Adilson C. Benjamin

Finite Element Modeling of the Failure Behavior of Pipelines Containing Interacting Corrosion Defects

This paper describes the application of solid finite element models in the analysis of five tubular specimens containing interacting corrosion defects. Each of these specimens has been submitted to hydrotest up to failure as part of a previous research project. The specimens were cut from longitudinal welded tubes made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). The analyses accounted for large strains and displacements, stress-stiffening and material nonlinearity. The failure pressures predicted by the solid finite element models are compared with the failure pressures of these specimens measured in the laboratory burst tests carried out previously. Also the failure behavior of each specimen is described and illustrated by contour plots of stresses.Copyright

Burst Tests on Pipeline Containing Interacting Corrosion Defects

In this paper the burst tests of seven tubular specimens are presented. In these tests the tubular specimens were loaded with internal pressure only. The specimens were cut from longitudinal welded tubes made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). The specimen IDTS 1 is a defect-free pipe. The specimen IDTS 2 contains only one defect, herein called base defect. The base defect is an external flat bottomed defect with uniform width (circumferential dimension). The other five specimens contain groups of interacting defects constituted by the combination of two or more base defects. All the defects were machined using spark erosion. Measurements were carried out in order to determine the actual dimensions of each tubular specimen and its respective groups of defects. Tensile specimens and impact test specimens were tested to determine material properties. The failure pressures measured in the laboratory tests are compared with those predicted by six assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects, the RPA method, the RSTRENG Effective Area method and the DNV RP-F101 method for interacting defects.Copyright

Burst Tests on Pipeline Containing Closely Spaced Corrosion Defects

In this paper the burst tests of five tubular specimens are presented. In these tests the tubular specimens were loaded with internal pressure only. The specimens were cut from a longitudinal welded tube made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). The specimen IDTS 8 contains only one defect, herein called base defect. The base defect is an external flat bottomed defect with uniform width (circumferential dimension). The other four specimens contain groups of interacting defects constituted by the combination of three or more base defects. All the defects were machined using spark erosion. Measurements were carried out in order to determine the actual dimensions of each tubular specimen and its respective groups of defects. Tensile specimens and impact test specimens were tested to determine material properties. The failure pressures measured in the laboratory tests are compared with those predicted by five assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects, the RPA method and the RSTRENG Effective Area method.Copyright

Coupled and uncoupled solutions for the nonlinear dynamic behaviour of guyed deep water platforms

The platform presented in this work is a compliant tower in which the structural elements that produce the righting forces are guylines. The behaviour of this tower, under operating and storm conditions, is investigated by analysing the following models: a three-dimensional model for eigenvalue and nonlinear static analysis, a stick model and a coupled model, for nonlinear dynamic analysis. The equilibrium equations governing the nonlinear static analysis problem are solved using the Newton-Raphson incremental-iterative method. The eigenvalue problem is solved through the subspace iteration method. The equations of motion describing the nonlinear dynamic analysis problem are integrated using the Newmark method.

Predicting the Failure Pressure of Pipelines Containing Nonuniform Depth Corrosion Defects Using the Finite Element Method

PETROBRAS is conducting a research project with the purpose of investigating the behavior of pipelines containing long nonuniform depth corrosion defects. In the first phase of this project, burst tests of two tubular specimens were carried out. Each of the two specimens had one external nonuniform depth corrosion defect, machined using spark erosion. This defect consists of two short and deep defects within a long and shallow corrosion patch, longitudinally oriented. The second phase of the project aims at appraising the performance of two different finite element models: a shell model and a solid model. This paper describes the application of these models in the analysis of the two tubular specimens containing a long nonuniform depth defect that were tested in the first phase of this project. The failure pressures predicted by the two types of FE models are compared with the burst pressures measured in the laboratory tests. Also a comparison between the results obtained by these models is presented. It is concluded that the solid model is more accurate than the shell model, but both models proved to be capable of simulating the failure behavior of defects constituted by a long and shallow corrosion patch with deep defects over it.Copyright

Finite Element Models for the Prediction of the Failure Pressure of Pipelines With Long Corrosion Defects

