Finite Element Modelling and Retained Life Estimation of Corroded Pipelines in Consideration of Burst Pressures—A Fractural Mechanics Approach

Chinedu Ossai

doi:10.3390/infrastructures2040015

Abstract

This study used Finite Element Modelling (FEM) to determine the relationship between the burst pressure (Pb) of internally, circumferentially corroded pipelines, with the corrosion defect depth (d), pipe wall thickness (t) and the pipe diameter (D). After modelling X46 and X52 grades of pipes, the Pb estimated was compared with those determined experimentally and with industry standard models—ASME B31G (modified), RSTRENG, DNV F101, SHELL92 and FITNET FFS. The comparison specified a Root Mean Square Percentage Error (RMSPE) that ranged from 7.06% to 20.4% and a coefficient of determination (R2) that varied from 0.7932 to 0.9813. Multivariate regression was also used to compute a general linear relationship between the burst pressure (Pb) and (d/t), (L/D) and (L/√Dt). The resulting FEM burst-pressure model, developed with multivariate regression, was later used to estimate the expected allowable operating pressure of a corroded X46 grade pipeline over the lifecycle duration, for low, mild, high and severe corrosion categories. It was observed that the burst pressure retention ratio (Rr), which is an indicator of the reliability of the pipeline, decreased with the increase in (d) but did not show distinctive changes with the increase in (L). Considering the robustness of the FEM developed in this study, it can be concluded that it will be very vital for flowline design and pipeline integrity management.

Highlights

The problems of uncertainties and stochasticity associated with some natural phenomena make them mathematically unpredictable, due to geometrical irregularities and the trendless nature of events recurrences [1]
Since pipeline corrosion is full of uncertainties, because of the difficulties associated with the measurement of the geometry and the recurrence times of the corrosion defects, the stochastic perturbation technique was introduced
This study implemented finite element modelling (FEM), which is a spectral analysis procedure that subjects nodes to random excitation, using the knowledge of two or three other nodal moments

Summary

Introduction

The problems of uncertainties and stochasticity associated with some natural phenomena make them mathematically unpredictable, due to geometrical irregularities and the trendless nature of events recurrences [1]. Since pipeline corrosion is full of uncertainties, because of the difficulties associated with the measurement of the geometry and the recurrence times of the corrosion defects, the stochastic perturbation technique was introduced To this end, this study implemented finite element modelling (FEM), which is a spectral analysis procedure that subjects nodes to random excitation, using the knowledge of two or three other nodal moments. TToo ffuurrtthheerr vvaalliiddaattee tthhee FFEEMM mmooddeelllliinngg,, iinndduussttrryy ssttaannddaarrdd mmooddeellss iinncclluuddiinngg AASSMMEE BB3311GG ((mmooddiififieedd)),, RRSSTTRREENNGG,, DDNNVV FF110011,, SSHHEELLLL9922 aanndd FFIITTNNEETT FFFFSS [[1144––1177]] wweerree used These models depend on the corrosion defect geometries—corrosion defect depths and lengths, bending stresses and operating pressures—characterized with numerical and experimental results, for the developed empirical formulas (Equations (4)–(8)). This variation may be attributed to flaws in the experiments, which could include measurement and calculation errors that must have been introduced at various times by the diverse people who handled the experiments

Burst Pressure Prediction for Circumferentially-Corroded Pipelines

Conclusions