Crack Interaction With Loss of Metal in Round
1
CRACK INTERACTION WITH LOSS OF METAL IN ROUND UNDER INTERNAL PRESSURE VESSELS. Martínez Moreno Miguel Ángel, M.C. Contreras Hernández Álvaro Technological Institute Of Tuxtepec. Dr. Víctor Bravo A. road s/n. Tuxtepec, Oaxaca, México. C.P. 60300. ABSTRACT In this research, testing is intended in cylindrical vessels piping here, as all pipe has cracks induced by hydrogen (AIH) depending on the type of gas or liquid flowing through it and therefore repair work performed continuous, involving high costs due to operations to replace the damaged section and as consequent stoppage of production and high risk activities undertaken. For that reason it is necessary to develop a study on the behavior of a pipeline to present this type of defect to determine the limits of reliable operation and prevent costs generated not required. INTRODUCTION The problem of hydrogen induced cracking (IAH) of pipes, as in the thermoelectric power plants, refineries, chemical plants, sugar mills, boilers and pressure vessels are highly costly elements essential and vital to its operation. Any line that present a defect whose dimensions exceed the maximum value established by the standards must be replaced. For this reason it is necessary to develop a study on the behavior of a pipeline that present this type of defect to determine limits of reliable operation and thus avoid the generation costs in work not required. The objective of this research work is to know the distribution of efforts in a tube modeling in three dimensions in the presence of a laminating in the thickness and subjected to internal pressure using the finite element method (FEM), in order to determine their behavior at different pressure levels to establish the effectiveness of the same. This work refers to the forms of harm and cracking of the driving lines of hydrocarbons using the simulation in the ANSYS software in which we will get the results and analysis to define the behavior of the stress field in function of the pressure in the presence of a lamination. THEORETICAL FRAMEWORK Forms of damage to pipelines of sour gas, made up of small amounts of water vapor in suspensions (H2O), carbon dioxide (CO2) and sulfuric acid (H2S) increased to 0.001 % mol, have different forms of damage caused by the service, as well as manufacturing defects and of welded connections, and variations in the specifications for materials, which are not detected in inspections prior to the commissioning and operation. Some of the most common forms of damage and their consequences in the operation and safety of pipelines are: • Identaciones, Dents, And Geometric Discontinuities. They are caused by external forces due to mishandling of the pipes, accidents and welds poorly applied. Its magnitude can be from defects located barely notable, to complete changes in the geometry of the tube as folds, misalignment and ovalamientos. These defects have effects on the line, such as: ‒ Decreased resistance. The geometric discontinuities can cause a concentration of efforts of failure is reached faster than in the damaged part and this fracture in prematurely. ‒ Increase in the rate of corrosion. A discontinuity can lead to a local concentration of corrosive agents or an increase in the energy of the metal, which accelerates the process of corrosion and cracking. ‒ Leaks and explosions. When they are severe these discontinuities, such as in welds with incomplete filling and undermined, it can happen a leak or explosion in any potential pinch points. • Corrosion. Mechanical defects of the corrosion in pipes can be grouped into two categories: ‒ The loss of thickness of the pipe wall. ‒ The alteration of properties of the steel. • Cracks. Any crack in a structure presents three stages in their growth: ‒ Nucleation or initialization. Associated with pre-existing defects. ‒ Stable propagation. Between the 80 and 90% of the useful life of a structure transcurrete within this stage. It is said that the stable, since if it reduces or eliminates the driving force behind the growth of the crack, this slows and vice versa. ‒ Unstable or catastrophic propagation. The characteristics of this stage will determine the severity of the failure (leakage or explosion). DESIGN OF THE EXPERIMENT A pipe section which develop three important design cases analyzed, this in order to analyze the interaction of internal pressure cracks under some combinations of these defects were modeled by varying its radius ranging from 10%, 30% and HT 40%, which is caused by the effect of the accumulation of atomic hydrogen diffused through a thickness by interaction with the fluid transported. The surface as well as inside the tube has a pressure deformation since the tube is subjected to loads of low, medium and high pressure also including the case where there is only pressure on the defect in the cracking tube. The material considered in the models is an API 5L X52 grade steel, which is a low carbon steel and represents most of the products used for oil pipelines. It is assumed that the material is isotropic and homogeneous and no significant temperature variations generate additional to those produced by the applied loads efforts. The system was simulated using the finite element method in nonlinear conditions of material with isotropic hardening law, by plastic deformation at the time of internal cracks of the tube. • Material properties. The array of combinations to perform simulations using FEM is obtained from a factorial product, which states that any product of factors diagonally give the total number of combinations, the value of each cell the product of the variables involved in this intersection. The simulation to determine the stress field and main directions: Analysis mode only 1/3 tube pattern in which shall be subject to internal and external pressure. Stress field and main directions in static mode analysis for different models used. The size of the defect is represented by a real form of internal cracking of the tube, this enabled building models FEM with a very similar way to reality. To design the model we need ANSYS tube program which allows us