills the pipe cross-sectional area and propagates though the axial direction, the guided wave testing screens 100 % volume of pipe wall for cross-sectional area change such as corrosion and erosion. The volumetric inspection of piping significantly reduces the location for follow-up inspection.

     The guided wave propagates through the pipe wall so that the followings are advantages:

1.       Long-length of pipeline can be inspected giving comprehensive condition information in a short time.
2.       Inaccessible locations can be inspected: soil-air interface, concrete-air interface (if the concrete is not bonded to the pipe), wall penetration, buried pipeline, road crossing pipeline, etc.
3.      Long length of pipeline can be screened with several access locations for installing the guided wave probe and for follow-up testing if indication is found. It significantly reduces preparation time and labour for installing scaffold of high-elevation pipeline, removing insulation of insulated pipeline, and excavating buried pipeline.
4.      High temperature pipeline (up to 500 °C) pipeline can be inspected or monitored during normal operation without removing heat tracer lines.

     The weld in pipeline plays important roles in long-range guided wave testing. It is an important reflector ranging from 10 to 30 percent depending on operating frequency, and weld bead height relative to wall thickness. It represents a reference in estimating defect size in cross-sectional area and a reference for phase checking of signal. For a good condition of pipeline, the phase is used for differentiating defect from geometric features.  The weld is also used for determining inspection range of guided wave testing. Because the weld is a big reflector, we can calculate the inspection range with the signal-to-noise ratio of weld signal. The weld signal is especially useful for inspecting buried pipeline for measuring inspection range and estimating attenuation and defect size.