Analysis of HDPE Failure Data in Support of Development of Flaw Acceptance Criteria for Butt Fusion Joints

2020 ◽  
Author(s):  
Cheng Liu ◽  
Douglas Scarth ◽  
Douglas P. Munson ◽  
Ryan Wolfe
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Failure Time ◽  
Slow Crack Growth ◽  
Time To Failure ◽  
Acceptance Criteria ◽  
Failure Data ◽  
Criteria For Evaluation ◽  
Hdpe Pipes

Abstract There is a need for ASME B&PV Code procedures and acceptance criteria for evaluation of flaws detected by inspection of high density polyethylene (HDPE) piping items in safety Class 3 systems. To support the development of flaw acceptance criteria for butt fusion joints in HDPE pipes, a series of coupon tests have been completed for specimens cut from butt fused HDPE pipes with surface or subsurface flaws placed in the joints prior to fusion process. Specimens containing known flaw sizes were tested under axial load at accelerated stresses and temperatures until failure; or until a prescribed number of test hours was reached. The failure time from the tests has been correlated to the net section stress and the stress intensity factor, and the results showed that the failure time can be better represented by the stress intensity factor. The test results were then used to fit the Brown and Lu formula that predicts the time to failure due to the slow crack growth of flaws as a function of stress intensity factor and temperature. With the developed Brown and Lu equation, the allowable stress intensity factors for a piping lifetime of 50 years at the maximum code allowable temperature of 60°C have been proposed for both surface and subsurface flaws in HDPE butt fusion joints. Examples of what might be corresponding allowable flaw sizes in the butt fusion joints of piping are also provided.

Slow Crack Growth in Glasses and Ceramics Under Residual and Applied Stresses

1989 ◽  
Vol 111 (1) ◽  
pp. 61-67 ◽  
Author(s):  
F. Erdogan
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Threshold Value ◽  
Crack Arrest ◽  
Growing Crack ◽  
Applied Stresses

The problem of slow crack growth under residual stresses and externally applied loads in plates is considered. Even though the technique developed to treat the problem is quite general, in the solution given it is assumed that the plate contains a surface crack and the residual stresses are compressive near and at the surfaces and tensile in the interior. The crack would start growing subcritically when the stress intensity factor exceeds a threshold value. Initially the crack faces near the plate surface would remain closed. A crack-contact problem would, therefore, have to be solved to calculate the stress intensity factor. Depending on the relative magnitudes of the residual and applied stresses and the threshold and critical stress intensity factors, the subcritically growing crack would either be arrested or become unstable. The problem is solved and examples showing the time to crack arrest or failure are discussed.

Time-Dependent Fracture of Polyimide Films

1993 ◽  
Vol 115 (3) ◽  
pp. 264-269 ◽  
Author(s):  
S. F. Popelar ◽  
C. H. Popelar ◽  
V. H. Kenner
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Practical Implication ◽  
Slow Crack Growth ◽  
Polymeric Materials ◽  
Polyimide Films ◽  
Test Protocol ◽  
Fracture Tests

A fracture mechanics approach for quantifying slow crack growth in thin polyimide films and assessing their structural integrity and life expectancy is presented. The methodology and techniques developed in this investigation may also be applied to other polymeric materials. A test protocol for studying slow crack growth is described. Room temperature fracture tests were performed and an analysis model was developed and validated to analyze the fracture tests. Correlations between the rate of crack growth and the crack driving force as measured by the stress intensity factor were made and contrasted for Kapton 100HN, 300H and 500HN polyimide films. The crack growth rate was found to depend very strongly upon the stress intensity factor. The practical implication of this finding is that the fracture of these polyimide films may be approximated as being controlled by a critical value of the stress intensity factor.

Assessment of Slow Crack Growth Test Methodologies Used to Predict Service Life of High Density Polyethylene Piping

2013 ◽  
Author(s):  
S. Kalyanam ◽  
P. Krishnaswamy ◽  
D.-J. Shim ◽  
Y. Hioe ◽  
S. Kawaguchi ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Service Life ◽  
Intensity Factor ◽  
Crack Growth ◽  
Failure Modes ◽  
Slow Crack Growth ◽  
Failure Times ◽  
Hdpe Pipe ◽  
T Stress

