Pipeline Maintenance in Geotechnically Unstable Areas: A Case Study

2000 ◽  
Author(s):  
Michelle L. Sorensen
Keyword(s):  
Risk Mitigation ◽  
Probability Distributions ◽  
Slope Instability ◽  
Ground Movement ◽  
Data Uncertainty ◽  
Strain Gauges ◽  
Mitigation Options ◽  
Soil Movement ◽  
Fort Mcmurray

The 22″ Alberta Oilsands Pipeline transports synthetic crude oil from Syncrude Canada Limited in Fort McMurray to Edmonton, Alberta. The pipeline crosses the House River approximately 100 kilometers south of Fort McMurray. The slope has been monitored since 1991 by three slope indicators. A finite element stress analysis indicated that total ground movement since installation in 1977 could correspond to pipeline compressive strains in excess of 0.32%, a level of risk unacceptable to the pipeline owner. A probability-based model was developed to determine cost and benefit of risk mitigation options. Parameters such as soil movement and pipe strain were input as probability distributions. The mitigation options included: reduce slope instability; reduce pipe stress; reduce pipe-to-soil interaction; implement long term monitoring; determine current pipe strain level (to decrease data uncertainty); do nothing. A Monte Carlo simulation was used to establish probability of failure and probable cost distributions for each option. The results were presented as a combined cost of failure and mitigation over 10 years. The analysis indicated that the optimum solution was to remove the existing soil traction loading on the pipe and mitigate long-term slope movement. The decision was made to relieve the pipe strain by excavating. Current pipe strain was measured in situ using residual strain measurement. Long term strain gauges were installed. Slope mitigation was deferred until the strain gauges indicate total pipeline strain levels approaching 0.32%.

scholarly journals DESIGN WAVES AND THEIR PROBABILITY DENSITY FUNCTIONS

1988 ◽  
Vol 1 (21) ◽  
pp. 61 ◽  
Author(s):  
J. Rossouw
Keyword(s):  
Probability Distributions ◽  
Confidence Bands ◽  
Data Uncertainty ◽  
Data Set ◽  
Wave Heights ◽  
Period Wave ◽  
Best Fit ◽  
Selection Of ◽  
Made In

Design wave heights were estimated from measured data using a virtually continuous data set consisting of 8 years of waverider data. Evidence is given which shows that waveriders tend to malfunction during storms. Special care was taken to select independant and identically distributed samples from the data before fitting a number of probability distributions to the selected wave heights. Bootstrap techniques were used to select the models that give the best fit to the data as well as to determine the confidence bands for the predicted design wave heights. It is shown that once the model for the long term distribution of wave height is chosen, relatively narrow confidence bands can be obtained for the most probable value of up to the 100 year return period wave if maximum use is made of the available data. Uncertainty about the selection of the model and the representativeness of the measurements however reduces the usefulness of these confidence bands. A plea is also made in the paper to stop using the concept of a wave with a certain recurrence interval but rather to specify a wave with a given risk of being exceeded within the design life of the structure.

Investigation of a New Approach to Predict Water Quality Extremes with a Case Study of Chemical Determinands in Stream Water

1991 ◽  
Vol 24 (6) ◽  
pp. 25-33
Author(s):  
A. J. Jakeman ◽  
P. G. Whitehead ◽  
A. Robson ◽  
J. A. Taylor ◽  
J. Bai
Keyword(s):  
Water Quality ◽  
Stream Water ◽  
Probability Distributions ◽  
Management Strategies ◽  
Hybrid Modelling ◽  
Trend Model ◽  
Environmental Extremes ◽  
Modelling Approach

The paper illustrates analysis of the assumptions of the statistical component of a hybrid modelling approach for predicting environmental extremes. This shows how to assess the applicability of the approach to water quality problems. The analysis involves data on stream acidity from the Birkenes catchment in Norway. The modelling approach is hybrid in that it uses: (1) a deterministic or process-based description to simulate (non-stationary) long term trend values of environmental variables, and (2) probability distributions which are superimposed on the trend values to characterise the frequency of shorter term concentrations. This permits assessment of management strategies and of sensitivity to climate variables by adjusting the values of major forcing variables in the trend model. Knowledge of the variability about the trend is provided by: (a) identification of an appropriate parametric form of the probability density function (pdf) of the environmental attribute (e.g. stream acidity variables) whose extremes are of interest, and (b) estimation of pdf parameters using the output of the trend model.

