J and CTOD Estimation Procedure for Circumferentially Cracked Pipes Under Combined Bending and Internal Pressure

2011 ◽  
Author(s):  
Lui´s F. S. Parise ◽  
Claudio Ruggieri
Keyword(s):  
Internal Pressure ◽  
Structural Integrity ◽  
Biaxial Loading ◽  
Numerical Solutions ◽  
Driving Forces ◽  
Crack Depth ◽  
Bending Moment ◽  
Estimation Procedure ◽  
Wide Range ◽  
Bending Load

This work provides an estimation procedure to determine the J-integral and CTOD for pipes with circumferential surface cracks subjected to combined bending load and internal pressure for a wide range of crack geometries and material (hardening) based upon fully-plastic solutions. The present investigation broadens the applicability of current evaluation procedures for J and CTOD which enter directly into structural integrity analyses and flaw tolerance criteria. Extensive 3-D nonlinear analyses of circumferentially cracked pipes with surface flaws having different crack depth (a) over pipe wall thickness (t) ratios and varying crack length for different strain hardening properties provide the dimensionless parameters relating the elastic-plastic crack-tip driving forces with the applied (remote) bending moment and internal pressure. The investigation provides a fairly comprehensive body of numerical solutions for J and CTOD in circumferentially cracked pipes subjected to biaxial loading.

An Evaluation Procedure for Crack Driving Forces in Mismatched Welds and its Applicability to ECA Analysis of Undermatched Clad Pipe Girth Welds

2014 ◽  
Author(s):  
Rodolfo F. de Souza ◽  
Claudio Ruggieri
Keyword(s):  
Structural Integrity ◽  
Driving Forces ◽  
Evaluation Procedure ◽  
Piping System ◽  
Large Set ◽  
Alloy 625 ◽  
Wide Range ◽  
Bending Load ◽  
Critical Flaw ◽  
Girth Welds

Structural integrity of submarine risers and flow lines transporting corrosive and aggressive hydrocarbons represents a key factor in operational safety of subsea pipelines. Advances in existing technologies favor the use of C-Mn steel pipelines (for example, API X65 grade steel) either clad or mechanically lined with a corrosion resistant alloy (CRA), such as Alloy 625, for the transport of corrosive hydrocarbons. However, while cost effective, specification of critical flaw sizes for their girth welds become more complex due to the dissimilar nature of these materials. In particular, effective fracture assessments of undermatched girth welds remain essential to determine more accurate acceptable flaw sizes for the piping system based upon engineering critical assessment (ECA) procedures. This work focuses on development of an evaluation procedure for the elastic-plastic crack driving force (as characterized by the J-integral) in pipeline girth welds with circumferential surface cracks subjected to bending load for a wide range of crack geometries and weld mismatch levels based upon the GE-EPRI framework. The study also addresses the effects of an undermatching girth weld on critical flaw sizes for a typical clad pipe employed in subsea flowlines having an Alloy 625 girth weld. The extensive 3-D numerical analyses provide a large set of solutions for J in cracked pipes and cylinders with mismatched girth welds while, at the same time, gaining additional understanding of the applicability of ECA procedures in welded cracked structural components.

Investigation on Structural Behaviors of Reactor Pressure Vessel With the Effects of Critical Heat Flux and Internal Pressure

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Jianfeng Mao ◽  
Jianwei Zhu ◽  
Shiyi Bao ◽  
Lijia Luo ◽  
Zengliang Gao
Keyword(s):  
Heat Flux ◽  
Internal Pressure ◽  
Critical Heat Flux ◽  
Pressure Vessel ◽  
Structural Integrity ◽  
Reactor Pressure Vessel ◽  
Wide Range ◽  
Depth Analysis ◽  
Structural Behaviors ◽  
Reactor Pressure

The so-called “in-vessel retention (IVR)” is a severe accident management strategy, which is widely adopted in most advanced nuclear power plants. The IVR mitigation is assumed to be able to arrest the degraded melting core and maintain the structural integrity of reactor pressure vessel (RPV) within a prescribed hour. Essentially, the most dangerous thermal–mechanical loads can be specified as the combination of critical heat flux (CHF) and internal pressure. The CHF is the coolability limits of RPV submerged in water (∼150 °C) and heated internally (∼1327 °C), it results in a sudden transition of boiling crisis from nucleate to film boiling. Accordingly, from a structural integrity perspective, the RPV failure mechanisms span a wide range of structural behaviors, such as melt-through, creep damage, plastic deformation as well as thermal expansion. Furthermore, the geometric discontinuity of RPV created by the local material melting on the inside aggravates the stress concentration. In addition, the internal pressure effect that usually neglected in the traditional concept of IVR is found to be having a significant impact on the total damage evolution, as indicated in the Fukushima accident that a certain pressure (up to 8.0 MPa) still existed inside the RPV. This paper investigates structural behaviors of RPV with the effects of CHF and internal pressure. In achieving this goal, a continuum damage mechanics (CDM) based on the “ductility exhaustion” is adopted for the in-depth analysis.

