Tomographic Reconstruction and Wall Thickness Measurement with Special Attention to Scattered Radiation for In-Service Inspection of Pipes

Abstract

ABSTRACT Accurate assessment of pipe-wall thickness directly from the pipe's tomographic images, restored from only a few X-ray tangential projections, made in a limited observation sector, is discussed. Because the effects of scattered radiation and beam hardening contribute up to 50% of the primary radiation, ignoring these effects yields image blurring, strong artifacts, and inaccurate sizing. A computerized technique has been developed that simulates the contribution of the scattered radiation, beam hardening, and screen nonlinearity, which is used to correct the projection data. The iterative Bayesian techniques are then used to reconstruct pipes images from the modified projections, using volumetric and/or hull representation of the pipe. Using these techniques, the error of the pipe-wall-thickness assessment from projection data can be as small as 300 μm. This article shows that standard projection techniques using X- or gamma rays in combination with X-ray film or imaging plates for the data acquisition can be used to reconstruct wall-thickness profiles in an in-field environment.