PSI - Issue 40

N.A. Makhutov et al. / Procedia Structural Integrity 40 (2022) 283–295 N.A. Makhutov at al. / Structural Integrity Procedia 00 (2022) 000 – 000

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If conditions (18) - (21) are met, operation of the pipeline section can be continued. 5. Pipeline operating life assessment Based on the analysis of data on local deformation in concentration zones ( ) using expressions (8, 9, 14, 15) and data on cyclic changes in the loading scenarios by Lisin et al. (2018) and Mahutov (2008) ( ) over time τ S for pressure ( ) we get (Fig. 7) information on extents ∆ ( ), as a difference between maximum ( τ S ) and ( τ S ) values of deformation during each cycle max max max ( ) ( ) ( ) I II e s e s e s e e e      (21)





0

Fig. 7. Extent of local deformations in the stress concentration zone during changes in loading conditions.

Since the total equivalent number of loading cycles N by inside pressure during operation is relatively low ( N ≤ 104), exponential expression can be used for low-cycle loading area

1 1

e m

( ) ( ) N   

ln

,

(22)

e



max

e

s

s

2 1



k where – material characteristic; – relative contraction in sample throat from static tension. for pipe steels is determined experimentally or assigned, taking into consideration that as the strength increases the value of m e increases from 0.5 to 0.55. During the cracks growth stage ( ) according to Fig. 3, b) the cracks growth rate is determined using non-linear fracture mechanics equation, respectively