HAZ Toughness: Realistic Testing for Pipeline Integrity

2011 ◽  
Author(s):  
Alexander U. Amadioha ◽  
Adam C. Bannister ◽  
Simon Slater ◽  
Martin Connelly
Keyword(s):  
Fracture Toughness ◽  
Large Scale ◽  
Crack Depth ◽  
Small Scale ◽  
Specific Test ◽  
Fracture Toughness Testing ◽  
Seam Weld ◽  
Wide Range ◽  
Toughness Testing ◽  
Haz Toughness

Fracture toughness testing of the heat-affected zone (HAZ) of linepipe seam welds is a requirement for most pipeline projects. Occasionally, low individual values can be measured in the HAZ and these have been attributed to, among other factors, the statistical nature of the HAZ and the associated probability of encountering local brittle zones. The structural significance of these outliers has remained a subject of debate between linepipe users and manufacturers [1], especially as their low significance can be demonstrated via large-scale structurally-representative tests [2–3]. To circumvent the higher cost of such large-scale testing, constraint-corrected fracture toughness testing can be used such that the conditions in the small-scale test more closely reflect those in service. However, there is little consistency between the many test and application codes in terms of how such tests should be carried out, and what steps are required to demonstrate that the measured toughness is structurally representative. Furthermore, the level of benefit to be obtained cannot be easily predicted. In the current study, a range of fracture mechanics tests was conducted on the HAZ of the longitudinal seam weld of a grade X65 U-O-E SAW pipe. Varying degrees of constraint, scale and loading mode were evaluated to establish the characteristic toughness of the HAZ in a statistical manner, with over fifty specimens tested in total. The specimens tested included notched bend (SENB) and tension (SENT) designs as well as surface notched tension (SNT), all with varying crack depth. The range of specimen and loading types, when compared with the requirements of the various relevant standards, highlighted the contradictory nature of current standards. The toughness established for each set of specific test conditions was used in a theoretical Engineering Critical Assessment (ECA) assuming various levels of applied stress, residual stress and flaw size inputs. The wide range of conclusions that would have been reached based on the small-scale toughness tests carried out under varying levels of constraint was easily demonstrated via the ECA. The conflicting requirements of several testing and application standards for longitudinal welds should be addressed, and their consistency with current approaches for girth welds improved. The study also shows that a single-parameter fracture criterion is an insufficient indicator of real HAZ toughness and constraint (metallurgical and geometrical) level must also be considered. The use of standard deeply-notched CTOD specimens, representing high constraint, gives a highly pessimistic view of seam weld integrity, especially when subsequently combined with an ECA.

Constraint Based Fracture Assessment of Seam-Welded Pipes Containing Axial Flaws

2006 ◽  
Author(s):  
Yuri Tkach ◽  
Anthony Horn ◽  
Adam Bannister ◽  
Edmund Bolton
Keyword(s):  
Fracture Toughness ◽  
Crack Depth ◽  
High Stress ◽  
Stress Triaxiality ◽  
Single Edge ◽  
Fracture Toughness Testing ◽  
Single Edge Notch ◽  
Seam Weld ◽  
Edge Notch ◽  
Toughness Testing

An Engineering Critical Assessment (ECA) of a pipeline containing an axial defect is usually conservative if standard fracture test pieces are used for the fracture toughness testing. Conventional fracture toughness testing standards employ specimens containing deep cracks in order to guarantee conditions leading to high stress triaxiality and crack-tip constraint. In the current work, single edge notch bend (SENB) and single edge notch tension (SENT) test specimens of two different a/W (crack depth/specimen width) ratios (0.15 and 0.6) were used to obtain HAZ fracture toughness of a seam weld. The influence of specimen geometry and a/W ratio on fracture toughness was investigated. The Master Curve methodology was employed to characterise HAZ fracture toughness of the seam weld in the ductile-to-brittle transition region. The reference temperature T0 was estimated using the test results obtained on specimens of different geometries and constraint levels. A series of ECAs of the pipe containing a surface axial flaw was performed and the benefits of a constraint based fracture mechanics analysis were demonstrated.

Fracture Toughness Testing and its Implications to Engineering Fracture Mechanics Analysis of Energy Pipelines

2018 ◽  
Author(s):  
Sergio Limon ◽  
Peter Martin ◽  
Mike Barnum ◽  
Robert Pilarczyk
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Test Data ◽  
Fracture Mode ◽  
Fracture Process ◽  
Fracture Behavior ◽  
Fracture Initiation ◽  
Fracture Toughness Testing ◽  
Final Fracture ◽  
Toughness Testing

