PSI - Issue 59

V. Makarenko et al. / Procedia Structural Integrity 59 (2024) 385–390 V. Makarenko et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction As practice shows, critical parts and metal structures in sanitary facilities are operated in aggressive environments (water). Therefore, they quickly fail, causing extensive material and financial losses and severe environmental consequences in the housing and communal services industry (Samoylenko (2009), Goncharenko et al. (2013), Makarenko et al. (2023)). For example, during the operation of pipeline structures in direct contact with household (contaminated) water, pronounced corrosion damage was detected with subsequent destruction of pipe structures, which took place mainly underground, in a relatively short period (2-3 years) as shown by Radkevich et al. (2000), Nasonina et al. (2019). It is known from the works of Tkachev (2000) and Panasyuk et al. (1987) that during long-term operation, metal is overburdened, which negatively affects the impact strength and plastic properties of carbon and low-alloy steels. Moreover, hydrogen not only reduces the value of impact strength, but also increases the tendency to cold breakage. It follows from Borisova et al. (1986) and Panasyuk et al. (1987) that hydrogenation, especially at subzero temperatures (up to - 30 °C), significantly reduces the number of cycles before the destruction of samples in the presence of stress concentrators, especially in conditions of low-cycle fatigue failure. Lowering the temperature to -20 ... – 40 ° C decreases the metal's impact strength and deformation ability. The purpose of the work is an experimental study of the influence of harmful steel elements (hydrogen, sulfur, oxygen) on the degradation of structural steels of underground sewer systems. 2. Methods and materials of research The complex studies of damaged metal of steel structures of long-term sewer systems included, along with standard types of research, also special, in particular, various variants of X-ray spectral analysis using a scanning electron microscope JSM-35CF (Geol, Japan); SEM- 515 with a microanalyzer “Link” from Philips; scanning discretely-point Auger electron spectroscopy (AE-2000 microanalyzer); secondary ion mass spectroscopy (Las-2000 installation with MS-156 device). In addition, the content and distribution pattern of hydrogen, oxygen and sulfur in the metal were determined: a) by local mass spectral analysis (LMSA) with a laser microprobe; b) by melting metal samples (chips) in a carrier gas stream using a Leco installation. Microhardness was determined according to GOST 9450-80 using a diamond Pyramid together with a metallographic microscope. The object of research was the steel of sewer structures of grades 09G2S, 17G1S, 20, 10, 3, and long-term operated in aggressive environments. Samples were cut from steel pipelines during routine or emergency repairs. The service life of sewer structures is up to 40 years (pipe wall thickness is 14 mm). 3. Research results The combination of corrosion damage to the metal with its significant local hydrogen saturation, oxidation, and embrittlement, which applies to various steels, has been established for most of the studied damage cases (Goncharenko et al. (2013), Makarenko et al. (2021)). An idea of this is given by the data shown in Fig. 1, which shows the distribution of concentrations of elements (hydrogen, oxygen and sulfur) in the metal of the cross-section of pipes (including a corrosion defect) of sewer systems operated at municipal facilities. The data shown in Fig. 1 shows that over time, the corroded surface layers of metal are enriched by elements (hydrogen, oxygen and sulfur). This is especially evident in the area of a corrosion defect. The probing route passed partially through the base metal of the sewer pipes – sections A-B and D-E (undamaged surface near the microdefect) and along the corrosion defect (section B-C-D), which is directly adjacent to the cavity of the defect. Data analysis shows that with increasing service life, the surface layers of the metal are enriched by hydrogen, oxygen and sulfur, which negatively affects the corrosion and mechanical properties of the metal. For example, during operation for 40 years, the maximum concentration of hydrogen in the site (B-C-D) increases by two times, and compared with the hydrogen content in the sites (A-B) and (D-E) – by 1.5 times. A similar pattern is observed concerning sulfur and oxygen concentrations. In particular, the maximum concentration of sulfur at the site (B-C-D) increases by 1.3 times, and compared with the concentration of sulfur at