Significance of Splits and Pop-Ins Observed During Fracture Toughness Testing of Line Pipe Steel

2008 ◽  
Author(s):  
Henryk G. Pisarski ◽  
Ruth Hammond ◽  
Keith Watt
Keyword(s):  
Fracture Toughness ◽  
Low Temperature ◽  
Fracture Mechanics ◽  
Fracture Initiation ◽  
Assessment Procedure ◽  
Line Pipe ◽  
Apparent Fracture Toughness ◽  
Line Pipe Steel ◽  
Toughness Testing ◽  
Test Record

The occurrence of pop-in on the test record of fracture toughness tests and appearance of splits on the fracture surface, coupled with failure to meet Charpy toughness requirements, raised doubts about the fracture integrity of a parent pipe to API 5L X65 for low temperature operation. The cause of pop-in was investigated using fractographic and metallographic methods and additional fracture mechanics testing was conducted using different notch orientations. In addition, fitness-for-service was assessed using a fracture mechanics assessment procedure. It is shown that for typical flaw orientations that might be present, the apparent fracture toughness at pop-in is not representative. Nevertheless, it is shown that for the stress levels considered, the pipeline is tolerant to flaws without risk of fracture initiation at low temperature.

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.

The Effect of Inclusions on the Fracture Toughness of Local Brittle Zones in the HAZ of Girth Welded Line Pipe

2013 ◽  
Author(s):  
Philippa Moore ◽  
Joanna Nicholas
Keyword(s):  
Fracture Toughness ◽  
Fracture Initiation ◽  
Large Set ◽  
Parent Metal ◽  
Line Pipe ◽  
Subsequent Fracture ◽  
Post Test ◽  
Toughness Testing ◽  
Grain Boundary Pinning ◽  
Girth Welds

A programme of testing and research has been carried out to deliberately identify the causes of, and measure the fracture toughness of, potential local brittle zones (LBZs) in the heat affected zone (HAZ) of girth welds in a 20mm thick API 5L X70 grade pipe. This involved determining the most susceptible test temperature and notch location within the HAZ of two different welds by Charpy testing to define the T40J. Subsequent fracture toughness testing of a large set of fracture mechanics specimens notched into this region and tested at a low temperature based on T40J was able to achieve occasional low fracture toughness results. Post-test metallography identified that the inclusions in the parent metal affected the risk of brittle fracture initiation in two ways; firstly large and clustered inclusions acted as local brittle zones and/or fracture initiation sites; secondly, the large inclusions had reduced the effect of grain boundary pinning, as would be expected from well-dispersed smaller inclusions. This then resulted in significant grain coarsening in the HAZ fusion line, which could also act as a low toughness fracture initiation region. The inclusion types were chemically analysed, and recommendations were made to the steel producer in order to further improve the fracture toughness of the X70 pipe at increasingly lower temperatures.

The Use of Optimized ERW Technique to Improve Low Temperature Fracture Toughness of Welded Pipes

2020 ◽  
Author(s):  
Muhammad Rashid ◽  
Timothy Hylton ◽  
Neil Anderson ◽  
Laurie Collins ◽  
Leijun Li
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Low Temperature ◽  
Weld Seam ◽  
Peak Temperature ◽  
Line Pipe ◽  
Squeeze Pressure ◽  
Treatment Practices ◽  
Treatment Techniques ◽  
Research Activities

Abstract It is understood that the bondline microstructure of the line pipe ERW seam can be a zone of weakness in the pipe. To overcome this weakness, several research projects utilizing various line pipe steel grades and welding and heat treatment techniques have been conducted at EVRAZ NA. The overall goal of these efforts has been to understand the development of bondline microstructure during the ERW process and improve the weld seam fracture toughness for low temperature applications. These research activities included mill trials and Gleeble simulations. It was realized that a high toughness ERW weld seam is only possible through a tightly controlled combination of weld power, forging (squeeze) pressure, and welding speed. Research studies have indicated that the as-welded seam may not pass the standard ERW destructive tests if proper heat input and adequate squeeze pressure are not applied. Post weld heat treatment (normalizing) practice was also found to be a key element in the development of the appropriate bondline microstructure for higher toughness. Samples from pipes normalized using different heat treatment practices produced different bondline microstructures and hence different toughness properties. It was found through this study that a low (but still higher than the upper critical temperature Ac3) normalizing peak temperature and adequate soak time at the peak temperature result in improved Charpy toughness of ERW bondline microstructure.

