Specifying Material Toughness to Avoid Brittle Fracture Initiation in Pipe Fittings and Components

2012 ◽  
Author(s):  
Gery M. Wilkowski ◽  
Do-Jun Shim
Keyword(s):  
Brittle Fracture ◽  
Fracture Initiation ◽  
Pipe Material ◽  
Charpy Test ◽  
Proof Testing ◽  
Fracture Transition ◽  
Brittle Fractures ◽  
Pipe Fittings ◽  
Shear Area ◽  
Area Percent

Recently, there have been a few failures with brittle fractures occurring during hydrostatic or pneumatic proof testing in pipe fittings that rekindled the need for paying attention on how to specify the toughness for pipe fittings and other components such as valves. This paper shows how an analysis procedure called the “Master Curve of Fracture Transition Temperatures” can be used to specify a Charpy shear area percent at some target temperature so that ductile initiation behavior occurs for either a surface or through-wall cracks in fittings, components or pipe material at the minimum design temperature. Due to differences in thickness, loading rate, and constraint conditions, the Charpy test transition temperature will not be at the same temperature as the minimum design temperature. In addition to the background and summary of prior efforts, several examples of full-scale pipe and fitting/valve fracture tests on different materials will be presented to show that the methodology works well. It is also possible from this method to specify the Charpy shear area percent at some temperature to ensure that brittle fracture propagation will not occur. There are some limits on this methodology for some newer steels that have very high Charpy energy values, and those conditions are also summarized.

Prediction of the Absence of Brittle Failure Risk for Ferritic Steel Piping Components in the Brittle-Ductile Region

2011 ◽  
Author(s):  
S. Marie ◽  
J. Schwab ◽  
S. Vidard
Keyword(s):  
Brittle Fracture ◽  
Fracture Risk ◽  
Brittle Failure ◽  
Risk Evaluation ◽  
Critical Stress ◽  
Ferritic Steel ◽  
Loading Condition ◽  
Maximum Principal Stress ◽  
Fracture Transition ◽  
Secondary Loop

This paper deals with the brittle fracture risk evaluation for a C-Mn piping component in the upper shelf of the brittle to ductile fracture transition temperature range, with the main objective to validate a predictive criteria, able to demonstrate the complete absence of brittle fracture risk. The criteria is based one a critical stress and the volume around the crack were the maximum principal stress exceed this critical stress. The model is calibrated on notched tensile specimens and CT specimens. A four-points bending pipe test has then been designed using this criterion to insure that no brittle fracture will occurs at a temperature that all CT specimens failed by cleavage. The material is a French secondary loop Tu42C ferritic steel and the pipe dimensions for the test are the same than the size of the principal secondary loop pipes. The results of the pipe test confirm the prediction with the model and the interpretation lead to define an equivalence between the loading conditions (based on the J parameter) of the pipe and the loading condition of a CT specimen.

scholarly journals On the Characteristics of Brittle Fracture Initiation in a Structurally Stress Concentrated Region (2nd Report)

1980 ◽  
Vol 1980 (148) ◽  
pp. 169-176 ◽  
Author(s):  
Kin-ichi Nagai ◽  
Hiroshi Yajima ◽  
Katsuya Kajimoto ◽  
Takahiro Hino ◽  
Nagio Minami
Keyword(s):  
Brittle Fracture ◽  
Fracture Initiation

scholarly journals A New Fracture Analysis Technique for Charpy Impact Test Using Image Processing

2021 ◽  
Vol 59 (1) ◽  
pp. 61-66
Author(s):  
Tae Chang Park ◽  
Beom Suk Kim ◽  
Ji Hee Son ◽  
Yeong Koo Yeo
Keyword(s):  
Image Processing ◽  
Brittle Fracture ◽  
Ductile Fracture ◽  
Impact Test ◽  
Charpy Impact ◽  
Charpy Impact Test ◽  
Fracture Analysis ◽  
Binary Image ◽  
Fracture Area ◽  
Brittle Fractures

The Charpy impact test is used to identify the transition between ductility and brittleness. The percentages of ductile and brittle fractures in steel can be evaluated based on each fracture area, which is presently determined by an analyzer with the naked eye. This method may lead to subjective judgement, and difficulty accurately quantifying the percentage. To resolve this problem, a new analysis method based on image processing is proposed in this study. A program that can automatically calculate the percentage of the ductile and brittle fractures has been developed. The analysis is performed after converting an RGB fracture image into a binary image using image processing techniques. The final binary image consists of 0 and 1 pixels. The parts with the pixel values of 1 correspond to the brittle fracture areas, and the pixel values of 0 represent the ductile fracture areas. As a result, by counting the number of 0 pixels in the entire area, it is possible to automatically calculate the percentage of ductile fracture. Using the proposed automatic fracture analysis program, it is possible to selectively distinguish only the brittle fracture from the entire fracture area, and to accurately and quantitatively calculate the percentages of ductile and brittle fractures.

