Estimates of Crack-Driving Force in Surface-Cracked Elbows

2000 ◽  
Vol 123 (1) ◽  
pp. 32-40 ◽  
Author(s):  
Gery M. Wilkowski ◽  
Raj Mohan ◽  
Thomas J. Kilinski
Keyword(s):  
Crack Length ◽  
Driving Force ◽  
Stress Index ◽  
Simple Relationship ◽  
Surface Cracks ◽  
Straight Pipe ◽  
Crack Driving Force ◽  
Large Matrix ◽  
Simplified Procedure ◽  
J Estimation

The objective of this effort was to assess whether a simple relationship could be developed between the behavior of surface cracks in straight pipe and in elbows. If such a geometric relationship could be developed, then a simple multiplier could be applied to the current straight-pipe solutions that are already used in codes and standards such as the ASME or other codes. In order to accomplish this objective, solutions from elbow and straight-pipe elastic-plastic fracture mechanics (EPFM) analyses were used along with experimental data. The elbow EPFM solution came from a J-estimation scheme developed during the IPIRG-2 program. These solutions were for an elbow with a pressure at the design stress limits of Section III of the ASME Code for typical nuclear piping steels. Significant efforts were undertaken in that program to develop J-estimation schemes for axial (along the side of the elbow) and circumferential surface cracks (centered on the extrados) in elbows under constant pressure and in-plane bending. These analyses were developed using the GE/EPRI methodology of determining an elastic and plastic contribution to J, and developing the appropriate functions through a matrix of EPFM finite element analyses. Even with this large matrix of FEM analyses, only one circumferential crack length and one axial crack length were investigated. Hence, it was desirable to develop a method to extend the analysis capabilities to other crack geometry, as well as developing a simplified procedure. A comparison of the elbow to straight-pipe moment versus crack-driving force curves showed that there is a simple multiplier linearly related to the ASME B2 stress index for elbows of different R/t ratios. Hence, a simplified procedure was determined where the straight-pipe solution could be multiplied by a function of the elbow stress indices to give the maximum load prediction of the surface-cracked elbow. Comparisons were made to circumferential surface-cracked elbow data from the IPIRG-2 program, and an axial surface-cracked elbow test conducted by EDF. The comparisons showed the simplified methods to be quite promising.

J-Estimation Schemes for Internal Circumferential and Axial Surface Cracks in Pipe Elbows

1998 ◽  
Vol 120 (4) ◽  
pp. 418-423 ◽  
Author(s):  
R. Mohan ◽  
A. Krishna ◽  
F. W. Brust ◽  
G. M. Wilkowski
Keyword(s):  
Shell Model ◽  
Driving Force ◽  
Three Dimensional ◽  
Surface Cracks ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Crack Driving Force ◽  
Cracked Structures ◽  
Axial Surface ◽  
J Estimation

In the spirit of GE/EPRI fracture mechanics procedure, estimation schemes for the crack driving force for circumferentially and axially surface-cracked pressurized elbows subjected to bending are developed. These schemes are based on the results of line-spring/shell model. The line-spring/shell model offers an attractive and inexpensive alternative to performing a large number of analyses of surface-cracked structures. This model has been shown to provide accurate predictions in comparison with the more involved three-dimensional model by Mohan (1998). Using the results of this model and following the GE/EPRI procedure, the coefficient functions, F1 and h1, which provide the necessary information for predicting the crack driving force in cracked elbows, for several elbow and crack geometries are tabulated.

Fully-Plastic Strain-Based J Estimation Scheme for Circumferential Surface Cracks in Pipes Subjected to Reeling

2013 ◽  
Author(s):  
Luís F. S. Parise ◽  
Claudio Ruggieri ◽  
Noel P. O’Dowd
Keyword(s):  
Driving Force ◽  
Driving Forces ◽  
Fracture Behaviour ◽  
Applied Strain ◽  
J Integral ◽  
Surface Cracks ◽  
Crack Driving Force ◽  
Numerical Assessment ◽  
Estimation Scheme ◽  
J Estimation

Modern installation techniques for marine pipelines and subsea risers are often based on the reel-lay method, which introduces significant (plastic) strains on the pipe during reeling and un-reeling. The safe assessment of crack-like flaws under such conditions requires accurate estimations of the elastic-plastic crack driving forces, ideally expressed in a strain-based formulation to better account for the displacement controlled nature of the reeling method. This paper aims to facilitate such assessments by presenting a strain-based expression of the well-known EPRI estimation scheme for the J integral, which is directly based upon fully plastic descriptions of fracture behaviour under significant plasticity. Parametric finite element simulations of bending of circumferentially cracked pipes have been conducted for a set of crack geometries, pipe dimensions and material hardening properties representative of current applications. These provide the numerical assessment of the crack driving force upon which the non-dimensional factors of the EPRI methodology, which scale J with applied strain, are derived. Finally, these factors are presented in convenient graphical and tabular forms, thus allowing the direct and accurate assessment of the J integral for circumferentially cracked pipes subjected to reeling.

