Assessment of Crack in Corrosion Defects in Natural Gas Transmission Pipelines

2008 ◽  
Author(s):  
Duane Cronin ◽  
Alan Plumtree ◽  
Millan Sen ◽  
Richard Kania
Keyword(s):  
Numerical Investigation ◽  
Finite Length ◽  
Defect Depth ◽  
Hybrid Form ◽  
Line Pipe ◽  
Collapse Pressure ◽  
Corrosion Defect ◽  
Natural Gas Transmission ◽  
Defect Repair ◽  
Corrosion Defects

Crack-like defects may occur coincident with corrosion defects and represent a new hybrid form of defect in gas and oil pipelines that is not directly addressed in the current codes or methods of assessment. There is a need to provide assessment and evaluate the integrity of the line as well as identify requirements for defect repair or line hydrotest. A numerical investigation was undertaken to evaluate the predicted collapse pressure of crack in corrosion (CIC) defects in typical line pipe. Longitudinally oriented CIC defects were evaluated as long cracks occurring within long, corrosion grooves of uniform depth. This was a conservative representation of a finite length CIC defect. It was found that the collapse pressure for CIC defects varied between that of a long uniform depth crack and a long uniform depth corrosion defect. The transition to corrosion defect behaviour only occurred when the corrosion defect depth was significant (greater than 75% of the total defect depth). Finite-length CIC defects were then investigated using a numerical investigation to identify the effect of crack and corrosion length. The collapse pressure of a finite length crack within an infinitely long corrosion defect was found to be lower than a crack of equivalent total depth and length. This reduction in collapse pressure was attributed to increased local stresses in the vicinity of the crack due to the coincident corrosion. The predicted collapse pressure increased towards the crack-only value when the length of the corrosion defect was decreased to that of the crack. CIC defects were evaluated as cracks using the NG-18 approach and BS 7910 code (Level 2A FAD). The NG-18 approach conservatively predicted lower collapse pressures than the FE analysis, whereas the FAD approach was conservative for shallow defects and could be non-conservative for deeper defects. These results are attributed to the presence of the corrosion and the fact that no factor of safety was included in the analysis. Future studies will investigate experimental validation of the FE and FAD methods for this type of defect.

Burst Tests on Pipeline Containing Irregular Shaped Corrosion Defects

2008 ◽  
Author(s):  
Adilson C. Benjamin ◽  
Aldo R. Franzoi ◽  
Jose´ Luiz F. Freire ◽  
Ronaldo D. Vieira ◽  
Jorge L. C. Diniz
Keyword(s):  
Depth Profile ◽  
Effective Area ◽  
Metal Loss ◽  
Defect Depth ◽  
Corrosion Defect ◽  
Spark Erosion ◽  
X80 Steel ◽  
Corrosion Defects ◽  
Tubular Specimens ◽  
Outside Diameter

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.

Prediction of Corrosion Defect Failure Pressure for Finite Length Defects

2004 ◽  
Author(s):  
Duane S. Cronin
Keyword(s):  
Finite Length ◽  
Three Dimensional ◽  
Defect Depth ◽  
Material Loss ◽  
Element Analysis ◽  
Failure Pressure ◽  
Dimensional Finite Element ◽  
Corrosion Defects ◽  
Three Dimensional Finite Element ◽  
Analytical Approaches

Corrosion defects commonly occur on operating pipelines due to a loss of protection in a corrosive environment. These defects require practical and accurate assessment, particularly for older pipeline systems, to determine the need for remediation or allow for continued operation. Previous research has shown that appropriate application of full three-dimensional finite element analysis, and newly developed analytical approaches, can provide very accurate predictions of failure pressure but require detailed material and geometric data. Although this is important, a simpler method that allows for efficient evaluation of large amounts of data is also desirable. A method has been developed from an existing analytical solution by assuming a defect can be characterized in terms of the total defect length, and a constant defect depth equal to the maximum defect depth. In general this produces a conservative estimate of the material loss. This finite-length defect solution is in good agreement with experimental data for idealized defects, and provides reasonable predictions of burst pressure, with a minimum amount of data, when applied to real corrosion defects.