A Review of Crack Detection In-Line Inspection Case Studies

2010 ◽  
Author(s):  
Neil Bates ◽  
David Lee ◽  
Clifford Maier
Keyword(s):  
Crack Growth ◽  
Case Studies ◽  
Crack Detection ◽  
Growth Parameters ◽  
Probability Distributions ◽  
Low Frequency ◽  
Probability Of Failure ◽  
Probability Of Detection ◽  
Inspection Data

This paper describes case studies involving crack detection in-line inspections and fitness for service assessments that were performed based on the inspection data. The assessments were used to evaluate the immediate integrity of the pipeline based on the reported features and the long-term integrity of the pipeline based on excavation data and probabilistic SCC and fatigue crack growth simulations. Two different case studies are analyzed, which illustrate how the data from an ultrasonic crack tool inspection was used to assess threats such as low frequency electrical resistance weld seam defects and stress corrosion cracking. Specific issues, such as probability of detection/identification and the length/depth accuracy of the tool, were evaluated to determine the suitability of the tool to accurately classify and size different types of defects. The long term assessment is based on the Monte Carlo method [1], where the material properties, pipeline details, crack growth parameters, and feature dimensions are randomly selected from certain specified probability distributions to determine the probability of failure versus time for the pipeline segment. The distributions of unreported crack-related features from the excavation program are used to distribute unreported features along the pipeline. Simulated crack growth by fatigue, SCC, or a combination of the two is performed until failure by either leak or rupture is predicted. The probability of failure calculation is performed through a number of crack growth simulations for each of the reported and unreported features and tallying their respective remaining lives. The results of the probabilistic analysis were used to determine the most effective and economical means of remediation by identifying areas or crack mechanisms that contribute most to the probability of failure.

scholarly journals Snow Avalanches and Acoustic Emissions

1983 ◽  
Vol 4 ◽  
pp. 271-276 ◽  
Author(s):  
R. A. Sommerfeld ◽  
H. Gubler
Keyword(s):  
Acoustic Emissions ◽  
Limited Range ◽  
Slope Instability ◽  
Type I ◽  
Type Ii ◽  
Noise Levels ◽  
Active Layers ◽  
Differential Movement ◽  
Emission Activity

Analyses of several years of data show that acoustic emission activity is greater from unstable snowpacks than from stable snowpacks. Two types of signals have been identified: type I spikes and type II long-term elevation of the noise level. It is thought that the type I signals originate from macroscopic cracks. The type II signals may originate from differential movement on shearing surfaces, but this is less certain. Increased noise levels of both types correlate well with slope instability, when the slope stability is known. In some climates the limited range of signal detection might be a significant problem. A foam-mounted geophone set into the snow near active layers appears to be the best sensor available at present.

Pipeline Geohazard Assessment: Bridging the Gap Between Integrity Management and Construction Safety Contexts

2018 ◽  
Author(s):  
Rodney S. Read
Keyword(s):  
Construction Safety ◽  
Worker Safety ◽  
Ground Movement ◽  
Pipeline Construction ◽  
Probability Estimates ◽  
Subject Matter Expertise ◽  
Management Context ◽  
Integrity Management ◽  
Geohazard Assessment