The Effects of Classification of Misalignment-Induced Stresses in Engineering Critical Assessments of Welded Joints With Some Misalignment

2010 ◽  
Author(s):  
Liwu Wei
Keyword(s):  
Welded Joints ◽  
Driving Force ◽  
Limit Load ◽  
Surface Cracks ◽  
Plastic Limit ◽  
Secondary Stress ◽  
Butt Weld ◽  
Crack Driving Force ◽  
Plastic Limit Load

In the ECA of a structure or component such as a pipeline girth weld, the bending stress component arising from misalignment across the weld is often classified as primary, partly because standards such as BS 7910 and API 579-1/ASME FFS-1 do not give definitive guidance on this subject. This approach may be over-conservative as the σmis is localised. In order to obtain a more realistic assessment of the structural integrity of structures containing misalignment, it is necessary to understand the conservatism or non-conservatism in an ECA associated with the classification of σmis. To address the above concerns, systematic investigations were carried out of surface cracks in a plate butt-weld including some misalignment, external circumferential surface cracks and external fully circumferential cracks in a misaligned pipe connection. FEA of these cracked welded joints with some misalignment (typically from 1mm to 2mm) was performed to calculate crack driving force and plastic limit load. The results from FEA were compared with the existing solutions of KI and σref in BS 7910 generated by assuming three options of treating the σmis. The three options were: (1) classification of σmis wholly as primary stress; (2) 15% of σmis as primary and 85% of σmis as secondary stress; and (3) classification of σmis wholly as secondary stress. Variations in parameters (eg misalignment, crack size, loading, weld overmatch and base material properties) were taken into account in order to determine the effects of these parameters on plastic limit load and crack driving force. The implication of different classifications of σmis in terms of ECAs of misaligned welded joints was revealed by conducting BS 7910 Level 2B assessments with the use of a FAD. It was found in this work that for the cases examined, use of the σmis as entirely primary bending in an ECA was over-conservative, and even treatment of σmis as entirely secondary bending was generally shown to be still conservative, when compared with the assessments based on FEA solutions. Furthermore, caution should be exercised in using the solutions of KI and σref given in the existing BS 7910 for crack-containing structures subjected to a bi-axial or tri-axial stress state. A non-conservative estimate may result from the use of these solutions which have been derived based on a uniaxial stress condition.

Development of Z-Factor for Circumferential Part-Through Surface Cracks in Dissimilar Metal Welds

2008 ◽  
Author(s):  
D.-J. Shim ◽  
G. M. Wilkowski ◽  
D. L. Rudland ◽  
F. W. Brust ◽  
Kazuo Ogawa
Keyword(s):  
Correction Factor ◽  
Carrying Capacity ◽  
Limit Load ◽  
Maximum Load ◽  
Load Carrying Capacity ◽  
Surface Cracks ◽  
Crack Driving Force ◽  
Dissimilar Metal ◽  
Load Carrying ◽  
J Estimation

Section XI of the ASME Code allows the users to conduct flaw evaluation analyses by using limit-load equations with a simple correction factor to account elastic-plastic fracture conditions. This correction factor is called a Z-factor, and is simply the ratio of the limit-load to elastic-plastic fracture mechanics (EPFM) maximum-load predictions for a flaw in a pipe. The past ASME Section XI Z-factors were based on a circumferential through-wall crack in a pipe rather than a surface crack. Past analyses and pipe tests with circumferential through-wall cracks in monolithic welds showed that the simplified EPFM analyses (called J-estimation schemes) could give good predictions by using the toughness, i.e., J-R curve, of the weld metal and the strength of the base metal. The determination of the Z-factor for a dissimilar metal weld (DMW) is more complicated because of the different strength base metals on either side of the weld. This strength difference can affect the maximum load-carrying capacity of the flawed pipe by more than the weld toughness. Recent work by the authors for circumferential through-wall cracks in DMWs has shown that an equivalent stress-strain curve is needed in order for the typical J-estimation schemes to correctly predict the load carrying capacity in a cracked DMW. In this paper, the Z-factors for circumferential surface cracks in DMW were determined. For this purpose, a material property correction factor was determined by comparing the crack driving force calculated from the J-estimation schemes to detailed finite element (FE) analyses. The effect of crack size and pipe geometry on the material correction factor was investigated. Using the determined crack-driving force and the appropriate toughness of the weld metal, the Z-factors were calculated for various crack sizes and pipe geometries. In these calculations, a ‘reference’ limit-load was determined by using the lower strength base metal flow stress. Furthermore, the effect of J-R curve on the Z-factor was investigated. Finally, the Z-factors developed in the present work were compared to those developed earlier for through-wall cracks in DMWs.

