FORECASTING THE DURATION OF OPERATION OF THE PIPELINE AFTER AN EMERGENCY REPAIR

Abstract

Statistics show that the number of accidents at pipelines tends to grow. The failures are caused mainly by corrosion deterioration and ageing of pipelines, imperfect design solutions, manufacturing defects in pipes, defects in construction-assembly and repair works, fault of operating personnel and other reasons. Various defects on the pipeline walls, grouped or continuous corrosion sores reduce the pipeline’s load-bearing capacity and can lead to failures. Pipeline rupture accidents are relatively rare, but even a minor rupture can cause enormous damage due to environmental contamination, possible explosions and fires, loss of life and the disruption of oil, gas and petroleum product supplies to customers. Maintaining the integrity of the linear part of pipelines is therefore one of the main challenges in pipeline transport. Often pipelines, especially industrial pipelines, develop perforating faults. Therefore, prompt and qualitative elimination of these damages is of great importance. The breakdowns of in-field pipelines are often accompanied by big losses of oil and pollution of the environment. Therefore, the problem of emergency repair of oil-field pipelines is very important and urgent. The most simple and widespread way to eliminate emergency situations at operating pipelines is to apply different kinds of overlaying elements and steel plugs. The existing methods for prognosis of pipeline life taking into account cyclic loading are based on the known Coffin-Manson low-cycle damage equation. In this case the initial basic parameters are amplitude of deformation ε and relative contraction ψ. From our point of view, such approach is expedient for limited types of structural elements, for which it is possible to determine local (in the defect place) values of ε and ψ. The estimation of local value ε for structural elements of pipelines is problematic if only because radii of most defect tops practically cannot be determined. In the paper a method of evaluation of low cycle fatigue life of damaged pipes after emergency repair is proposed.