The fracture process of energy pipelines can be described in terms of fracture initiation, stable fracture propagation and final fracture or fracture arrest. Each of these stages, and the final fracture mode (leak or rupture), are directly impacted by the tendency towards brittle or ductile behavior that line pipe steels have the capacity to exhibit. Vintage and modern low carbon steels, such as those used to manufacture energy pipelines, exhibit a temperature-dependent transition from ductile-to-brittle behavior that affects the fracture behavior. There are numerous definitions of fracture toughness in common usage, depending on the stage of the fracture process and the behavior or fracture mode being evaluated. The most commonly used definitions in engineering fracture analysis of pipelines with cracks or long-seam weld defects are related to fracture initiation, stable propagation or final fracture. When choosing fracture toughness test data for use in engineering Fracture Mechanics-based assessments of energy pipelines, it is important to identify the stage of the fracture process and the expected fracture behavior in order to appropriately select test data that represent equivalent conditions. A mismatch between the physical fracture event being modeled and the chosen experimental fracture toughness data can result in unreliable predictions or overly conservative results. This paper presents a description of the physical fracture process, behavior and failure modes that pipelines commonly exhibit as they relate to fracture toughness testing, and their implications when evaluating cracks and cracks-like features in pipelines. Because pipeline operators, and practitioners of engineering Fracture Mechanics analyses, are often faced with the challenge of only having Charpy fracture toughness available, this paper also presents a review of the various correlations of Charpy toughness data to fracture toughness data expressed in terms of KIC or JIC. Considerations with the selection of an appropriate correlation for determining the failure pressure of pipelines in the presence of cracks and long-seam weld anomalies will be discussed.

Equipment for fracture toughness testing of specimen at low temperatures

1988 ◽  
Vol 20 (5) ◽  
pp. 698-702
Author(s):  
I. D. Abushenkov ◽  
A. I. Alekseev ◽  
V. Ya. Il'ichev ◽  
N. I. Mokryi ◽  
A. I. Telegon ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Low Temperatures ◽  
Fracture Toughness Testing ◽  
Toughness Testing

Coupled Thermo-Hydro-Geochemical Models of Engineered Barrier Systems: The Febex Project

2000 ◽  
Vol 663 ◽  
Author(s):  
J. Samper ◽  
R. Juncosa ◽  
V. Navarro ◽  
J. Delgado ◽  
L. Montenegro ◽  
...  
Keyword(s):  
Large Scale ◽  
Reference Model ◽  
Numerical Models ◽  
Full Scale ◽  
Small Scale ◽  
Model Parameters ◽  
In Situ Test ◽  
Wide Range ◽  
Engineered Barrier

ABSTRACTFEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project dealing with the bentonite engineered barrier designed for sealing and containment of waste in a high level radioactive waste repository (HLWR). It includes two main experiments: an situ full-scale test performed at Grimsel (GTS) and a mock-up test operating since February 1997 at CIEMAT facilities in Madrid (Spain) [1,2,3]. One of the objectives of FEBEX is the development and testing of conceptual and numerical models for the thermal, hydrodynamic, and geochemical (THG) processes expected to take place in engineered clay barriers. A significant improvement in coupled THG modeling of the clay barrier has been achieved both in terms of a better understanding of THG processes and more sophisticated THG computer codes. The ability of these models to reproduce the observed THG patterns in a wide range of THG conditions enhances the confidence in their prediction capabilities. Numerical THG models of heating and hydration experiments performed on small-scale lab cells provide excellent results for temperatures, water inflow and final water content in the cells [3]. Calculated concentrations at the end of the experiments reproduce most of the patterns of measured data. In general, the fit of concentrations of dissolved species is better than that of exchanged cations. These models were later used to simulate the evolution of the large-scale experiments (in situ and mock-up). Some thermo-hydrodynamic hypotheses and bentonite parameters were slightly revised during TH calibration of the mock-up test. The results of the reference model reproduce simultaneously the observed water inflows and bentonite temperatures and relative humidities. Although the model is highly sensitive to one-at-a-time variations in model parameters, the possibility of parameter combinations leading to similar fits cannot be precluded. The TH model of the “in situ” test is based on the same bentonite TH parameters and assumptions as for the “mock-up” test. Granite parameters were slightly modified during the calibration process in order to reproduce the observed thermal and hydrodynamic evolution. The reference model captures properly relative humidities and temperatures in the bentonite [3]. It also reproduces the observed spatial distribution of water pressures and temperatures in the granite. Once calibrated the TH aspects of the model, predictions of the THG evolution of both tests were performed. Data from the dismantling of the in situ test, which is planned for the summer of 2001, will provide a unique opportunity to test and validate current THG models of the EBS.

Forming mechanism of delamination cracks observed during tensile and fracture toughness testing of X70 pipeline steel

2017 ◽  
Vol 209 (1-2) ◽  
pp. 223-229 ◽  
Author(s):  
Dong-Yeob Park ◽  
Babak Shalchi Amirkhiz ◽  
Jean-Philippe Gravel ◽  
Jie Liang ◽  
Renata Zavadil ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Pipeline Steel ◽  
X70 Pipeline Steel ◽  
Forming Mechanism ◽  
Fracture Toughness Testing ◽  
Toughness Testing ◽  
Delamination Cracks
Sign in / Sign up

Export Citation Format

Share Document