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A mathematical model has been developed to simulate the initial projections for computed tomography of large-sized oil and gas pipes and to transform the projections into the mass thickness distributions. The simulated projections of steel pipes with a diameter from 530 mm to 1420 mm are given with variation of ADC capacity and the number of photons incident on the front surface of the multichannel bremsstrahlung detector. The necessity of correct selection of these parameters is proved. A possibility to estimate the density distribution over a pipe cross section based on the inverse Abel transform for the fan-beam of bremsstrahlung is illustrated. The issues related to the technical feasibility of the computed tomography method for inspecting of large-sized pipes and concerning the estimation of the total scan time and the choice of ADC capacity are considered. Recommendations on the adjustment of the analog and digital signals ranges are given. The obtained results make it possible to evaluate the feasibility of designing a computer tomography system for monitoring large-sized oil and gas pipes.

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The mathematical model of the broadband transmission X-ray thickness gauge is developed. The mathematical model consists of sectors: generation and transformation of radiometric signals; equation of transmission X-ray thickness gauge; error estimation of thickness measurement; performance rating. The example of the use of the proposed model to calculate of the transmission X-ray thickness gauge for aluminum items is provided. In the example the dependences of integral mass X-ray attenuation coefficients and the thickness of monitored objects made from aluminum are calculated. The range of optimum measured thickness depending on the maximum X-ray energy was selected, the measurement time to provide the desired thickness measurement error was estimated. The possibility of measuring the thickness of a cooper test object for a wide beam conditions has been experimentally confirmed.