Corrosion failure probability analysis of buried gas pipelines based on subset simulation

Structural reliability is an engineering method that focuses on the calculation and prediction of the probability of failure for a structural system. Structural reliability is used by many pipeline operators to assess the probability of failure, and these probability of failure estimates are then used to manage safety, environmental, and operational risks for threats such as corrosion, cracking, and third-party damage. In the structural reliability approach, the probability of failure is obtained from a multi-dimensional integral, for which the solution is commonly estimated numerically using Direct Monte Carlo (DMC) simulation. DMC is straight-forward and robust but requires a significant amount of computational effort to estimate small probabilities, which are typical of threats to pipeline integrity. Subset Simulation is an approach that improves on the efficiency issues of DMC by representing the rare event probability as the product of a number of more frequent events, which are each estimated separately. Previous work published at IPC in 2020 by Bandstra and Fraser [1] showed very close agreement between DMC and Subset Simulation for a single defect reference case with a single limit state. This study extends that initial work by applying Subset Simulation to various failure models for a variety of pipeline defects. Subset Simulation is applied to the CSA corrosion model, PRCI MAT-8 crack model, and the EPRG dent failure model, and the performance is evaluated by comparing the results to DMC. For each of these comparisons, simulations are performed across a large-scale grid of validation cases that consider a range of pipeline and defect sizes. An approach that utilizes Subset Simulation to handle multiple limit states is also presented and applied for relevant failure models and the results are evaluated against DMC.

The landslide disaster tends to cause safe hidden trouble to the normal operation of the pipeline and pipeline is likely to take place accident and get failed under the action of a landslide. According to the theory of winkler, in the condition of pipeline landslide, the mechanical model is established and calculated the stress distribution under different landslide scale. According to the calculation result, the dangerous section of pipe is obtained. Based on the pipeline's own strength and pipeline working stress in the landslide, the limit state equation of the pipes is set up by using the third strength theory. Finally according to the distribution of stress and strength, the pipeline reliability index and failure probability are obtained by means of the first order second moment method improved. The achievement of this paper has great value .to the buried gas pipeline risk assessment. Key words: landslides; The third strength theory; The first order second moment method; Reliability index; Failure probability

ABSTRACTIn the present study, reliability analysis of near surface disposal facility is performed, by assessing the probability of sequential failure of the multi barrier system using the contaminant transport model. The concentration and dose rate of the radionuclide evolve with time hence there is a need for time dependent reliability analysis. Due to the low values of expected probabilities of failure, an enhanced Monte Carlo (EMC) method and Subset simulation is employed. The Result of the analysis show that, the EMC method is useful to evaluate the probability of failure associated with the barrier system which has low probability of failure.

Subsurface explosions seriously threaten the safety and reliability of buried oil and gas pipeline. In order to investigate the mechanical responses of buried steel pipeline under subsurface explosion load, a numerical model of pipeline–soil coupling under explosion load was developed. Stress, displacement, plastic deformation, and local buckling of the buried pipeline were investigated. The effects of trinitrotoluene (TNT) magnitude, pipeline diameter-thickness ratio, pipeline's buried depth, explosive depth, and explosive offset on the mechanical response of pipeline were studied. The results show that the response time of buried pipeline is very short under the explosion load. There is a dent appearing on the pipeline section toward the exploding location. Cross-sectional area of the pipeline decreases along the time during the explosion, but it gradually increases for the elastic recovery. Pipeline's deformation and total energy increase gradually with the increasing of trinitrotoluene magnitude or diameter-thickness ratio, but they decrease with the increasing of the buried depth or explosive offset. With the explosive depth increases, the pipeline's plastic deformation first increases and then decreases. The pipeline's energy curve can be used to determine the buckling state under explosion load. The empirical formulas of the maximum strain and dent rate for buried pipelines have been obtained and can be used for the pipeline safety assessment.

In the practical engineering, to solve the small failure probabilities with correlated high-dimensional variables, the subset simulation (SS) is combined together with the Monte Carlo and importance sampling (IS) method. The samples from the probability density functions (PDF) of the importance sampling are used to construct the intermediate failure events, by which the small failure probabilities are turned into a Markov chain (MC), which is a continuous product made of a series large failure probability or conditional failure probability (CFP) which is easily answered, on which the structural reliability can be efficiently simulated by directly obtaining the samples with correlated ones. Finally, the 3 planet carriers of 3 grade planetary reducers in shield tunneling machine(STM) are as examples to check the algorithm above, the results show that the SS of the IS with correlated variables can highly simulate failure probability.