Crack in Corrosion Defect Assessment in Transmission Pipelines

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
A. Hosseini ◽  
D. Cronin ◽  
A. Plumtree
Keyword(s):  
Crack Depth ◽  
Evaluation Criteria ◽  
Average Error ◽  
Failure Behavior ◽  
Pipe Material ◽  
Line Pipe ◽  
Collapse Pressure ◽  
Defect Assessment ◽  
Level 3 ◽  
Corrosion Defects

Cracks may occur coincident with corrosion representing a new hybrid defect in gas and oil pipelines known as crack in corrosion (CIC) that is not directly addressed in the current codes or assessment methods. Hence, there is a need to provide an assessment of CIC and evaluate the line integrity, as well as identify the requirements for defect repair or line hydrotest. An experimental investigation was undertaken to evaluate the collapse pressures of lines containing corrosion, cracks, or (CIC) defects in a typical line pipe (API 5L Grade X52, 508 mm diameter, 5.7 mm wall thickness). The mechanical properties of the pipe were measured using tensile, Charpy, and J-testing for use in applying evaluation criteria. Rupture tests were undertaken on end-capped sections containing uniform depth, finite length corrosion, cracks, or CIC defects. Failure occurred by plastic collapse and ductile tearing for the corrosion defects, cracks, and CIC geometries tested. For the corrosion defects, the corroded pipe strength (CPS) method provided the most accurate results (13% conservative on average). The API 579 (level 3 failure assessment diagram (FAD), method D) provided the least conservative collapse pressure predictions for the cracks with an average error of 20%. The CIC collapse pressures were bounded by those of a long corrosion groove (upper bound) and a long crack (lower bound), with collapse dominated by the crack when the crack depth was significant. Application of API 579 to the CIC provided collapse pressure predictions that were 18% conservative. Sixteen rupture tests were successfully completed investigating the failure behavior of longitudinally oriented corrosion, crack, and CIC. The pipe material was characterized and these properties were used to predict the collapse pressure of the defects using current methods. Existing methods for corrosion (CPS) and cracks (API 579, level 3, method D) gave conservative collapse pressure predictions. The collapse pressures for the CIC were bounded by those of a long corrosion groove and a long crack, with collapse dominated by the crack when the crack depth was significant. CIC failure behavior was determined by the crack to corrosion depth ratio, total defect depth and its profile. The results showed that the failure pressures for CIC were reduced when their equivalent depths were similar to those of corrosion and using crack evaluation techniques provided an approximate collapse pressure.

Experimental Database for Corroded Pipe: Evaluation of RSTRENG and B31G

2000 ◽  
Author(s):  
Duane S. Cronin ◽  
Roy J. Pick
Keyword(s):  
Tensile Tests ◽  
Line Pipe ◽  
Experimental Database ◽  
Corrosion Defect ◽  
Defect Assessment ◽  
Simple Geometry ◽  
Corrosion Defects ◽  
Failure Predictions ◽  
External Corrosion ◽  
Assessment Procedures

The evaluation and development of the current corrosion defect assessment procedures for pipelines has been based on experimental burst tests of line pipe. In these tests, external corrosion has often been simulated with machined defects of simple geometry. As a result, assessment procedures which model the corrosion defect geometry with only a few parameters, such as ASME B31G, show reasonable agreement with the experiments. However, the degree of conservatism in these assessment methods is undefined when they are applied to complex corrosion defects. The authors have burst over 40 pipes removed from service due to corrosion defects. All corrosion defects on each pipe were measured in detail and the material properties were determined from tensile tests. The currently accepted assessment procedures for corroded line pipe (B31G and RSTRENG) have been applied to the database. The degree of conservatism in these procedures is quantified and a statistical model for the failure predictions is proposed.

