The Effect of Microstructure on the Hydrogen-Assisted Fatigue of Pipeline Steels

2013 ◽  
Author(s):  
Andrew J. Slifka ◽  
Elizabeth S. Drexler ◽  
Douglas G. Stalheim ◽  
Robert L. Amaro ◽  
Damian S. Lauria ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
High Pressures ◽  
Load Ratio ◽  
Fatigue Tests ◽  
Hydrogen Gas ◽  
The Other ◽  
Stress Intensity Factor Range ◽  
Pipeline Steels

Tests on the fatigue crack growth rate were conducted on four pipeline steels, two of grade API 5L-X52 and two API 5L-X70. One X52 material was manufactured in the mid-1960s and the other was manufactured in 2011. The two X70 materials had a similar vintage and chemistry, but the microstructure differs. The fatigue tests were performed in 5.5 and 34 MPa pressurized hydrogen gas, at 1 Hz and (load ratio) R = 0.5. At high pressures of hydrogen and high values of the stress intensity factor range (ΔK) there is no difference in the fatigue crack growth rates (da/dN), regardless of strength or microstructure. At low values of ΔK, however, significant differences in the da/dN are observed. The older X52 material has a ferrite-pearlite microstructure; whereas, the modern X52 has a mixture of polygonal and acicular ferrites. The X70 materials are both predominantly polygonal ferrite, but one has small amounts (∼5%) of upper bainite, and the other has small amounts of pearlite (<2%) and acicular ferrite (∼5%). We discuss the fatigue test results with respect to the different microstructures, with particular emphasis on the low ΔK regime.

Summary of an ASME/DOT Project on Measurements of Fatigue Crack Growth Rate of Pipeline Steels

2014 ◽  
Author(s):  
Andrew J. Slifka ◽  
Elizabeth S. Drexler ◽  
Robert L. Amaro ◽  
Damian S. Lauria ◽  
Louis E. Hayden ◽  
...  
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Yield Strength ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Hydrogen Gas ◽  
Lessons Learned ◽  
Pipeline Steels

The National Institute of Standards and Technology has been testing pipeline steels for about 3 years to determine the fatigue crack growth rate in pressurized hydrogen gas; the project was sponsored by the Department of Transportation, and was conducted in close collaboration with ASME B31.12 Committee on Hydrogen Piping and Pipelines. Four steels were selected, two X52 and two X70 alloys. Other variables included hydrogen gas pressures of 5.5 MPa and 34 MPa, a load ratio, R, of 0.5, and cyclic loading frequencies of 1 Hz, 0.1 Hz, and a few tests at 0.01 Hz. Of particular interest to ASME and DOT was whether the X70 materials would exhibit higher fatigue crack growth rates than the X52 materials. API steels are designated based on yield strength and monotonic tensile tests have historically shown that loss of ductility correlates with increase in yield strength. The X70 materials performed on par with the X52 materials in fatigue. The test matrix, the overall set of data, implications for the future, and lessons learned during the 3-year extensive test program will be discussed.

A Two-Parameter Fatigue Crack Growth Correlation Using ΔK and KMAX Parameters

2014 ◽  
Author(s):  
Phani C. R. Sree ◽  
Daniel Kujawski
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Master Curve ◽  
Load Ratio ◽  
Single Equation ◽  
The Other ◽  
Method Of Correlation ◽  
Two Parameter ◽  
Dominant Influence

The paper presents a correlation of fatigue crack growth rate (FCGR) behavior for different load ratios R (= min load/max load). The proposed method of correlation is explained in detail using comprehensive experimental FCGR data from 2524 aluminum alloy. The consistency of the proposed method has been verified using test data taken from literature for more than 10 different materials including aluminum, steel, titanium and other alloys. For all the materials studied, a transition load ratio Rt was found, which marks the transition between a dominant influence of ΔK or Kmax on FCGR behavior. For R>Rt the FCGR is dominated by ΔK. On the other hand, for R<Rt it is found that Kmax is to be the dominating parameter. Two equations, in terms of ΔK or Kmax, have been developed to represent FCGR curves for various load ratios. ΔKdriving is used to represent FCGR behavior for R>Rt and Kmax driving for R<Rt. The study reveals that the FCGR curves for different R-ratios can be collapsed into two narrow scatter bands, where each band is influence by either ΔK or Kmax. The final correlation was further simplified to a single equation, which represents “the master curve” corresponding to the transition load ratio, Rt. Thus by knowing FCGR data for one load ratio and using the proposed method, FCGR curves for any other load ratio may be predicted within a narrow scatter band.

scholarly journals Measurement of Fatigue Crack Growth Relationships in Hydrogen Gas for Pressure Swing Adsorber Vessel Steels

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Brian P. Somerday ◽  
Monica Barney
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Load Cycle ◽  
Hydrogen Gas ◽  
Stress Intensity Factor Range ◽  
Cycle Frequency ◽  
Pressure Swing ◽  
Crack Growth Rates

