Prediction of brittle fracture initiating at ends of CJP groove welded joints with defects: study into applicability of failure assessment diagram approach

2003 ◽  
Vol 25 (14) ◽  
pp. 1815-1826 ◽  
Author(s):  
Tsutomu Iwashita ◽  
Yoshiaki Kurobane ◽  
Koji Azuma ◽  
Yuji Makino
Keyword(s):  
Brittle Fracture ◽  
Welded Joints ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Diagram Approach

Constraint in the Failure Assessment Diagram Approach for Fracture Assessment

1995 ◽  
Vol 117 (3) ◽  
pp. 260-267 ◽  
Author(s):  
R. A. Ainsworth ◽  
N. P. O’Dowd
Keyword(s):  
Crack Size ◽  
Structural Constraint ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
T Stress ◽  
Fracture Assessment ◽  
The Subject ◽  
Constraint Effects ◽  
Two Parameters ◽  
Diagram Approach

This paper presents a framework for including constraint effects in the failure assessment diagram approach for fracture assessment. As parameters for describing constraint are still the subject of development, the framework is illustrated using both the elastic T-stress and the hydrostatic Q-stress. It is shown that constraint effects can be treated by modifying the shape of the failure assessment curve. In their simplest form, the modifications involve only two parameters: one quantifying the magnitude of structural constraint which depends on geometry and crack size; and the second quantifying the influence of constraint on fracture toughness.

Numerical Validation of a Strain-Based Failure Assessment Diagram Approach to Fracture

2009 ◽  
Author(s):  
Peter J. Budden ◽  
Michael C. Smith
Keyword(s):  
Finite Element ◽  
Plastic Strain ◽  
Present Author ◽  
Plastic Relaxation ◽  
Failure Assessment Diagram ◽  
Defect Assessment ◽  
Failure Assessment ◽  
Basic Approaches ◽  
Assessment Procedures ◽  
Diagram Approach

The basic approaches in defect assessment procedures such as R6 consider the stresses on the section containing the flaw. Such approaches can be overly conservative and lead to unacceptably small estimates of limiting defect sizes for cases where the applied loads are due to displacements or strains well in excess of yield, when significant plastic relaxation of stress occurs. The potential for over-conservative assessments has led to a renewed interest in recent years in strain-based assessment methods, in both the power and pipeline industries. Significant levels of plastic strain can be imposed across the flawed section in some cases. Recently, the present author has published a general approach to strain-based fracture that uses a strain-based failure assessment diagram (SB-FAD). This includes a range of Options similar to that of the basic R6 approach. The present paper describes some validation of the SB-FAD approach based on elastic-plastic cracked-body finite element data for plates and cylinders.

Assessing Brittle Fracture in Pressurized Equipment Using a FAD

2008 ◽  
Author(s):  
David R. Thornton
Keyword(s):  
Fracture Mechanics ◽  
Brittle Fracture ◽  
Flaw Size ◽  
The Other ◽  
Failure Assessment Diagram ◽  
Failure Assessment

While the probability of brittle fracture in pressurized equipment has typically been rare, the consequences are usually unacceptable from a risk standpoint. This article first briefly reviews the method used to prevent brittle fracture in new equipment used by most codes. The article then presents the approaches of increasing complexity to preventing brittle fracture in existing equipment with an emphasis on the fracture mechanics approach and the use of a Failure Assessment Diagram (FAD). Two examples are discussed, one of determining the maximum acceptable flaw size for a given operating scenario and the other of determining an acceptable operating envelope for a given flaw size.

Revision of ISO 27306 for CTOD Toughness Correction for Constraint Loss

2016 ◽  
Vol 879 ◽  
pp. 54-59
Author(s):  
Fumiyoshi Minami ◽  
Mitsuru Ohata ◽  
Yasuhito Takashima
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Stress Criterion ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
International Standardization ◽  
Diagram Approach ◽  
Weibull Stress

As the result of the international standardization work in Japanese IST project, ISO 27306 were published in 2009 for correction of CTOD fracture toughness for constraint loss in steel components. ISO 27306 employs an equivalent CTOD ratio based on the Weibull stress criterion, which leads to more accurate fracture assessment than the conventional fracture mechanics assessment. On the occasion of the 1st periodical review, the revision of ISO 27306 has been proposed from Japan. This paper describes the key contents of the new ISO 27306. A case study is included on the fracture assessment of a wide plate component according to FAD (failure assessment diagram) approach specified in BS 7910:2013.

Evaluation of a Weld Overlay Design for a Bimetallic Weld Using the Failure Assessment Diagram

2014 ◽  
Author(s):  
Jens Heldt ◽  
Christopher Lohse ◽  
Nathaniel G. Cofie ◽  
Michael Lashley
Keyword(s):  
Brittle Fracture ◽  
Failure Modes ◽  
Limit Load ◽  
Resistance Curve ◽  
Weld Overlay ◽  
Ductile Tearing ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Asme Code ◽  
Overlay Design

