Depressurization-Induced Crack Growth Enhancement for Pipeline Steels Exposed to Near-Neutral pH Environments

2014 ◽  
Author(s):  
Mengshan Yu ◽  
Weixing Chen ◽  
Richard Kania ◽  
Greg Van Boven ◽  
Jenny Been
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Pressure Fluctuations ◽  
Loading Frequency ◽  
Constant Amplitude ◽  
Growth Mechanisms ◽  
Pipeline Steels ◽  
Neutral Ph ◽  
Loading Scheme

Pressure fluctuations are recognized as the driving force for the crack growth of pipeline steels in near-neutral pH environments; however, the crack growth mechanisms are still not fully understood. Difficulty in understanding the crack growth mechanisms is present due to two dilemmas between laboratory testing and field findings: high frequency study in the laboratory versus low frequency pressure fluctuations in the field; constant amplitude cyclic laboratory tests versus random pressure fluctuations in the actual spectra. To bridge the dilemmas, the crack growth behavior of X60 pipeline steel was investigated in near-neutral pH solution at frequencies as low as 1×10−5 Hz under variable amplitude cyclic loading. Special attention was given to the loading scheme consisting of minor cycles with R ratios (minimum stress/maximum stress) as high as 0.9 and underloads with a relatively lower R ratio of 0.5. It was found that the constant amplitude crack growth rate in near-neutral pH solution in the frequency region below 1×10−3 Hz decreases with decreasing loading frequency, and it reaches a constant value at very low frequencies. This crack growth rate-frequency relation is opposite of that found in the high loading-frequency regime, where crack growth rate was found to increase with decreasing loading frequency. Crack growth rate was observed to increase by a factor of up to 10 when the underload plus minor cycle loading scheme, as mentioned previously, was applied. Based on the findings obtained from the investigation, recommendations of pressure control were also made to minimize the crack growth during pipeline operation.

Application of Load Sequence to Control Crack Growth in Steel Pipelines Under Near Neutral pH SCC

2016 ◽  
Author(s):  
Olayinka Tehinse ◽  
Weixing Chen ◽  
Jenny Been ◽  
Karina Chevil ◽  
Sean Keane ◽  
...  
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Oil And Gas ◽  
Pressure Fluctuations ◽  
Operating Pressure ◽  
Variable Amplitude ◽  
Neutral Ph ◽  
Novel Approach ◽  
Load Sequence

Pipelines are designed to operate below a maximum operating pressure in service. However, there are pressure fluctuations during operation. The presence of pressure fluctuations creates a drive for crack growth in steel pipes. In order to prevent catastrophic failure of pipelines, there is need for better understanding of the contribution of pressure fluctuations to crack growth rate in steel pipelines. Analysis of pressure fluctuation data in oil and gas pipelines shows that there are different types of fluctuations in a pipe due to friction loss with distance from the pump or compressor station. All these fluctuation types show a form of variable amplitude loading classified in this research as underload, mean load and overload. Studies of some structural systems shows that underload can cause acceleration of crack growth while retardation of crack growth is observed after an overload. This research aims to apply pressure fluctuations to manage integrity of steel pipelines through a novel approach of load sequence involving underload and overload in near neutral pH environment. Clear knowledge of the effect of load interaction involving load sequence of underload and overload is vital to control crack growth in steel pipelines under near neutral pH environment. The result of crack growth rate under different load sequence on X65 steel indicate that increase in overload ratio of 2, 3 and 4 caused an increase in crack growth rate of 1.68E−3, 1.89E−3 and 2.31E−3 mm/block respectively. These results are compared with results from other tests under variable amplitude without load sequence. Analyses were carried out on the morphology of the crack tip and the fracture surface after the test.

Fatigue Crack Growth of Alloy 7050-T7451 Plate in L-S Orientation

2012 ◽  
Vol 525-526 ◽  
pp. 221-224
Author(s):  
Rui Bao ◽  
Xiao Chen Zhao ◽  
Ting Zhang ◽  
Jian Yu Zhang
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Growth Characteristics ◽  
Stress Intensity Factor Range ◽  
Constant Amplitude ◽  
Stress Ratios

Experiments have been conducted to investigate the crack growth characteristics of 7050-T7451 aluminium plate in L-S orientation. Two loading conditions are selected, i.e. constant amplitude and constant stress intensity factor range (ΔK). The effects of ΔK-levels and stress ratios (R) on crack splitting are studied. Test data shows that crack splitting could result in the reverse of crack growth rate trend with the increasing R ratio at high ΔK-level. The appearance of crack splitting depends on both ΔK and R.

