Reliability Analysis Of Pipelines Research Articles

Probabilistic assessment of complex corrosion in pipelines considering River-Bottom Profile information

One of the important causes of failure and incidents in pipelines is corrosion. Due to the severe consequences and impact in several social, economic, and environmental areas, pipelines must be regularly inspected. The possibilities for pipeline assessment are standard equations and numerical simulations. While the first is simple and fast, it tends to be conservative and the second is expensive. The finite element method (FEM) has been successfully used to predict the failure pressure of pipelines under different conditions. Commonly assessment methods overlook the uncertainties for failure predictions, often relying on safety factors. However, it is imperative to consider uncertainties to ascertain the reliability and risk of corroded pipes. While the reliability analysis of pipelines with idealized defects has been extensively explored in the literature, studies considering complex corrosion profiles, are still demanding. This paper addresses this gap considering the traditional Monte Carlo (MC) and first-order reliability (FORM) methods. The assessment is based on the Effective Area Method (EAM) within the failure function. As well know, MC can be expensive due to the high number of function evaluations. To mitigate this, FORM is employed as it requires fewer function evaluations. However, function gradients are required as it relies on an iterative optimization algorithm. Particularly challenges arise when computing the gradient using EAM for burst pressure estimation. The EAM is an iterative procedure, and small perturbations can yield incorrect sensitivity values, causing problems for FORM convergence. To address this, we propose a novel procedure for efficiently and less conservatively obtaining the gradients required by FORM using EAM as a failure function. The modified FORM method achieved convergence within 15 iterations for all test cases. This alternative approach offers a faster, more precise and less conservative method for Level-2 probabilistic failure analysis of complex-shaped corrosion defects compared to traditional Level-1 methods.

Probabilistic modeling for reliability analysis of buried pipelines subjected to spatiotemporal earthquakes

Reliability analysis of buried pipelines subjected to spatiotemporal seismic involves modeling multiple uncertainties related to loads, soil, and mechanical mechanisms. The present study proposes a probabilistic modeling method that can couple random spatiotemporal seismic vibrations in the axial and transverse directions of the pipeline, enabling probabilistic incorporation of stochastic uncertainty (random variability) into the seismic response analysis of structures. Uncertainties of soil properties are probabilistically modeled to simulate the random pipe–soil interaction effect. Spatiotemporal dynamic response of the pipelines is discretized using extreme value distribution theory, thus making the seismic reliability analysis of the pipeline within a time-invariant framework. The applicability and accuracy of the proposed method are illustrated by numerical studies. The application of the probabilistic modeling method supports reliability- and risk-based inspection and maintenance planning for buried pipelines subjected to spatiotemporal earthquakes.

Reliability assessment of pitting corrosion of pipeline under spatiotemporal earthquake including spatial-dependent corrosion growth

The pitting corrosion of pipelines subjected to the spatio-temporal earthquake was evaluated to illustrate the failure probability of multiple loading conditions. The pipeline vibration was modeled as a coupled 3D vibration equation considering the uncertain soil parameters. Using a combination of the Gamma process and Gaussian copula function implemented time-dependent corroded growth of single defect as well as the spatial-dependent between corroded depth growths of different defects. All modeling was embedded in a frame of Bayesian inference and Markov chain Monte Carlo (MCMC) simulation techniques to predict the future corroded growth by reported in-line inspections (ILIs). Moreover, the Monte Carlo simulation (MC) technique was used to evaluate the reliability of the pipeline system, including multiple corroded defects. A case study was employed to prove the application of all proposed models. The results indicate that the reliability analysis of pipelines under the earthquake considering pitting corrosion growth is of considerable significance to the accuracy of the evaluation, which can inform operators from process industry to mitigate the risk of pipeline failure.

A comparative reliability study of corroded pipelines based on Monte Carlo Simulation and Latin Hypercube Sampling methods

Internal corrosion is categorized as one of the most destructive phenomena for pipeline services. This study compares the reliability analysis of pipelines against internal corrosion based on Monte Carlo Simulation (MCS) and Latin Hypercube Sampling (LHS) methods. Three different failure mechanisms (pitting perforation, local burst and rupture) have been considered for single corrosion defect and only local burst has been investigated for multiple corrosion defects. Furthermore, the effects of correlation between the defect depth and defect length for single defects as well as the correlation between the neighboring segments for multiple defects on the failure probability of the pipelines, have been comprehensively studied. The results show that LHS method could lead to quite acceptable accuracy with considerably less computational effort. Regarding multiple corrosion defects, the correlation between the defect depth or defect length of the neighboring segments can change the system failure probability without any monotonic trend.

Reliability Analysis of Pipelines With Local Corrosion Defects Under External Pressure

This paper aims at assessing the reliability of pipelines with local corrosion defects subjected to external pressure. Several collapse strength models are calibrated and then used to formulate the reliability problem of corroded pipelines. Model uncertainty factors are derived for the various collapse strength models based on available experimental results to better predict the effect of local corrosion defects on the reduction of the collapse strength of pipelines. The model uncertainty factor is defined as function of the depth of the local corrosion defect and calibrates the overconservative predictions of collapse strength models that deal with the effect of corrosion defects by considering a uniform reduction of the pipe thickness. The collapse strength models together with the corresponding model uncertainty factors are then used to formulate the reliability problem of pipelines with local corrosion defects subjected to external pressure. Parametric and sensitivity analyses are performed for different levels of corrosion damages to identify the influence of the various parameters on the collapse probability of corroded pipelines under external pressure. Finally, an approach is suggested to calibrate a design code formulation that is conservative when the minimum pipe thickness is used to represent a local corrosion defect. The approach consists of identifying an equivalent depth of the corrosion defect, corresponding to an intermediate thickness of the corroded pipeline larger than the minimum thickness, that adjusts the design code to match the safety levels of the collapse strength model calibrated to the experimental results.

