ECA for Operation: Is Today’s Practice of Relying on SENB Instead of SENT Testing While Not Taking Internal Pressure Into Account Conservative?

2011 ◽  
Author(s):  
Erlend Olso̸ ◽  
Espen Heier ◽  
Ba˚rd Nyhus ◽  
Erling O̸stby
Keyword(s):  
Fracture Mechanics ◽  
Internal Pressure ◽  
Current Practice ◽  
Biaxial Stress ◽  
Plastic Range ◽  
Industry Practice ◽  
Longitudinal Strains

Today’s analytical equations that are the basis for most engineering critical assessments (ECA) are not currently able to account for the effect of internal pressure, and the industry does not have a common recognized procedure for assessing the integrity of pipelines for longitudinal strains in the plastic range during operation. An industry practice has therefore developed where more conservative SENB specimens are used to compensate for the current lack of ability of analytical equations to account for the effect of biaxial stress of in-service pipelines. This paper investigates whether current practice of using fracture mechanics data from SENB testing while ignoring internal pressure during operation is conservative, or whether non-conservative assessments may be the result.

Overall Framework of Strain-Based Design and Assessment of Pipelines

2014 ◽  
Author(s):  
Yong-Yi Wang ◽  
Ming Liu ◽  
David Horsley ◽  
Mamdouh Salama ◽  
Millan Sen
Keyword(s):  
Current Practice ◽  
Compressive Strain ◽  
Life Time ◽  
Building Blocks ◽  
Strain Capacity ◽  
Industry Practice ◽  
Integrity Management ◽  
Longitudinal Strains ◽  
Tensile Strain Capacity ◽  
Made In

Significant progress has been made in recent years in the development of tensile and compressive strain capacity models. These models, along with various methods of strain demand determination, form the basic building blocks for the strain-based design and assessment (SBDA) of pipelines. At the same time, gaps exist between the current industry practice and the data needed for the proper application of those models. Furthermore the current practice of independently determining the tensile strain capacity, compressive strain capacity, and strain demand may not accurately represent field conditions as these elements interact and influence each other as opposed to act independently. Key elements related to SBDA are provided for the planning and execution of life-time integrity management of pipelines subjected to high longitudinal strains. The paper places emphasis on two aspects of SBDA: (1) overall framework and (2) considerations that are not adequately covered in the current general industry practices. The entire processes of SBDA, including but not limited to design, material specifications, construction, post-construction field monitoring, and mitigation are covered at high-levels to assist decision-making in practical projects. Detailed methodologies for executing components of SBDA are not covered in this paper, but can be found in the cited references.

Post-Buckling Failure Modes of X65 Steel Pipe: An Experimental and Numerical Study

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Nima Mohajer Rahbari ◽  
Mengying Xia ◽  
Xiaoben Liu ◽  
J. J. Roger Cheng ◽  
Millan Sen ◽  
...  
Keyword(s):  
Internal Pressure ◽  
Cross Section ◽  
Failure Modes ◽  
Bending Test ◽  
Bending Load ◽  
Post Buckling ◽  
X65 Steel ◽  
Bending Loads ◽  
Buckling Failure ◽  
Longitudinal Strains

In service pipelines exhibit bending loads in a variety of in-field situation. These bending loads can induce large longitudinal strains, which may trigger local buckling on the pipe's compressive side and/or lead to rupture of the pipe's tensile side. In this article, the post-buckling failure modes of pressurized X65 steel pipelines under monotonic bending loading conditions are studied via both experimental and numerical investigations. Through the performed full-scale bending test, it is shown that the post-buckling rupture is only plausible to occur in the pipe wall on the tensile side of the wrinkled cross section under the increased bending. Based on the experimental results, a finite element (FE)-based numerical model with a calibrated cumulative fracture criterion was proposed to conduct a parametric analysis on the effects of the internal pressure on the pipe's failure modes. The results show that the internal pressure is the most crucial variable that controls the ultimate failure mode of a wrinkled pipeline under monotonic bending load. And the post-buckling rupture of the tensile wall can only be reached in highly pressurized pipes (hoop stress no less than 70% SMYS for the investigated X65 pipe). That is, no postwrinkling rupture is likely to happen below a certain critical internal pressure even after an abrupt distortion of the wrinkled wall on the compressive side of the cross section.

