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.

Prediction of the Remaining Life of High-Temperature/Pressure Reactors Made of Cr-Mo Steels

1985 ◽  
Vol 107 (3) ◽  
pp. 230-238 ◽  
Author(s):  
T. Iwadate ◽  
J. Watanabe ◽  
Y. Tanaka
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Prediction Model ◽  
Crack Growth ◽  
Life Prediction ◽  
Temper Embrittlement ◽  
Pressure Vessels ◽  
Remaining Life ◽  
Life Prediction Model

The Cr-Mo steels widely used for pressure vessels have a potential for temper embrittlement. Therefore, embrittlement during long-term service is expected, and it leads to the decrease of the critical flaw size of brittle fracture and/or to the reduction of the remaining life of a pressure vessel. In this paper, the concept of a remaining life prediction model is presented. And also, experimental data on the temper embrittlement and fracture toughness after long-term exposure and sub-critical crack growth rate, such as creep crack growth rate, were collected, and the data were analyzed for use in the remaining life prediction model. Examples of the remaining life prediction of a 2 1/4 Cr-1Mo steel hydrogenation reactor and a 1 1/4Cr-1/2Mo steel catalytic reforming reactor were calculated from the statistical data base.

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.

The Impact of Pressure Fluctuations on the Early Onset of Stage II Growth of High pH Stress Corrosion Crack

2020 ◽  
Author(s):  
Hamid Niazi ◽  
Hao Zhang ◽  
Lyndon Lamborn ◽  
Weixing Chen
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Stress Corrosion ◽  
Crack Growth ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Crack Size ◽  
Stage I ◽  
Stage Ii ◽  
R Ratio

Abstract Steel pipelines undergo the following sequential stages prior to high pH stress corrosion cracking (HpHSCC) failure, viz., formation of environmental condition, initiation of the intergranular cracks followed by cracks coalescence to form critical crack size (Stage I), mechanically dictated crack growth with higher rate (Stage II) compared to Stage I, rapid crack propagation to failure (Stage III). From fracture mechanics perspective, the crack size reaches the critical value at the onset of stage II; consequently, stress intensity factor (K) ahead of the crack tip exceed the critical value (KISCC). Although many researches have been devoted to understanding HpHSCC behavior, the mechanical conditions that accelerate the onset of stage II remains unknown. This study investigates the mechanical loading conditions that yield to early onset of stage II with respect to the most severe loading condition in operating pipeline, underload-minor-cycle type of pressure fluctuation. In this study, several loading scenarios were applied to pre-cracked CT specimens exposed to 1 N NaHCO3-1N Na2CO3 at 40° C and −590 mVSCE. The first series of tests were conducted through applying variable amplitude loading waveforms to determine the K value below the KISCC. It was observed the crack growth rate decreases from 1.5 × 10−7 mm/s to 2.5 × 10−8 mm/s when Kmax decreases from 36 to 15 MPa·m0.5. Then, both constant amplitude and variable amplitude loading scenarios with the Kmax = 15 MPa·m0.5 were applied to pre-cracked CT specimens. It was observed that low R-ratio constant amplitude cycles yield to highest crack growth rate (3.6 × 10−7 mm/s), which was one order of magnitude higher than other waveforms. However, comparing the intergranular crack advancement per block resulted in similar crack growth rates for those waveforms containing low R-ratio cycles. These results imply that stage I of crack growth is assisted by fatigue due to low R-ratio cycles. It was observed that loading/unloading frequency of low R-ratio cycles has a direct relation with crack growth rate at stage I, i.e., high frequency cycles accelerate onset of stage II. The implication of these results for pipeline operator is that pressure fluctuation, particularly large and rapid pressure fluctuation at the sites susceptible to HpHSCC, threatens the pipeline integrity. Avoiding such pressure fluctuations, if possible, increase pipeline lifespan and prevents catastrophic damages by intergranular stress corrosion crack growth through delaying the onset of stage II of HpHSCC crack growth.

Rainflow-on-the-Fly Methodology: Fatigue-Crack Growth under Aircraft Spectrum Loading

2014 ◽  
Vol 891-892 ◽  
pp. 771-776 ◽  
Author(s):  
James C. Newman
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Life Prediction ◽  
Constraint Factor ◽  
Wide Range ◽  
Reduction Methods ◽  
Twist Level ◽  
Life Predictions ◽  
Spectrum Loading

Crack-growth-rate tests were conducted on compact, C(T), specimens made of 7075-T7351 aluminum alloy over a wide range of constant-amplitude loading (R = Pmin/Pmax = 0.1 to 0.9) to establish the baseline crack-growth-rate curve for life-prediction analyses. Both compression precracking and load-reduction methods were used. A crack-closure analysis was used to collapse the ΔKeff-rate data into a fairly narrow band over many orders of magnitude in rates using an appropriate plane-strain constraint factor. Life predictions were made on C(T) specimens using the FASTRAN Version 5.42 life-prediction code. Some improvements had been made in the code and the predictions were made under cycle-by-cycle simulations. Life predictions under Christmas-Tree-type loading using the rainflow-on-the-fly methodology were very good. And the predicted results on three different aircraft spectrum loading histories (a modified Falstaff, modified Mini-TWIST (Level III), and a modified Wing-Gust-Maneuver spectrum), agreed to within 20% of the test data.

Technical Basis for Revised Reference Crack Growth Rate Curves for Pressure Boundary Steels in LWR Environment

1980 ◽  
Vol 102 (4) ◽  
pp. 433-442 ◽  
Author(s):  
W. H. Bamford
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Maximum Load ◽  
Reference Curve ◽  
The Past ◽  
R Ratio ◽  
Pressure Vessel Steels ◽  
Reference Curves ◽  
Technical Basis

Reference fatigue crack growth rate curves have been contained in Appendix A of Section XI since its inception. The curves have been designed to be applicable to carbon and low alloy pressure vessel steels exposed to either air or light water reactor coolant environments. Data obtained over the past several years have shown a different behavior of these steels in the LWR environment than that predicted by the present reference curve. A revised set of reference curves have been formulated, incorporating a new curve shape as well as a dependency of growth rate on R ratio (minimum load/maximum load). This article provides the background and justification for such a revision, details the methodology used to develop the revised curves, and includes an evaluation of the adequacy and impact of the revised curves as compared with the single curve which they replace.

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