Issue 51

Y. Dubyk et alii, Frattura ed Integrità Strutturale, 51 (2020) 459-466; DOI: 10.3221/IGF-ESIS.51.34 466 with the results of numerical simulation shows the effectiveness of the proposed procedures. However, equivalent load method underestimates the peak stress concentration value, but it predicts quite good the stress profile. The peak stress value can be adjusted by a simple semi-analytical correction. Obtained semi-analytical solution allowed to conduct parametric studies for different dent shapes, radius to thickness ratio at different nominal stress level:  for small dents with increasing depth the stresses concentration increases and for small dents, this growth was more significant  the influence of pressure, for unproportional dent was more significant than in case of axial force loading;  concentration due to the pressure load was more significant, and must be taken into account, especially for short dents, since it can exceed the nominal stress level by an excessive value;  increasing in nominal stress level gives a reduction in stress concentration factor, and for pressure loading this decreasing was more significant;  increasing in R to h ratio leads to increasing in stress concentration factor. For pressure and axial force loading this effect is different and should be accounted for very flexible pipelines. The proposed semi-analytical solution is a powerful method for dents assessment, it is especially useful for parametric analysis, and it can be used to understand the factors that influence the pipeline safe operation. R EFERENCES [1] EGIG. (2015). Gas Pipeline Incidents. 9th Report of the European Gas Pipeline Incident Data Group. Available at: https://www.egig.eu/reports/ $97/$155. [2] Kec, J. and Cerny, I. (2017). Stress-strain assessment of dents in wall of high pressure gas pipeline, Procedia Structural Integrity, 5, pp. 340–346. DOI: 10.1016/j.prostr.2017.07.180. [3] Li, C., and Dang, C. (2017). Plastic damage analysis of oil and gas pipelines with unconstrained and constrained dents. Engineering Failure Analysis, 77, pp. 39–49. DOI: 10.1016/j.engfailanal.2017.02.009. [4] Ying Wu, Y., Jiewen Xiao, J. and Peng Zhang, P. (2016). The analysis of damage degree of oil and gas pipeline with type II plain dent, Engineering Failure Analysis, 66, pp. 212–222. DOI: 10.1016/j.engfailanal.2016.04.004. [5] Calladine, C. R. (1972). Structural Consequences of Small Imperfections in Elastic Thin Shells of Revolution, International Journal of Solids and Structures, 8(5), pp. 679–697. DOI: 10.1016/ 0020-7683(72)90036-4 . [6] Rinehart, A. J. and Keating, P. B. (2007). Stress Concentration Solution for a 2D Dent in an Internally Pressurized Cylinder, Journal of Engineering Mechanics, 133(7), pp. 792–800 DOI: 10.1061/(ASCE)0733-9399(2007)133:7(792). [7] Godoy, L. A. (1996). Thin-Walled Structures with Structural Imperfections, New York, Pergamon. DOI: 10.1016/B978-0-08-042266-4.X5000-3. [8] Godoy, L. A. (1993). On loads equivalent to Geometrical imperfections in shells, J. Eng. Mech, 119(1), pp. 186-190. DOI: 10.1061/(ASCE)0733-9399(1993)119:1(186). [9] API 579-1/ASME FFS-1. (2016). Fitness-For-Service. [10] Leissa, A. W. (1973). Vibration of Shells, NASA-SP-288.