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Wavemaker results a) and b) opposite are for test locations on the near and far sides of the wall, respectively. In each result the green line indicates the actual position the pipe was tested from and the wall entry points are labelled +F1 and +F2. The observed locations of the wall, welds, corrosion and simple supports have also been marked. The results show how attenuation, due to leakage of the guided torsional wave into the earth has reduced the amplitude of the weld echos by a factor of 12. Result a) shows a large, non-symmetric echo (red curve) from the entry point (+F1) which is from the corrosion patch shown above. The second test shows no such echo on the entry point from the other side (+F2) indicating no significant corrosion.It is important to note that it is difficult to detect the defect at +F1 in result b) due to high attenuation.This case study has demonstrated the ability of the WPSS to screen pipes which run through earth walls and has highlighted the benefit of testing from both sides of the wall.

Location of testingequipment

Location of corrosionwhich was detected

Defect detail

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+F1 +F2

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Concrete coated earth walls are a common feature in some petrochemical plants. Corrosion of the pipe often occurs around the entry point and within the wall but it is difficult and costly to inspect these areas using conventional UT techniques.The photograph oppsosite shows the WPSS screening a 10" diameter pipe. Visual inspection indicated that the general condition of the pipe was good. However, an area of severe corrosion was found at the location indicated and is shown in the inset to the photograph. The severity of this corrosion was not apparent from visual inspection.

a)

0.0 5.0 10.0 15.0Distance (m)

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+F1 +F2

b)