Inspection Range

In ideal circumstances, the test range can be more than 200 meters (650 feet) in each direction. However, the actual inspection range varies depending on several factors including:

the coating (The thicker and more viscous the coating, the more it will attenuate the waves)
if it is buried (the waves can leak into the surrounding medium – more for dense well bonded materials like concrete)
how corroded the pipe is (reflections from corrosion reduce the range of propagation).
the pipe geometry (we cannot inspect through flanges and prefer to minimize the number of bends that need to be propagated through)
the required sensitivity (the quoted inspection distance is normally for the minimum defect size, but larger defects can often be detected after this)

This figure provides a guide to the typical and average inspection range for GUL Screening:

Intersection of Call DAC & Detection Threshold

As part of analyzing the result, an inspector will mark the actual achieved inspection range for that test for the declared call level. If the test is not limited by certain pipe features such as flanges or elbows, this is done by determining by the intersection of the Call and Detection Threshold (DT), which is typically defined as 6 dB above the noise level.

By using this method, the known range for a known call level can be verified for each test result.