Strength and durability tests of pipeline supports for the areas of above-ground routing under the influence of operational loads

The present article deals with integrated research works and tests of pipeline supports for the areas of above-ground routing of the pipeline system “Zapolyarye - Pur-pe” which is laid in the eternally frozen grounds. In order to ensure the above-ground routing method for the oil pipeline “Zapolyarye - Pur-pe” and in view of the lack of construction experience in case of above-ground routing of oil pipelines, the leading research institute of JSC “Transneft” - LLC “NII TNN” over the period of August, 2011 - September, 2012 performed a research and development work on the subject “Development and production of pipeline supports and pile foundation test specimens for the areas of above-ground routing of the pipeline system “Zapolyarye - Pur-pe”. In the course of the works, the test specimens of fixed support, linear-sliding and free-sliding pipeline supports DN1000 and DN800 were produced and examined. For ensuring the stable structural reliability of the supports constructions and operational integrity of the pipelines the complex research works and tests were performed: 1. Cyclic tests of structural elements of the fixed support on the test bed of JSC “Diascan” by means of internal pressure and bending moment with the application of specially prepared equipment for defining the pipeline supports strength and durability. 2. Tests of the fixed support under the influence of limit operating loads and by means of internal pressure for confirming the support’s integrity. On the test bed there were simulated all the maximum loads on the support (vertical, longitudinal, side loadings, bending moment including subsidence of the neighboring sliding support) and, simultaneously, internal pressure of the carried medium. 3. Cyclic tests of endurance and stability of the displacements of sliding supports under the influence of limit operating loads for confirming their operation capacity. Relocation of the pipeline on the sliding supports from temperature expansion in case of preheated oil charge into a “cold” pipeline was simulated. 4. Cyclic tests of durability of frictional couples under the influence of operational and maximum loads. On the test bed there were examined various materials for the sliding surface of the supports, ensuring the norm friction coefficient

The application of the finite element method for the low-cycle fatigue calculation of the elementsof the pipelines’ fixed support construction for the areas of above-ground routing of the oil pipeline «Zapolyarye — NPS „Pur-Pe“»

The present article studies the order of performing low-cycle fatigue strength calculation of the elements of the full-scale specimen construction of the fixed support DN 1000 of the above-ground oil pipeline “Zapolyarye — Purpe” during rig-testing. The calculation is performed with the aim of optimizing the quantity of testing and, accordingly, cost cutting for expensive experiments. The order of performing the calculation consists of two stages. At the first stage the calculation is performed by the finite element method of the full-scale specimen construction’s stressed-deformed state in the calculation complex ANSYS. Thearticle describes the main creation stages of the finite element calculation model for the full-scale specimen in ANSYS. The calculation model is developed in accordance with a three-dimensional model of the full-scale specimen, adapted for rig-testing by cyclic loads. The article provides the description of the full-scale specimen construction of the support and loading modes in rig-testing. Cyclic loads are accepted as calculation ones, which influence the support for the 50 years of the oil pipeline operation and simulate the composite impact in the process of the loads’ operation connected to the changes in the pumping pressure, operational bending moment. They also simulate preloading in the case of sagging of the neighboring free support. For the determination of the unobservable for the diagnostic devices defects impact on the reliability of the fixed support and welding joints of the fixed support with the oil pipeline by analogy with the full-scale specimen, artificial defects were embedded in the calculation model. The defects were performed in the form of cuts of the definite form, located in a special way in the spool and welding joints. At the second stage of calculation for low-cycle fatigue strength, the evaluation of the cyclic strength of the full-scale specimen construction’s elements of the fixed support was performed in accordance with the requirements of Russian State Standard GOST R 52857.6—2007 on the basis of the overall and local stress condition, received according to the results of the calculation in ANSYS. In accordance with the results of the conducted work the conclusion was drawn about fulfilling the standard requirements for the low-cycle fatigue strength of the developed full-scale specimen of the support. Therefore, the application of the modern approaches to the numerical modeling of the fixed support construction operation allowed minimizing the quantity of full-scale tests of the specimen with the cyclic load, escaping the excessive conservatism in evaluation of the cyclic strength and developing of the optimal for the metal intensity construction