Brittle Fracture Assessment and Failure Assessment Diagrams

2021 ◽  
pp. 1-8
Author(s):  
Brian Macejko
Keyword(s):  
Fracture Mechanics ◽  
Brittle Fracture ◽  
Flaw Size ◽  
Process Equipment ◽  
Reliable Prediction ◽  
Fracture Failure ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
Assessment Procedures

Abstract A detailed fracture mechanics evaluation is the most accurate and reliable prediction of process equipment susceptibility to brittle fracture. This article provides an overview and discussion on brittle fracture. The discussion covers the purpose for evaluating, provides a brief summary of historical failures that were found to be a result of brittle fracture, and describes key components that drive susceptibility to a brittle fracture failure, namely stress, toughness/temperature, and flaw size. It also presents industry codes and standards that assess susceptibility to brittle fracture. Additionally, a series of case study examples are presented that demonstrate assessment procedures used to mitigate the risk of brittle fracture in process equipment.

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.

scholarly journals Comparison of Methods for Predicting the Influence of Residual Stresses on Brittle Fracture

2007 ◽  
Author(s):  
Ali Mirzaee-Sisan ◽  
Saeid Hadidi-Moud ◽  
David John Smith
Keyword(s):  
Brittle Fracture ◽  
Residual Stresses ◽  
Outer Surface ◽  
Ferritic Steel ◽  
Statistical Approach ◽  
Type Model ◽  
Comparison Of Methods ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
Assessment Procedures

This paper compares different methods for predicting the influence of residual stresses on brittle fracture. Comparison is made between fracture predictions of a local statistical approach based on the Beremin type model, with those of a well-known fracture assessment procedures, BS7910 and R6 that uses a failure assessment diagram (FAD). The results from both methods are discussed and compared. The study focuses on the behaviour of a ferritic steel pipe containing a part-through circumferential thumb-nail crack on the outer surface of the vessel.

Proposed Modifications to API 579 Part 3 Brittle Fracture Screening Procedures

2019 ◽  
Author(s):  
Brian R. Macejko ◽  
Seetha Ramudu Kummari ◽  
Phillip E. Prueter
Keyword(s):  
Fracture Mechanics ◽  
Brittle Fracture ◽  
State Of The Art ◽  
Acceptance Criteria ◽  
Evaluation Procedures ◽  
Failure Assessment ◽  
Level 3 ◽  
Screening Procedures ◽  
Level 1 ◽  
Level 2

Abstract Significant inconsistencies and inadequacies exist in the current brittle fracture screening procedures in the 2016 edition of API 579-1/ASME FFS-1, Fitness-For-Service (API 579). Results from an evaluation completed using the current published guidance could prove unsafe in some instances. The ASME/API Joint Committee on Fitness-For-Service (FFS) recently initiated a project to rewrite API 579 Part 3, Assessment of Existing Equipment for Brittle Fracture. The intent of the project is to establish new Level 1 and Level 2 evaluation procedures and acceptance criteria developed using state-of-the-art fracture mechanics consistent with the Part 9 Failure Assessment Diagram (FAD) approach, currently employed in Level 3 FFS evaluations. This paper will provide a comprehensive summary of deficiencies and concerns with current published methods for evaluating susceptibility of pressure equipment to potential brittle fracture failures. Additionally, the paper will provide an overview of the methodology employed in the recently proposed procedure modifications for Part 3 of API 579 to mitigate the current deficiencies.

Assessment of Brittle Fracture for Single Edge Notched Bend Specimens With Different Machined-Notch Depth

2013 ◽  
Author(s):  
Tsutomu Iwashita ◽  
Ryohei Kobayashi ◽  
Koji Azuma
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Brittle Fracture ◽  
Fatigue Cracks ◽  
Notch Depth ◽  
Single Edge ◽  
Defect Assessment ◽  
Plastic Constraint ◽  
Assessment Procedures ◽  
Weibull Stress

Current defect assessment procedures based on fracture mechanics usually assume flaws to be infinitely sharp. While this assumption may be appropriate for fatigue cracks, it can be an over-conservative assumption and give a large safety factor for non-sharp flaws such as porosity or weld undercut because of the loss of plastic constraint. Fracture toughness tests are performed for four types of single-edge notched bend steel specimens with different degrees of plastic constraint caused by a machined-notch and a shallow notch. This paper shows the ability of the Weibull stress approach to predict brittle fracture under both high and low plastic constraint conditions. The Weibull stress approach predicts the effects accurately.

Fracture Mechanics Analysis of Clad Subsea Equipment in Sour HPHT Conditions

2017 ◽  
Author(s):  
Colum Holtam ◽  
Rajil Saraswat ◽  
Ramgopal Thodla
Keyword(s):  
Finite Element ◽  
Fracture Mechanics ◽  
Internal Surface ◽  
Design Guidelines ◽  
Assessment Methods ◽  
Element Analysis ◽  
High Pressure High Temperature ◽  
Failure Assessment ◽  
The Finite Element Analysis

