Reduction Factors for Estimating the Probability of Failure of Mechanical Damage Due to External Interference

2008 ◽  
Author(s):  
Andrew Cosham ◽  
Jane Haswell ◽  
Neil Jackson
Keyword(s):  
Structural Reliability ◽  
Historical Data ◽  
Mechanical Damage ◽  
Probability Of Failure ◽  
Risk Assessments ◽  
External Interference ◽  
Failure Data ◽  
Major Accident ◽  
The Uk ◽  
Reduction Factors

Quantified risk assessments (QRAs) are widely used in the UK to assess the significance of the risk posed by major accident hazard pipelines on the population and infrastructure in the vicinity of the pipeline. A QRA requires the calculation of the frequency of failures and the consequences of failures. One of the main causes of failures in onshore pipelines is mechanical damage due to external interference, such as a dent, a gouge, or a dent and gouge. In the published literature, two methods have been used to calculate the probability of failure due to external interference: • historical failure data and • limit state functions combined with historical data (i.e. structural reliability-based methods). Structural reliability-based methods are mathematically complicated, compared to using historical failure data, but have several advantages, e.g. extrapolation beyond the limited historical data, and the identification of trends that may not be apparent in the historical data. In view of this complexity, proposed supplements to the UK pipeline design codes IGE/TD/1 (natural gas) and PD 8010 (all substances) — on the application of QRAs to proposed developments in the vicinity of major accident hazard pipelines — include simple ‘reduction factors’ for use in ‘screening’ risk assessments. These ‘reduction factors’ are based on a comprehensive parametric study using a structural reliability-based model to calculate the probability of failure due to mechanical damage, defined as: gouges, and dents and gouges. The two ‘reduction factors’ are expressed in terms of the design factor and wall thickness of the pipeline. It is shown that, through appropriate normalisation, the effects of diameter, grade and toughness are secondary. Reasonably accurate, but conservative, estimates of the probability of failure can be obtained using these ‘reduction factors’. The proposed methodology is considerably simpler than a structural reliability-based analysis. The development and verification of these ‘reduction factors’ is described in this paper.

A Methodology for the Prediction of Pipeline Failure Frequency Due to External Interference

2008 ◽  
Author(s):  
C. Lyons ◽  
J. V. Haswell ◽  
P. Hopkins ◽  
R. Ellis ◽  
N. Jackson
Keyword(s):  
Damage Mechanism ◽  
External Interference ◽  
Gas Industry ◽  
Failure Frequency ◽  
Failure Data ◽  
Mechanics Model ◽  
The United Kingdom ◽  
Pipeline Failure ◽  
The Uk ◽  
Operational Failure

The United Kingdom Onshore Pipeline Operators Association (UKOPA) is developing supplements to the UK pipeline codes BSI PD 8010 and IGE/TD/1. These supplements will provide a standardized approach for the application of quantified risk assessment to pipelines. UKOPA has evaluated and recommended a methodology: this paper covers the background to, and justification of, this methodology. The most relevant damage mechanism which results in pipeline failure is external interference. Interference produces a gouge, dent or a dent-gouge. This paper describes the fracture mechanics model used to predict the probability failure of pipelines containing dent and gouge damage and contains predictions of failure frequency obtained using the gas industry failure frequency prediction methodologies FFREQ and operational failure data from the UKOPA fault database. The failure model and prediction methodology are explained and typical results are presented and discussed.

How Many Pipelines in North America Have Failed by Fatigue and Why?

2016 ◽  
Author(s):  
Andrew Cosham ◽  
Phil Hopkins
Keyword(s):  
United States ◽  
Historical Data ◽  
Mechanical Damage ◽  
The United States ◽  
Transportation Safety ◽  
Valuable Insight ◽  
Gas Pipelines ◽  
Manufacturing Defects ◽  
Failure Data ◽  
Incident Reports