Implementation of CSA Z662-15 Annex K Option 2 on a 610mm Liquid Pipeline

2016 ◽  
Author(s):  
Rory Belanger ◽  
Derrick Sarafinchan
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Test Specimen ◽  
Critical Assessment ◽  
Fracture Criteria ◽  
Weld Profile ◽  
Failure Assessment ◽  
Toughness Testing ◽  
Considerable Benefit ◽  
Brittle Fracture Criteria

For more than two decades, CSA Z662 Annex K has provided a method for developing alternative acceptance criteria for weld flaws in mechanized welded pipelines. Increasingly, over the years, fracture mechanics practitioners have found the method overly conservative and restrictive with respect to brittle fracture criteria when compared to other accepted fracture mechanics-based engineering critical assessment ECA codes and methods. These limitations rendered the CSA Annex K method difficult to implement on pipelines constructed with materials not possessing optimal toughness and in cases requiring consideration of fracture toughness at temperatures lower than the typical minimum design metal temperature (MDMT) of −5°C. This paper presents experiences implementing CSA Z662-15 Annex K Option 2 methodology on a 610 mm diameter liquids pipeline and compares and contrasts the utility and benefits of the code revision. This pipeline required consideration for installation during winter months, necessitating installation temperatures as low as −30°C. In addition to evaluation of actual ECA results, analytical evaluations of the Option 2 methodology were also conducted considering parameters outside those used on the project. The new Annex K Option 2 method was found to be of considerable benefit in preparation of a practical ECA. Since fracture toughness testing was conducted at the anticipated lowest installation temperature, the flaw criteria were, as expected, principally controlled by elastic/plastic crack growth consideration. The failure assessment diagram implemented into the CSA Z662-15 Annex K Option 2 provided tolerance for both longer and deeper flaws than that afforded by Option 1 (which resorts to the former 2011 Annex K method). Furthermore, the reduced restriction to the surface interaction ligament (p distance) offers additional advantages including increased flexibility in weld profile design and weld pass sequencing. Fracture toughness (CTOD) testing of TMP pipeline steels used in the project at −30°C often produced transitional fracture toughness results. It was found that the particular project materials were quite sensitive to the level of test specimen pre-compression (an acceptable plastic straining method to reduce residual stress gradients) applied to the CTOD specimens to enhance fatigue crack-front straightness. It was found that optimizing the level of pre-compression (to achieve acceptable pre-crack straightness while minimizing plastic pre-strain) achieved a balance between fully satisfying testing requirements, providing a conservative assessment of CTOD, and facilitating a functional Annex K ECA.

Fracture Toughness Testing for Improving the Safety of Gas Pipelines

2016 ◽  
Vol 821 ◽  
pp. 464-470
Author(s):  
Ľubomír Gajdoš ◽  
Martin Šperl
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Mechanical Tests ◽  
Internal Stresses ◽  
Pipe Material ◽  
Cylindrical Wall ◽  
Fracture Toughness Testing ◽  
Toughness Testing ◽  
Thin Walled

For standard fracture mechanical tests flat specimens (principally CT or SENB) are required. When investigating fracture mechanical properties of thin – walled pipes this brings about a problem because it is necessary to straighten pipe bands. However, this operation causes internal stresses to be induced not only in the semi-product subjected to straightening but also in finished specimens. A question therefore arises to what extent are then the magnitudes of the fracture toughness determined representative for the actual cylindrical wall. To solve this problem fracture mechanics tests were caried out on flat (straightened) CT specimens as well as on curved CT specimens with the natural curvature. The R – curves as well as the resulting parameters of the fracture toughness, obtained for both types of CT specimens, were compared and it was concluded that the fracture toughness of the pipe material determined on straightened CT specimens was practically the same as that obtained on curved CT specimens.