FEM Stress Analysis and Leakage Behavior of Pipe-Socket Threaded Joints Subjected to Bending Moment and Internal Pressure

2020 ◽  
Author(s):  
Satoshi Nagata ◽  
Shinichi Fujita ◽  
Toshiyuki Sawa
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Bending Moment ◽  
Experimental Tests ◽  
Element Analysis ◽  
Contact Conditions ◽  
Sealing Performance ◽  
Bending Load ◽  
Threaded Joints ◽  
Thread Root

Abstract This paper is a report of the studies on the mechanical behaviors and leakage characteristics of pipe-socket threaded joints subjected to bending moment as well as internal pressure by means of experimental tests and finite element simulations. The paper dealt with the 3/4″ and 3″ joints, and the joints for both sizes have two different combinations of thread types in the pipe and socket, i.e. taper-taper thread combination or taper-parallel one, respectively. Experimental bending leak tests showed that the taper-taper joints could retain internal pressure under bending load up to nearly plastic collapse. The taper-parallel joints, however, could hardly keep internal pressure against bending moment even the sealing tape was applied to enhance the sealing performance. Finite element analysis was carried out to simulate those bending tests, especially to clarify the deformation and the stress distribution in the engaged threads in detail. The analysis demonstrated that the sealing performance of the joints highly depend on the contact conditions not only at the thread crest to thread root but also in between flank surfaces. A complicated leak path across the engaged threads under bending moment was identified by the simulation.

Ratcheting Studies on Type 304LN Stainless Steel Elbows subjected to Combined Internal Pressure and In-Plane Bending Moment

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
S. Vishnuvardhan ◽  
G. Raghava ◽  
P. Gandhi ◽  
M. Saravanan ◽  
D. M. Pukazhendhi ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Internal Pressure ◽  
Accumulation Rate ◽  
Bending Moment ◽  
Cyclic Bending ◽  
Ratcheting Strain ◽  
Bending Load ◽  
304Ln Stainless Steel ◽  
Number Of Cycles ◽  
Opening And Closing

“Ratcheting” is a phenomenon which leads to reduction in fatigue life of a structural component by loss of ductility due to cycle by cycle accumulation of plastic strain. Ratcheting occurs in a structure subjected to a combination of steady/sustained and cyclic loads such that the material response is in inelastic region. Ratcheting studies were carried out on Type 304LN stainless steel elbows, subjected to steady internal pressure and cyclic bending. The elbows filled with water were pressurized between 27.6 MPa and 39.2 MPa. Cyclic bending load, under opening and closing moments, was applied on the elbows at ambient temperature. Number of cycles corresponding to occurrence of a through-wall crack was recorded. Crack was observed in the bent portion at one of the crown locations in all the four specimens. Maximum strain was observed at the intrados and crown locations of the elbows. The ratcheting strain increased with number of cycles at crown and intrados locations. However, the strain accumulation rate decreased with number of cycles. Strain was observed to be minimum at the extrados location and the same stabilized toward the end of the tests. The specimens have failed by occurrence of through-wall axial crack accompanied by simultaneous ballooning. The ballooning was found to be varying from 3.8% to 5.8% with respect to the original circumference in the bent portion. The reduction in thickness was found to be around 12%–15%.

Study of Bending Capacity of an HPHT CRA-Lined Seamless Pipeline

2014 ◽  
Author(s):  
Cyprian Gil ◽  
Knut Tørnes ◽  
Per Damsleth
Keyword(s):  
Internal Pressure ◽  
Strain Localization ◽  
Local Buckling ◽  
Bending Moment ◽  
Design Criteria ◽  
Design Codes ◽  
Moment Capacity ◽  
Wide Range ◽  
Global Buckling ◽  
The Moment

