DETERMINATION OF THE MAXIMUM ALLOWABLE PRESSURE FOR STRENGTH TESTING OF MAIN OIL-AND-GAS PIPELINE SECTIONS

High-pressure testing of main oil-and-gas pipeline sections for strength is one of the methods for their technical condition assessment. At the same time, testing pipelines with pressure exceeding the working pressure is a very important and rather complex technological process that requires a reasonable definition and strict adherence to test parameters. In order to achieve the effectiveness of high-pressure testing, the test pressure must be sufficient to identify weak points in terms of pipeline strength ensuring during its operation. Besides, it is necessary to exclude the occurrence of new defects due to the effect of high test pressure. Set of rules SP 86.13330.2014 «Main Pipelines» re uires that when testing pipelines, the test pressure on pipes guaranteed by the plants must not be exceeded. In accordance with the requirement of SP 36.13330.2012 «Main Pipelines», each pipe must be tested at the manufacturing plants with a pressure that causes a stress in the pipe wall equal to 95 % of the standard yield strength. Since the stress value in the pipe wall depends on the method of sealing the pipe cavity during testing, SP 36.13330.2012 requires that the test pressure value at the plant for pipes be determined depending on the method of sealing the pipe cavity. It should be noted that sealing the pipeline cavity by rigidly connecting (for example, by welding) the plug to the pipe wall leads to an increase in the level of mechanical stress in the pipe wall. Determining the allowable maximum test pressure without taking into account the specified requirement of the set of rules may lead to a negative impact of the test on the technical condition of the tested pipe or a pipeline section. In addition, when testing pipeline sections with changes in the geometric characteristics of the pipes, increased stress occurs in their wall compared to sections with constant values of the specified characteristics. In accordance with the requirements of SP 86.13330.2014, standard test pressures are established depending on the category of sections and the working pressure. In this case, the allowable test pressure according to SP 36.13330.2012 from the condition of pipe strength ensuring must be no less than the standard test pressure. The standard test pressure is the minimum allowable test pressure for main oil-and-gas pipelines. In design practice, there may be cases when the standard test pressure exceeds the calculated allowable test pressure of the pipeline. In these cases, it is necessary to apply solutions to increase the allowable test pressure. Increasing the allowable test pressure will help to identify weak points in terms of ensuring strength and thereby increase the efficiency of pipeline testing. The purpose of the work is to increase the efficiency of assessing pipeline technical condition by testing with increased pressure based on a reasonable determination of the test pressure. Research methods – analysis and theoretical studies of a pipeline stress-strain state due to internal pressure in areas where pipe geometric characteristics change. Results – the dependences of the maximal allowable test pressure of pipeline sections on pipe geometric characteristics and equipment installed on the pipeline are obtained. Recommendations are proposed to increase the allowable test pressure of main oil-and-gas pipeline sections.