Lumped Damage Mechanics

2015 ◽  
pp. 362-411
Keyword(s):  
Structural Analysis ◽  
Fracture Mechanics ◽  
Structural Damage ◽  
Damage Mechanics ◽  
Structural Behavior ◽  
Numerical Implementation ◽  
Plastic Range ◽  
Structural Collapse ◽  
Framed Structures ◽  
Damage And Fracture

As aforementioned, buildings in seismic zones must be designed to behave elastically under service loads or earthquakes of small intensity, and they can enter in the plastic range for events of intermediate intensity. Severe earthquakes are defined as those that are improbable but not impossible to happen during the lifetime of the structure. In these cases, structural damage, even damage that cannot be repaired, is allowed as long as there is no structural collapse. In order to design or certify safe structures, it is necessary to have computational tools that allow for the quantification of structural damage and that are able to describe structural behavior accurately near collapse. The elasto-plastic models present serious limitations in this sense. Damage and fracture mechanics represent a more rational option. The goal of this chapter is to describe how the concepts presented in Chapter 9 can be included in the mathematical models for the analysis of framed structures and its numerical implementation in structural analysis programs.

The Effect of Bonding Flaws on the Splitting Process in the Smart-Cut Technology

2013 ◽  
Vol 762 ◽  
pp. 437-444 ◽  
Author(s):  
Bin Gu ◽  
Wei Feng Yuan ◽  
You Jun Ning ◽  
Dan Lu Song
Keyword(s):  
Thin Film ◽  
Fracture Mechanics ◽  
Internal Pressure ◽  
Silicon On Insulator ◽  
Efficient Technology ◽  
High Quality ◽  
Mechanics Model ◽  
Defect Growth ◽  
Splitting Process

Smart-Cut®is an innovative and highly efficient technology to fabricate high quality Silicon-on-Insulator (SOI) wafers, especially when the top film of SOI wafers is very thin. In the present paper, a fracture mechanics model is established to examine the effect of bonding flaws on defect growth in the Smart-Cut process. It is found that although defect growth can occur in a practical Smart-Cut process, large bonding flaws are inclined resulting in severe deviation of the direction of defect propagation, leading to a non-transferred area of thin film when splitting. Moreover, at the expense of low defect growth, increasing the internal pressure of bonding flaws decreases the defect growth deviation and thus benefits to improve the quality of final SOI wafer. The mechanism of relaxation of stiffener constraint is proposed to clarify the effect of bonding flaws. Finally, progress of the splitting process is analyzed when bonding flaws are present.

Effect of Biaxial Stress on Crack Driving Force

2006 ◽  
Author(s):  
G. Shen ◽  
W. R. Tyson
Keyword(s):  
Internal Pressure ◽  
Driving Force ◽  
Axial Stress ◽  
Axial Strain ◽  
Biaxial Stress ◽  
J Integral ◽  
Longitudinal Stress ◽  
Secondary Stress ◽  
Stress Strain ◽  
Strain Equation

A stress-strain equation of Ramberg-Osgood type is proposed to correlate the longitudinal stress with longitudinal strain of a thin plate when a constant stress is applied transversely. The same approach can be used to correlate the axial stress with axial strain for a thin-walled pipe in axial tension with internal pressure. The proposed stress-strain equation relating the longitudinal stress and strain closely approximates that of deformation theory. The effect of a secondary stress (hoop stress) on the J-integral for a circumferential crack in a pipe under axial load and internal pressure is evaluated by finite element analysis (FEA). The results show that the J-integral decreases with internal pressure at a given axial stress but increases with internal pressure at a given axial strain. It is concluded that while a secondary stress may be safely neglected in a stress-based format because it decreases the driving force at a given applied stress, it should not be neglected in a strain-based format because it significantly increases the driving force at a given applied strain.

An Evaluation of the Use of Fracture Mechanics Techniques for the Design of Orthotropic Decks

2007 ◽  
Vol 348-349 ◽  
pp. 285-288
Author(s):  
Wouter de Corte ◽  
Philippe Van Bogaert
Keyword(s):  
Fracture Mechanics ◽  
Fatigue Resistance ◽  
Current Practice ◽  
Bridge Deck ◽  
Hot Spot ◽  
Bridge Decks ◽  
Academic Research ◽  
Design Guidelines ◽  
Hot Spot Stress ◽  
Academic Researchers

