PSI - Issue 68

Oleksii Milenin et al. / Procedia Structural Integrity 68 (2025) 1010–1016 Oleksii Milenin et al./ Structural Integrity Procedia 00 (2025) 000–000

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The application of criterion (8) enabled an assessment of the probability of cold crack initiation based on the initial concentration of diffusible hydrogen in the pipeline metal and the preheating temperature of the repair area. As illustrated in Fig. 4 a, the influence of diffusible hydrogen on the susceptibility of the pipe metal to cold cracking is substantial; an increased hydrogen content can elevate the probability of crack initiation by over a hundred times. Conversely, preheating the repair area to a temperature of 100 °C significantly reduces the probability of cold cracking to a level not exceeding 5×10⁻³ across a wide range of diffusible hydrogen content. This finding aligns with the requirements outlined in current standards for repair work. Additionally, Fig. 4 b presents a typical calculated relationship between the probability of cold cracking in the pipeline metal and the preheating temperature of the repair area for initial hydrogen content V H =20 ml/100 g. It could be seen, that the preheating of repair area is the most effective for preheating temperature range up to 80 o C.

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(b)

Fig. 4. Calculated dependencies of the probability p of cold crack initiation in the pipeline metal on the initial content of diffusible hydrogen V H (a) and the preheating temperature T p of the repair area (b).

For practical application, it is beneficial to present the calculation results in the form of diagrams that relate the content of diffusible hydrogen in the pipe that is dependent on the composition of the gas-hydrogen blend, to the preheating temperature of the repair area. These diagrams indicate the conditions necessary to achieve a specific level of cold crack probability (from 10 -5 up to 10 -4 ). An example of such diagrams is provided in Fig. 5. The data clearly demonstrate that utilizing the existing gas transportation system for transporting gas-hydrogen blends necessitates a reevaluation of standardized requirements for technological measures to ensure reliability and maintain structural integrity.

Fig. 5. Calculation diagrams showing the relationship between the preheating temperature T p of the repair zone and the diffusible hydrogen content V H in the pipe for various allowable probabilities p of cold cracking.