Effects of a Single Overload on Fatigue Crack Growth of Type 316 Stainless Steel

2021 ◽  
Author(s):  
Koji Miyoshi ◽  
Masayuki Kamaya
Keyword(s):  
Growth Rate ◽  
Stainless Steel ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Opening ◽  
Constant Amplitude ◽  
Single Overload ◽  
Tensile Overload

Abstract The effect of a single overload on the fatigue crack growth rate was investigated for Type 316 stainless steel. Fatigue crack growth tests were conducted by controlling strain and load. Tensile and compressive overloads were applied during constant amplitude cycling. The overload ratio, which was defined as the ratio of overload size to baseline constant amplitude, was also changed. The constant amplitude tests were conducted at the strain or the stress ratio of −1.0 which was defined as the ratio of the minimum value to the maximum value. The crack opening point was obtained by the unloading elastic compliance method. The crack growth rate increased after the single compressive overload. The accelerating rate increased with the overload ratio. In contrast, not only the acceleration but also the retardation of the crack growth rate was observed for some tensile overload cases. The crack growth rate increased for relatively small tensile overload cases and decreased for relatively large tensile overload cases. The change in the crack opening level was examined. The crack growth rates after tensile and compressive single overloads correlated with the effective strain and stress intensity factor ranges both for load and strain controlling modes.

The Effect of Crack Growth Retardation when Comparing Constant Amplitude to Variable Amplitude Loading in an Aluminium Alloy

2014 ◽  
Vol 891-892 ◽  
pp. 948-954 ◽  
Author(s):  
Madeleine Burchill ◽  
Simon A. Barter ◽  
Michael Jones
Keyword(s):  
Growth Rate ◽  
Fatigue Life ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Growth Retardation ◽  
Crack Front ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Growth Increments ◽  
Crack Growth Retardation

It has often been observed that the growth of short fatigue cracks under variable amplitude (VA) cyclic loading is not well predicted when utilising standard constant amplitude (CA) crack growth rate/stress intensity data (da/dN v DK). This paper outlines a coupon fatigue test program and analyses, investigating a possible cause of crack growth retardation from CA-only testing. Various test loading spectra were developed with sub-blocks of VA and CA cycles, then using quantitative fractography (QF) the sub-block crack growth increments were measured. Comparison of these results found that, after establishing a consistent uniform crack front using a VA load sequence, the average crack growth rate then progressively slowed down with the number of subsequent CA load cycles applied. Further fractographic investigation of the fracture surface at the end of each CA and VA sub-block crack growth, identified significant crack front morphology differences. Thus it is postulated that a variation or deviation from an efficient crack path is a driver of local retardation in short crack growth during CA loading. This may be a source of error in analytical predictions of crack growth under VA spectra loading that may need to be considered in addition to other potential effects such asless closure whilst cracks are small. For aircraft designers, using solely CA data for fatigue life predictions this may result in non-conservative estimates of total crack fatigue life, producing unexpected failures or an increased maintenance burden.

Development and Validation of Load-Interaction Based Models for Crack Growth Prediction

2014 ◽  
Author(s):  
Jiaxi Zhao ◽  
Weixing Chen ◽  
Sean Keane ◽  
Jenny Been ◽  
Greg Van Boven
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Life Prediction ◽  
Pressure Fluctuations ◽  
Remaining Life ◽  
The Past ◽  
Oil Pipelines ◽  
Rainflow Counting ◽  
Development And Validation

This investigation primarily focused on the validation of the software being developed for crack growth and remaining life prediction using SCADA data. A total of nine pressure spectra, four for oil pipelines and five for gas pipelines, have been collected and used as inputs for the software. It was found that these spectra could be categorized as the underload-, the meanload- and the overload-dominant spectra; each of them have shown different effects on crack growth: the underload spectra, typical of pressure fluctuations at the discharging sites, are most susceptible to crack growth because of load interactions between the minor pressure fluctuations and the unload cycles; while the overload spectra, often found at the suction site, have exhibited retarded crack growth due to the retardation effects caused by overloading. The relative severity of the load interactions in terms of crack growth rate for a given spectrum was quantified using a parameter termed as the Spectrum Factor. A Spectrum Factor greater than one indicates the enhanced crack growth rate by load interactions, such as the case where unloading is frequently present in the pressure spectra, while a Spectrum Factor lower than one may be associated with a retarded crack growth, which can be seen in pressure spectra with predominant overloading events. The predictions made by the models being developed were also compared with those made by the rainflow counting method. The software allows for the SCADA/pressure fluctuation data, in excel spreadsheet format, to be directly analyzed producing a projected remaining life of the pipeline based on the past pressure fluctuations and the assumed future pressure fluctuations.

