Developing a Predictive Model of Near Neutral pH Stress Corrosion Cracking of Underground Pipelines

2012 ◽  
Author(s):  
Brett Conrad ◽  
Weixing Chen ◽  
Reg Eadie ◽  
Richard Kania ◽  
Greg Van Boven ◽  
...  
Keyword(s):  
Stress Corrosion ◽  
Predictive Model ◽  
Stress Corrosion Cracking ◽  
Field Data ◽  
Corrosion Cracking ◽  
Loading Conditions ◽  
Neutral Ph ◽  
Ph Stress ◽  
External Corrosion ◽  
The One

Near neutral pH Stress Corrosion Cracking (NNpHSCC) associated with external corrosion of pipelines is an issue facing industry today. Determining areas of NNpHSCC susceptibility is crucial to developing Integrity Management Programs and inspection dig schedules. This research involved collecting pertinent field data (inspection dig reports, failure reports, loading histories) and developing a predictive model to help identify areas and lines most susceptible to NNpHSCC. The predictive model focused on the loading history (in this case, SCADA data) patterns to classify different groups of loading conditions. Hydrogen has been identified and established in previous literature to be a major contributor to NNpHSCC. Different Hydrogen Enhancement Factors (HEF) were applied based on how the mechanisms of hydrogen embrittlement react to the respective loading conditions. The predictive model illustrated a dormancy behaviour, similar to the one seen in field conditions and a mechanically activated growth dependent on both hydrogen and previous loading scenarios. A correlation was shown between a limited field sampling and the predicted values. Further improvements and calibrations can be made with the gathering of more field data and continued experimental validation. Once this validation has been performed, this model has the possibility to illustrate what loading conditions increase a segments susceptibility to NNpHSCC.

Modeling the Interactions of Hydrogen, Stress and Dissolution in Near-Neutral pH Stress Corrosion Cracking of Pipelines

2006 ◽  
Author(s):  
Frank Y. Cheng
Keyword(s):  
Stress Corrosion ◽  
Dissolution Rate ◽  
Crack Growth ◽  
Anodic Dissolution ◽  
Hydrogen Concentration ◽  
Stress Corrosion Cracking ◽  
Crack Tip ◽  
Corrosion Cracking ◽  
Neutral Ph ◽  
Ph Stress

A thermodynamic model was developed to determine the interactions of hydrogen, stress and anodic dissolution at the crack-tip during near-neutral pH stress corrosion cracking in pipelines. By analyzing the free-energy of the steel in the presence and absence of hydrogen and stress, it is demonstrated that a synergism of hydrogen and stress promotes the cracking of the steel. The enhanced hydrogen concentration in the stressed steel significantly accelerates the crack growth. The quantitative prediction of the crack growth rate in near-neutral pH environment is based on the determination of the effect of hydrogen on the anodic dissolution rate in the absence of stress, the effect of stress on the anodic dissolution rate in the absence of hydrogen, the synergistic effect of hydrogen and stress on the anodic dissolution rate at the crack-tip and the effect of the variation of hydrogen concentration on the anodic dissolution rate.

SCC Inspection and Mitigation Program on Suncor OSPL Pipeline: Field Data Trends and Observations

2006 ◽  
Author(s):  
Robert Leeson ◽  
Derek K. Spitzmacher
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Field Data ◽  
Analysis Data ◽  
Corrosion Cracking ◽  
Metal Loss ◽  
Thin Wall ◽  
Neutral Ph ◽  
Pump Station ◽  
Short Period