to create the base model which can be used for simulations of 10,30 and 40% HT in which we can choose the type of material which is a solid 8 node 82 which select the type plane strain after doing this can return to the preprocessor and meshing to mesh it in but we can add a concentration of efforts on the internal nodes of the crack this case is to assess the three forms of the element and can mayar each element contained (1) figure (2) and figure (3). Property Magnitude Yield stress sy 358 MPa Tensile strength su 453 MPa Modulus of elasticity E 203 GPa Relation of Poisson 0.3 % of area reduction 47% % of lengthening 25% Table 1: Properties of steel API5LX52 Figure 1. Element Meshing with the case of 10% Figure 2. Meshing of the element in the case of 30% Figure 3. Meshing element in the case of 40%en RESULTS The result of the simulation to determine the stress and strain field in: The area of the defect and its environment, determining the regions of maximum and minimum effort and its main directions. In the remote region of the defect, where the equations must verify known for thin-walled tubes, allowing corroborate the results obtained for healthy tube portion. This graph shows the maximum efforts deformation of the three elements with a maximum effort to reach 608.37 plasticity showing in Figure (7). Figure 4. Efforts deformation with maximum effort of 608.302 for the model case 1. Figure 5. Efforts von Mises stress deformation of the case 30% 608.044 maximum effort. Figure 6. Deformation stress for the case of 40% Figure 7. Graph of maximum deformation stresses the same for all three elements. CONCLUSIONS: Internal pressure produces defects such plasticizing an interaction region between the crack tip, which precedes their interconnection, causing a defect. Symmetric not reduce the structural integrity defects since the higher default radius lower internal pressure resists. The crack tip region is of practical interest because the mechanical behavior of these defects due to internal pressure is manifested in an increase in the extent of the plastic zone, this is indicative of coalescence thereof. REFERENCES: – González J.L., J.M Hallen, Mecánica de Fractura en Ductos de Recolección y Transporte de Hidrocarburos, 3er Congreso de Ductos PEMEX, 1, 183-191 (1998). – Hirth J., Effects of hydrogen on the properties of iron and steel, The Metallurgical Society of AIME, 11 A, (1980). – Ikeda A., Y. Morita, On the Hydrogen Induced Cracking of Pipeline Steel Under Wet Hydrogen Sulfide Environment, second Intl. Cong. Hydrogen in Metals (1997). – Moussa W.A., R. Bell, The Interaction of Two Parallel Semi-Elliptical Surface Cracks Under Tensión and Bending, Journal of Pressure Vessel Technology, (1999).
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Transcript of Crack Interaction With Loss of Metal in Round
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CRACK INTERACTION WITH LOSS OF METAL IN ROUNDUNDER INTERNAL PRESSURE VESSELS.
Martnez Moreno Miguel ngel, M.C. Contreras Hernndez lvaroTechnological Institute Of Tuxtepec. Dr. Vctor Bravo A. road s/n. Tuxtepec, Oaxaca, Mxico. C.P. 60300.
ABSTRACTIn this research, testing is intended in cylindrical vessels piping here, as all pipe has cracksinduced by hydrogen (AIH) depending on the type of gas or liquid flowing through it andtherefore repair work performed continuous, involving high costs due to operations to replacethe damaged section and as consequent stoppage of production and high risk activitiesundertaken. For that reason it is necessary to develop a study on the behavior of a pipeline topresent this type of defect to determine the limits of reliable operation and prevent costsgenerated not required.
INTRODUCTIONThe problem of hydrogen induced cracking (IAH) of pipes, as in the thermoelectric powerplants, refineries, chemical plants, sugar mills, boilers and pressure vessels are highly costlyelements essential and vital to its operation. Any line that present a defect whose dimensionsexceed the maximum value established by the standards must be replaced. For this reason itis necessary to develop a study on the behavior of a pipeline that present this type of defectto determine limits of reliable operation and thus avoid the generation costs in work notrequired. The objective of this research work is to know the distribution of efforts in a tubemodeling in three dimensions in the presence of a laminating in the thickness and subjectedto internal pressure using the finite element method (FEM), in order to determine theirbehavior at different pressure levels to establish the effectiveness of the same. This workrefers to the forms of harm and cracking of the driving lines of hydrocarbons using thesimulation in the ANSYS software in which we will get the results and analysis to define thebehavior of the stress field in function of the pressure in the presence of a lamination.
THEORETICAL FRAMEWORKForms of damage to pipelines of sour gas, made up of small amounts of water vapor insuspensions (H2O), carbon dioxide (CO2) and sulfuric acid (H2S) increased to 0.001 % mol,have different forms of damage caused by the service, as well as manufacturing defects andof welded connections, and variations in the specifications for materials, which are notdetected in inspections prior to the commissioning and operation. Some of the most commonforms of damage and their consequences in the operation and safety of pipelines are: Identaciones, Dents, And Geometric Discontinuities.They are caused by external forces due to mishandling of the pipes, accidents and weldspoorly applied. Its magnitude can be from defects located barely notable, to completechanges in the geometry of the tube as folds, misalignment and ovalamientos. These defectshave effects on the line, such as: Decreased resistance. The geometric discontinuities can cause a concentration of efforts
of failure is reached faster than in the damaged part and this fracture in prematurely. Increase in the rate of corrosion. A discontinuity can lead to a local concentration of
corrosive agents or an increase in the energy of the metal, which accelerates the processof corrosion and cracking.
