Analysis of the integrity of welded pipes of gas mains by the FITNET procedures

We have evaluated the integrity of a rectilinear element of a welded pipe of a gas main after its operation for 40 years with the use of the FITNET procedures according to the Failure-Assessment-Diagram approach. We have determined the critical sizes of defects in the base (17G1S steel) and weld metal of a longitudinal welded joint of a reserve pipe. Two levels of the gas pressure in the pipeline (4.5 and 7.0 MPa) are taken as critical values. It has been shown that, in the absence of corrosion and hydrogenating influence of the transported medium, the base metal of pipes both in as-received state and after long-term operation is more susceptible to fracture due to reaching the critical stressed state than the weld metal.     

Gas transmission pipeline failure probability estimation and defect repairs activities based on in-line inspection data

Degradation of an underground pipeline during its service life leads to reduction of the pipe wall thickness. Periodic in-line inspections are performed by onshore pipelines operators to detect corrosion anomalies and size their depth and width. In the paper, a simple analytical method of burst pressure calculation for a straight pipeline repaired with a composite sleeve was investigated. Repair activities after an in-line inspection of a gas transmission pipeline were considered in this research to assess the pressure of a pipe with a flaw reinforced with a different number of layers of a fiber-based polymer sleeve. Det Norske Veritas criteria and formulation of a limit state function were applied to determine the burst pressure and corresponding failure probability of a pipeline with a large number of single and non-interacting part-wall defects. The Monte Carlo method was selected for estimation of pipeline failure probability and cumulative failure probability due to the external corrosion considering fluid pressure fluctuations in dynamic flow effects with respect to statistical distribution of input parameters were examined in this research. The proposed novel 3-step approach was validated on the real data collected from an onshore high pressure gas pipeline DN 700, MOP 5.5 MPa provided by two magnetic flux leakage inspections repeated at an interval of twelve years. A probabilistic methodology was applied to evaluate the part-wall external corrosion defects and their deterministic linear growth with time and repair activities on gas transmission pipelines were analyzed. The results of this study shall help maintenance engineers solve the problems of an optimal strategy in reliability-based high pressure gas pipelines management.     

Revised burst model for pipeline integrity assessment

Failure of pipeline is often caused by corrosion. It affects the health, safety, environment and economy considerably. To prevent pipeline failure, it is necessary to focus on the corrosion and pressure of the structures. Burst pressure is a key factor to assess the integrity of a pipeline. There are three means to determine burst pressure. These are lab testing, evaluation criteria and the Finite Element Method (FEM) modeling. However, the results of the burst pressure assessment using evaluation criteria are too conservative compared to the results of an actual pipe burst experiment and FEM modeling.The objectives of this paper are to analyze the changing trend of burst pressure of pipelines with different defect dimensions; to compare the FEM results with those of the evaluated criteria (DNV model) to indicate the conservative property; to revise the DNV model and verify its validity with actual burst experiments. The revised DNV model predicts burst pressure more reliably that could result in better engineering design of pipelines.     

Assessment on failure pressure of high strength pipeline with corrosion defects

An accurate prediction on the failure pressure of line pipe is very important in the engineering design and integrity assessment of oil and gas transmission pipelines. This paper analytically investigates the failure pressure of line pipes with or without corrosion defects, and focus on the high strength steels. Based on von Mises strength failure criterion, a classic strength failure criterion, the failure pressure of end-capped and defect-free pipe p_M is theoretically deduced with the strain hardening material. In order to derive a general solution for corrosion defect assessment of high strength pipelines, an extensive series of finite element analyses on various elliptical corrosion defects was performed. Finally, a new formula for predicting the failure pressure of corroded pipe in the material of high strength steels is formulated, based on the FE models and p_M, and is validated using 79 groups of full-scale burst test data, which contain the low, middle and high strength pipeline. The results indicated that the proposed formula for predicting the failure pressure is closely matches the experimental data for the high strength steels.     

Ductile fracture of a pipe with a rectangular three-dimensional defect

A model is constructed to describe the ductile fracture of a pipe with a rectangular three-dimensional defect. Upper and lower bounds are obtained for the burst pressure. The first is calculated for a rectangular crack, while the second is calculated for an axisymmetric three-dimensional defect. It is shown that if the half-width of the defect b₀ is equal to 2(Rt_n)^1/2 — where R is the radius of the pipe and t_n is the net thickness of the pipe wall—then the defect can be regarded as axisymmetric. Calculated values of burst pressure are compared with literature data from full-scale tests of pipes. The results can be used to analyze actual defects in pipelines (pitting, etc.), as well as in conducting full- scale tests of pipes and pressure vessels.Translated from Problemy Prochnosti, No. 9, pp. 55–66, September, 1995.     

