.... The second type of response involves observation of multiple back wall echoes from the near wall. Total reflection occurs at the back wall of steel structure where the medium beyond the boundary is gaseous, such as air. A portion of energy is transmitted across the boundary where the medium is a liquid...

... the evaluation of pipelines integrity.. Many standards require or recommend the use of corrosion probes as corrosion monitoring items. The use of the traditional coupons is not feasible for subsea pipelines except in the topside sections, i.e., normally in the pipeline's beginning and end. echoe...