IMPROVING STRENGTH OF HOT-ROLLED PIPES IN OIL AND GAS PIPELINE TRANSPORTATION SYSTEMS AND HEAT SUPPLY SYSTEMS

Abstract

Purpose. Development of new anticorrosion treatment technologies including prevention of inter-crystalline corrosion propagation inside the solid material in order to increase hot-rolled pipes life.Methodology. Based on the analysis of pipes manufacture and operation conditions, the main reason for reduction of the life of oil and gas transport pipelines made of hot-rolled pipes has been defined to be the poor corrosion resistance, which consequently causes propagation of fatigue processes. In course of theoretical and practical studies, one of the reasons for low corrosion resistance was revealed – complete absence of anticorrosion treatment inside the solid metal in order to prevent propagation of dangerous inter-crystalline corrosion.Results. Based on the conducted experimental studies, practices have been developed to carry out anticorrosion treatment inside the solid material by ensuring feeding of the inhibitor in ionic form into the solid material. This is done through plastic flow deformation of the material with grain refinement. As a result, mobility of grains and their fragments under conditions of deformation cause formation of "conductance channels", along which the inhibitor ions are transported to the solid material under the influence of electrostatic fields of the natural or, if necessary, artificial background. The most important result of this is the inhibitory treatment of the grains surface inside the solid material with prevention of electrochemical inter-crystalline corrosion propagation.Originality. Based on the practical works, anticorrosion treatment inside the solid material has been carried out for the first time, thereby eliminating the extremely dangerous inter-crystalline corrosion that latently propagates inside the solid material. A prerequisite for transportation of the inhibitor in ionic form inside the solid material are numerous examples of various elementary formations movements inside the solid body of material. This fact can be confirmed by inter-crystalline corrosion propagation in the solid material that generates in the manner of electrochemical corrosion, i.e. with water involved. This suggests the presence of water molecules in the solid material and possible channels of its penetration into the solid body. Many other examples can be given; their analysis reveals a common feature – in all cases there is an electrical nature, including water molecules that have an electrical dipole moment. Another precondition for the possibility of the inhibitor transportation is the presence of transportation channels. They are formed of free volumes, that are characteristic for crystalline structures, and volumes generated as a result of plastic flow deformation. The third precondition for the inhibitor ions transportation inside the solid material is the presence of driving forces; the forces of the electrical nature act in this case, ensuring "instantaneous" movements of micro-objects. Their source is the electrostatic fields of the material being the result of a large number of potential differences arising from the numerous and diverse inhomogeneities of materials. They form the natural electrostatic background, which ensures movement of micro-objects in the "solid body" of the material in vivo. If necessary, it can be supplemented with the artificial electrostatic background created by a grinding brush that removes scale from the pipe surface.Practical implications. The deterioration degree of operated pipeline systems is high; the required amount of repair work significantly exceeds the scope of work for the newly constructed systems. A similar situation both in terms of operating conditions and in technical state is with heating pipeline systems, also being of great length. Failures in operation of both abovementioned systems due to their underground laying bring high economic losses; the same is in case of their repair. For these reasons, extension of hot-rolled pipes service life is of great economic importance, which is hard to overestimate.