PSI - Issue 72

Lazar Jeremić et al. / Procedia Structural Integrity 72 (2025) 91–96

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al. (2021a, 2023, 2024), Zheng et al. (2023), Mehmanparast et al. (2022), Jovanović et al. (2023) and Abdelmoumene et al. (2023), Non-destructive testing (NDT) plays a very important role during out-service and in-service inspection of pressure vessel equipment in general to assess their structural integrity Jarić et al (2024a, 2024b), Kawiak et al. (2024), Jeremić et al. (2020) , since the lifespan of any pressure vessel depends on absence of harmful defects especially in welded joint region. In this paper, structural integrity assessment of an oil storage will be presented in the term of application of NDT methods with its specifics according to API 653 standard criteria. Analyzed pressure vessel equipment is located in Serbia (Fig. 1) and in Norway (Fig. 2). NDT inspection was implemented as a method for monitoring the integrity of pressure vessel equipment in the oil and gas industry, having very important role for both economic and safety reasons. Collected data was used to evaluate the overall integrity and fitness for continued service of the oil tank. Inspection and structural integrity analysis included assessment of each part of the tank: foundations, shell, roof and floor/bottom. The importance of NDT methods and used criteria were shown on ‘critical’ locations of tank (which refer predominantly to welded joints), revealing critical defects which need to be repair.

Fig. 1. Oil storage tank Serbia: a) North side view; b South side view.

Fig. 2. Methanol storage tank in Norway

2. Testing methods and parameters Due to the importance of structural integrity of pressure equipment in securing functionality and safety of such structures (particularly in the case of petroleum and gas industry, one must use a detailed approach to its assessment. One of the ways to achieve this is by using advanced NDT inspection, which was implemented here as a method for monitoring the pressure tanks. Phased array ultrasonic testing (PAUT) was performed here, on welds and materials in carbon steel vessels and tanks. The integrity of pressure equipment is essential for ensuring the safe storage and a safe working life without stress concentration and/or excess deformation that will lead to the initiation of cracks, and ultimately, to failure with potentially disastrous consequences. All pressure vessel equipment should be tested according to some reference standards in order to determine structural integrity response, such as examples presented in Iwashita et al. (2003), Vukojević et al. (2024) and Lee et al. (2004) . As for the welding of joints, it was performed as a combination of manual arc welding (MAW) process for vertical welds and the submerged arc welding (SAW) for the rest. Even though these are very well-known and common welding techniques for pressure equipment, it is still recommended to regularly inspect welded joints, since they are among the most critical locations in pressure equipment. The operation parameters of the tanks (Fig. 1 and Fig. 2) are shown in Table 1. PAUT as an advanced NDT inspection method was applied to the most critical welded joint, which in this case was the corner joint (a fillet weld) between the shell and the bottom, since this is the area where tensile stresses were the highest (some examples are shown in Aranđelović et al. (2021b), Opačić et al. (2024) and Nicolson et al. (2024) . The calibration block used for this analysis is shown in Figure 3, and the relative indications on the standard calibration block in Figure 4.