High pressure high temperature (HPHT) design is a significant new challenge facing the subsea sector, particularly in the Gulf of Mexico. API 17TR8 provides HPHT Design Guidelines, specifically for subsea applications. This paper presents the results of a fatigue based fracture mechanics assessment case study conducted on a fully clad subsea HPHT component. The component was assumed to be constructed from F22 low alloy steel internally clad with alloy 625 and exposed to 20ksi (137.8MPa) and 400°F (204°C) internal pressure and temperature. A number of different assessment methods were evaluated as part of this study, including standard failure assessment diagram (FAD) based assessment methods, such as those found in API 579-1/ASME FFS-1 and BS 7910, as well as finite element (i.e. crack mesh) methods. A detailed description of the finite element analysis (FEA) of the uncracked and cracked component is provided. An internal surface flaw assumed to be exposed to sour production fluids was evaluated. The results of the fatigue and fracture assessments are summarized along with the key differences between the assessment methods adopted. The sensitivity of the assessment results to other variables such as welding residual stresses is also discussed.

scholarly journals Predicting the Influence of Residual Stresses on Brittle Fracture Using Local Approach

2008 ◽  
Author(s):  
Ali Mirzaee-Sisan ◽  
Saeid Hadidi-Moud ◽  
David Smith
Keyword(s):  
Residual Stress ◽  
Brittle Fracture ◽  
Residual Stresses ◽  
Surface Flaw ◽  
Assessment Procedure ◽  
Local Approach ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
Failure Predictions

This paper explores the application of the local approach to brittle fracture to predict the influence of residual stresses in a relatively thick pipe. Three different surface flaw sizes were assumed on the outside surface of the pipe and failure predictions were made using the local approach. Then the results of local approach prediction were compared with the well-known fracture assessment procedure, BS7910 which uses a failure assessment diagram (FAD). It has found that the local approach has an advantage of taking into account the details of stress re-distribution of residual stress around the crack tip compared to the conventional assessment procedure.

BS 7910: History and Future Developments

2009 ◽  
Author(s):  
Isabel Hadley
Keyword(s):  
Assessment Methods ◽  
Weld Strength ◽  
Assessment Procedure ◽  
Metallic Structures ◽  
History Of ◽  
Fracture Assessment ◽  
Offshore Industry ◽  
Crack Tip Constraint ◽  
The Uk ◽  
Assessment Procedures

BS 7910, the UK procedure for the assessment of flaws in metallic structures, was first published almost 30 years ago in the form of a fracture/fatigue assessment procedure, PD6493. It provided the basis for analysing fabrication flaws and the need for repair in a rational fashion, rather than relying on long-established (and essentially arbitrary) workmanship rules. The UK offshore industry in particular embraced this new approach to flaw assessment, which is now widely recognised by safety authorities and specifically referred to in certain design codes, including codes for pressure equipment. Since its first publication in 1980, PD6493/BS 7910 has been regularly maintained and expanded, taking in elements of other publications such as the UK power industry’s fracture assessment procedure R6 (in particular the Failure Assessment Diagram approach), the creep assessment procedure PD6539 and the gas transmission industry’s approach to assessment of locally thinned areas in pipelines. The FITNET European thematic network, run between 2002 and 2006, has further advanced the state of the art, bringing in assessment methods from SINTAP (an earlier European research project), R6, R5 and elsewhere. In particular, the FITNET fracture assessment methods represent considerable advances over the current BS 7910 methods; for example, weld strength mismatch can be explicitly analysed by using FITNET Option 2, and crack tip constraint through Option 5. Corrosion assessment methods in FITNET are also more versatile than those of BS 7910, and now include methods for vessels and elbows as well as for pipelines. In view of these recent advances, the BS 7910 committee has decided to incorporate many elements of the FITNET procedure into the next edition of BS 7910, to be published c2012. This paper summarises the history of the development of BS 7910, its relationship with other flaw assessment procedures (in particular FITNET and R6) and its future.

Technical Basis of Proposed New Acceptance Standards for Class 1, 2 and 3 Piping

2007 ◽  
Author(s):  
Katsumasa Miyazaki ◽  
Kunio Hasegawa ◽  
Naoki Miura ◽  
Koichi Kashima ◽  
Douglas A. Scarth
Keyword(s):  
Fracture Mechanics ◽  
Ultrasonic Inspection ◽  
Limit Load ◽  
Flaw Size ◽  
High Fracture Toughness ◽  
Evaluation Procedure ◽  
High Fracture ◽  
Development Methodology ◽  
Class 1 ◽  
Technical Basis

Acceptance Standards in Section XI of the ASME Boiler and Pressure Vessel Code have an important role as the first step in the flaw evaluation procedure. When a flaw size is within the allowable flaw size in the Acceptance Standard, the flaw is acceptable and analytical evaluation is not required. Although ASME Section XI has Acceptance Standards for Class 1 piping in IWB-3500, there are no Acceptance Standards for Class 2 and 3 piping. Furthermore, the development of the current Acceptance Standards for Class 1 piping was based on flaw detectability by ultrasonic inspection and consideration of fracture mechanics. In this paper, the development of proposed new Acceptance Standards for Class 2 and 3 piping, as well as for Class 1 piping, is described. The development methodology is based on a fracture mechanics approach. For Class 1 piping with high fracture toughness, the allowable flaw sizes were determined by limit load solution. For Class 1 piping, the intent was to maintain overall consistency with the current Acceptance Standards. Proposed Acceptance Standards for Class 2 and 3 austenitic piping were also developed by the methodology used to develop the proposed new Acceptance Standards for Class 1 piping. Allowable flaw sizes for both surface flaws and subsurface flaws for preservice and inservice examinations were developed.

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