Влияние Температурного Перепада И Количества Трубоукладчиков На Технологические Параметры Капитального Ремонта Трубопроводов С Подъемом В Траншее

Overhaul of the linear part of trunk pipelines with insulating coating replacement remains one of the main means of main tainingthe pipeline system repair. For pipelines with a diameter of up to 720 mm, the process scheme with pipeline lifting in the trench to a specified height is the most widely used one. The process parameters include the pipeline lifting height, the bent section length, the lifting forces exerted by the pipelayers, and the distances between them. The current methods for determining the process parameters of lifting treat the exposed section as a beam under transverse loads and leave aside the longitudinal force arising in the pipeline restrained by soil due to the temperature differential and the internal pressure. Meanwhile, the longitudinal force changes the shape of the elastic line and, together with it, the bending moments in the design sections, the hook loads and the bent section length, so that its consideration is necessary both for pipe strength and for planning the earthwork volume. The paper applies an analytical method for calculating the pipeline stress and strain state during lifting. A parametric study has been carried out on the influence of the temperature differential in the range from minus 30 °C to 30 °C and of the number of pipelayers from one to six on the bent section length, the maximum deflection, the total longitudinal stresses and the hook loads. The calculations have been performed for oil pipelines with diameters 530 × 9 and 720 × 10 mm at an internal pressure of 2 MPa. It has been established that the influence of the number of pipelayers is determined by the parity of the arrangement scheme: for an odd number the design section is the mid section of the bent part, and for an even number it is the section of the pipelayer nearest to the middle; this position is preserved over the whole range of temperature differentials considered. It is shown that the effect of the longitudinal force on the bending moment increases with the bent section length, that is why the stress curves for different schemes intersect and an increase in the number of pipelayers does not in all cases reduce the stress level. Each stress curve has a minimum whose position shifts when the arrangement scheme changes; the most loaded case is repair at a significant deviation of the metal temperature from the tie-in temperature. The hook loads decrease monotonically with the temperature differential and with the number of pipelayers, so that the strength condition, rather than the lifting capacity of the equipment, determines the choice of the scheme. The position of the stress curve is determined by the ratio of the pipelayer spacing to the bent section length, which makes it possible to control the stress level by adjusting the arrangement without increasing the number of machines. The character of the obtained relationships is preserved for both pipe sizes. The reliability of the method has been confirmed by earlier experimental studies and numerical simulation. Recommendations have been formulated on the choice of the number of pipelayers, the lifting height, the arrangement of the equipment and the period of the repair work.