Investigation of the Microstructure Factors Affecting the Brittle Fracture Initiation of Pre-Cracked Charpy-Type Samples of VVER-1000 RPV Steel

2013 ◽  
Vol 592-593 ◽  
pp. 635-638
Author(s):  
Evgenia A. Kuleshova ◽  
Maxim A. Artamonov ◽  
Artem D. Erak
Keyword(s):  
Brittle Fracture ◽  
Base Metal ◽  
Fracture Initiation ◽  
Type Specimens ◽  
Fracture Origin ◽  
Factors Affecting ◽  
Three Point Bending ◽  
Weld Metals ◽  
Rpv Steel ◽  
Higher Temperature

The correlation between fracture toughness parameter KJc and cleavage initiation distance (CID) for the three point bending (3PB) pre-crecked Charpy type specimens of VVER-1000 reactor pressure vessel base and weld metals was observed. Two types of brittle fracture origin sites were found: nonmetallic inclusions and grain or subgrain boundaries. It was shown that KJc values are shifted to the higher temperature area for weld metal with respect to base metal data. In case when the initiation origin is grain or subgrain boundary, the KJc values are higher for base metal at the same CID values. This indicates the higher crack resistance of base metal.

The Practical Application of Fracture Control to Natural Gas Pipelines

2008 ◽  
Author(s):  
K. A. Widenmaier ◽  
A. B. Rothwell
Keyword(s):  
Natural Gas ◽  
Large Scale ◽  
High Strength ◽  
Fracture Initiation ◽  
Opening Angle ◽  
Pipe Material ◽  
Design Factor ◽  
Line Pipe ◽  
Natural Gas Pipelines ◽  
Crack Tip Opening

The use of high strength, high design-factor pipe to transport natural gas requires the careful design and selection of pipeline materials. A primary material concern is the characterization and control of ductile fracture initiation and arrest. Impact toughness in the form of Charpy V-notch energies or drop-weight tear tests is usually specified in the design and purchase of line pipe in order to prevent large-scale fracture. While minimum values are prescribed in various codes, they may not offer sufficient protection in pipelines with high pressure, cold temperature, rich gas designs. The implications of the crack driving force arising from the gas decompression versus the resisting force of the pipe material and backfill are examined. The use and limitations of the Battelle two-curve method as the standard model are compared with new developments utilizing crack-tip opening angle and other techniques. The methodology and reasoning used to specify the material properties for line pipe are described and the inherent limits and risks are discussed. The applicability of Charpy energy to predict ductile arrest in high strength pipes (X80 and above) is examined.

Brittle Fracture Arrest in High Charpy Energy Steels: Comparisons With Some Existing Data

2014 ◽  
Author(s):  
G. Wilkowski ◽  
D-J. Shim ◽  
Y. Hioe ◽  
S. Kalyanam ◽  
M. Uddin
Keyword(s):  
Brittle Fracture ◽  
Pipe Steels ◽  
Shelf Energy ◽  
Line Pipe ◽  
Pipe Burst ◽  
Sensitivity Studies ◽  
Shear Area ◽  
Fracture Arrest ◽  
Pipeline Design ◽  
Very High

Current line-pipe steels have significantly higher Charpy upper-shelf energy than older steels. Many newer line-pipe steels have Charpy upper-shelf energy in the 300 to 500J range, while older line-pipe steels (pre-1970) had values between 30 and 60J. With this increased Charpy energy comes two different and important aspects of how to predict the brittle fracture arrestability for these new line-pipe steels. The first aspect of concern is that the very high Charpy energy in modern line-pipe steels frequently produces invalid results in the standard pressed-notch DWTT specimen. Various modified DWTT specimens have been used in an attempt to address the deficiencies seen in the PN-DWTT procedure. In examining fracture surfaces of various modified DWTT samples, it has been found that using the steady-state fracture regions with similitude to pipe burst test (regions with constant shear lips) rather than the entire API fracture area, results collapse to one shear area versus temperature curve for all the various DWTT specimens tested. Results for several different materials will be shown. The difficulty with this fracture surface evaluation is that frequently the standard pressed-notch DWTT only gives valid transitional fracture data up to about 20-percent shear area, and then suddenly goes to 100-percent shear area. The second aspect is that with the much higher Charpy energy, the pipe does not need as much shear area to arrest a brittle fracture. Some analyses of past pipe burst tests have been recently shown and some additional cases will be presented. This new brittle fracture arrest criterion means that one does not necessarily have to specify 85-percent shear area in the DWTT all the time, but the shear area needed for brittle fracture arrest depends on the pipeline design conditions (diameter, hoop stress) and the Charpy upper-shelf energy of the steel. Sensitivity studies and examples will be shown.

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