Pipelines are aging: more than half of all pipelines in Europe and the United States are over 40 years old. Historically, only a small number of pipeline failures have been attributed to fatigue; however, as pipelines age, this might change. Indeed, two of the most serious pipelines failures in recent years in the United States were partly attributed to fatigue. The issue with fatigue is not so much how it should be addressed, but if or when, and where, it will become more of a problem. Historical failure data provides a valuable insight into the number and cause of failures that have been attributed to fatigue, and an indication of what might happen in the future. Historical failure data for onshore gas and liquid pipelines in the United States of America and Canada has been reviewed in order to estimate the number and cause of failures that can be attributed to fatigue; specifically, the OPS 30-day Incident Reports, the listing of pipeline rupture events compiled by the National Energy Board, and the findings of failure investigations conducted by the National Transportation Safety Board (NTSB) and the Transportation Safety Board of Canada (TSB). Failures that can (at least partly) be attributed to fatigue are not readily identifiable in the historical data, because fatigue is not listed as a secondary cause (as it is, strictly, only a growth mechanism). The narrative descriptions in historical data sets, as in the OPS 30-day Incident Reports, and the detail in the Pipeline Investigation Reports or Accident Briefs published by the NTSB, and the Pipeline Investigation Reports published by the TSB are essential for identifying the relevant failures and their causes. Failures in pipelines that can be attributed to fatigue are relatively rare, but fatigue failures have been reported in both onshore gas and liquid pipelines in both the United States and Canada, mostly originating from pre-existing mechanical damage or manufacturing defects. Corrosion-fatigue has been identified as a contributing factor in a minority of the failures. The number of failures in liquid pipelines is (as would be expected) higher than that in gas pipelines. The number of failures in onshore liquid pipelines in the United States that can be attributed to fatigue has increased, with over half of such failures having occurred in the last ten years. The increase is statistically significant. There has also been an increase, albeit smaller and not statistically significant, in the number in onshore gas pipelines. The increase in the number of failures is consistent with an ageing system.

An Update to the Recommended UKOPA External Interference Frequency Prediction Model and Pipeline Damage Distributions

2018 ◽  
Author(s):  
Graham Goodfellow ◽  
Chris Lyons ◽  
Susannah Turner ◽  
Fraser Gray ◽  
Simon Joyce
Keyword(s):  
Failure Rate ◽  
Structural Reliability ◽  
Operating Experience ◽  
External Interference ◽  
Failure Frequency ◽  
Depth Analysis ◽  
Product Loss ◽  
Distribution Parameters ◽  
The Uk ◽  
Incident Rates

The United Kingdom Onshore Pipeline Operators Association (UKOPA) was formed by UK pipeline operators to provide a common forum for representing operators interests in the safe management of pipelines. This includes providing historical failure statistics for use in pipeline quantitative risk assessment and UKOPA maintain a database to record this data. The UKOPA database holds data on product loss failures of UK major accident hazard pipelines from 1962 onwards and currently has a total length of 21,845 km of pipelines reporting. Overall exposure from 1952 to 2016 is 927,351 km years of operating experience with a total of 197 product loss incidents since 1962. The low number of failures means that the historical failure rate for pipelines of some specific diameters, wall thicknesses and material grades is zero or statistically insignificant. It is unreasonable to assume that the failure rate for these pipelines is actually zero. In addition to product loss incidents, the UKOPA database contains extensive data on measured part wall damage that did not cause product loss, unlike the European Gas Incident data Group (EGIG) database, which also includes the UK gas transmission pipeline product loss data. The data on damage to pipelines caused by external interference can be assessed to derive statistical distribution parameters describing the expected gouge and dent dimensions resulting from an incident. Overall external interference incident rates for different class locations can also be determined. These distributions and incident rates can be used in structural reliability based techniques to predict the failure frequency due to external interference for a given set of pipeline parameters. The current distributions of external interference damage were derived from data up to 2009 and presented as Weibull distributions for gouge depth, gouge length and dent depth. Analysis undertaken for the COOLTRANS CO2 pipeline project, undertaken by National Grid in the UK, has identified several improvements to the recommended UKOPA approach to external interference failure frequency prediction. This paper summarises those improvements and presents updated damage distribution parameters from data up to 2016.

Quantifying the Probability of Failure During the Pre-Commissioning Hydrotest

2006 ◽  
Author(s):  
Andrew Cosham ◽  
Phil Hopkins ◽  
Jan Spiekhout
Keyword(s):  
Structural Reliability ◽  
Axial Stress ◽  
Probability Of Failure ◽  
Line Pipe ◽  
Test Pressure ◽  
Mill Test ◽  
Upper Bound Estimate ◽  
Definition Of ◽  
The Uk ◽  
Low Pressures

