Annual Probability Of Failure Research Articles

Evaluation of predictive assessment reliability on corroded transmission pipelines

Oil and Gas operators have to deal with the ageing process of their transmission pipeline grid. Some of these pipelines can be inspected using In Line Inspection (ILI) tools. In order to maintain an acceptable integrity level, re-inspection operations have to be performed. This process needs to be optimized in terms of resources and cost. CRIGEN, GDF SUEZ Research and Development Center, has developed a methodology which prioritizes rehabilitation operations on a pipeline after in-line inspections, and determines the optimal interval for re-inspection. A reliable help decision software tool, GADPro, which applies the methodology has also been developed. Dealing with defects assimilated to external electrochemical corrosion, the developed methodology is based on: ▪ ILI features reported in depth dimensions in order to assess a probable corrosion growth rate, ▪ Probabilistic distribution of input parameters (defect geometrical characteristics, pipeline characteristics and corrosion growth rate), ▪ Failure probability calculation. The calculation results take the form of three probabilities of failure: ▪ A punctual probability of failure for each defect, ▪ An annual probability of failure for each defect, ▪ An annual probability of failure per kilometer of pipe. To interpret the results, the annual probability of failure per kilometer of pipe is then compared with threshold values from safety studies that can be associated with location places and failure modes. In year 2009, the re-inspection of two 24 inches coil tar enamel gas transmission pipeline formerly inspected in year 1999 gave the opportunity to evaluate the consistency of the predictive assessment from GADPRO tool. The first pipeline was 125 km long. The second one was 93 km long. To reach that goal, a first step consisted to match the metal losses from the two run for each pipe section. Then, corrosion growth rates were calculated from the sizing evolution of the matched defect from the two ILI runs. Results were compared with the corrosion growth rate determined with the assumptions made in GADPro tool. Finally, the preventive intervention program which could have been determined after the 1999 ILI was compared to the one established using the results of the inspection performed on the same line in year 2009. This article presents the procedures employed to carry out a probabilistic assessment of corroded pipelines inspected with ILI tools as well as the methodology validation study based on pipeline re-inspection data analysis.

A probabilistic finite element analysis of embankment stability under transient seepage conditions

Flood protection structures lend themselves to probabilistic design given the large uncertain variables. Taking into account the historical discharge statistics of rivers, the annual probability of failure by slope instability of an embankment along the river Elbe in Eastern Germany is determined using a finite element analysis. The effect of transient seepage within the embankment and its effect on embankment stability are considered. Whereas a steady-state seepage line is most critical for the embankment stability, a transient seepage calculation including the rise and drop of the river water level reveals stability reserves. It has been demonstrated that the First-Order Reliability Method with Adaptive Response Surface is an efficient calculation technique for coupling numerical simulations to a reliability analysis.

Reliability Evaluation of Corroding Pipelines Considering Multiple Failure Modes and Time-Dependent Internal Pressure

A methodology is developed to evaluate the annual failure probabilities of a pressurized pipeline at an active metal-loss corrosion defect. The methodology takes into account three different failure modes at the defect (i.e., small leak, large leak, and rupture) and the time dependency of the pipe’s internal pressure by modeling the pressure as a simple stochastic process consisting of a sequence of independent and identically distributed random variables, each occupying a period of one year. The impact of periodic maintenance actions on the failure probabilities is incorporated in the methodology. Two numerical examples are used to illustrate the methodology. The sensitivity of the calculated failure probabilities with respect to the time dependency of the internal pressure is also investigated.

Reliability analysis of a bulk carrier in ultimate limit state under combined global and local loads in the hogging and alternate hold loading condition

The alternate hold still-water loading in hogging combined with wave loading is critical for the safe design of bulk carriers. The ultimate longitudinal strength of the hull girder of bulk carriers in this condition has been found to be considerably reduced by the action of local lateral pressure loads. In the present paper, an interaction equation based on the ultimate hull girder strength assessment obtained by nonlinear finite element analyses is adopted to consider the relationship between ultimate longitudinal bending capacity and average external sea pressure over the bottom. This interaction equation is used as the basis for the failure function. The annual probability of failure is obtained by FORM analysis considering two typical load cases, namely, pure longitudinal hogging bending moment and combined global hogging bending moment and local lateral pressure loads. The effect of heavy weather avoidance on the failure probability is evaluated. The results show that the local lateral pressure has a significant influence on the annual probability of failure of bulk carriers in the hogging and alternate hold loading condition.