Engineering Treatment Model (ETM) for Crack Driving Force Estimation of Structures With Stress Concentration

1993 ◽  
Vol 115 (2) ◽  
pp. 164-170 ◽  
Author(s):  
H. Su ◽  
A. Cornec ◽  
K.-H. Schwalbe
Keyword(s):  
Stress Concentration ◽  
Driving Force ◽  
High Stress ◽  
Limit Load ◽  
Pressure Vessels ◽  
Simple Relationship ◽  
Treatment Model ◽  
Force Estimation ◽  
Crack Driving Force ◽  
Corner Cracks

A simple relationship for estimating the limit load of a structure with a crack located in a zone with high stress-strain concentration has been suggested using Neuber’s relation. Then, based on the engineering treatment model (ETM), a method for calculating the crack driving force in the structure with a stress concentration was developed. It has also been proved that under deformation plasticity theory and monotonic loading, the ETM can be justified theoretically. Relationships between ETM and other engineering methods have also been established. The predictions by ETM agree well with the test results of full-scale pressure vessels with corner cracks at the joint between cylinder and nozzle.

Fully-Plastic Strain-Based J Estimation Scheme for Circumferential Surface Cracks in Pipes Subjected to Reeling

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Luís F. S. Parise ◽  
Claudio Ruggieri ◽  
Noel P. O'Dowd
Keyword(s):  
Finite Element ◽  
Driving Force ◽  
Driving Forces ◽  
Finite Element Simulations ◽  
J Integral ◽  
Crack Driving Force ◽  
Numerical Assessment ◽  
Estimation Scheme ◽  
The Given ◽  
J Estimation

Modern installation techniques for marine pipelines and subsea risers are often based on the reel-lay method, which introduces significant (plastic) strains on the pipe during reeling and unreeling. The safe assessment of cracklike flaws under such conditions requires accurate estimations of the elastic–plastic crack driving forces, ideally expressed in a strain-based formulation to better account for the displacement controlled nature of the reeling method. This paper aims to facilitate such assessments by presenting a strain-based expression of the well-known Electric Power Research Institute (EPRI) estimation scheme for the J integral, which is directly based upon fully plastic descriptions of fracture behavior under significant plasticity. Parametric finite element simulations of bending of circumferentially cracked pipes have been conducted for a set of crack geometries, pipe dimensions, and material hardening properties representative of current applications. These provide the numerical assessment of the crack driving force upon which the nondimensional factors of the EPRI methodology, which scale J with applied strain, are derived. Finally, these factors are presented in convenient graphical and tabular forms, thus allowing the direct and accurate assessment of the J integral for circumferentially cracked pipes subjected to reeling. Further results show that crack driving force values estimated using the proposed methodology and the given g1 factors are in very close agreement to those obtained directly from the finite element simulations.

Crack Interaction Criteria in Pressure Vessels and Pipe

1995 ◽  
Vol 117 (4) ◽  
pp. 260-264 ◽  
Author(s):  
D. S. Kim ◽  
K. H. Lo
Keyword(s):  
Driving Force ◽  
Physical Distance ◽  
Pressure Vessels ◽  
Load Factor ◽  
Surface Cracks ◽  
Crack Interaction ◽  
Planar Surface ◽  
Characteristic Distance ◽  
Crack Driving Force ◽  
Element Method

An attempt was made to define a new crack interaction criterion for pressurized cylinders with two co-planar surface cracks. Elastic-plastic finite element method with line spring concept (line spring element method) was used to verify the validity of the new interaction criterion and to establish the relative conservatism built into various codes/standards. The crack interaction criteria of two co-planar surface cracks as defined by ASME Section XI and BS PD6493 were studied and a new interaction criterion which accounts for crack shape and load factor was introduced. The basic idea behind the crack interaction criteria for co-planar surface cracks was the plastic zone and stress interaction near crack tips. To verify the new crack interaction criterion, comparisons of J-integral values were made for various crack sizes with different distances between cracks and loading conditions. Based upon these comparisons, the new crack interaction criteria, comparing a physical distance, s, to a characteristic distance d=(σ/σy)2(c1Q1 + c2Q2), proved to be a reasonable parameter for indication of the crack driving force interaction for co-planar cracks. The characteristic distance also represents a rigorous measure of an equivalent crack driving force for interacting cracks.

