International project support by Plant Integrity Ltd
Project carried out in Japan by TTS
The first project was carried out by TTS, one of Plant Integrity's Japanese customers. In this case the legs were protected by lightweight concrete. The following photograph shows how the coating was cut away to allow access for the Teletest® tool.
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Normal full weight concrete attenuates ultrasound rapidly. However, this relatively thin, lightweight coating was less attenuative and TTS were able to 'shoot' the full 6m height of the 10" and 14" diameter legs. The results fell into three categories - no corrosion, general corrosion and localised corrosion.
TTS's client expressed total satisfaction with the inspections and monitoring of their sphere legs using Teletest is now planned on a regular basis.
Project carried out in France
The second project was performed by Plant Integrity working through the Institut de Soudure for Hydro Agri France a subsidiary of Norsk Hydro. In this case the legs were 22" diameter. They were protected by external 26" steel tubes, as shown in the sketch.
Rain was prevented from entering the space between the pipes by a conical rain guard. The Teletest tool was positioned above the cone and inspection was carried out 'shooting' down the leg, as shown in the photograph. The rain guard was a complicating factor, because ultrasound was transmitted into it and was then reflected backwards and forwards within it. Despite this, it was possible to carry out a successful inspection of the leg - the inner tube.
Plant Integrity Limited were tasked with finding flaws as small as 20mm diameter and about 2mm deep. Teletest indicated that there were small anomalies at specific points in three of the eight legs. Scattered corrosion pits were found at these points when the outer casings were cut away.
The target sensitivity for Teletest is 9% of cross sectional area. However, in this case flaws as small as 1-1.5% of the leg cross-section were found. This confirms a finding from other projects that the sensitivity increases with increasing pipe diameter, when the flaw size is expressed as a percentage of the total cross section.