DSE-T: A Program for Strain Based Assessment of Pipeline Dents With Complex Shape

Abstract

According to ASME B31.8 - Gas Transmission and Distribution Piping Systems, plain dents or dents on ductile welds of any depth are acceptable provided strain levels associated with the deformation do not exceed 6% and 4%, respectively. Appendix R of the Code presents a method for estimating strains in dents. In order to use this method, some technique is usually necessary to evaluate strains based on the pipe surface contour information captured from in-line inspection (ILI) tools or from direct measurement. In previous papers the authors have presented techniques based on B-spline curves or B-spline surfaces to evaluate the bending strains on dents which have a “well-behaved” topology or on dents having a complex shape, respectively. The B-splines are used to interpolate the geometry of the dent, to infer its radii of curvature and to calculate the bending strain components using a procedure similar to that suggested on the Appendix R of the ASME B31.8 Code. The strains are combined in order to obtain an equivalent strain field that does not take into account the effect of the membrane strains or include the effect of the longitudinal membrane component through an expression like that contained on the code. These techniques which were implemented in the DSE-B and the DSE-R programs, respectively, make the dent strain estimation based on data coming from in-line inspections (ILI) tools easier and automatic. This paper presents the DSE-T program, which uses the methodology implemented in the DSE-B program to calculate bending strains, and a dedicated finite element method to estimate membrane strains. Bending and membrane strains are combined to give the total strain fields on the inside and outside surfaces of the indented pipe. The program also enables the user to verify whether the dent is smooth or kinked and to simulate the effects of measuring the dent shape using “virtual” geometric tools with different degrees of resolution. Results obtained using the DSE-T are compared to results from nonlinear finite element analyses.