Formal reliability analysis of oil and gas pipelines

Depending on the operational environment, installation location, and aging of oil and gas pipelines, they are subject to various degradation mechanisms, such as cracking, corrosion, leaking, and thinning of the pipeline walls. Failure of oil and gas pipelines due to these degradation mechanisms can lead to catastrophic events, which, in the worst case, may result in the loss of human lives and huge financial losses. Traditionally, paper-and-pencil proof methods and Monte Carlo based computer simulations are used in the reliability analysis of oil and gas pipelines to identify potential threats and thus avoid unwanted failures. However, paper-and-pencil proof methods are prone to human error, especially when dealing with large systems, while simulation techniques primarily involve sampling-based methods, i.e., not all possible scenarios of the given systems are tested, which compromises the accuracy of the results. As an accurate alternative, we propose to use a higher-order-logic theorem proving for the reliability analysis of oil and gas pipelines. In particular, this paper presents the higher-order-logic formalization of commonly used reliability block diagrams (RBDs), such as series, parallel, series–parallel, and k-out-of- n, and provides an approach to utilize these formalized RBDs to assess the reliability of oil and gas pipelines. For illustration, we present a formal reliability analysis of a pipeline transportation subsystem used between the oil terminals at the Port of Gdynia, Poland, and Dębogórze.

Stochastic process corrosion growth models for pipeline reliability

Linear random variable corrosion models are extensively employed in reliability analysis of pipelines. However, linear models grossly neglect well-known characteristics of the corrosion process. Herein, a non-linear model is proposed, where corrosion rate is represented as a Poisson square wave process. The resulting model represents inherent time-variability of corrosion growth, produces continuous growth and leads to mean growth at less-than-one power of time. Different corrosion models are adjusted to the same set of actual corrosion data for two inspections. The proposed non-linear random process corrosion growth model leads to the best fit to the data, while better representing problem physics.

06/02418 Reliability analysis of pipelines carrying H 2S for risk based inspection of heavy water plants : Santosh, A. et al. Reliability Engineering & System Safety, 2006, 91, (2), 163–170.

06/02418 Reliability analysis of pipelines carrying H 2S for risk based inspection of heavy water plants : Santosh, A. et al. Reliability Engineering & System Safety, 2006, 91, (2), 163–170.

Reliability analysis of pipelines carrying H 2S for risk based inspection of heavy water plants

Reliability analysis of pipelines containing corrosion defects due to H 2S is presented. The pipeline carrying H 2S is more susceptible to the internal corrosion thereby reducing the pipeline's load carrying capacity. The objective of this study is to obtain the pipelines' failure probabilities that are required in establishing a Risk Based Inspection (RBI) programme for heavy water plants. The reliability assessment of pipelines involves the estimation of failure pressure and evaluating the limit state function. Several failure pressure models were studied for this purpose and it was found that the modified B31G failure pressure model is most suitable for the pipeline failure pressure modeling. Due to the presence of non-linearity in the limit state function and non-normal variables, the first order reliability method has been employed for carrying out the reliability analysis. The uncertainty of the random variables on which the limit state function depends is modeled using normal and non-normal probabilistic distributions. The failure probabilities and the categories of the pipelines connected to the first pair of first stage of exchange towers are presented. In addition, a sensitivity analysis was carried out on random variables involved in the problem. The results of sensitivity analysis are also presented.

Reliability Analysis of Pipelines During Laying, Considering Ultimate Strength Under Combined Loads

Abstract Structural reliability methods are applied to establish a measure of safety for pipelines during laying, and especially to calibrate semi-probabilistic ultimate limit state criteria based on measures of uncertainty, method of reliability, and a given target level. Ultimate collapse of thick tubes under combined external pressure, tension, and bending loads are studied applying the finite element method. Nonlinear effects of large deformations, effects of initial ovality, residual stresses, strain-hardening, yield anisotropy, and loading paths were accounted for in the analysis. A set of interaction equations is proposed. Load effects in the pipelines during installation by the S-lay method are studied. The effects of uncertainties in yield stress, mass, stiffness of the stinger, response amplitude operator and peak period for the wave spectrum were accounted for in the analysis. The major factors affecting strain concentration due to concrete coating are taken into account. A combination of design point calculation and importance sampling procedure is used to calculate the probability of failure. The study includes calibration of partial safety factors for the design format selected. The most important random variable is the model uncertainty for bending capacity, while the uncertainty of the load effect has minor importance for the probability of failure. The system effect is taken into account considering the correlation along the pipeline. The probability of failure is referred both to the total laying period as well as a 3-h period demonstrating that the target level needs to be defined in view of the reference time period. [S0892-7219(00)01501-6]