Development of the BS 7910 Failure Assessment Diagram for Strain Based Design With Application to Pipelines

2012 ◽  
Author(s):  
Simon Smith
Keyword(s):  
Yield Strength ◽  
Driving Force ◽  
Critical Assessment ◽  
Complex Structures ◽  
Crack Driving Force ◽  
Failure Assessment ◽  
Proposed Modification ◽  
Force Data ◽  
Suitable Modification ◽  
J Estimation

Engineering Critical Assessment (ECA) uses J estimation schemes to derive the crack tip loading of complex structures to determine their tolerance to crack-like flaws. The methods currently being used were derived in the 1980s for structures with primary stresses below the material yield strength. These are now being extensively used for loads beyond this level for what has been called Strain Based Design (SBD). Some papers have shown the standards BS7910:2005 and R6 Revision 4 can be unconservative when used for SBD. A possible reason has been identified and a suitable modification proposed. The proposed modification is briefly reviewed in the present paper together with a comparison of the method with suitable crack driving force data.

Application of the strain-based FAD to failure assessment of surface cracked components

2015 ◽  
Vol 6 (6) ◽  
pp. 689-703
Author(s):  
Igor Varfolomeev ◽  
Michael Windisch ◽  
Gerben Sinnema
Keyword(s):  
Boundary Conditions ◽  
Strain Hardening ◽  
Driving Force ◽  
Design Methodology ◽  
Surface Cracks ◽  
Crack Driving Force ◽  
Content Type ◽  
Failure Assessment Diagram ◽  
Aerospace Applications ◽  
Failure Assessment

Purpose – The purpose of this paper is to validate the strain-based failure assessment diagram (SB-FAD) approach for surface cracks in components subjected to displacement controlled boundary conditions. Design/methodology/approach – Numerical analyses are performed for several crack geometries and materials representative for aerospace applications. The performance of the SB-FAD is judged by comparing numerically calculated J-integrals to respective analytical estimates, using both Options 1 and 2 approximations. Findings – In the most cases, both Options 1 and 2 SB-FAD method results in reasonably conservative J-estimates. Exceptions are for surface cracks in a pressurized vessel made of a material with low-strain hardening, for which Option 2 assessment produces non-conservative results. In contrast, Option 1 assessment is conservative for all geometries considered. In general, Option 1 results in a considerable overestimation of the crack driving force, whereas Option 2 produces rather accurate results in many cases. Originality/value – The results demonstrate both the potential of the SB-FAD method and needs for its further improvements.

Numerical Analysis of the Crack Driving Force of Mismatched Girth Welded Pipes Subject to Large Plastic Deformations

2021 ◽  
Author(s):  
Kai Wu ◽  
Hong Zhang ◽  
Yue Yang ◽  
Xiaoben Liu
Keyword(s):  
Crack Length ◽  
Driving Force ◽  
Crack Depth ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Plastic Deformations ◽  
Crack Driving Force ◽  
Ground Deformations ◽  
Global Strain ◽  
Large Plastic Deformations

Abstract Strength mismatched pipes with part-through cracks can suffer large plastic deformation from permanent ground deformations caused by geohazards. Thus, the crack driving force involved in engineering critical assessments plays an important role in guaranteeing pipeline integrity when pipes are subjected to complex loads induced by a hostile environment. In this paper, Python scripts are developed to generate up to 200 finite element models of strength mismatched pipes with various crack sizes under large plastic deformations based on the commercial software ABAQUS. The effects of crack length, crack depth, and strength mismatch factors on the evolution of crack tip opening displacement (CTOD) and global strain were investigated. An approximately linear relationship was observed in all cases tested with global strain values varying from 0.5% to 3%. Meanwhile, the value of the CTOD increased with the increase of crack length and crack depth, and decreased with increasing mismatch factor from the undermatch to the overmatch conditions. The effect of the crack depth on the CTOD is comparatively larger than the crack length, which presented an obvious change of the CTOD for deep cracks coupled with undermatched conditions. Overmatched welding only affected the value of CTOD slightly, while a drastic increase of CTOD value was observed for the undermatched welding conditions, especially for deep and long cracks.

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