A study has been performed to better understand ultimate bending moment and strain capacities of pipelines in relation to criteria defined in the design codes. An 18″ HPHT flowline was designed to undergo global buckling on uneven seabed and to resist trawl gear interference. The high temperature (155 degC) and pressure (300 bar) posed considerable design challenges for material selection and design criteria. A CRA-lined X60 CMn pipeline was selected for the project. The pipeline was of seamless manufacture for which the stress/strain characteristics are subject to the effect of Lüders bands. The DNV-OS-F101 code covers a wide range of D/t but does not specifically address Lüder’s material behaviour which could significantly reduce the bending moment capacity of pipe. The global buckling and trawl pull-over FE analysis results indicated the pipe was highly utilized, requiring excessive amounts of seabed intervention at great cost to meet the DNV LCC criteria. Detailed FE simulation of limit states for local buckling and strain localization of a 3D solid element pipe model was performed, with both Roundhouse and Lüders material properties, to investigate pipe capacity in relation to that stipulated by the design codes. The pipe moment capacity was established by obtaining the moment curvature relationship by bending the local pipe section subject to internal pressure until the maximum resistance was reached. Imperfections were introduced to initiate local buckling at the desired location. To determine strain concentration factors and strain localization, the effects of thickness changes and weld misalignment were also studied. The DNV OS-F101 LCC moment criterion formulation computes a decreasing moment capacity for increasing internal pressure. It has been suggested in the literature that this is correct for higher D/t but the criterion may be conservative for pipes with lower D/t. The combination of Lüders material with low D/t is not specifically addressed by any design code. Clarification of these aspects will provide a better understanding of the risk of failure for highly utilized seamless pipelines and allow for modified design criteria that will reduce seabed intervention costs. The results of the study showed that a higher bending moment criterion and associated strain criterion could be adopted for the design that allows for the higher initial strain caused by Lüder’s plateau. The ultimate bending moment capacity of low D/t pipe with Lüder’s material was found to be similar to that of Roundhouse material due to work hardening. In addition, it was demonstrated that the potential strength of the CRA liner could enhance the moment capacity of the seamless pipe.

Fully-Plastic J and CTOD Solutions for Pipes With Circumferential Surface Cracks Subjected to Combined Bending and Tension

2011 ◽  
Author(s):  
Lui´s F. S. Parise ◽  
Claudio Ruggieri
Keyword(s):  
Material Properties ◽  
Tensile Load ◽  
Estimation Procedure ◽  
Large Set ◽  
J Integral ◽  
Surface Cracks ◽  
Defect Assessment ◽  
Wide Range ◽  
Bending Load ◽  
Assessment Procedures

This work provides an estimation procedure to determine the J-integral and CTOD for pipes with circumferential surface cracks subjected to combined bending and tensile load for a wide range of crack geometries and material (hardening) based upon fully-plastic solutions. A summary of the methodology upon which J and CTOD are derived sets the necessary framework to determine nondimensional functions h1 and h2 applicable to a wide range of crack geometries and material properties characteristic of structural, pressure vessel and pipeline steels. The extensive nonlinear, 3-D numerical analyses provide a large set of solutions for J and CTOD which enters directly into fitness-for-service (FFS) analyses and defect assessment procedures of cracked pipes and cylinders subjected to bending load.

J and CTOD Estimation Procedure for Circumferentially Cracked Pipes Based on Fully-Plastic Solutions

2010 ◽  
Author(s):  
Mario S. G. Chiodo ◽  
Claudio Ruggieri
Keyword(s):  
Pressure Vessel ◽  
Material Properties ◽  
Estimation Procedure ◽  
Large Set ◽  
J Integral ◽  
Surface Cracks ◽  
Defect Assessment ◽  
Wide Range ◽  
Bending Load ◽  
Assessment Procedures

This work provides an estimation procedure to determine the J-integral and CTOD for pipes with circumferential surface cracks subjected to bending load for a wide range of crack geometries and material (hardening) based upon fully-plastic solutions. A summary of the methodology upon which J and CTOD are derived sets the necessary framework to determine nondimensional functions h1 and h2 applicable to a wide range of crack geometries and material properties characteristic of structural, pressure vessel and pipeline steels. The extensive nonlinear, 3-D numerical analyses provide a large set of solutions for J and CTOD which enters directly into fitness-for-service (FFS) analyses and defect assessment procedures of cracked pipes and cylinders subjected to bending load.