Vector-Valued Fragility Analysis Using PGA and PGV Simultaneously as Ground-Motion Intensity Measures

Seismic risk analysis usually expresses ground-motion intensity using a single index such as peak ground acceleration (PGA), spectral acceleration for a specified period, or peak ground velocity (PGV). Limiting the number of indices, however, adds greater uncertainty when estimating annual failure probability given by convolving seismic hazard and fragility curves. This is because information other than ground-motion intensity is missing. Author proposed seismic hazard analysis using PGA and PGV simultaneously as groundmotion input measures. After analyzing the correlation coefficient between PGA and PGV using K-NET and KiK-net databases, probabilistic seismic hazard for seven sites in Kanto district in Japan was evaluated. In this study, seismic fragility analysis using PGA and PGV is conducted followed by advantage of vector-valued fragility analysis.

Fatigue design of steel containment cylinders for CNG ship application

A reliable methodology is required for fatigue design of steel cylinders for Compressed Natural Gas (CNG) carriers in order to meet target safety level at an acceptable cost. This includes description of physical models that represents actual long term fatigue capacity of the Cargo Containment cylinders. The design methodology includes length of welds, fabrication tolerances, fabrication methodology and non destructive testing. It also involves definition of characteristic values for loading and capacity in addition to recommended Design Fatigue Factors. Three alternative fatigue design procedures requiring different Design Fatigue Factors to achieve a system target safety level of annual probability of failure less or equal to 10 −5 are presented.

Enhancement of seismic sustainability of critical facilities through system analysis

Proper functioning of critical facilities such as acute care hospitals and fire stations are essential in the aftermath of a severe earthquake. For these facilities to remain operational, not only their building structures must remain safe for continued occupancy, but also their nonstructural components/systems must remain functional. Motivated by a previous study by the second author, this paper demonstrates a probabilistic system analysis for enhancing the sustainability of deficient critical facilities. The analysis, in principle, utilizes event and fault tree procedures to evaluate the system fragility defined by the probability that the system will not perform its intended purpose. Enhancement of sustainability is demonstrated by using a representative numerical model of an existing facility. The study shows that by selecting the most vulnerable components, utilizing the concept of annual sensitivity index, the annual probability of failure can be reduced significantly in a cost-effective way.

Risk-based stabilization planning for soil cut slopes

Abstract. Risk-based slope stabilization planning integrates the failure probability and the failure consequence systematically and shows promise for use in the practice. This paper attempts to develop a risk-based methodology for stabilization planning for deteriorating soil cut slopes. First, a framework of risk-based stabilization planning for slopes is proposed. Then the time-dependent reliability of deteriorating slopes is analyzed based on observed performance. Thereafter, the slope failure consequence is assessed in terms of expected numbers of fatality. After obtaining the time-dependent risk of slope failure, the time for slope stabilization is determined according to selected risk criteria. Finally, the effect of slope maintenance on the reliability of slopes is evaluated. Based on the analyses, the annual probability of failure of soil cut slopes would increase exponentially in the early stage of service if no maintenance were implemented. As a slope deteriorates, the risk of slope failure increases with time and may reach an intolerable level at a certain time. The risk of slope failure may also reach an intolerable level due to a change of elements at risk. The derived stabilization time depends on the factors that cause the slopes to deteriorate, consequence of slope failure, selected risk criteria, and vulnerability of the affected population.

Maintenance and decommissioning real options models for life-cycle cost-benefit analysis of offshore platforms

Maintenance and decommissioning real options (RO) models are developed for life-cycle cost-benefit (LCCB) analysis of offshore platforms. Uncertainties about hydrocarbon prices, maintenance costs, environmental loading, structural capacity and damage due to deterioration are taken into consideration in the RO modelling. Expressions are derived for expected costs and benefits in terms of the availability function of the platform, which depends on the hazard and restoring functions, and on the annual probability of failure of the structure. Results show that the use of the net present value (NPV) approach can significantly underestimate the LCCB. The RO formulation developed is shown to provide a proper framework to account for the value of the managerial flexibility to consider different options along the service lifetime of the structure, such as maintenance and decommissioning, and to make decisions adapting to future information.

