Pipeline Science and Technology, Vol. 3, No. 2, December 2019 135 Pipeline Science and Technology, Vol. 3, No. 2, December 2019 134 *Corresponding author: Sergei S. Sherbakov, e-mail: sherbakovss@mail.ru http://doi.org/10.28999/2514-541X-2019-3-2-135-148 © 2019 Pipeline Science and Technology. Published by Pipeline Transport Institute in association with Great Southern Press Pty Ltd. All rights reserved. The cross-disciplinary approach to analysis and forecast of operational damage tolerance of the oil pipeline system – part 1 by Sergei S. Sherbakov* 1, 2 1 State Committee on Science and Technology of the Republic of Belarus, Minsk, Belarus 2 Belarusian State University, Minsk, Belarus ARTICLE INFO Received: 18 April 2019 Accepted: 25 July 2019 RESEARCH PAPER ABSTRACT T he paper presents the cross-disciplinary approach to the analysis of the oil pipeline system based on the methodologies of tribo-fatigue and mechanothermodynamics. The pipeline section is analyzed as a complex system pipe-soil- fow of liquid subject to the set of mechanical, thermal and friction loads. It is shown that theses loads are mainly repeatedly-alternated, and the pipe metal works in the multi-cycle fatigue conditions. The procedure of resonance accelerated fatigue tests is proposed, and their results are presented. Also, the unorthodox method of integrated wear-fatigue tests of the pipeline steel was proposed with the model of simultaneous pressure and wall friction actions. The presented feld test results of pipes subject to the long-term operation showed that their fracture may occur not only in the near-weld zone, but also in the vicinity of internal corrosion damages. New models of three-dimensional stress- strain state and volumetric damage tolerance for the system pipe-soil-liquid fow were developed. These models were applied with regard to the pipe internal corrosion damages, defned using the inline inspection technique. A new effcient method to describe static and cyclic elastic-plastic fracture of the pipe steel with crack using the transverse strain is proposed and tested. Results of the computer-simulated propagation of the crack-like damage are based upon the model of deformed solid with dangerous volume. The new model is proposed for risk and safety assessment with regard to the ultrasonic inspection data. The algorithm of the ‘oil line pipe’ problem solution is presented for drafting a short-term plan of particular R&D actions. Key words: oil pipeline, tribo-fatigue, mechanothermodynamics, damage, stress-strain state, safety, mechanical fatigue, feld tests, crack resistance, management. INTRODUCTION The problem of ‘oil line pipe’ is cross-disciplinary. Really, such scientifc disciplines as hydraulics and fuid mechanics, thermodynamics, mechanics of deformable solids, mechanics of materials, elasticity theory, strength theory, linear and non-linear fracture mechanics, metal science, damage theory, corrosion theory, etc. are used to solve the problem of the line pipe performance capability assessment and improvement. As it is known, individual sciences enable us to receive answers only to partial questions, while the ‘oil line pipe’ problem is an integrated one. Thus, the cross-disciplinary approach is needed to assess the operational reliability of oil line pipes. This approach may be based on the contemporary achievements of tribo-fatigue (new chapter of mechanics [1–5]) (Fig. 1) and mechanothermodynamics (new chapter of physics [6–9]). Therefore, this paper formulates (in the frst approximation, of course) and justifes the R&D activities in the area of ‘oil line pipe’ (OLP) with regard to well-known programs [3, 11]: fundamental studies and updating of the theories of pipeline operational damage tolerance, mathematical models of its interaction with the environment, including soil masses, updating methods in practical analysis of strength, lifetime, reliability, and safe operating time, development and implementation of the resource management methods based on the assessment of integrated quality of the linear part of the pipeline. The innovative algorithm to the problem solution is proposed in Fig. 2 for discussion. Surely, its detailed and full analysis is outside of this paper scope, but the formulation of the most relevant, in the author’s opinion, problems are briefy discussed below. This is a sort of concept outline of the algorithm: the pipe as a tribo-fatigue system – the role of the wall friction – the necessity to consider the stage of dispersed damages based on the stress-strain state (SSS) analysis in the vicinity of many small and large defects, including the soil pressure component – formation of dangerous volumes as integrated assessment of the damage tolerance level – use of ILI results to analyze the multiple damages level and assessment of its possible progress – transition to the stage of concentrated (local) cracks and analysis of their propagation risk – ageing processes – multifactor analysis of the limit state – integrated assessment of the system quality, risk and operational safety – resource optimization based upon integrated technical- economic studies. For practical implementation of this algorithm (OLP), development of methods (including rights to inventions) and correct laboratory tests for experimental determining the service properties (σ lim , K fc , i lim ,…) of the material and pipe components under conditions close to operational and with regard to ageing and damaging processes is very important. The key objective of the OLP-algorithm shown in Fig. 2 is to improve the assessment and forecast accuracy for the mechanical states of oil pipeline systems during their operation in various conditions based on the achievements of the contemporary science. These states shall be understood as SSS, dispersed and local damages, risk/safety, ageing criteria, limit state and, in integrated term, the quality state. Thus, the optimal resource management of the oil pipeline systems and their individual sections is provided with certain economic effect. The development of the package of software and regulatory documents including State standards will enable, in our opinion, to implement and support a non-contradictory unifed organizational, methodological and technological policy in the oil transport industry in order to ensure the Figure 1. Tribo-fatigue as an integrated scientifc discipline. Figure 2. Possible algorithm of formulating and solving the ‘oil line pipe’ (OLP) problem.