Geohazards are threats of a geological, geotechnical, hydrological, or seismic/tectonic nature that may negatively affect people, infrastructure and/or the environment. In a pipeline integrity management context, geohazards are considered under the time-independent threat category of Weather-related and Outside Force in the American standard ASME B31.8S. Geotechnical failure of pipelines due to ground movement is addressed in Annex H and elsewhere in the Canadian standard CSA-Z662. Both of these standards allow flexibility in terms of geohazard assessment as part of pipeline integrity management. As a result of this flexibility, many systems for identifying, characterizing, analyzing and managing geohazards have been developed by operators and geotechnical engineering practitioners. The evolution of these systems, and general expectations regarding geohazard assessment, toward quantitative geohazard frequency assessment is a trend in recent pipeline hearings and regulatory filings in Canada. While this trend is intended to frame geohazard assessment in an objective and repeatable manner, partitioning the assessment into a series of conditional probability estimates, the reality is that there is always an element of subjectivity in assigning these conditional probabilities, requiring subject matter expertise and expert judgment to make informed and defensible decisions. Defining a specific risk context (typically loss of containment from a pipeline) and communicating uncertainty are important aspects of applying these types of systems. Adoption of these approaches for alternate risk contexts, such as worker safety during pipeline construction, is challenging in that the specific geohazards and threat scenarios considered for long-term pipeline integrity may or may not adequately represent all credible threats during pipeline construction. This paper explores the commonalities and differences in short- and long-term framing of geohazard assessment, and offers guidance for extending geohazard assessment for long-term pipeline integrity to other contexts such as construction safety.

scholarly journals Between Foragers and Farmers: Climate Change and Human Strategies in Northwestern Patagonia

Quaternary ◽  
2020 ◽  
Vol 3 (2) ◽  
pp. 17
Author(s):  
Adolfo F. Gil ◽  
Ricardo Villalba ◽  
Fernando R. Franchetti ◽  
Clara Otaola ◽  
Cinthia C. Abbona ◽  
...  
Keyword(s):  
Human Population ◽  
Probability Distributions ◽  
Southern Annular Mode ◽  
Population Based ◽  
Hunter Gatherers ◽  
Temperature And Precipitation ◽  
N Isotopes ◽  
Wild Resources ◽  
C And N

In this paper we explore how changes in human strategies are differentially modulated by climate in a border area between hunter-gatherers and farmers. We analyze multiple proxies: radiocarbon summed probability distributions (SPDs), stable C and N isotopes, and zooarchaeological data from northwestern Patagonia. Based on these proxies, we discuss aspects of human population, subsistence, and dietary dynamics in relation to long-term climatic trends marked by variation in the Southern Annular Mode (SAM). Our results indicate that the farming frontier in northwestern Patagonia was dynamic in both time and space. We show how changes in temperature and precipitation over the last 1000 years cal BP have influenced the use of domestic plants and the hunting of highest-ranked wild animals, whereas no significant changes in human population size occurred. During the SAM positive phase between 900 and 550 years cal BP, warmer and drier summers are associated with an increase in C4 resource consumption (maize). After 550 years cal BP, when the SAM changes to the negative phase, wetter and cooler summer conditions are related to a change in diet focused on wild resources, especially meat. Over the past 1000 years, there was a non-significant change in the population based on the SPD.

Comparison of Spar and Semisubmersible Floater Concepts of Offshore Wind Turbines Using Long-Term Analysis

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Hasan Bagbanci ◽  
D. Karmakar ◽  
C. Guedes Soares
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Transfer Functions ◽  
Probability Distributions ◽  
Offshore Wind ◽  
Short Term ◽  
Offshore Wind Turbines ◽  
Floating Wind Turbine ◽  
Offshore Floating Wind Turbine

The long-term probability distributions of a spar-type and a semisubmersible-type offshore floating wind turbine response are calculated for surge, heave, and pitch motions along with the side-to-side, fore–aft, and yaw tower base bending moments. The transfer functions for surge, heave, and pitch motions for both spar-type and semisubmersible-type floaters are obtained using the fast code and the results are also compared with the results obtained in an experimental study. The long-term predictions of the most probable maximum values of motion amplitudes are used for design purposes, so as to guarantee the safety of the floating wind turbines against overturning in high waves and wind speed. The long-term distribution is carried out using North Atlantic wave data and the short-term floating wind turbine responses are represented using Rayleigh distributions. The transfer functions are used in the procedure to calculate the variances of the short-term responses. The results obtained for both spar-type and semisubmersible-type offshore floating wind turbine are compared, and the study will be helpful in the assessments of the long-term availability and economic performance of the spar-type and semisubmersible-type offshore floating wind turbine.

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