Several key aspects in operation of oil pipelines at a pressure higher than design pressure

In order to ensure the safe operation of oil pipelines at a pressure higher than design pressure, a series of studies were conducted on three key factors (i.e. pipe mechanical property, pipeline critical defect size, and girth welds quality verification) influencing pipeline bearing capacity, after the pressures along pipelines were calculated. The yield strength of small specimen was calculated and tested, and the difference of yield strength between specimen and actual pipe was analyzed. The critical defect sizes of pipes were calculated and the internal inspection precision was analyzed. Moreover, girth welds quality verification programs were investigated. It is shown that the ratio of maximum operation pressure to design pressure is the ratio of actual yield strength to the required minimum yield strength of pipes. With the increasing of operation pressure, the allowable critical defect sizes during the operation of pipelines decrease. When the defect is over the critical size, the defect shall be detected by the detector inside the pipeline. Otherwise, it is necessary to decrease the operation pressure, so as to increase the size of the critical defect. Before any operation at a pressure higher than the design pressure, a field pressure test with the corresponding strength shall be performed, in order to eliminate abnormal girth welds.