Estimation of Through-Wall Cracking Frequency of RPV Under PTS Events Using PFM Analysis Method for Identifying Conservatism Included in Current Japanese Code

2014 ◽  
Author(s):  
Kazuya Osakabe ◽  
Koichi Masaki ◽  
Jinya Katsuyama ◽  
Genshichiro Katsumata ◽  
Kunio Onizawa
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Structural Integrity ◽  
Probabilistic Approach ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Analysis Method ◽  
Integrity Assessment ◽  
The U.S

To assess the structural integrity of reactor pressure vessels (RPVs) during pressurized thermal shock (PTS) events, the deterministic fracture mechanics approach prescribed in Japanese code JEAC 4206-2007 [1] has been used in Japan. The structural integrity is judged to be maintained if the stress intensity factor (SIF) at the crack tip during PTS events is smaller than fracture toughness KIc. On the other hand, the application of a probabilistic fracture mechanics (PFM) analysis method for the structural reliability assessment of pressure components has become attractive recently because uncertainties related to influence parameters can be incorporated rationally. A probabilistic approach has already been adopted as the regulation on fracture toughness requirements against PTS events in the U.S. According to the PFM analysis method in the U.S., through-wall cracking frequencies (TWCFs) are estimated taking frequencies of event occurrence and crack arrest after crack initiation into consideration. In this study, in order to identify the conservatism in the current RPV integrity assessment procedure in the code, probabilistic analyses on TWCF have been performed for certain model of RPVs. The result shows that the current assumption in JEAC 4206-2007, that a semi-elliptic axial crack is postulated on the inside surface of RPV wall, is conservative as compared with realistic conditions. Effects of variation of PTS transients on crack initiation frequency and TWCF have been also discussed.

IN-787

Alloy Digest ◽  
1973 ◽  
Vol 22 (3) ◽  
Keyword(s):  
Fracture Toughness ◽  
Corrosion Resistance ◽  
Low Temperature ◽  
Atmospheric Corrosion ◽  
High Strength ◽  
Heat Treating ◽  
Line Pipe ◽  
International Nickel Company ◽  
Pipe Welding ◽  
Low Temperature Toughness

Abstract IN-787 is an age-hardenable, high-strength structural steel. It is characterized by low-temperature toughness, good atmospheric corrosion resistance and excellent weldability, even under adverse field conditions such as line-pipe welding. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as fracture toughness. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SA-286. Producer or source: International Nickel Company Inc..

Fracture Mechanics Study on the Effects of Various Notch Radii by Using FE Analysis

2015 ◽  
Author(s):  
Zalikha Murni Abdul Hamid ◽  
Keun-Hyung Bae ◽  
Gyo-Geun Youn ◽  
Dae-Young Lee ◽  
Yun-Jae Kim ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Fracture Strain ◽  
Notch Root ◽  
Damage Model ◽  
Fe Analysis ◽  
Experiment Data ◽  
Apparent Fracture Toughness ◽  
Notch Root Radius ◽  
Plane Strain Deformation

This paper predicts the effects of notch root radius on the ductile fracture behavior of the structure through evaluation based on fracture mechanics concept. To understand the effects of notch radii on structure, FE analysis of J-integral for plane strain deformation fields with various size of notches were predicted. The fracture toughness of the specimens with various notch radii were determined by stress modified fracture strain damage model FE simulation that was established based on notched bar tensile test data. The simulated results were validated by comparison with the experiment data. Findings show that the value of apparent fracture toughness increases with the increase in the notch radii. Therefore, indicates the increase in the resistance to the crack propagation. Similar trend can be shown for both C(T) and M(T) specimen. Thus, shows that the proposed method can be used to obtain effects of various notch radii.

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