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.

Failure assessment diagrams. III. Mappings and failure assessment lines when the crack driving force is a functional

1994 ◽  
Vol 444 (1922) ◽  
pp. 497-508 ◽  
Keyword(s):  
Driving Force ◽  
Curve Analysis ◽  
General Situation ◽  
Crack Driving Force ◽  
Tearing Instability ◽  
Tangency Condition ◽  
Theory Of Plasticity ◽  
Failure Assessment ◽  
Natural Way ◽  
Flow Theory Of Plasticity

In two previous papers a natural mapping was noted between the ( a, J ep ) diagram of R-curve analysis and the ( L r , K r ) failure assessment diagram (FAD) of the R6-revision 3 procedure. In these papers it was assumed that the applied crack driving force J ep was obtained by a deformation theory of plasticity and so could be treated as a function of its arguments. Here the analysis is generalised to consider the situation where J ep is not a function but a functional of its arguments, as in the flow theory of plasticity. As in I the discussion has been given in terms of the J based parameters. But the conclusions hold equally well for any other parameters describing crack driving force and crack resistance. A unique R-curve image (the RCl) in the FAD can still be established in a natural way. Moreover, if this RCl is used as the failure assessment line (FAL), the treatments of ductile tearing instability in R-curve analysis and in the FAD are still equivalent. The interesting situation then arises, however, that the tangency condition can be defined in the FAD but not in R-curve analysis, because in the latter the usual applied J ep curves do not exist. Some difficulties in using the FAD in this more general situation are discussed. An FAL can be obtained when J ep is a function of its arguments by considering a sequence of RCl curves for similar structures of ever increasing size and this procedure can be extended to the situation where J ep is a functional. The R-curve plays a central role in the argument when J ep is a function and even more so when J ep is a functional. In the latter situation, the analysis rests essentially on the consideration of increments of crack driving force and fracture resistance and it is suggested that a fracture mechanics based on the values of these increments rather than on the values of the parameters themselves might be developed.

ECAs, FE and Bi-Axial Loading: A Critique of DNV-OS-F101, Appendix A

2015 ◽  
Author(s):  
Andrew Cosham ◽  
Kenneth A. Macdonald
Keyword(s):  
Finite Element ◽  
Driving Force ◽  
Longitudinal Strain ◽  
Axial Loading ◽  
Limit Load ◽  
Fe Analysis ◽  
Plastic Limit ◽  
Crack Driving Force ◽  
Failure Assessment ◽  
Plastic Limit Load

Controlled lateral buckling in offshore pipelines typically gives rise to the combination of internal over-pressure and high longitudinal strains (possibly exceeding 0.4 percent). Engineering critical assessments (ECAs) are commonly conducted during design to determine tolerable sizes for girth weld flaws. ECAs are primarily conducted in accordance with BS 7910, often supplemented by guidance given in DNV-OS-F101 and DNV-FP-F108. DNV-OS-F101 requires that finite element (FE) analysis is conducted when, in the presence of internal over-pressure, the nominal longitudinal strain exceeds 0.4 percent. It recommends a crack driving force assessment, rather than one based on the failure assessment diagram. FE analysis is complicated, time consuming and costly. ECAs are, necessarily, conducted towards the end of the design process, at which point the design loads have been defined, the welding procedures qualified and the material properties quantified. In this context, ECAs and FE are not an ideal combination for the pipeline operator, the designer or the installation contractor. A pipeline subject to internal over-pressure is in a state of bi-axial loading. The combination of internal over-pressure and longitudinal strain appears to become more complicated as the longitudinal strain increases, because of the effect of bi-axial loading on the stress-strain response. An analysis of a relatively simple case, a fully-circumferential, external crack in a cylinder subject to internal over-pressure and longitudinal strain, is presented in order to illustrate the issues with the assessment. Finite element analysis, with and without internal over-pressure, are used to determine the plastic limit load, the crack driving force, and the Option 3 failure assessment curve. The results of the assessment are then compared with an assessment using the Option 2 curve. It is shown that an assessment based Option 2, which does not require FE analysis, can potentially give comparable results to the more detailed assessments, when more accurate stress intensity factor and reference stress (plastic limit load) solutions are used. Finally, the results of the illustrative analysis are used to present an outline of suggested revisions to the guidance in DNV-OS-F101, to reduce the need for FE analysis.

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.

An improved crack driving force estimation approach for stress-based engineering critical assessment of reeled pipes

2019 ◽  
Vol 103 ◽  
pp. 102312 ◽  
Author(s):  
Yizhe Li ◽  
Baoming Gong ◽  
Giuseppe Lacidogna ◽  
Alberto Carpinteri ◽  
Dongpo Wang
Keyword(s):  
Driving Force ◽  
Critical Assessment ◽  
Force Estimation ◽  
Crack Driving Force

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.

Probabilistic Failure Assessment of a Complex Nozzle Structure With Flaw Defect Based on FITNET Procedure

2016 ◽  
Author(s):  
Yan Wang ◽  
Yan-Wei Wang ◽  
Hanxin Chen ◽  
Linwei Ma
Keyword(s):  
Crack Growth ◽  
Failure Probability ◽  
Driving Force ◽  
Complex Geometry ◽  
Crack Depth ◽  
Initial Crack ◽  
Structural Safety ◽  
Crack Driving Force ◽  
Failure Assessment ◽  
Nozzle Structure

A probabilistic failure assessment based on the fracture and fatigue modules of European FITNET procedure is presented in this work. Analysis of the leak probability of a complex nozzle structure with postulated flaw defect under thermal mechanical loading is performed. Crack growth is calculated using FITNET fatigue module, in which the crack driving force ΔKeq considering mixed-mode load is applied. For the structural safety evaluation, the failure assessment diagram (FAD) within the frame of FITNET fracture module is utilized with the parameter Keff combing KI and KII. The fracture mechanical parameters are calculated using finite element (FE) method because of the complex geometry and load conditions. To meet the needs of probabilistic analyses, formulas calculating crack driving force are developed specific for this nozzle structure through nonlinear regression based on the FE results. With an initial crack depth of 5 mm, the nozzle failure probability in form of leak comes to 1.84×10−4 in next fifty years. The good agreement of the results of Monte Carlo simulation and stratified sampling technique confirms that the crack growth parameter C and the initial crack shape ratio c/a have considerable effect on the structural failure probability.

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.

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.

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.

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