Prediction on Failure Pressure of Pipeline Containing Corrosion Defects Based on ISSA-BPNNModel

Oil and gas pipelines are affected by many factors,such as pipe wall thinning and pipeline rupture.Accurate prediction of failure pressure of oil and gas pipelines can provide technical support for pipeline safety management.Aiming at the shortcomings of the BP Neural Network(BPNN)model,such as low learning efficiency,sensitivity to initial weights,and easy falling into a local optimal state,an Improved Sparrow Search Algorithm(ISSA)is adopted to optimize the initial weights and thresholds of BPNN,and an ISSA-BPNN failure pressure prediction model for corroded pipelines is established.Taking 61 sets of pipelines blasting test data as an example,the prediction model was built and predicted by MATLAB software,and compared with the BPNN model,GA-BPNN model,and SSA-BPNN model.The results show that the MAPE of the ISSA-BPNN model is 3.4177%,and the R2 is 0.9880,both of which are superior to its comparison model.Using the ISSA-BPNN model has high prediction accuracy and stability,and can provide support for pipeline inspection and maintenance.

Failure pressure calculation of fracturing well based on fluid-structure interaction

Failure pressure is a key parameter in reservoir hydrofracturing operation. Existing analytical methods for calculating the failure pressure are based on the assumption that borehole fluid is under two extreme conditions: non-infiltration or complete infiltration. The assumption is not suitable for the actual infiltration process, and this will cause a great error in practical calculation. It shows that during the injection process, the dynamic variation in effective stress-dependent permeability has an influence on the infiltration, and the influence also brings about calculation errors. Based on the fluid-structure interaction and finite element method (FEM), considering partial infiltration during injection process, a numerical model for calculating rock failure pressure is established. According to the analysis of permeability test results and response-surface method, a new variation rule of rock permeability with the change of effective stress is presented, and the relationships among the permeability, confining pressure and pore pressure are proposed. There are some differences between the dynamic value of permeability-effective-stress coefficient observed herein and the one obtained by the classical theory. Combining with the numerical model and the dynamic permeability, a coupling method for calculating failure pressure is developed. Comparison of field data and calculated values obtained by various methods shows that accurate values can be obtained by the coupling method. The coupling method can be widely applied to the calculation of failure pressure of reservoirs and complex wells to achieve effective fracturing operation.

Failure Pressure Analysis of Corroded Moderate-to-High Strength Pipelines

Based on the elastic-plastic, large-deformation finite element method, burst capacity of steel pipeline with longitudinal corrosion defect subjected to internal pressure is studied. The appropriate stress-based criterion is used to predict the failure pressure of finite element model of corroded pipeline under internal pressure. By considering the pipe steel grades and geometries of corrosion defects, a series of finite element analyses is conducted. The effects of corrosion depth, length and width on burst capacity are also discussed. A specific failure pressure solution for the assessment of corrosion defects in moderate-to-high strength pipeline is proposed on the base of numerical results. The failure pressures predicted by the proposed method are in better agreement with the experimental results than the results by the other methods.

Deformation and failure study of surrounding rocks of dynamic pressure roadways in deep mines

In order to understand the change rules of stress-displacement in surrounding rocks of dynamic pressure roadways in deep mines and to obtain a theoretical basis for analyses of roadway stability and designs of support, we established a coupling equation of adjacent rock strength, mining stress and supporting resistance on the basis of an elastic-plastic theory of mechanics. We obtained an analytical solution for stress and displacement distribution of elastic and plastic regions in surrounding rock of dy-namic pressure roadway.. Based on this theory, we have analyzed the changes in stress-displacement in elastic and plastic regions of surrounding rocks of dynamic pressure roadways in the Haizi Coal Mine. The results show that: 1) radial and tangential stress change violently within the first 4 m from the inner surface of a roadway after excavation; radial stress increases while tangential stress decreases within a range of about 6 m from the inner surface of the roadway as a function of q3; 2) radial and tangential stress increase with an increase in the mining pressure coefficient k; the increase in the rate of tangential stress is greater than that of ra-dial stress; 3) the radial displacement of the inner surface of roadways decreases with an increase in q3, provided that k remains unchanged.