During routine inspection of an N5 feedwater nozzle dissimilar metal weld (DMW) of a BWR, an axial flaw was detected in the weld. The flaw was mitigated by applying a full structural weld overlay (WOL) repair consisting of Alloy 52M weld metal and using the gas tungsten arc welding process (GTAW). Because of the ductile nature and very high toughness of the Alloy 52M material, the limit load approach of ASME Code, Section XI, Appendix C was used for the sizing of the overlay. The use of limit load for the design of weld overlays for Alloy 52M material is supported by several studies documented in the industry [1]. In order to address other fracture failure modes such as failure by ductile tearing and brittle fracture, a failure assessment diagram (FAD) approach was used to evaluate the acceptability of the weld overlay design. FADs have been used for evaluating flaws in piping components, but not for acceptance of flaws in WOLs. The FAD evaluation was performed in accordance with the ASME Code, Section XI, Appendix H requirements which address brittle fracture, elastic-plastic fracture mechanics (ductile tearing), and limit load failure modes. The applicable stress combinations were used in combination with the materials JR resistance curve to determine flaw acceptability at the end of the evaluation period. The evaluation considered the presence of both a circumferential flaw (360° around the circumference and 100% through the original pipe wall; the design basis for the full structural weld overlay) and an axial flaw. For both circumferential and axial flaws, several assessment points corresponding to the JR resistance curve were determined and plotted on the FAD curve for austenitic steels in ASME Section XI, Appendix H. The FAD curve in Appendix H was derived based on strength properties of stainless steel and is considered conservative in application to Alloy 52M since Alloy 52M has higher strength. All the assessment points were found to be below the FAD curve thus indicating the acceptability of the weld overlay with consideration to all the three possible fracture regimes.

Extensions of the Failure Assessment Diagram Approach Semi-Elliptical Flaw in Pressurized Cylinder

1985 ◽  
Vol 107 (1) ◽  
pp. 25-29 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Safety Assessment ◽  
Pressure Vessels ◽  
Failure Assessment Diagram ◽  
The United Kingdom ◽  
Safety Margins ◽  
Failure Assessment ◽  
Assessment Approach ◽  
Model Versus ◽  
Pressurized Cylinder ◽  
Diagram Approach

A simple, viable engineering method for assessing the integrity of nuclear pressure vessels has been developed at Babcock & Wilcox. The method uses results given in a plastic fracture handbook developed by General Electric and which are in the format of the Central Electricity Generation Board of the United Kingdom R-6 failure assessment diagram. The method is currently limited to two-dimensional/axisymmetric structural models with continuous flaws. Failure assessment of nuclear pressure vessels with assumed continuous flaws result in the calculation of overly conservative safety margins. This paper presents the extension of the existing failure assessment approach to include semi-elliptical flaw models, as well as example problems which demonstrate increased safety margins over the continuous flaw assumptions. In particular, failure assessment diagram curves and the corresponding failure assessment point expressions for an axially cracked pressurized cylinder with an ASME Section III, Appendix G semi-elliptical flaw are presented. The results of the example problems considering the less conservative semi-elliptical flaw model versus the continuous flaw model dramatically illustrate increased safety margins of 50 percent when more realistic semi-elliptical flaws are postulated. The results given in this paper are particularly valuable in the safety assessment of PWR vessels which have low toughness welds in their beltline regions.

Evaluation of Bending Limit of 9Cr-1Mo-V Steel by Master Curve and Failure Assessment Diagram Method: Evaluation of Base Metal

2018 ◽  
Author(s):  
Kazuo Oda ◽  
Mitsuyoshi Nakatani ◽  
Tomohiro Tanaka ◽  
Masamitsu Abe ◽  
Yasuhito Takashima ◽  
...  
Keyword(s):  
Brittle Fracture ◽  
Master Curve ◽  
Steel Plate ◽  
Fracture Probability ◽  
Pressure Vessels ◽  
Unstable Fracture ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Bending Process ◽  
Loading Tests

We investigated the bending and rolling limit of 9Cr-1Mo-V steel plate used in pressure vessels for the purpose of improving its manufacturing efficiency. Hereafter in this report, the bending limit refers to bending by press or by roller. It includes acceptable crack size, temperature, introduced plastic strain and other factors. When fracture toughness tests of 9Cr-1Mo-V steel plate were performed at bending temperature in production, unstable fracture rarely occurred. Since fracture probability during the bending process seems to be low, it was not possible to evaluate aspects of the degree of safety factor for brittle fracture. To estimate the bending limit at high temperature where unstable fracture rarely occurs, a method was proposed for estimating fracture probability using master curve and failure assessment diagram (FAD). In order to verify the proposed method, loading tests simulating the bending process were performed. The bending limits obtained from the loading tests were in good agreement with the values predicted by the proposed method. In this study, guidelines such as required toughness value and bending temperature for preventing brittle fracture during the bending process of 9Cr-1Mo-V steel plate were investigated.

scholarly journals Failure Assessment Diagram (FAD) analysis of fatigue test results for X65 welded joints

2018 ◽  
Vol 165 ◽  
pp. 21011
Author(s):  
Hsin Jen Hoh ◽  
John Hock Lye Pang ◽  
Kin Shun Tsang
Keyword(s):  
Welded Joints ◽  
Oil And Gas ◽  
Fatigue Cracks ◽  
Local Limit ◽  
Limit Load ◽  
Test Results ◽  
Offshore Pipelines ◽  
Failure Assessment Diagram ◽  
Four Point Bending ◽  
Failure Assessment

Offshore pipelines transfer oil and gas from seabed to production facility on the surface. The long pipelines are formed by welding of pipe segments, where these welded joints are a source of stress concentration and defects from which fatigue cracks can grow. This work aims to study the behaviour of deep fatigue cracks. In this current work, finite-element based on a parametric study of four-point bending is used to assess the stress intensity factors (SIFs) of deep surface cracks in X65 specimens, while considering local limit load the remaining load bearing ligament. These deep cracks take on a non-regular shape and have widths that exceed that of the specimen. They will be compared to empirical expressions from derived standards such as British Standards BS7910, which may be more conservative. The existing large flaw is also assessed via the failure assessment diagram (FAD). The effects of limit load solutions and reference stresses used to determine the FAD diagram will be discussed.

Sign in / Sign up

Export Citation Format

Share Document