Combined Loading Tests of Large Diameter Corroded Pipelines

2000 ◽  
Author(s):  
Marina Q. Smith ◽  
Christopher J. Waldhart
Keyword(s):  
Internal Pressure ◽  
Thermal Stresses ◽  
Failure Modes ◽  
Prediction Models ◽  
Large Diameter ◽  
Bending Moment ◽  
Combined Loading ◽  
Analytical Models ◽  
Bending Load ◽  
Full Scale Tests

Current methods for estimating the remaining strength of aging, corroded pipelines have been restricted to the capabilities of pressure based engineering models that rely on the definition of hoop stress in the pipe wall. Because in practice, pipelines are subjected to a variety of loading conditions (e.g.; axial bending from settlement and thermal stresses) that act in concert with those derived by internal pressure, a multi-year combined testing and analysis program was initiated by the Alyeska Pipeline Service Company aimed at developing computer tools for the prediction of rupture and wrinkling in corroded pipes. During the program, seventeen full-scale tests of mechanically corroded 48-inch diameter (1219-mm), X65 pipes subjected to internal pressure, axial bending, and axial compression were performed to provide data necessary for the verification of analytical models and failure prediction models. While all of the tests were designed to produce rupture, wrinkling, as defined by the occurrence of a limit moment during the application of bending loads, was produced in eleven of the tests either prior to or instead of rupture. Loading of the pipe was intended to simulate that which would be observed by a pipe in-service and included both load control and displacement control of the applied bending load, and in some tests, intended to define the amount of additional pressure required to cause burst after wrinkling was produced. Results of the tests showed that two different failure modes are produced depending on whether the bending moment is transmitted to the pipe as a fixed load or a fixed displacement, and consequently, the burst capacity of the corroded pipe may not be compromised by the presence of axial loads. This paper discusses the tests performed, including a description of the load schedule and corrosion geometries, and key results of the tests that were used in the development of a new strain-based burst prediction procedure for corroded pipes subjected to combined loads.

Fracture Response of Girth-Welded Pipeline With Canoe Shape Embedded Crack Subjected to Large Plastic Deformation

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Lie Seng Tjhen ◽  
Zhang Yao ◽  
Zhao Hai Sheng
Keyword(s):  
Plastic Deformation ◽  
Finite Element ◽  
Internal Pressure ◽  
Structural Integrity ◽  
Biaxial Loading ◽  
Finite Element Simulations ◽  
Critical Parameters ◽  
Large Plastic Deformation ◽  
Long Distance ◽  
Fracture Assessment

Long-distance offshore pipelines always suffer large plastic deformation during installation and operation. Accompanied by high internal pressure, potential flaws are found to initiate from the girth welds, and this brings a significant challenge to the structural integrity of the pipelines. The currently used procedures for fracture assessment of pipelines are usually stress based, which are unsuitable for application to cracked pipeline subjected to large plastic deformation. Therefore, the aim of this paper is to investigate the fracture assessment of pipeline subjected to large plastic deformation and identify and understand the critical parameters influencing the fracture responses under actual loading conditions. The evolution of crack tip opening displacement (CTOD) of a pipeline segment with an embedded canoe shape crack located in the middle of the girth weld is investigated under pure bending and biaxial loading through 3D elastic–plastic finite-element simulations. The effects of crack width, crack length, pipeline thickness, material hardening, and internal pressure on fracture response are discussed. Finally, a strain-based failure assessment diagram (FAD) is developed, and comparison between fracture assessment by BS7910:2013 and finite-element simulations concludes that the former produces conservative predictions for deep crack.

Fitness-for-Service Fracture Assessments of Dissimilar Pipe Girth Welds Incorporating New Crack Driving Force Solutions

2014 ◽  
Author(s):  
Rodolfo F. de Souza ◽  
Claudio Ruggieri
Keyword(s):  
Driving Force ◽  
Large Scale ◽  
Structural Integrity ◽  
Numerical Solutions ◽  
Driving Forces ◽  
Limit Load ◽  
Assessment Procedure ◽  
Crack Driving Force ◽  
Alloy 625 ◽  
Girth Welds

The increasing demand for energy and natural resources has spurred a flurry of exploration and production activities of oil and natural gas in more hostile environments, including very deep water offshore production. Currently, structural integrity of submarine risers and flowlines conducting corrosive and aggressive hydrocarbons represents a key factor in operational safety of subsea pipelines. Advances in existing technologies favor the use of CMn steel pipelines (for example, API X65 grade steel) clad or mechanically lined with a corrosion resistant alloy (CRA), such as Alloy 625, for the transport of corrosive fluids. This work focuses on a fitness-for-service defect assessment procedure for strength mismatched welded components incorporating new crack driving force and limit load solutions. The study broadens the applicability of current evaluation procedures for J and CTOD which enter directly into structural integrity analyses and flaw tolerance criteria to provide a fairly comprehensive body of numerical solutions for crack driving forces in mismatched girth welds with circumferential surface cracks. This investigation also provides mismatch yield load solutions which are central to accurately predict failure load in strength mismatched structures subjected to large scale plasticity and ductile behavior. An approach is utilized to analyze the potential effects of the undermatching girth weld on critical flaw sizes for a typical lined pipe employed in subsea flowlines having a girth weld made of Alloy 625.

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