Standards and methods for dent assessment and failure prediction of pipelines:A critical review

Dent,a common mechanical damage on pipelines,is associated with a significant local plastic deformation.Dents can cause pipeline failures,especially when they are combined with other types of defects such as gouges,fatigue,corrosion,and cracks.In this work,a systematic review of various assessment methods and standards for pipeline dents,including the combination of a dent with other defects,is conducted.Generally,the methods available today are not sufficiently accurate and reliable to assess pipeline dents,especially the dent-defect combinations.For plain dents on pipelines,both the depthbased criterion and the strain-based criterion are commonly used in engineering.Their main problems include inaccuracy and conservatism.For a dent combined with other defects,the existing assessment techniques are not mature enough to give reliable results.Both experimental testing and numerical modeling through finite element(FE)analysis are capable of investigating the influence of dents and dent-defect combinations on burst failure pressure of the pipelines,although an approximation to the reality is still the main difficulty existing in the experimental testing and FE analysis.Nowadays,relevant studies on assessment techniques for plain dents,a dent with fatigue and a dent with a single gouge have been common in literature.The combinations of a dent with corrosion or cracks have been rarely assessed due to complicated mechanisms involving a multi-physics coupling effect.Development of novel assessment methods by integrating mechanical stress and strain,electrochemical reactions and steel metallurgy will be a key topic to accurately assess the dent-defect combinations for improved pipeline integrity.

Numerical modeling of permeability evolution based on degradation approach during progressive failure of brittle rocks

The permeability evolution of rock during the progressive failure process is described. In combination with the strength degradation index, the degradation formulas of s and a, which are dependent on the plastic confining strain component, the material constants of Hock-Brown failure criterion are presented, and a modified elemental scale elastic-brittle-plastic constitutive model of rock is established. The rela- tionship between volumetric strain and permeability through tri-axial compression is investigated. Based on the above, a permeability evolution model is established. The model incorporates confining pressure- dependent degradation of strength, dilatancy and corresponding permeability evolution. The model is implemented in FLAC by the FISH function method. The permeability evolution behavior of rock is inves-tigated during the progressive failure process in a numerical case. The results show that the model is cap- able of reproducing, and allowing visualization of a range of hydro-mechanical responses of rock. The effects of confining pressure on degradation of strength, dilatancy and permeability evolution are also reflected.

Study on Interaction Relationship for Submarine Pipeline with Axial Corrosion Defects

Corrosion is one of the main reasons to cause the operation accident of submarine oil and gas transmission pipelines. As the major corrosion pattern in submarine pipelines, the effects of corrosion clusters consisting of the adjacent corrosion defects on failure pressure are investigated through non-linear large-deformation finite element method. Typically, the failure behavior and limit strength of submarine pipeline with axial groove- groove corrosion defect pair exposed to interhal pressure are analyzed. The effects of corrosion depth and axial spacing between a pair of corrosion defects on failure pressure are concluded. An interaction relationship for corrosion defects in pipelines, as well as prediction formulations for assessing the remaining strength of corroded pipelines are proposed. The expressions based on the proposed interaction relationship give more accurate results than the methods used in the existing design guidelines.

Limit Load Analysis of Pipes with Local Wall-thinning

The loss of metal in a pipe due to corrosion usually results in localized thinned areas with various depths and an irregular shape on its surface. In this paper, a number of numerical models of pipes with different size defects are established. The limit loads of these pipes are researched using the nonlinear finite element method. The effect of defect parameters of the local wall-thinning pipes on the limit load is discussed. The results show that limit loads decrease obviously when the depths and lengths of the defect increase. However, when the defect length reaches a certain value, the effect of defect length on limit loads is not significant. These results are compared with the results of the method of API 579. When the defect length is adequately small, the results of FEM are in good agreement with the ones of APl 579, but when the defect depth and length is adequately large, the API 579 is not suitable.

Risk Assessment Based on Fault Tree Analysis for Damaged Pipe Repair During Operation in Petrochemical Plant

In petrochemical plant, the in-operation repairing is usually a repairing strategy with pressured inoperation repairing for avoiding huge economic losses caused by unplanned shutdown when some slight local leakage happens in pipes. This paper studies the effects of repairing strategies on the failure probability of the pipe systems in process industries based on the time-average fault tree approach, especially the in-operation repairing strategies including pressured in-operation repairing activities. The fault tree model can predict the effect of different repairing plans on the pipe failure probability, which is significant to the optimization of the repairing plans. At first pipes are distinguished into four states in this model, i.e., successive state, flaw state, leakage state and failure state. Then the fault tree approach, which is usually applied in the studies of dynamic equipment, is adopted to model the pipe failure. Moreover, the effect of pressured in-operation repairing is also considered in the model. In addition, this paper proposes a series of time-average parameters of the fault tree model, all of which are used to calculate node parameters of the fault tree model. At last, a practical case is calculated based on the fault tree model in a repairing activity of pipe thinning.