Hydrogen-assisted fatigue crack growth rates (da/dN) were measured for SA516 Grade 70 steel as a function of stress-intensity factor range (ΔK) and load-cycle frequency to provide life-prediction data relevant to pressure swing adsorber (PSA) vessels. For ΔK values up to 18.5 MPa m1/2, the baseline da/dN versus ΔK relationship measured at 1 Hz in 2.8 MPa hydrogen gas represents an upper bound with respect to crack growth rates measured at lower frequency. However, at higher ΔK values, baseline da/dN data must be corrected to account for modestly higher crack growth rates at the lower frequencies relevant to PSA vessel operation.

scholarly journals Fatigue Measurement of Pipeline Steels for the Application of Transporting Gaseous Hydrogen1

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Andrew J. Slifka ◽  
Elizabeth S. Drexler ◽  
Robert L. Amaro ◽  
Louis E. Hayden ◽  
Douglas G. Stalheim ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Yield Strength ◽  
Crack Growth ◽  
Upper Bound ◽  
American Petroleum Institute ◽  
Hydrogen Gas ◽  
Growth Data ◽  
Pipeline Steels ◽  
Code Modification

A comprehensive testing program to determine the fatigue crack growth rate (FCGR) of pipeline steels in pressurized hydrogen gas was completed. Four steels were selected, two X52 and two X70 alloys. Other variables included hydrogen gas pressures of 5.5 MPa and 34 MPa, a load ratio, R, of 0.5, and cyclic loading frequencies of 1 Hz, 0.1 Hz, and 0.01 Hz. Of particular interest was whether the X70 materials would exhibit higher FCGRs than the X52 materials. The American Petroleum Institute steel designations are based on specified minimum yield strength (SMYS), and monotonic tensile tests have historically shown that loss of ductility correlates with an increase in yield strength when tested in a hydrogen environment. The X70 materials performed within the experimental spread of the X52 materials in FCGR, except for the vintage X52 material at low (5.5 MPa) pressure in hydrogen gas. This program was developed in order to provide a modification to the ASME B31.12 code that is based upon fatigue, the primary failure mechanism in pipelines. The code modification is a three-part Paris law fit of the upper bound of measurements of FCGR of pipeline steels in pressurized hydrogen gas. Fatigue crack growth data up to 21 MPa (3000 psi) are used for the upper bound. This paper describes, in detail, the testing that formed the basis for the code modification.

Fatigue Crack Growth in an Al-Mg-Si Alloy under Negative Load Ratio

2017 ◽  
Vol 754 ◽  
pp. 43-46 ◽  
Author(s):  
Marcelo A.S. Torres ◽  
B.R.L. Silva ◽  
D.H.S. Costa ◽  
C.A.R.P. Baptista ◽  
V. Pastoukhov
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Life Prediction ◽  
Load Ratio ◽  
Propagation Rate ◽  
Stress Intensity Factor Range ◽  
Negative Part ◽  
Compressive Loads ◽  
Semi Empirical

The usual approaches for Fatigue Crack Growth (FCG) assessment are based on semi-empirical models that consider the stress intensity factor range of fracture mechanics, ΔK, as the governing driving force for crack propagation. However, FCG data incorporating compressive loads have brought discussions and controversies. The compressive loads are not taken into account in the usual life prediction codes and the negative portion of the loading cycle is neglected. In the present work, constant amplitude fatigue crack growth tests with load ratios-1 and 0 are performed, for two diferent stess levels, in AA 6005 alloy centre-notched middle tension M(T) specimens and the obtained results are discussed. It is shown that the crack closure concept, that usually work well for positive ratios, is not enough to satisfactorily explain the negative load ratio effects. The results also showed how the negative part of the load affected the propagation rate of the crack, mainly for larger cracks and smaller loads. Finally, it is shown that a previously proposed expression for the stress distribution ahead of the crack can shed some light on this question.

scholarly journals Oxygen Impurity Effects on Hydrogen Assisted Fatigue and Fracture of X100 Pipeline Steel

2018 ◽  
Author(s):  
Joseph Ronevich ◽  
Chris San Marchi ◽  
Robert Kolasinski ◽  
Konrad Thurmer ◽  
Norm Bartelt ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Pipeline Steel ◽  
Load Ratio ◽  
Hydrogen Gas ◽  
Mixed Gas ◽  
X100 Pipeline Steel ◽  
Crack Growth Rates