Numeral Simulation Study on Pipeline Corrosion Defects under Different Sizes and Pressures Based on FEM

2012 ◽  
Vol 215-216 ◽  
pp. 1154-1157
Author(s):  
Han Wu Liu ◽  
Rui Hua Dong ◽  
Han Xun Lv
Keyword(s):  
Magnetic Field ◽  
Finite Element ◽  
Electric Current ◽  
Three Dimensional ◽  
Element Model ◽  
Defect Depth ◽  
Element Analysis ◽  
Corrosion Defect ◽  
Corrosion Defects ◽  
Pipeline Corrosion

Finite element analysis software ANSYS is used to establish a three-dimensional finite element model of the pipeline corrosion defects by applying the boundary conditions of square wave excitation to simulate the distributions of current and induced magnetic field in the pipeline under various defect volumes. The results of the study show: When there is no corrosion defect in the pipeline, the electric current in the pipeline is basically even distribution. The magnetic field is distributed for the symmetrical vortex shape from head to foot, and it has not obviously gather phenomenon. When there are some corrosion defects in the pipeline, the electric current forms partial symmetrical vortex shape in both sides of the corrosion defect, and it is obviously assembled in the defect place. The simulation results of the different size defects show that the maximum magnetic field strength and the maximum current value increase with the defect depth increasing, while the output voltage decreases with the defect depth increasing. For the analysis of the stress distributions of the pipeline corrosion defect with certain size under different pressures, it was found that the maximum stress is 596 MPa when the bearing limit work pressure of the pipeline is 7 MPa, which is smaller than the yield strength with ensuring the safely running of the pipelines with defects.

Failure Pressure Prediction of Cracks in Corrosion Defects Using XFEM

2020 ◽  
Author(s):  
Xinfang Zhang ◽  
Allan Okodi ◽  
Leichuan Tan ◽  
Juliana Leung ◽  
Samer Adeeb
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Extended Finite Element Method ◽  
Crack Depth ◽  
Average Error ◽  
Extended Finite Element ◽  
Defect Depth ◽  
Failure Pressure ◽  
Corrosion Defects ◽  
Element Method

Abstract Coating and cathodic protection degradation can result in the generation of several types of flaws in pipelines. With the increasing number of aging pipelines, such defects can constitute serious concerns for pipeline integrity. When flaws are detected in pipelines, it is extremely important to have an accurate assessment of the associated failure pressure, which would inform the appropriate remediation decision of repairing or replacing the defected pipelines in a timely manner. Cracks-in-corrosion (CIC) represent a class of defect, for which there are no agreed upon method of assessment, with no existing analytical or numerical models to predict their failure pressures. This paper aims to create a set of validated numerical finite element analysis models that are suitable for accurately predicting the failure pressure of 3D cracks-in-corrosion defects using the eXtended Finite Element Method (XFEM) technique. The XFEM for this study was performed using the commercially available software package, ABAQUS Version 6.19. Five burst tests of API 5L X60 specimens with different defect depths (varying from 52% to 66%) that are available in the literature were used to calibrate the XFEM damage parameters (the maximum principal strain and the fracture energy). These parameters were varied until a reasonable match between the numerical results and the experimental measurements was achieved. Symmetry was used to reduce the computation time. A longitudinally oriented CIC defect was placed at the exterior of the pipe. The profile of the corroded area was assumed to be semi-elliptical. The pressure was monotonically increased in the XFEM model until the crack or damage reached the inner surface of the pipe. The results showed that the extended finite element predictions were in good agreement with the experimental data, with an average error of 5.87%, which was less conservative than the reported finite element method predictions with an average error of 17.4%. Six more CIC models with the same pipe dimension but different crack depths were constructed, in order to investigate the relationship between crack depth and the failure pressure. It was found that the failure pressure decreased with increasing crack depth; when the crack depth exceeded 75% of the total defect depth, the CIC defect could be treated as crack-only defects, since the failure pressure for the CIC model approaches that for the crack-only model for ratios of the crack depth to the total defect depth of 0.75 and 1. The versatility of several existing analytical methods (RSTRENG, LPC and CorLAS) in predicting the failure pressure was also discussed. For the corrosion-only defects, the LPC method predicted the closest failure pressure to that obtained using XFEM (3.5% difference). CorLAS method provided accurate results for crack-only defects with 7% difference. The extended finite element method (XFEM) was found to be very effective in predicting the failure pressure. In addition, compared to the traditional Finite Element Method (FEM) which requires extremely fine meshes and is impractical in modelling a moving crack, the XFEM is computationally efficient while providing accurate predictions.

