Issue 51

Y. Dubyk et alii, Frattura ed Integrità Strutturale, 51 (2020) 459-466; DOI: 10.3221/IGF-ESIS.51.34 465 Figure 4 : Effect of initial stress: a) Axial force loading, b) Internal pressure loading; R=400mm, h =10mm: 0 R  = 0 x =60mm; 0 R  =90mm, 0 x =60mm; 0 R  =60mm, 0 x =90mm. In Fig. 5, the effect of shell radius to thickness ratio was analyzed and again it is possible to see the different behavior for internal pressure and axial force loading. It can be clearly seen from Fig. 5 that with increasing R to h ratio a higher SCF was obtained and the stress concentration can be up to 40 times. In oil and gas industries typical trunk pipelines have R/h=15…40, so the results will be in the lower part of Fig. 5 and with the increasing of the nominal stress level SCF factor will decrease (see Fig. 4) and this effect will be more significant for flexible shells. Nevertheless, if using high strength steels for piping, the thickness can be reduced and must be aware of the increasing in SCF for dents in very flexible shells. Figure 5 : Effect of radius to thickness ration: a) Axial force loading, b) Internal pressure loading; σ nom =1MPa, h =10mm: 0 R  = 0 x =60mm; 0 R  =90mm, 0 x =60mm; 0 R  =60mm, 0 x =90mm; C ONCLUSIONS simple engineering approach was developed for analysis of stress-strain state of dented pipelines using equivalent load method. Using the harmonic imperfection model, an explicit analytical solution for a single dent was received and for a reliable accurate solution 50 terms in Fourie expansion must be used. Comparison of analytical stresses A