Failures during the pre-commissioning hydrostatic test of a newly constructed pipeline are rare, but occasionally they do occur. Structural reliability techniques can be used to estimate the probability of failure during the precommissioning hydrotest, and to investigate the sensitivity of the probability of failure to the test pressure. This paper describes a study of the probability of failure during the hydrotest, based on data for the BBL Pipeline. The BBL Pipeline is a 36 in. outside diameter, approximately 235 km long pipeline designed to export natural gas from the Netherlands to the UK. The definition of failure is limited to failure of the line pipe due to internal pressure loading. Failure of fittings (e.g. flanges, valves, etc.) is not considered. With this definition of failure, three different scenarios are considered: 1. Failure of defect-free pipe. 2. Failure of pipe containing a ‘workmanship’ defect (i.e. a defect in the pipe body or a weld that is acceptable to the relevant specifications or standards). 3. Failure of pipe containing a defect not acceptable to workmanship levels (e.g. a crack, or a dent on a weld). Defects larger than workmanship defects encompass defects that would not fail at the design pressure, but would fail at higher pressures, and ‘gross’ defects that would fail at very low pressures. It is difficult to estimate the probability of failure of such defects because it is highly dependent on the probability of these defects being present in the pipeline. Conversely, it is relatively straightforward to obtain a reasonable upper bound estimate of the probability of failure due to defect-free pipe or a workmanship defect. Consequently, in this study, only the probability of failure due to (1) or (2) has been calculated using structural reliability techniques. Inferences about (3) are drawn from the results of (1) and (2), and from historical data on hydrotest failures. It is shown that there is a hydrotest level below which the probability of failure is predicted to be zero. For defect-free pipe this is at least equal to the level of the mill test. In general, this hydrotest level depends upon factors such as: the ratio of the axial stress to the hoop stress in the mill test and the hydrotest, and the size of defects in the pipeline.

Reliability Based Assessment of Deck Elevations for Offshore Jacket Platforms

2004 ◽  
Vol 126 (4) ◽  
pp. 331-336 ◽  
Author(s):  
Ernesto Heredia-Zavoni ◽  
Dante Campos ◽  
Gallegher Ramı´rez
Keyword(s):  
Reliability Index ◽  
Structural Reliability ◽  
Failure Modes ◽  
Probability Of Failure ◽  
Upper And Lower Bounds ◽  
Series System ◽  
Wave Loading ◽  
System Components ◽  
Storm Wave ◽  
Wave Heights

Structural reliability analyses of fixed marine platforms subjected to storm wave loading are performed to assess deck elevations. Platforms are modeled as a series system consisting of the deck and jacket bays. The structural reliability analyses are carried out assuming dominant failure modes for the system components. Upper and lower bounds of the probability of failure are computed. The variation of the reliability index per bay component as a function of wave height, with a focus on those wave heights that generate forces on the deck, is analyzed. A comparison is given for the deck probability of failure and the lower bound probability of failure of the jacket in order to assess how the deck or the jacket controls the probability of failure of the system. Results are also given for reliability analyses considering different deck elevations. Finally, an analysis of the total probabilities of failure, unconditioned on wave heights, is given.

Efficient Reliability Assessment With the Conditional Probability Method

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Rami Mansour ◽  
Mårten Olsson
Keyword(s):  
Conditional Probability ◽  
Structural Reliability ◽  
A Priori ◽  
Reliability Assessment ◽  
Probability Of Failure ◽  
Assessment Method ◽  
Probability Method ◽  
Probability Of Survival ◽  
Design Variables ◽  
Reliability Method

Reliability assessment is an important procedure in engineering design in which the probability of failure or equivalently the probability of survival is computed based on appropriate design criteria and model behavior. In this paper, a new approximate and efficient reliability assessment method is proposed: the conditional probability method (CPM). Focus is set on computational efficiency and the proposed method is applied to classical load-strength structural reliability problems. The core of the approach is in the computation of the probability of failure starting from the conditional probability of failure given the load. The number of function evaluations to compute the probability of failure is a priori known to be 3n + 2 in CPM, where n is the number of stochastic design variables excluding the strength. The necessary number of function evaluations for the reliability assessment, which may correspond to expensive computations, is therefore substantially lower in CPM than in the existing structural reliability methods such as the widely used first-order reliability method (FORM).

