The proper thermal diagnostics of pipeline insulation is an important problem. The heat losses from the pipelines depend distinctly on the quality of this insulation. Changes in weather conditions cause transient accumulation of energy in the pipeline insulation and may cause difficulties during evaluation of the quality of the pipeline thermal insulation. Generally, the goal of this investigation was to identify the scale of energy accumulation inside thermal insulation. This is important because during the calculation of heat losses from thermal pipelines on the basis of infrared camera temperature measurement results usually a steady thermal state inside the insulation is assumed. In order to determine the distributions of the temperature inside the insulation, the calculations of the temperature changes inside the pipeline insulation for real changeable meteorological conditions with the use of software ansys-fluent and others have been carried out. Both the heat transfer between the inner pipeline tube and outer pipeline shell and energy accumulation inside the pipeline elements were considered. For the pipeline insulation evaluation purpose, different coefficients for the analysis of energy accumulation scale were defined and used. The measurement results of the temperature of inner pipeline tube and outer pipeline shell gathered during the operation of the special experimental rig were used as input data for the aforementioned numerical simulations. In these calculations, they constituted the first (Dirichlet's) boundary condition. The conclusions resulting from this work are useful for specialists involved in the technical evaluation of the thermal protection features of pipelines.