Leaks and explosions. When they are severe these discontinuities, such as in welds withincomplete filling and undermined, it can happen a leak or explosion in any potential pinchpoints.
Corrosion.Mechanical defects of the corrosion in pipes can be grouped into two categories: The loss of thickness of the pipe wall. The alteration of properties of the steel. Cracks.Any crack in a structure presents three stages in their growth: Nucleation or initialization. Associated with pre-existing defects. Stable propagation. Between the 80 and 90% of the useful life of a structure transcurrete
within this stage. It is said that the stable, since if it reduces or eliminates the driving forcebehind the growth of the crack, this slows and vice versa.
Unstable or catastrophic propagation. The characteristics of this stage will determine theseverity of the failure (leakage or explosion).
DESIGN OF THE EXPERIMENTA pipe section which develop three important design cases analyzed, this in order to analyzethe interaction of internal pressure cracks under some combinations of these defects weremodeled by varying its radius ranging from 10%, 30% and HT 40%, which is caused by theeffect of the accumulation of atomic hydrogen diffused through a thickness by interactionwith the fluid transported. The surface as well as inside the tube has a pressure deformationsince the tube is subjected to loads of low, medium and high pressure also including the casewhere there is only pressure on the defect in the cracking tube. The material considered inthe models is an API 5L X52 grade steel, which is a low carbon steel and represents most ofthe products used for oil pipelines. It is assumed that the material is isotropic andhomogeneous and no significant temperature variations generate additional to thoseproduced by the applied loads efforts. The system was simulated using the finite elementmethod in nonlinear conditions of material with isotropic hardening law, by plasticdeformation at the time of internal cracks of the tube.
Material properties.
The array of combinations to perform simulations using FEM is obtained from a factorialproduct, which states that any product of factors diagonally give the total number ofcombinations, the value of each cell the product of the variables involved in this intersection.The simulation to determine the stress field and main directions:Analysis mode only 1/3 tube pattern in which shall be subject to internal and external pressure.Stress field and main directions in static mode analysis for different models used. The size of thedefect is represented by a real form of internal cracking of the tube, this enabled buildingmodels FEM with a very similar way to reality.To design the model we need ANSYS tube program which allows us to create the base modelwhich can be used for simulations of 10,30 and 40% HT in which we can choose the type ofmaterial which is a solid 8 node 82 which select the type plane strain after doing this can returnto the preprocessor and meshing to mesh it in but we can add a concentration of efforts on theinternal nodes of the crack this case is to assess the three forms of the element and can mayareach element contained (1) figure (2) and figure (3).
Property MagnitudeYield stress sy 358 MPaTensile strength su 453 MPaModulus of elasticity E 203 GPaRelation of Poisson 0.3% of area reduction 47%% of lengthening 25%
Table 1: Properties of steel API5LX52
Figure 1. Element Meshing with the case of10%
Figure 2. Meshing of the element in the case of30% Figure 3. Meshing element in the case of 40%en
RESULTSThe result of the simulation to determine the stress and strain field in:The area of the defect and its environment, determining the regions of maximum and minimumeffort and its main directions. In the remote region of the defect, where the equations mustverify known for thin-walled tubes, allowing corroborate the results obtained for healthy tubeportion.
This graph shows the maximum efforts deformation of the three elements with a maximumeffort to reach 608.37 plasticity showing in Figure (7).
Figure 4. Efforts deformation withmaximum effort of 608.302 for the model
case 1.Figure 5. Efforts von Mises stress
deformation of the case 30% 608.044maximum effort.
Figure 6. Deformation stress for the case of40%
Figure 7. Graph of maximumdeformation stresses the same for all three elements.
CONCLUSIONS:Internal pressure produces defects such plasticizing an interaction region between the crack tip,which precedes their interconnection, causing a defect. Symmetric not reduce the structuralintegrity defects since the higher default radius lower internal pressure resists. The crack tipregion is of practical interest because the mechanical behavior of these defects due to internalpressure is manifested in an increase in the extent of the plastic zone, this is indicative ofcoalescence thereof.
REFERENCES: Gonzlez J.L., J.M Hallen, Mecnica de Fractura en Ductos de Recoleccin y Transporte de
Hidrocarburos, 3er Congreso de Ductos PEMEX, 1, 183-191 (1998). Hirth J., Effects of hydrogen on the properties of iron and steel, The Metallurgical Society of
AIME, 11 A, (1980). Ikeda A., Y. Morita, On the Hydrogen Induced Cracking of Pipeline Steel Under Wet Hydrogen
Sulfide Environment, second Intl. Cong. Hydrogen in Metals (1997). Moussa W.A., R. Bell, The Interaction of Two Parallel Semi-Elliptical Surface Cracks Under
Tensin and Bending, Journal of Pressure Vessel Technology, (1999).
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