Assessment of Parameters Influencing Mechanical Response of Constrained and Unconstrained Dents Using Finite Element Modelling

2013 ◽  
Author(s):  
W. Hanif ◽  
S. Kenny
Keyword(s):  
Finite Element ◽  
Mechanical Response ◽  
Mechanical Damage ◽  
Numerical Data ◽  
Performance Criterion ◽  
Metal Loss ◽  
Data Sets ◽  
External Interference ◽  
Seismic Fault ◽  
Girth Welds

Pipelines may experience damage (e.g. dent, gouge) during handling, installation and normal operations due to external interference. Pipelines in offshore environment may be prone to mechanical damage from events such as ice gouging, frost heave, and seismic fault movement. Damage mechanisms can be associated with deformation or metallurgical/metal loss that may include pipe dent, pipe ovality, ice gouging, pipe buckling, corrosion etc. The type and severity of pipe damage may influence operational, repair and intervention strategies. For conventional pipelines, the assessment of mechanical damage plays an important role in the development of integrity management programs that may be of greater significance for pipeline systems located in remote harsh environments due to remote location and logistical constraints. This study examines the effects of plain dents on pipe mechanical response using continuum finite element methods. ABAQUS/Standard (6.10-1) environment was used to simulate damage events and pipe response. Modelling procedures were developed and calibrated against physical and numerical data sets available in public domain. Once confidence in numerical procedures was achieved, an analysis matrix was established to account for a range of influential parameters including Diameter to wall thickness ratio (D/t), indenter diameter to pipe diameter ratio (ID/OD), hoop stress due to internal pressure to yield strength ratio (σh/σy), and kinematic boundary conditions. The results from this study provide a basis to support a broader initiative for developing an engineering tool for the assessment of damage interaction with pipeline girth welds and development of an engineering performance criterion.

An Update to the UKOPA Pipeline Damage Distributions

2012 ◽  
Author(s):  
Graham Goodfellow ◽  
Susannah Turner ◽  
Jane Haswell ◽  
Richard Espiner
Keyword(s):  
Failure Rate ◽  
Structural Reliability ◽  
Operating Experience ◽  
Quantitative Risk Assessment ◽  
External Interference ◽  
Failure Frequency ◽  
Product Loss ◽  
Distribution Parameters ◽  
Transmission Pipeline ◽  
Incident Rates

The United Kingdom Onshore Pipeline Operators Association (UKOPA) was formed by UK pipeline operators to provide a common forum for representing operators interests in the safe management of pipelines. This includes providing historical failure statistics for use in pipeline quantitative risk assessment and UKOPA maintain a database to record this data. The UKOPA database holds data on product loss failures of UK major accident hazard pipelines from 1962 onwards and currently has a total length of 22,370 km of pipelines reporting. Overall exposure from 1952 to 2010 is of over 785,000 km years of operating experience with a total of 184 product loss incidents during this period. The low number of failures means that the historical failure rate for pipelines of some specific diameters, wall thicknesses and material grades is zero or statistically insignificant. It is unreasonable to assume that the failure rate for these pipelines is actually zero. However, unlike the European Gas Incident data Group (EGIG) database, which also includes the UK gas transmission pipeline data, the UKOPA database contains extensive data on measured part wall damage that did not cause product loss. The data on damage to pipelines caused by external interference can be assessed to derive statistical distribution parameters describing the expected gouge length, gouge depth and dent depth resulting from an incident. Overall 3rd party interference incident rates for different class locations can also be determined. These distributions and incident rates can be used in structural reliability based techniques to predict the failure frequency due to 3rd party damage for a given set of pipeline parameters. The UKOPA recommended methodology for the assessment of pipeline failure frequency due to 3rd party damage is implemented in the FFREQ software. The distributions of 3rd party damage currently used in FFREQ date from the mid-1990s. This paper describes the work involved in updating the analysis of the damage database and presents the updated distribution parameters. A comparison of predictions using the old and new distributions is also presented.

Adjusting Environmental Contours for Specified Expected Number of Unwanted Events

2020 ◽  
Author(s):  
Erik Vanem
Keyword(s):  
Reliability Analysis ◽  
Return Period ◽  
Environmental Conditions ◽  
Structural Reliability ◽  
Probability Of Failure ◽  
Expected Number ◽  
Probability Of Exceedance ◽  
Underlying Distribution ◽  
Extreme Loads ◽  
Time Period

Abstract Environmental contours are applied in probabilistic structural reliability analysis to identify extreme environmental conditions that may give rise to extreme loads and responses. Typically, they are constructed to correspond to a certain return period and a probability of exceedance with regards to the environmental conditions that can again be related to the probability of failure of a structure. Thus, they describe events with a certain probability of being exceeded one or more times during a certain time period, which can be found from a certain percentile of the underlying distribution. In this paper, various ways of adjusting such environmental contours to account for the expected number of exceedances within a certain time period are discussed. Depending on how such criteria are defined, one may get more lenient or more stringent criteria compared to the classical return period.

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