PSI - Issue 16

Lubomyr Poberezhny et al. / Procedia Structural Integrity 16 (2019) 141–147 /XERP\U 3REHUH]KQ\ et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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detect, predict or prevent at the design stage of the pipeline or under operation due to corrosion products covering pits. However, pitting corrosion can cause a great deal of pipeline damage (Obanijesu et al. (2011)). The problem is complex due to physical and chemical processes that depend on the size of the formed hydrate, the stage and the period of contact with the pipeline, which results in breaching of protective films on the pipe surface. Acidic gases such as H 2 S and CO 2 , which are components in the formation of gas hydrates, dissolving in water can accelerate internal corrosion of gas pipelines (Poberezhny et al. (2017a)). Since the mechanism of corrosion in chloride environments is common for both internal and soil corrosion, for better description of the process and more accurate establishment of the general regularities of the influence of chloride ions on a metal, in addition to the results obtained in the study, the previously obtained data for soil corrosion were used (Poberezhny et al. (2017b)). The objective of the paper is to determine the regularities of the mutual effect of the corrosion environment, mechanical stresses and hydrate formation on corrosion of gathering pipelines. 2. Research technique Long-term exploitation of pipelines leads to significant changes of physical and mechanical properties of material, which results in formation of hardly predicted and controlled stress-strain condition in a pipeline. Therefore, developing methodological approaches, based on simulation of operation of structural elements and providing an effective control of static process of deformation and fracture by determining key parameters, is very important. The automated test system with computer, developed and described in detail by Kryzhanivskyy et al. (2001, 2004), was modified. The scheme of the test system is shown in Fig. 1. It includes the MV-1K and KN-1 test machines; it is used for a comprehensive study of kinetics of deformation, fracture and electrode potential of a pipe steel. The laboratory test system consists of computer, Mtech digital recorder, device for scanning fracture surfaces, further processing of received digital imprints in a graphic editor using a computer database and a Cole-Parmer A48405-25 metallographic microscope. Based on a reactor developed by specialists of Poltava National Technical University (Poberezhny et al. (2017a)), the reactor for synthesis of gas hydrates on the surface of pipeline steel specimens (Fig. 1b) was constructed and experimentally tested.

Fig. 1. General scheme of the laboratory test system (a), scheme of the installation for synthesis of gas hydrates (b): 1 – experimental reactor, 2 – drain pipe, 3 – gas cylinder, 4 – inlet pipe, 5 – pressure gauge, 6 – refrigerating chamber, 7 – support, 8 – gear transmission, 9 – engine.

The developed methodology consists in the following procedure. The first stage is synthesis of gas hydrates (Fig. 1b). Several schemes for the formation of gas hydrates are singled out: scheme without mechanical vibration of the reactor, and scheme with mechanical vibration of the reactor. The second scheme is similar to the first one, but after the formation of hydrate on the sample surface the oscillator generator reactor is additionally activated. This method of testing makes it possible to better assess the