Edmundo Q. de Andrade

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

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

Failure Behavior of Colonies of Corrosion Defects Composed of Symmetrically Arranged Defects

This paper presents a case study on the failure behavior of four colonies of corrosion defects using solid Finite Element models. These analyses accounted for large strains and displacements, stress-stiffening and material nonlinearity. Colonies 1 and 2 are each composed of two longitudinally aligned defects. Colonies 3 and 4 are each composed of four defects (two longitudinally aligned defects and two circumferentially aligned defects) arranged in a rhombus shape. For each of the four colonies a parametric study is performed in which the longitudinal spacing sL between the two defects longitudinally aligned is varied from a small value (sL )min to a large value (sL )max . Based on the results obtained the failure behavior of each colony is described and illustrated by contour plots of stresses. The failure pressures predicted by the Finite Element analyses 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 (Part B), the RPA method, the RSTRENG Effective Area method and the DNV RP-F101 method for interacting defects (Part B).Copyright

Titanium Stressjoint Design for the Top Connection of a SCR in HPHD

The top connection for the SCRs is one of the main critical points of their design. This situation becomes more challenging principally when there are high pressures and high deep water (HPHD) combined with extreme environmental loads — as is the case in the Gulf of Mexico. PETROBRAS became aware of this problem during the conceptual study of SCRs for ultra-deep waters, where the SWL is in the vicinity of 8200 ft, and with internal pressure of 12100 psi to 15000 psi. With this scenario in mind, a Titanium stressjoint began to be considered as the principal solution to the top connection. Due to this, PETROBRAS — in partnership with RTI ENERGY SYSTEM — developed a study to design a stressjoint model which would validate the SCR. This paper broadly discusses the search for this top connection solution. Dynamic global and local analyses were performed, which led us to the final solution of a titanium and steel mixed stressjoint.Copyright