INFLUENCE OF OPERATIONAL LOADS ON BALLASTING PARAMETERS OF UNDERWATER CROSSINGS OF TRUNK OIL AND GAS PIPELINES

The trunk oil and gas pipelines are under operational loads affecting the strength and reliability of the structure. The most significant effect of loads is manifested at pipeline crossings across rivers. The stability of underwater pipeline design position and thus its reliability is achieved by ballasting with the required intensity. The current regulatory document SP 36.13330.2012 provides for the required intensity determination, taking into account the water buoyancy force and pipeline crossing along the longitudinal profile of the transition. At the same time, it should be noted that ensuring pipeline bending along the longitudinal profile of the crossing with the use of ballasting of the required intensity also depends on the internal forces acting in the pipeline wall during operation. However, this document does not take into account operational loads when determining the required ballasting intensity. In addition, ballasting with the ensuring pipeline bending along the longitudinal profile of the crossing leads to the occurrence of bending stresses, in some cases quite high, which affect the level of total stresses, strength and reliability of the structure. In many cases, water occupies only part of the concave section of the pipeline at crossings. Taking into account the above conditions and features, studies of the ballasting of underwater crossings of trunk oil and gas pipelines were carried out. The aim of the work is to obtain analytical dependences of the ballasting intensity and bending stress in an underwater pipeline at different altitude water levels at the transition from operational loads and geometric characteristics of the crossing. The research method is a theoretical study of the stress-strain state of an underwater pipeline under the action of operational loads and weights. The dependences of ballasting intensity with weights of the underwater pipeline on the operational loads and the geometric characteristics of the transition at different elevations of the water level at the transition are obtained, and the highest bending stresses in the pipeline wall at the underwater crossing are determined. Recommendations to reduce the total longitudinal stress level in an underwater pipeline are given.