Risk Based Structural Integrity Management of Marine Platforms Using Bayesian Probabilistic Nets

The present paper introduces a general framework for integrity management of offshore steel jacket structures allowing for the risk based planning of inspections and maintenance activities with a joint consideration of various relevant deterioration and damage processes. The suggested approach relates the relevant deterioration and damage processes to damage states, which in turn may be related to the overall integrity of the jacket structural system as measured through the reserve strength ratio. Each state of degradation, irrespective of the cause, can then be assessed in terms of their impact on the annual probability of failure for the structure. Based on data and subjective information regarding the annual probabilities of occurrence of the relevant deterioration and damage processes, together with a probabilistic modeling of the quality of condition control, it is possible to assess the structural effect of each type of deterioration and damage phenomenon. This facilitates the development of a general framework for risk based integrity management. In the present work such a framework is formulated using Bayesian probabilistic networks for evaluating the time varying global structural reliability of jackets subject to progressive deterioration of its members due to the combined effect of different sources of damage. In principle, system effects, i.e., the effect of damage in one element of the structural system on the capacity of other elements, can also be accounted for through a Bayesian probabilistic net; however, this is not considered in this work.

Probability and Risk of Slope Failure

This paper aims to demystify the use of risk assessment as a decision management tool and present a methodology that places quantitative risk assessment within reach of every geotechnical engineer, even for routine engineering assignments. In particular, we propose using quantification of expert judgment (i.e., subjective probabilities) as a practical alternative for determining probability of slope failure. The writers present a semiempirical relationship between factor of safety and annual probability of failure that permits estimation of slope failure probabilities with relatively modest effort. The case study for a tailings dam shows that risk assessment based on quantification of expert judgment provides a framework to arrive at rational management and engineering decisions related to dam safety and other geotechnical problems. Using the semiempirical relationship presented here, practicing engineers can use this helpful tool by applying their current skills.

STUDY ON ROAD SLOPE DISASTER PREVENTION INTEGRATED MANAGEMENT S YSTEM

In order to promote infrastructure management that takes into consideration the challenging social and economic conditions and the occurrence of many natural disasters in recent years, it is necessary to define what infrastructure management should be like from the viewpoints of both risk management and asset management. From these viewpoints, this paper proposes a GIS-based slope risk evaluation system implemented as part of the road slope disaster prevention integrated management system, and shows an example of a system applied to the evaluation of road slopes in a real road network. The slope risk evaluation system is a GIS-based package of analysis systems for a number of tasks including the automatic acquisition of slope data from three-dimensional topographic data, the calculation of the annual probability of rain-induced failure of each slope, and road network risk evaluation based on detour loss. The slope risk evaluation system is a promising tool for assisting in decision making that uses the risk evaluation technique for road slope disaster prevention. This study aims to define the direction of a road slope disaster prevention integrated management system that combines asset management and risk management.

Influence of grade on the reliability of corroding pipelines

This paper focuses on a comparative analysis of the reliability associated with the evolution of corrosion between normal and high-strength pipe material. The use of high strength steel grades such as X100 and X120 for high pressure gas pipeline in the arctic is currently being considered. To achieve this objective, a time-dependent reliability analysis using variable Y/ T ratios in a multiaxial finite strain analysis of thin-walled pipeline is performed. This analysis allows for the consideration of longitudinal grooves and the presence of companion axial tension and bending loads. Limit states models are developed based on suitable strain hardening models for the ultimate behavior of corroded medium and high strength pipeline material. In an application, the evolution of corrosion is modeled in pipelines of different grades that have been subjected to an internal corrosion inspection after a specified time which allows for a Bayesian updating of long-term corrosion estimates and, hence, the derivation of annual probabilities of failure as a function of time. The effect of grade and Y/ T is clearly demonstrated.

Reliability evaluation for the pump assembly using an accelerated test

The pump motor assembly in a washing machine is used to drain the dirty water generated during washing the clothes. This research was aimed to develop an accelerated test as to demonstrate a reliability goal of the assembly within an affordable amount of time and in an economic way. They were evaluated under step stress margin tests first in order to verify their operating limit in certain environmental stresses and then an accelerated test (AT) was conducted to measure the annual failure rate and MTTF of them. The high temperature and the voltage were used as stress factors to accelerate the failure of the assembly. The value of the acceleration factor was estimated by 16 at the high stress condition compared to the use condition. It also showed that all 18 units must survive for 500 h at the stress condition (40 °C, 264 V) to assure the 0.07% annual failure probability of the assembly at the use condition in 90% confidence level.