Hydrogen gas accelerates fatigue crack growth and reduces fracture toughness in ferritic structural materials such as pipelines and pressure vessels. The extent to which the crack growth rates are accelerated depends upon environment, mechanical loading conditions, and material. In this work, the effects of loading conditions and environment, specifically oxygen impurities, are examined on an X100 pipeline steel in high pressure hydrogen gas. Fatigue crack growth rates were measured in a gas mixture consisting of nominally 100 ppm O2 in a balance of H2 gas to evaluate the effects of pressure and load ratio (R-ratio) on the manifestation of hydrogen-accelerated fatigue crack growth (HA-FCG). Tests were performed at 21 MPa, 2.1 MPa, and 1.4 MPa and at load ratios of 0.5 and 0.1. The onset of HA-FCG was observed to be dependent on both absolute pressure and load ratio and it will be shown that a critical combination can result in complete mitigation of HA-FCG over the stress intensity factor range (ΔK) examined. Tests were predominantly performed at 10 Hz; however, a single test was performed at 1 Hz which exhibited negligible HA-FCG compared to a test at 10 Hz which did exhibit HA-FCG. Rising load fracture toughness tests were conducted via constant displacement rates to generate J-R curves in both pure H2 and 100 ppm O2 mixed gas. At similar absolute pressures, fracture toughness was measured to be greater in the 100 ppm O2 mixed gas compared to the pure H2. Hydrogen-assisted fracture was completely alleviated at pressures below 2.1 MPa in the 100 ppm O2 mixed gas, in which fracture toughness values were consistent with tests in air.

Influence of Cathodic and Internal Trapped Hydrogen on Fatigue Crack Growth in a NiCrMoV Structural Steel

1987 ◽  
Vol 109 (2) ◽  
pp. 119-123 ◽  
Author(s):  
A. Barbangelo
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Structural Steel ◽  
Crack Growth ◽  
Crack Tip ◽  
Plastic Zone Size ◽  
Fatigue Tests ◽  
Stress Intensity Factor Range ◽  
Austenite Grain Size ◽  
Electrolytic Hydrogen

Fatigue crack propagation has been investigated in a NiCrMoV structural steel in air or in electrolytic hydrogen charging environments. The behavior of this steel containing internal trapped hydrogen absorbed during the steelmaking processes was also considered. Hydrogen, both internal and adsorbed by the environment, causes accelerated crack growth over the entire stress-intensity factor range. As the loading conditions are varied, two different damage mechanisms, triggered by hydrogen, are observed, and are separated by a transition zone where the fatigue crack growth rate is constant. The results of the fatigue tests and of a fractographic analysis suggest that the phenomenon is controlled by the stress distribution at the crack tip, and that a transition occurs when the cyclic plastic zone size at the crack tip is larger than the prior austenite grain size.

scholarly journals Study on the Influence of the Gurson–Tvergaard–Needleman Damage Model on the Fatigue Crack Growth Rate

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1183
Author(s):  
Edmundo R. Sérgio ◽  
Fernando V. Antunes ◽  
Diogo M. Neto ◽  
Micael F. Borges
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Plastic Strain ◽  
Crack Growth ◽  
Damage Model ◽  
Crack Tip ◽  
Strength Parameter ◽  
Stress Intensity Factor Range

The fatigue crack growth (FCG) process is usually accessed through the stress intensity factor range, ΔK, which has some limitations. The cumulative plastic strain at the crack tip has provided results in good agreement with the experimental observations. Also, it allows understanding the crack tip phenomena leading to FCG. Plastic deformation inevitably leads to micro-porosity occurrence and damage accumulation, which can be evaluated with a damage model, such as Gurson–Tvergaard–Needleman (GTN). This study aims to access the influence of the GTN parameters, related to growth and nucleation of micro-voids, on the predicted crack growth rate. The results show the connection between the porosity values and the crack closure level. Although the effect of the porosity on the plastic strain, the predicted effect of the initial porosity on the predicted crack growth rate is small. The sensitivity analysis identified the nucleation amplitude and Tvergaard’s loss of strength parameter as the main factors, whose variation leads to larger changes in the crack growth rate.

Finite Element Simulation of Stable Fatigue Crack Growth Using Critical CTOD Determined by Preliminary Finite Element Analysis

2014 ◽  
Vol 891-892 ◽  
pp. 1675-1680
Author(s):  
Seok Jae Chu ◽  
Cong Hao Liu
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Finite Element Simulation ◽  
Crack Growth ◽  
Crack Tip ◽  
Stress Intensity Factor Range ◽  
Crack Tip Opening Displacement ◽  
Element Analysis ◽  
Element Simulation

Finite element simulation of stable fatigue crack growth using critical crack tip opening displacement (CTOD) was done. In the preliminary finite element simulation without crack growth, the critical CTOD was determined by monitoring the ratio between the displacement increments at the nodes above the crack tip and behind the crack tip in the neighborhood of the crack tip. The critical CTOD was determined as the vertical displacement at the node on the crack surface just behind the crack tip at the maximum ratio. In the main finite element simulation with crack growth, the crack growth rate with respect to the effective stress intensity factor range considering crack closure yielded more consistent result. The exponents m in the Paris law were determined.

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