PSI - Issue 59

Ihor Dmytrakh et al. / Procedia Structural Integrity 59 (2024) 74–81 Ihor Dmytrakh et al. / Structural Integrity Procedia 00 (2024) 000 – 000

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2

Nomenclature p

internal pressure in MPa crack depth in mm crack length in mm

a c

N number of fatigue loading in cycles da / dN fatigue crack growth rate in mm/cycle K stress intensity factor in MPa m Δ K  stress intensity factor range in MPa m Δ K th 

threshold stress intensity factor range in MPa m critical stress intensity factor range in MPa m

Δ K fc

hydrogen concentration in ppm

C H N f

number of fatigue loading to failure (residual durability) in cycles

1. Introduction One of the most dangerous phenomena was observed by Askari et al. (2019) during the operation of the underground pipelines is the stress corrosion cracking of metal. In the literature we can find a huge array of data on numerous cases of corrosion cracking of pipelines in different operating conditions, as well as the results of the studies of the causes and the mechanisms of the realization of this phenomenon (ANSI/NACE SP0502-2010 (2010)). For example, for pipelines, one of the negative factors which manifest itself during their long-term operation is damage and peeling of protective coatings due to the action of the external environment (Nyrkova (2020)). In this case, there is a situation of the free-corroding system which leads to the anodic electrochemical dissolution of the metal of the pipe, as well as to the release of hydrogen on its surface due to the realization of the counterpart cathodic reaction (Cheng (2007)). This creates the preconditions for hydrogen embrittlement of the pipeline metal (Dmytrakh et al. (2018, 2021)). In general, Andreikiv and Hembara (2022a,b); Bolzon et al. (2021); Dutkiewicz et al. (2023); Ohaeri et al. (2018); Skalskyi et al. (2018) indicated that the hydrogen factor is dominant in the stress corrosion cracking of low-alloyed pipelines steel. Therefore, the problem of the hydrogenation of low-alloyed steels under the operation of the gas pipelines is critical in terms of ensuring their reliable and safe operation. The presented work is devoted to the determination of the effect of hydrogen concentration in metal on the residual durability of defected pipelines. Here the crack-like defects of different shape and their location in the pipe were considered. The residual durability of the defected pipe was chosen as the basic parameter for the assessment of its serviceability. This value was determined as the number cycles of fatigue loading to failure of the considered pipe with the given defect under different values of the hydrogen concentration in the metal. Thus, all defects detected in the pipeline after inspection can be compared with received data and on this base the expert conclusion for the evaluation of the potential risk of each defect can be made. 2. Theoretical background During long-term operation, the pipelines are subjected to different types of fatigue loading (Bolzon et al. (2021)). This phenomenon leads to damage of the pipes on macro and micro structural level. In the result, pipes always contain the defects of different natures. The further development of these defects creates the danger of pipeline failure. This study grounds on the statement that time of crack-like defects growth defines the residual durability of the pipelines. At that, the process of the crack propagation is accelerated by several exploitation factors, among which the hydrogen factor can be a crucial. Here, the value of hydrogen concentration C H in the metal is considered as the most important parameter. The fracture mechanics approach was used for study of above-mentioned problem. To date, it is indisputably proved by Dmytrakh et al. (2012) that the fatigue crack growth in the material can be adequately described using the stress intensity factor as one of the basic parameters of linear fracture mechanics: