Spectra Energy (Canada)

Solar irradiance variability due to stochastic cloud dynamics can cause unwanted fluctuations in the output voltage of photovoltaic (PV) modules. These dynamics must in particular be understood at very-short and short time scales if grid interconnection and generation/load balance requirements are to be maintained for PV distributed across the grid edge. Using a recently-created database for Ottawa, Canada, a 6-month longitudinal study was conducted with a specific focus on cloud dynamics. A spectral pyranometer was used to derive full-range spectral and broadband global horizontal irradiance under all sky conditions every 250 ms. Exploiting the infrared (IR) measurement channel of this software-augmented multi-filter radiometer allowed the cloud dynamics to be probed across time scales ranging from the subsecond to minutes. Seven distinct sky conditions were self-consistently determined without sky imaging. Probability distributions, established via kernel density estimates (KDE), allowed the statistical dependence of these conditions on the spectral clear-sky index to be found. The stochastic nature of the spectral irradiance variability was probed using spectral clear-sky index increments, over time steps that were found to span three distinct variability regimes.

Abstract The quality of the indirect inspection data is a critical factor in conducting a successful ECDA. It is therefore essential to increase the accuracy of the field data collection, to improve the data processing and to effectively present the results. This paper describes several challenges faced during this continuous improvement process. Techniques for obtaining accurate field data for assessing the risk of AC corrosion are reviewed. Data processing considerations are presented in the context of a case of third-party damage. The implications for similar DCVG indications on the same line are discussed, and a mechanism for these “apparent” DCVG indications is presented. A new format for displaying the data is also presented, allowing a better visual co-ordination between the indications and the site features, as well as allowing immediate assessment of the proposed locations for direct examinations in terms of access and other challenges.

This investigation was initiated to provide governing equations for crack initiation, crack growth, and service life prediction of pipeline steels in near-neutral pH (NNpH) environments. This investigation has focused on the crack initiation and early-stage crack growth. The investigation considered a wide range of conditions that could lead to crack initiation, crack dormancy, and crack transition from a dormant state to active growth. It is concluded that premature rupture caused by stress cracking at a service life of about 20 to 30 years previously observed during field operation could take place only when the worst conditions responsible for crack initiation and growth have been realized concurrently at the site of rupture. This also explains the reason that over 95 pct of NNpH cracks remain harmless, while about 1 pct of them become a threat to the integrity of pipeline steels.

From extensive investigations for over 30 years since the discovery of near-neutral pH stress corrosion cracking (NNpHSCC), the physical processes of crack initiation and growth have been determined, despite that some details in various aspects of crack initiation and growth are still to be understood. The growth curve is a function of crack growth by direct dissolution of steels at localized areas on pipe surface during initiation or at the tip of a crack during early stage of crack growth (the dissolution growth curve), and by a process involving the interaction of fatigue and hydrogen embrittlement (corrosion fatigue, the hydrogen enhanced fatigue growth curve) in Stage II after crack initiation and early stage of crack growth. For the latter case, recent research shows that crack growth rate can be substantially enhanced by variable amplitude cyclic loading. One of the most severe scenarios of cyclic loading in terms of crack growth rate is the underload type of pressure fluctuations that is often found within 30 km downstream of a compressor station. This investigation is aimed to evaluate pressure scenarios that could reduce or retard crack growth during pipeline operation. Specifically, the effect of pressure holds was investigated. Different periods of static hold were performed to an X65 pipeline steel exposed to a near-neutral pH solution. It was found that a static hold at the maximum load for one hour immediately after a large depressurization-repressurization cycle (underload cycle) yielded the lowest crack growth rate, which was about one third of that of constant amplitude fatigue without the static hold. Static holds for a period shorter or longer than one hour have yielded higher crack growth rates. This observation can be applied to field pipelines during operations to retard crack propagation.

Abstract Two leaks were found on a recently installed (1999) pipeline which was coated with extruded polyethylene and protected with directly connected magnesium anodes. This paper describes the use of external corrosion direct assessment (ECDA) principles to identify locations where corrosion could pose a threat to pipeline integrity, and describes the challenges encountered in developing a mitigation program. The reliability of indirect inspection tools along directionally bored sections of pipe, in correlation with special soil conditions, is also discussed.

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.

In 2004, in response to a number of internal and external drivers, the Pipeline Integrity Working Group (PIWG) of the Canadian Energy Pipeline Association (CEPA) undertook to develop pipeline integrity performance indicators. The PIWG wished to create indicators that would assist in reporting performance to regulatory stakeholders and provide its member companies with a means of comparing their respective integrity performance with the performance of their peers in the industry. The development of meaningful performance indicators is not as straightforward as it might appear. The performance indicator analysis and reporting has evolved since the initial report prepared in 2004, and now trends in the indicators are emerging that can be used to improve understanding of the issues and successes related to pipeline integrity management. This paper describes development of the CEPA pipeline integrity performance indicators including: • Stakeholder expectations; • Characteristics of the CEPA performance indicators; • The steps in development the performance indicators; • Key elements; • Data collection; • Data analyses; • Reporting; • Significant modifications; • Issues; and • Next steps.

Corrosion fatigue and fatigue crack growth in air tests were comparatively conducted on an X52 pipelines steel. Fatigue crack growth rates in air were lower than corrosion fatigue crack growth rates due to the absence of hydrogen and mechanical dormancy arisen from low temperature creep at low cyclic frequencies. Mechanical dormancy can commonly occur during operation of both oil and gas pipelines. Crack growth in near neutral pH environments can be well rationalized by a combined loading factor, (ΔK)2Kmax/fα, which reflects the synergistic interaction between the mechanical driving force and the hydrogen effects. Hydrogen plays a decisive role in terms of crack growth in pipelines steels exposed to near neutral pH environments.