PETROBRAS is conducting a research project with the purpose of investigating the behavior of pipelines with long corrosion defects. In the first phase of this project a database containing the results of nine burst tests of tubular specimens with flat bottom defects was generated. The second phase of the project aims at appraising the performance of two different finite element models: a shell model and a solid model. This paper describes the application of these models in the analysis of four tubular specimens of the PETROBRAS database. The failure pressures predicted by the two types of finite element models are compared with the burst pressures measured in the laboratory tests. Also a comparison between the results obtained by these models is presented. It is concluded that the solid model is more accurate than the shell model, but both models proved to be capable of simulating the corroded pipe burst tests adequately.© 2002 ASME

The Critical Path Method for Assessment of Pipelines With Metal Loss Defects

The Critical Path (CP) Method (CPM proposes a set of rules allowing the drawing of failure lines that represent adjacent areas positioned along selected circumferential and longitudinal directions of pipelines that contain colonies of corrosion defects. Failure pressures are calculated for each of those lines to determine the most critical one. This selected line is considered as the most probable path of rupture, and it corresponds to the minimum calculated internal pressure to take the pipeline to fracture. The proposed method was checked against twelve burst pressure tests performed on pipeline tubular specimens. Three specimens were labeled as control specimens — one was a pipe without defect and the other two had single small base defects of different depths. Nine of the specimens contained interacting corrosion defects, which were composed of the combinations of two or more base defects. Comparisons were made of the measured burst pressures with those predicted by the CPM, by one recently proposed method called MTI, version 1, or MTI V1, and by four other Level-1 or Level-2 assessment methods, namely the American Society of Mechanical Engineers (ASME) B31G method, the Det Norske Veritas (DNV) RP-F101 for single and for complex and interacting defects, and the RSTRENG Effective Area method. The CPM and MTI V1 methods predicted the failure pressures closest to the actual test failure pressures, with the CPM presenting suitable small mean error of evaluation as well as very low standard deviation error for its predictions.Copyright

Burst Tests on Pipeline Containing Circumferential Corrosion Defects

Circumferential defects are the ones in which the width w is greater than the length L (w > L). In this paper the burst tests of three tubular specimens are presented. In these tests the tubular specimens were loaded with internal pressure only. The specimens were cut from longitudinal welded tubes made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). Each of the three specimens had one external circumferential corrosion defect, machined using spark erosion. Measurements were carried out in order to determine the actual dimensions of each tubular specimen and its respective defect. Tensile specimens and impact test specimens were tested to determine material properties. The failure pressures measured in the burst tests are compared with those predicted by five assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects (Part B), the RPA method and the Kastner equation.Copyright

Burst Tests on Pipeline Containing Irregular Shaped Corrosion Defects

A corrosion defect can be considered as being of a regular shape if its defect depth profile is relatively smooth and the longitudinal area of metal loss is approximately rectangular. A corrosion defect can be considered as being of an irregular shape if its defect depth profile presents one or more major peaks in depth. In this paper the burst tests of four tubular specimens are presented. In these tests the tubular specimens were loaded with internal pressure only. The specimens were cut from longitudinal welded tubes made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). Each of the four specimens had one external irregular shaped corrosion defect, machined using spark erosion. Measurements were carried out in order to determine the actual dimensions of each tubular specimen and its respective defect. Tensile specimens and impact test specimens were tested to determine material properties. The failure pressures measured in the laboratory tests are compared with those predicted by six assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects, the RPA method, the RSTRENG Effective Area method and the DNV RP-F101 method for complex shaped defects.Copyright

Stress Concentration Factors for a Drilling Riser Containing Corrosion Pits

The residual fatigue life of a corroded riser joint can be evaluated by means of a fatigue analysis based on S-N data. In this case nominal stresses are determined through a global riser analysis in which the drilling riser is modeled as a tensioned beam subjected to loads throughout its length and with boundary conditions at each end. The effect of the corrosion defects is taken into account multiplying the nominal stresses by stress concentration factors (SCFs) derived by local Finite Element (FE) analyses of the riser joints containing corrosion defects. In this paper stress concentration factors for a drilling riser containing corrosion pits are calculated using solid FE models. These pits are situated on the external surface of the riser joints. Three shapes of corrosion pits are considered: semi spherical, cylindrical wide and cylindrical narrow. Five depths of corrosion pits are considered: 12.6%, 20.1%, 30.2%, 40.3% and 50.3% of the riser wall thickness. The riser outside diameter and the riser wall thickness are 533.4 mm (21 in) and 15.9 mm (0.625 in), respectively.© 2007 ASME