Life-cycle cost-effective optimum design of steel bridges considering environmental stressors

This paper presents a practical and realistic LCC methodology for the LCC-effective optimum design of steel bridges considering the time effect of bridge reliability under environmental stressors such as corrosion and heavy truck traffic. The LCC functions considered in the LCC optimization consist of initial cost, expected life-cycle maintenance cost and expected life-cycle rehabilitation costs including repair/replacement costs, loss of contents or fatality and injury losses, road user costs, and indirect socio-economic losses. For the assessment of the life-cycle rehabilitation costs, the annual probability of failure which depends upon the prior and updated load and resistance histories should be accounted for. For the purpose, the Nowak live load model and a corrosion propagation model considering corrosion initiation, corrosion rate, and repainting effect are adopted in this study. The LCC methodology proposed in the paper is applied to the optimum design problem of an actual steel box girder bridge with three continuous spans, and various sensitivity analyses are performed to investigate the effects of various design parameters and conditions on the LCC-effectiveness. From the numerical investigation, it may be positively expected that the proposed methodology can be effectively utilized for the LCC-effective optimum design of steel bridges.

Seismic risk analysis of modified fan type cable stayed bridges

A seismic risk analysis of modified fan type cable stayed bridges is presented using the concept of damage probability matrix. The cable stayed bridge is modeled as a two dimensional system with the deck idealized as a continuous beam subjected to bending action and axial compression. The response of the bridge is obtained by the frequency domain spectral analysis. A double filtered power spectral density function with seismic intensity parameter taken as the magnitude of an earthquake and a correlation function between the support excitations are considered as seismic inputs. For a given magnitude of earthquake, the damage probability matrix is determined by defining three damage states namely, major, moderate and minor. The seismic risk index is determined by combining the damage probability matrix with the probability of occurrence of different magnitudes of earthquake. As an illustrative example, a three span modified fan type cable stayed bridge is analyzed for an extensive parametric study. The parameters include degree of correlation, angle of incidence of earthquake, ratio of the components of ground motion, and soil condition. Some of the important conclusions of the study indicate that (i) the longitudinal component of ground motion has a considerable effect on the annual probabilities of failure of the bridge deck; (ii) annual probabilities of failure are significantly more for soft soil condition; (iii) fully correlated ground motion between support excitation provides less value of the damage indices as compared to the uncorrelated ground motion; and (iv) annual probabilities of failure are not very sensitive to the variation of angle of incidence of an earthquake.

Corporate Failure and Equity Valuation

An important problem for portfolio managers is how to adjust the valuation of equity for the risk that the company may fail. Traditional adjustments seem ad hoc, and previous research on the topic has ignored the irreversible nature of failure. Here, a standard equity valuation model is extended to include a parsimonious but rigorous correction for a stationary annual probability of failure. Although the correction is nonlinear, it can be reduced to an equivalent function that enters the valuation equation in the traditional additive way. Empirical benchmarking suggests that, even without assuming risk-averse investors, this approach comes closer to predicting observed equity premiums than the traditional approach.

Harnessing data mining to explore incident databases

Large numbers of incident related databases have been established in the last three decades. The majority of attempts to explore these data marts were trials to identify patterns via first glance into the datasets. This study investigated a subset of incidents from fixed facilities in Harris County, TX, extracted from the National Response Center database. By classifying the information into groups and using data mining techniques, interesting patterns of incidents according to characteristics such as type of equipment involved, type of chemical released and causes involved were revealed and further these were used to modify the annual failure probabilities of equipments.

Should standard building structures in Brazil be guaranteed by a seismic resistant design?

Brazilian territory is situated on an intraplate region with low seismic activity, and so, it is important to answer an old question that remains unanswered: Should standard building structures in Brazil be guaranteed by a seismic resistant design? In this way , a methodology is described and used to evaluate the annual failure probability of a structure model subjected to ground motions compatible with a defined provincial seismicity; the model strength is taken as the maximum shear and overturning moment at the base. One considers five different structure models for each Brazilian state capital city and evaluates the annual failure probability which provides arguments to answer the above question.

Reliability of Deteriorating Slopes

The effect of deterioration on the reliability of slopes of various service periods has seldom been considered explicitly in the current reliability approach in slope engineering. Constant annual failure probabilities, that are commonly used in practice to evaluate reliability of a slope over a given expected service period, may not be capable of capturing the deteriorating characteristics of slopes. This paper presents a procedure to model probabilistically the deteriorating effect on the failure probability with time. Past performance of geotechnical systems of similar nature is systematically analyzed to evaluate the failure probabilities for systems of different ages and for different expected service periods. The method was applied to the stability performance of soil cut slopes in Hong Kong. Through this exercise, the reliability of slopes of different ages for different future service periods can be reasonably estimated. As such, a planner can benchmark a design standard and plan a slope improvement program in a more effective and defensible way.