Characterization of Precipitates and Formed Oxides in Fatigue Crack of Alloy 617 in a Steam Environment at 750°C

2020 ◽  
Author(s):  
Masumi Yoshida ◽  
Kosuke Araki ◽  
Yoichi Takeda ◽  
Susumu Nakano
Keyword(s):  
Power Generation ◽  
Growth Rate ◽  
Fatigue Crack ◽  
High Temperature ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Thermal Power ◽  
Crack Tip ◽  
Loading Frequency ◽  
Alloy 617

Abstract Alloy 617 is a Ni-base superalloy and is a candidate material for high temperature steam piping systems and casings for advanced ultra-supercritical power generation technology because of its excellent high temperature creep strength. It is expected in the near future that the installation of variable renewable energies with large output fluctuations will increase. Therefore, adjusting the supply and demand of electricity is requested for thermal power generation. This leads to the issue of fatigue damage caused by repeated thermal stress due to the startup and shutdown procedures. It was reported that the fatigue crack growth of alloy 617 changed from transgranular to intergranular at 750°C, with a decreasing loading frequency in a steam environment. It was also indicated that the increase in the crack growth rate in lower loading frequency conditions; however, the specific acceleration mechanism governing the crack growth has not been elucidated. In this study, morphology of oxide and precipitates at fatigue crack tip region were analyzed by transmission electron microscope. All of examined crack tip were filled with oxides. Especially, the double layered oxide film was formed in the crack tip which propagated under the lower loading frequencies. In addition, unoxidized precipitates mainly consisting of Mo and Co were observed in the intergranular cracks. It was suggested that the changes in the oxidation morphologies depending on the loading frequency influenced the crack growth rate.

Reliability Analysis of Corrosion Fatigue Crack Growth for 2024-T3 Aluminum Alloy

2008 ◽  
Vol 44-46 ◽  
pp. 105-110
Author(s):  
Sen Ge ◽  
Zhong Li ◽  
J.G. Zhang ◽  
Y.C. Xiao ◽  
G.Q. Liu ◽  
...  
Keyword(s):  
Growth Rate ◽  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Reliability Analysis ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Loading Frequency ◽  
Corrosive Environment

Fatigue crack growth rate experiments of center-cracked tension (CCT) specimens of the 2024-T3 aluminum alloy under constant-amplitude load in corrosive environment are carried out with 3 kinds of loading frequency. The fatigue crack growth rates in 3.5% NaCl solution are obtained by using seven-point incremental polynomial method. A probabilistic approach is presented for fatigue crack growth rate in corrosive environment with log-normal random variable model. The reliability analysis of crack propagation is conducted based on the experimental data. The crack exceedance probability at given service time and the distribution of the service time at given crack size are obtained by using the reliability analysis approach. The effect of loading frequency on crack propagation is studied. It is shown that the fatigue crack growth rate is increasing with loading frequency decreasing in corrosive environment. The predicted results by the presented method match the experimental results very well.

A Fatigue Crack Growth Model for Single Overload Tests

1994 ◽  
Vol 116 (2) ◽  
pp. 168-172 ◽  
Author(s):  
H. S. Goel ◽  
Satish Chand
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Functional Form ◽  
Rate Model ◽  
Constant Amplitude ◽  
Single Overload ◽  
Load Tests ◽  
Plastic Zones ◽  
Crack Growth Model

Crack growth rate experiments are conducted by applying an intermediate single overload cycle in constant amplitude load (CAL) tests. For a particular overload ratio, three to four tests are conducted by applying the overload cycle at different crack lengths. The loads are selected in such a way that for a given overload ratio, the size of the overload and CAL monotonic plastic zones are the same at each crack length. A functional form for the crack growth during the retardation was developed that accurately describes all the tests. For comparison, the corresponding CA-load tests are also conducted separately. Finally, a crack growth rate model is developed.

The Study of Fatigue Crack Growth of 304SS with the Influence of Loading Frequency and Temperature

2007 ◽  
Vol 120 ◽  
pp. 103-110
Author(s):  
Jien Jong Chen ◽  
Yan Shin Shih
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Austenitic Stainless Steels ◽  
Combined Effect ◽  
Loading Frequency ◽  
Mechanical Behaviors

James performed a series of experimental study on austenitic stainless steels and suggested an equation for assessing the influences of temperature, stress ratio and loading frequency on the fatigue crack growth rate. Authors have studied the effect of either loading frequency alone or of temperature alone on the fatigue crack growth rate by employing the mechanical behaviors of material. In this study, the mechanical behaviors of material are employed for evaluating the combined effect of loading frequency and temperature. Using the derived dimensionless functions of yielding stresses and Young’s modulus, the equation represented the combined effect of loading frequency and temperature on fatigue crack growth rate of 304SS was proposed.

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