HDPE pipe and piping components have been used successfully and safely for natural gas distribution around the world for several decades. The primary concerns for a 50-year life for buried HDPE piping involves designing against three primary failure modes — ductile fracture, rapid crack propagation (RCP), and slow crack growth (SCG) under sustained pressure loading. Although design methodologies for preventing ductile fracture, and RCP are well established, SCG remains to be a limiting failure mode in determining useful service life of HDPE piping as it may occur under sustained pressure and temperature. Although considerable amount of research has been conducted over the last two decades, SCG still remains less well understood than other failure modes. A critical evaluation of various test methodologies available to determine the SCG resistance of HDPE resins was conducted using FEA of various widely used laboratory test specimens. While there exist extensive information on the test methodologies and the applicability of each of the SCG testing methods, there is a growing concern as to whether any/all of these SCG tests give the same information akin to the industrial pipe application, particularly so when conflicting messages are obtained from time to failure predictions from two different SCG tests. While notched-pipe test (NPT) proves to be a direct approach to assess SCG resistance of the PE pipe with the use of temperature as a test accelerating factor; in the case of newer grade PE resins, the failure time of NPT can still be considerably large (∼5,000 to 10,000 hours). For this reason, some of the other coupon SCG tests are focus of recent investigations and especially sought after for rapid ranking/assessment of resins and understanding the manufactured HDPE pipe performance. In this study, FEA was conducted to facilitate a direct comparison of leading SCG test methods, through determination of both the stress intensity factor, KI, and existing constraint factors in various widely used specimen geometries. These results are then compared to pipe specimen with an OD (outer diameter) or ID (inner diameter) surface notch. Since, constraint can have a significant role in SCG initiation, T-stress, and biaxiality ratios (β), these were compared along the crack fronts to arrive at definitive reasons for the smaller failure times observed when testing some of the SCG test specimens, and also reasons for SCG mode of failure observed even under large applied loads (large KI compared to that in a notched pipe) when testing some of the SCG test specimens. The use of stress intensity factor, KI, along with the T-stress and biaxiality ratio (β), is found to provide a complete picture on the broad spectrum of failure times observed from various SCG test specimens and rationale for choosing a SCG test specimen when evaluating HDPE pipe or resins.

Numerical Analysis of Crack Propagation in Cyclic-Loaded Structures

1967 ◽  
Vol 89 (3) ◽  
pp. 459-463 ◽  
Author(s):  
R. G. Forman ◽  
V. E. Kearney ◽  
R. M. Engle
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Propagation ◽  
Crack Extension ◽  
Load Ratio ◽  
Stress Intensity Factor Range ◽  
Time To Failure ◽  
Excellent Correlation ◽  
Extensive Experimental Data

An improved theory is proposed for the crack-growth analysis of cyclic-loaded structures. The theory assumes that the crack tip stress-intensity-factor range, ΔK, is the controlling variable for analyzing crack-extension rates. The new theory, however, takes into account the load ratio, R, and the instability when the stress-intensity factor approaches the fracture toughness of the material, Kc. Excellent correlation is found between the theory and extensive experimental data. A computer program has been developed using the new theory to analyze the crack propagation and time to failure for cyclic-loaded structures.

Failure by stress corrosion of bundles of fibres

1981 ◽  
Vol 374 (1759) ◽  
pp. 475-489 ◽  
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Corrosion ◽  
Applied Load ◽  
Time To Failure ◽  
Corrosive Environment ◽  
Dominant Feature ◽  
Rate Of Failure ◽  
Two Parameter

Bundles of fibres loaded from their ends and immersed in a corrosive environment show times to failure that are extremely sensitive to the value of the applied load. This behaviour is accounted for by using the empirically established relation between rate of crack growth ( v ) and stress intensity-factor ( K I ) found for many brittle materials ( v ∝ K n 1 ) and by using a two-parameter Weibull distribution for the initial lengths of the cracks in the fibres. The theory accounts well for the time to failure of the bundle and for the rate of failure of individual filaments during stress corrosion. The dominant feature of the results is that time to failure depends on applied load to the power – n .

Slow crack-growth behavior of alumina ceramics

2000 ◽  
Vol 15 (1) ◽  
pp. 142-147 ◽  
Author(s):  
M. E. Ebrahimi ◽  
J. Chevalier ◽  
G. Fantozzi
Keyword(s):  
Stress Intensity Factor ◽  
Grain Size ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Crack Velocity ◽  
Slow Crack Growth ◽  
Velocity Versus ◽  
Water Molecules ◽  
Alumina Ceramics

The fracture behavior of high-purity alumina ceramics with grain sizes ranging from 2 to 13 μm is studied by means of the double torsion method. Crack-propagation tests conducted in air, water, and silicon oil, for crack velocities from 10−7 to 10−2 m/s, show that slow crack growth is due to stress corrosion by water molecules. An increase of the grain size leads to enhanced crack resistance, which is indicated by a shift of the V–KI (crack velocity versus applied stress intensity factor) plot toward high values of KI. Moreover, the slope of the curve is apparently higher for coarse grain alumina. However, if the R-curve effect is substracted from the experimental results, a unique V–KItip (crack velocity versus stress intensity factor at the crack tip) law is obtained for all alumina ceramics, independently of the grain size. This means that the crack-growth mechanism (stress corrosion by water molecules) is the same and that the apparent change of the V–KI law with grain size is a direct effect of crack bridging.