Although the use of fracture mechanics based techniques in the evaluation of fatigue resistance in civil engineering has expanded steadily, it’s application in the field of orthotropic bridge decks remains very small. This is remarkable, since especially orthotropic decks have numerous fatigue prone details, which could benefit from a fracture mechanics based approach, or alternatively from the hot spot stress method. Currently, all international design guidelines for orthotropic plated bridge deck are based on a traditional nominal stress S-N approach and Miner’s Rule, and, although suggested by various in field designers and bridge owners, a fracture mechanics approach is currently limited to academic research. The paper gives an overview of current practice in the field, as well as an overview of attempts made academic researchers to apply fracture mechanics techniques. The available literature suggests that the lack of implementation of fracture mechanics results from a combination of factors including the lack of experience with these methods, conservatism, but also the complexity of geometry and loading conditions resulting in numerous variables. This paper may contribute to the implementation of modern fracture mechanics based techniques in this field by pointing out the opportunities and warning for the difficulties.

Depth of penetration criteria on metallic surfaces for use in MMOD risk assessment

2019 ◽  
Author(s):  
Henry Nahra ◽  
Louis Ghosn ◽  
Eric Christiansen ◽  
Joshua Miller ◽  
Bruce A. Davis
Keyword(s):  
Risk Assessment ◽  
Fracture Mechanics ◽  
Failure Criterion ◽  
Pressure Vessels ◽  
Biaxial Stress ◽  
System Level ◽  
Ballistic Limit ◽  
Depth Of Penetration ◽  
Hypervelocity Impacts ◽  
Definition Of

Abstract System level assessment of hypervelocity impacts by micrometeoroids and orbital debris (MMOD) relies on the definition of the spacecraft geometry and trajectory, the natural environment of the micrometeoroids and induced environment of the orbital space debris, ballistic limit equations and the failure criteria. The definition of the MMOD environments provides the particles flux and when is combined with the ballistic limit equations will determine the number of the critical penetrating particles that could result in the failure of the underlying component is calculated and is used to calculate the risk based on some failure criterion. Spacecraft geometry provides the shielding configuration over the spacecraft critical body which defines the selection of the ballistic limit equations to be used in the risk assessment. The definition of the failure criterion for metallic pressure systems involves the definition of the allowable depth of penetration that could result in leakage or burst of the component. This paper addresses the definition of the allowable depth of penetration of generic metallic tanks from MMOD impacts. The allowable penetration depth of metal tanks is based on a fracture mechanics approach calibrated using biaxially stressed coupons tests subjected to Hypervelocity Impacts (HVI). The planar crack-crack spacing was based on the craters spacing distribution of the HVI coupon tests. The Stress Intensity Factor (SIF) as a function of crater depths and crater spacing and applied remote stress is calculated using NASGRO®, a linear fracture mechanics software. The calculated SIF is compared with the material fracture toughness to determine if the craters result in a failure of the coupons under biaxial stress. This work resulted in a recommended allowable depth of penetration of 20% on the surfaces of metallic pressure vessels on spacecraft.

Using MFL Corrosion Signals to Determine Biaxial Stress in Operating Pipelines

2000 ◽  
Author(s):  
Alfred E. Crouch
Keyword(s):  
Magnetic Flux ◽  
Internal Pressure ◽  
Pipe Wall ◽  
Axial Stress ◽  
Wall Stress ◽  
Biaxial Stress ◽  
Metal Loss ◽  
Pipe Surface ◽  
The Difference ◽  
Hoop Stresses

Previous work has shown that a corrosion assessment more accurate than B31.G or RSTRENG can be made if pipeline stresses are considered. A shell analysis can be carried out if both the corrosion profile and local pipe wall stresses are known. The corrosion profile can be approximated from analysis of magnetic flux leakage (MFL) signals acquired by an inline inspection tool (smart pig), but a measure of pipe wall stress has not been available. Approximations have been made based on pipe curvature, but a more direct measurement is desirable. Recent work has produced data that show a correlation between multi-level MFL signals from metal-loss defects and the stress in the pipe wall at the defect location. This paper presents the results of MFL scans of simulated corrosion defects in pipe specimens subjected to simultaneous internal pressure and four-point bending. MFL data were acquired at two different magnetic excitations using an internal scanner. The scanner’s sensor array measured axial, radial and circumferential magnetic flux components on the inner pipe surface adjacent to the defect. Comparison of the signals at high and low magnetization yields an estimate of the difference between axial and hoop stresses. If internal pressure is known, the hoop component can be determined, leaving data proportional to axial stress.

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