The Evaluation of Failure Pressure for Corrosion Defects Within Girth or Seam Weld in Transmission Pipelines

2004 ◽  
Author(s):  
Young-pyo Kim ◽  
Woo-sik Kim ◽  
Young-kwang Lee ◽  
Kyu-hwan Oh
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Limit Load ◽  
The Body ◽  
Element Analysis ◽  
Burst Test ◽  
Corrosion Defect ◽  
Seam Weld ◽  
Failure Assessment ◽  
Corrosion Defects

The failure assessment for corroded pipeline has been considered with the burst test and the finite element analysis. The burst tests were conducted on 762mm diameter, 17.5mm wall thickness and API 5L X65 pipe that contained specially manufactured rectangular corrosion defect. The failure pressures for corroded pipeline have been measured by burst testing and classified with respect to corrosion sizes and corroded regions — the body, the girth weld and the seam weld of pipe. Finite element analysis was carried out to derive failure criteria of corrosion defect within the body, the girth weld and the seam weld of the pipe. A series of finite element analyses were performed to obtain a limit load solution for corrosion defects on the basis of burst test. As a result, the criteria for failure assessment of corrosion defect within the body, the girth weld and the seam weld of API 5L X65 gas pipeline were proposed.

Assessment of Interacting Corrosion Defects in Thin-Walled Pipes

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Ahmed A. Soliman ◽  
Mohammad M. Megahed ◽  
Ch. A. Saleh ◽  
Mostafa Shazly
Keyword(s):  
Nonlinear Finite Element ◽  
Metal Loss ◽  
Test Results ◽  
Defect Depth ◽  
Element Analysis ◽  
Shell Elements ◽  
Codes Of Practice ◽  
Useful Life ◽  
Corrosion Defects ◽  
Interaction Rule

Abstract Corrosion in pipes is usually found in the form of closely spaced defects, which eventually reduce the pipe pressure carrying capacity and piping planned useful life. Codes and standards have been developed to evaluate the effect of such form of metal loss on the piping pressure carrying capacities. However, predictions of such codes are usually conservative, and hence, there is a need to assess their degree of conservatism. The present paper utilizes nonlinear finite element analysis (FEA) in estimating pressure carrying capacities of defective pipes, and hence provides an evaluation of codes degree of conservatism. Shell elements with reduced thickness at the corrosion defect are adopted and their accuracy is assessed by comparison with those of solid elements as well as experimental test results. The influence of defects interaction is investigated by considering two neighboring defects in an inclined direction to each other. The influence of inclination angle, inclined proximity distance between the two defects, and the defect depth to wall thickness ratio are investigated. Comparisons were made with predictions of codes of practice in all cases. Code predictions were found to be conservative compared to FEA results. Furthermore, the interaction rule embedded in the codes for checking for interaction leads to inaccurate predictions for closely spaced defects as it does not include the effect of defect depth.

A Simple Procedure for the Prediction of the Collapse Pressure of Pipelines With Narrow and Long Corrosion Defects: Uncertainty and Sensibility Analysis

2018 ◽  
Author(s):  
Nara Oliveira ◽  
Theodoro Netto
Keyword(s):  
Simple Procedure ◽  
Experimental Tests ◽  
External Pressure ◽  
Experimental Program ◽  
Small Scale ◽  
Test Results ◽  
Collapse Pressure ◽  
Operational Conditions ◽  
Sensibility Analysis ◽  
Corrosion Defects

The collapse pressure of pipelines containing corrosion defects is usually predicted by deterministic methods, either numerically or through empirical formulations. The severity of each individual corrosion defect can be determined by comparing the differential pressure during operation with the estimated collapse pressure. A simple deterministic procedure for estimating the collapse pressure of pipes with narrow and long defects has been recently proposed by Netto (2010). This formulation was based on a combined small-scale experimental program and nonlinear numerical analyses accounting for different materials and defect geometries. However, loads and resistance parameters have uncertainties which define the basic reliability problem. These uncertainties are mailyrelated to the geometric and material parameters of the pipe and the operational conditions. This paper presents additional experimental tests on corroded pipes under external pressure. The collapse pressure calculated using the equation proposed by Netto (2010) is compared with this new set of experiments and also with test results available in open literature. These results are used to estimate the equation uncertainty. Finally, a sensitivity analysis is performed to identify how geometric parameters of the defects influence the reduction of collapse pressure.

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