Multiscale thermodynamic analysis on hydrogen-induced intergranular cracking in an alloy steel with segregated solutes

2015 ◽  
Vol 33 (6) ◽  
pp. 547-557 ◽  
Author(s):  
Masatake Yamaguchi ◽  
Ken-ichi Ebihara ◽  
Mitsuhiro Itakura
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Slow Crack Growth ◽  
High Strength Steels ◽  
High Strength ◽  
Intergranular Cracking ◽  
Fracture Surfaces ◽  
Mobile Hydrogen ◽  
Threshold Stress Intensity Factor

AbstractA multiscale analysis has been conducted on hydrogen-induced intergranular cracking at ambient temperature in medium strength (840 MPa) Ni-Cr steel with antimony, tin, and phosphorous segregation. Combining first-principles calculations and fracture mechanics experiments, a multiscale relationship between threshold stress intensity factor (Kth) and cohesive energy of grain boundary (the ideal work of interfacial separation, 2γint) was revealed. The Kth was found to decrease rapidly under a certain threshold of 2γint, where the 2γint decreases mainly by mobile hydrogen segregation on fracture surfaces. This segregation is considered to arise during formation of the fracture surfaces under thermodynamic equilibrium in slow crack growth. The resulting strong decohesion probably makes it difficult to emit dislocations at the microcrack tip region, leading to a large reduction in stress intensity factor. Our analysis based on this mobile hydrogen decohesion demonstrates that the Kth decreases dramatically within a low and narrow range of hydrogen content in iron lattice in high-strength steels.

Crack Growth Resistance of Carbide Reinforced Composite Ceramics Based on Alumina

2009 ◽  
Vol 409 ◽  
pp. 231-236
Author(s):  
Magdalena Szutkowska ◽  
Marek Boniecki
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Length ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Crack Growth Resistance ◽  
Bending Test ◽  
Special Device ◽  
Three Point Bending

The relationship of KR versus crack length c (R curve) for Al2O3-30wt.% Ti(C,N).and for comparison alumina ceramics has been examined. The R-curve has been evaluated using pronounced long-crack formed during the three point bending (3PB) of the double edge notched beam. A combination of in situ microscopic crack growth observation and mechanical testing enabled measurement of crack growth resistance curves. The special device consisting of light microscope coupled with CCD camera, was fitted to Zwick 1446 testing machine. These observations reveal the existence of flat R-curve for Al2O3-30wt.% Ti(CN) and increasing R-curve for pure alumina. A study of slow-crack-growth (SCG) in tested materials was carried. The load-relaxation technique was used for observation at slow-crack-growth. The crack length was evaluated by linear-elastic analysis from the compliance of single-edge-notched specimen in three-point bending test. Parameters of stable crack growth n and logA, work-of fracture (WOF), stress intensity factor at the moment of crack initiation KI0 and maximum values of stress intensity factor KImax were determined. Mechanism of grain bridging responsible for occurrence of R-curve was observed by SEM and TEM.

Constraint Effects in Slow Crack Growth Test Methods for Service Life Prediction of High Density Polyethylene Piping

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
S. Kalyanam ◽  
P. Krishnaswamy ◽  
D.-J. Shim ◽  
Y. Hioe ◽  
S. Kawaguchi ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
High Density Polyethylene ◽  
Failure Modes ◽  
Slow Crack Growth ◽  
Test Methods ◽  
Failure Times ◽  
Hdpe Pipe ◽  
T Stress

Abstract High-density polyethylene (HDPE) pipe and piping components have been used successfully and safely for natural gas distribution around the world for several decades. The primary concerns for a 50-year life for buried HDPE piping involves designing against three primary failure modes—ductile fracture, rapid crack propagation (RCP), and slow crack growth (SCG) under sustained pressure loading. Although, design methodologies for preventing ductile fracture and RCP are well established, SCG remains to be a limiting failure mode in determining useful service life of HDPE piping as it may occur under sustained pressure and temperature. Although considerable amount of research has been conducted over the last two decades, SCG still remains less well understood than other failure modes. A critical evaluation of various test methodologies available to determine the SCG resistance of HDPE resins was conducted using finite element analysis (FEA) of various widely used laboratory test specimens. While there exist extensive information on the test methodologies and the applicability of each of the SCG testing methods, there is a growing concern as to whether any/all of these SCG tests give the same information akin to the industrial pipe application, particularly so when conflicting messages are obtained from time to failure predictions from two different SCG tests. While notched-pipe test (NPT) proves to be a direct approach to assess SCG resistance of the polyethylene (PE) pipe with the use of temperature as a test accelerating factor; in the case of newer grade PE resins, the failure time of NPT can still be considerably large (∼5000 to 10,000 h). For this reason, some of the other coupon SCG tests are focus of recent investigations and especially sought after for rapid ranking/assessment of resins and understanding the manufactured HDPE pipe performance. In this study, FEA was conducted to facilitate a direct comparison of leading SCG test methods, through determination of both the stress intensity factor, KI, and existing constraint factors in various widely used specimen geometries. These results are then compared to pipe specimen with an outer diameter (OD) or inner diameter (ID) surface notch. Since, constraint can have a significant role in SCG initiation, transverse/constraint stress (T-stress), and biaxiality ratios (β), these were compared along the crack fronts to arrive at definitive reasons for the smaller failure times observed when testing some of the SCG test specimens, and also reasons for SCG mode of failure observed even under large applied loads (large KI compared to that in a notched pipe) when testing some of the SCG test specimens. The use of stress intensity factor, KI, along with the T-stress and biaxiality ratio (β), was found to provide a complete picture on the broad spectrum of failure times observed from various SCG test specimens, and rationale for choosing a SCG test specimen when evaluating HDPE pipe or resins.

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