This paper reviews a recent extensive Stress Corrosion Cracking (SCC) inspection and mitigation program on Suncor Energy’s NPS 16 Oilsands Pipeline (OSPL). The primary focus of the paper will be on the findings, trends, and observations obtained from the actual “as found” field data. Suncor’s SCC management philosophy will also be discussed, including in-line inspection, engineering analysis, data collection and defect mitigation. Suncor Energy owns and operates the 426 km NPS 16” (406.4 mm) OSPL system from the Suncor Oilsands site north of Fort McMurray to Edmonton, Alberta, Canada. The pipeline operates as a batched system and transports a range of products from heavy viscous crude oil, light synthetic crude, naptha and diesel to natural gas liquids (NGL). This pipeline experienced a rupture in August of 2004. The cause of failure was determined to be near-neutral pH Stress Corrosion Cracking (SCC). An extensive excavation and inspection program was undertaken following a comprehensive in-line inspection (ILI) program to detect any crack, metal loss and geometry features. A total of 282 crack field and crack-like features as well as 57 notch-like and non-decidable features were excavated and inspected. A number of trends and observations were identified during the inspection and assessment program. Most of the SCC occurred in an area immediately downstream of a newly commissioned pump station. Also, all SCC was detected in thin wall pipe sections and no SCC was identified in heavy wall pipe sections. Most of the SCC occurred in locations with moderate well to rapidly drained glaciofluvial sands and loamy sands. Field observations and findings along with post rupture metallurgical analysis agreed with recent published developments in the mechanism of near-neutral pH SCC. Suncor completed an extensive integrity program in a relatively short period of time (less than a year). All crack-field and crack-like defects as identified by the UltraScan CD tool were mitigated. Suncor plans to continue their integrity program to ensure the continued safety and integrity of their pipeline facilities.

Statistical Predictive Modelling: A Methodology to Prioritize Site Selection for Near-Neutral pH Stress Corrosion Cracking

2010 ◽  
Author(s):  
Edgar I. Cote ◽  
James Ferguson ◽  
Nauman Tehsin
Keyword(s):  
Tensile Stress ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Probability Of Detection ◽  
Predictor Variables ◽  
Neutral Ph ◽  
Proactive Management ◽  
Ph Stress ◽  
Axial Defects

Pipelines are subjected to both residual and applied tensile stresses, and can form near-neutral pH SCC (transgranular stress corrosion cracking) if the pipeline is exposed to a conducive environment and is made from a material that is susceptible to SCC. This transgranular SCC is an ongoing integrity concern for pipeline operators. As part of an SCC Integrity Management Program (IMP), it is necessary to perform integrity assessments and prioritize segments of the pipelines to manage the SCC threat. Ultrasonic crack detection in-line inspection tools have proven capable of locating SCC, but reliability of these tools is not absolute and the reduced probability of detection of subcritical flaws limits options for proactive management. Hydrostatic retesting is a very effective program for removing near-critical axial defects, such as SCC, but does not provide useful information as to the location of SCC along the pipeline. NACE Standard RP0204-2004 (SCC Direct Assessment Methodology or SCCDA) outlines factors to consider and methodologies to employ to predict where the SCC is likely to occur, but the standard acknowledges that there are no well-established methods for predicting the presence of SCC with a high degree of certainty. The trend in probabilistic modelling has been to focus on establishing deterministic relationships between environmental factors, tensile stress and SCC formation, and growth; these models have achieved varying degrees of success. The Statistical Predictive Model (SPM) was previously developed to predict the likelihood of occurrence of near-neutral pH Stress Corrosion Cracking (SCC) for the NPS 10 Alberta Products Pipeline (APPL). SPM Phase 5 uses selected predictor variables representing tensile stress, environmental, pipe-related, corrosion control and operational relevant factors to determine the Probability of Occurrence of SCC. Regression techniques were used to create multi-variable logistic regression models. The results for each model are checked at locations where SCC is known to be present or absent to assess predictive accuracy, then used to prioritize susceptible segments for field excavation. The relative strength of individual predictor variables provides insight into the mechanism of near-neutral pH SCC crack initiation.

APPLICATION OF INVERSE BROYDEN'S METHOD FOR COMPUTATIONAL ANALYSIS OF HYDROGEN CONTRIBUTION TO THE NEAR-NEUTRAL PH STRESS CORROSION CRACKING

2013 ◽  
Vol 10 (05) ◽  
pp. 1350033
Author(s):  
IGOR TELICHEV ◽  
OLEG VINOGRADOV
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Computationally Efficient ◽  
Material Degradation ◽  
Broyden’S Method ◽  
Neutral Ph ◽  
Ph Stress ◽  
Bcc Iron ◽  
Broyden's Method

An Inverse Broyden's Method was applied in the context of a molecular statics approach for the analysis of the contribution of hydrogen to the near-neutral pH stress corrosion cracking. A 3D crystal structure was tested numerically. It is shown that the Inverse Broyden's Method provides a computationally efficient technique to evaluate the effect of hydrogen on the material degradation. Simulation results demonstrated that atoms of hydrogen placed near the crack tip produced a strong effect on deformation and crack propagation in bcc iron leading to a 15–20% loss in a residual strength of numerically tested samples.

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