Heliostats represent the most important maintenance cost in the solar power tower plant. The aim of this work is to provide a failure probability analysis for heliostat design in order to minimize this maintenance cost. Based on mechanics of material study and wind aerodynamic analysis, a performance function, with five random variables, has been developed wherein the random variables are: wind speed, inside and outside pedestal diameters, pedestal yield stress and mirror mass. Four main methods have been proposed: first order reliability method, second order reliability method, Monte Carlo (MC) method and subset simulation (SS) method. The variation of failure probability with the variation of pedestal wall thickness and wind speed, for different outside diameters and heliostat azimuth and elevation angles, has been simulated. The results show that SS is more efficient and accurate for small failure probabilities; however, MC is more accurate for high failure probabilities.

Estimation of the lower and upper bounds on the probability of failure using subset simulation and random set theory

Reliability analysis of subsea pipelines under spatially varying ground motions by using subset simulation

Time-dependent reliability is the probability that a system will perform its intended function successfully for a specified time. Unless many and often unrealistic assumptions are made, the accuracy and efficiency of time-dependent reliability estimation are major issues which may limit its practicality. Monte Carlo simulation (MCS) is accurate and easy to use but it is computationally prohibitive for high dimensional, long duration, time-dependent (dynamic) systems with a low failure probability. This work addresses systems with random parameters excited by stochastic processes. Their response is calculated by time integrating a set of differential equations at discrete times. The limit state functions are therefore, explicit in time and depend on time-invariant random variables and time-dependent stochastic processes. We present an improved subset simulation with splitting approach by partitioning the original high dimensional random process into a series of correlated, short duration, low dimensional random processes. Subset simulation reduces the computational cost by introducing appropriate intermediate failure sub-domains to express the low failure probability as a product of larger conditional failure probabilities. Splitting is an efficient sampling method to estimate the conditional probabilities. The proposed subset simulation with splitting not only estimates the time-dependent probability of failure at a given time but also estimates the cumulative distribution function up to that time with approximately the same cost. A vibration example involving a vehicle on a stochastic road demonstrates the advantages of the proposed approach.

Reliability based design and assessment (RBDA) technique is a developing direction of natural gas pipeline design method. In this paper, a framework for calculating the failure probability of natural gas pipeline is proposed. First, Java reflection mechanism is used in the management of the limit state functions, which enables the separation of the limit state algorithms and the calculations of the failure probability. Under this framework, more newly developed equations can be add into the library of the software readily. Second, a Monte Carlo reliability analysis algorithm capable of incorporating the basic input parameters and limit state functions is used to calculate failure probability of pipelines. Third, a post data processing algorithm is used to improve the efficiency. Finally, an example on natural gas pipeline is presented to illustrate the availability and effectiveness of the software. Experimental results indicate the ability of the proposed framework for pipeline quality control.

In permafrost regions, long distance buried pipelines are widely used to transport oil and natural gas resources. However, pipeline problems occur frequently due to the complicated surrounding environment and transportation requirement of positive temperature. In this study, a thermal insulation layer was applied to mitigate permafrost degeneration around the buried oil-gas pipelines. Based on engineering background of the Sebei-Xining-Lanzhou natural gas pipeline in China, an indoor model test was designed and carried out in which many key indices, such as the temperature regime, vertical displacement, pipeline wall stress, and water content, were closely monitored. The test results indicate that the large heat loss of the buried pipeline produces a rapid increase in ground temperatures which seriously reduces the bearing capacity of the permafrost foundation. The buried oil-gas pipelines with a thermal insulation layer can effectively reduce the thawing range and vertical displacement of the permafrost foundation around the buried pipelines, so as to control the stress of the pipeline wall in the normal range and protect the safe and stable operation of the buried oil-gas pipelines. The experimental results can serve as a reference for the construction, operation, and maintenance of buried oil-gas pipelines in permafrost regions.

Modified subset simulation method for reliability analysis of structural systems

Failure of in-service oil and gas steel pipelines can have disastrous environmental, social and economic impacts. Preventing or alleviating those negative impacts requires a methodology to predict the service life of corroded steel pipes that enables implementing preventive maintenance and repairs measures. Such predictions involve uncertainty and vary in time. This paper puts forward a time-variant reliability-based approach to assess the failure of corroded offshore pipelines. The proposed approach accounts for the uncertainty in the corrosion rate and mechanical characteristics of pipes. Two methods are proposed: One that employs the Monte Carlo sampling and one that is based on the first-order reliability method. The methodology is then applied to three corroded offshore gas pipelines located in India and the time-variant failure probability is estimated considering target reliability. Next, variability and sensitivity analyses are conducted to identify the most influential sources of uncertainty on the failure probability of pipelines. It can be asserted that corrosion rate has a substantial role in estimating the structural reliability of pipelines.

Strain attenuation of buried oil and gas pipelines with rockfall impact eccentricity

Statistical model and structural reliability analysis for onshore gas transmission pipelines