Physical and Mechanical Aspects of Corrosion Damage of Distribution Gas Pipelines After Long-Term Operation

The fractographic analysis of the corrosion damage of the pipe surface of the distribution gas pipeline after 40 and 56 years of operation is performed. The mechanisms of formation of corrosion pits, laminations, and deep crack-like defects are systematized. On the basis of laboratory studies, which simulate operation conditions of a distribution gas pipeline in corrosive medium, the basic regularities in general corrosion of steel St. 3 in neutral chloride electrolytes are determined, depending on the value of the current density and chemical composition of the medium.     

Damage to the Metal of Industrial Pipelines in a Hydrogen Sulfide Environment

We studied changes in the mechanical properties of the metal of pipelines of oil- and gas-production equipment after long-term operation. We established that the mechanical characteristics of internal surface layer of the metal change significantly up to a depth of 2 mm. The coefficient of metal degradation depending on the thickness of pipe wall was introduced. We showed that deformation under the action of loads stimulates hydrogen-induced cracking. The corrosion rate at the lower part of a pipeline is 5.5 times as high as at the upper. We also showed the expediency of inhibitor protection of pipelines.     

Fracture mechanics defect assessment diagram on pipe from steel P264GH with a notch

The design for a pipeline component is considered a tough challenge once defects in the base material develop. To address this issue, we present a gouge defect located in a pipe submitted to internal pressure. This problem is often encountered in the field of pipeline network and boiler components because of structural imperfection. To simulate the activity of such pressurized pipeline, a longitudinal cylindrical shell under pressure from a material of steel P264GH were involved in the research. Secondly, by this paper we propose a safety methodology to detect the boundary of failure assessment diagram (FAD), as a new solution to predict the service life of pipeline products. The methodology is connected to the modified FAD approach, whereas the specific parameters were settled using the Volumetric Method calculation, based on the notch Stress Intensity Factor, determined in the elasto-plastic field. This new modified FAD methodology entails an accurate solution, suitable to be used as expert tool for the assessment of workability and reliability of pipes network, in the case of corrosion defects presence.     

Analysis of shape and location effects of closely spaced metal loss defects in pressurised pipes

Metal loss due to corrosion is a serious threat to the integrity of pressurised oil and gas transmission pipes. Pipe metal loss defects are found in either single form or in groups (clusters). One of the critical situations arises when two or more defects are spaced close enough to act as a single lengthier defect with respect to the axial direction, causing pipe ruptures rather than leaks, and impacting on the pressure containing capacity of a pipe. There have been few studies conducted to determine the distance needed for defects to interact leading to a failure pressure lower than that when the defects are treated as single defects and not interacting. Despite such efforts, there is no universally agreed defect interaction rule and pipe operators around the world have various rules to pick and choose from. In this work, the effects of defect shape and location on closely spaced defects are analysed using finite element analysis. The numerical results showed that defect shapes and locations have a great influence on the peak stress and its location as well as the failure pressure of pipes containing interacting defects.     

Assessment of corrosion damage acceptance criteria in API579-ASME/1 code

This study presents a comparative evaluation of the various acceptance criteria in API579-ASME/1 fitness-for-service (FFS) code for equipment suffering from metal loss, using a case of severe corrosion in a pipe subjected to internal pressure and supplemental loads. All three assessment levels were conducted to evaluate the remaining life of the pipe under various acceptance criteria assuming constant corrosion rate. In particular, Level-3 assessment was performed using three-dimensional parametric limit finite element analysis to evaluate the remaining life. The model accounts for the observed metal loss, with the aim of evaluating the plastic collapse pressure of the corroded pipe. The remaining life was estimated using both global and local failure criteria and the conservatism of various methods and criteria is assessed. Results showed a potential trade-off of continued operation at the original design pressure for shorter period against a pressure de-rating procedure for extended operation.     

Incoloy 825/L360复合管焊接接头耐蚀性研究

目的研究Incoloy 825/L360复合管焊后的焊缝耐蚀性能。方法以Incoloy 825/L360复合管为研究对象,选用Inconel625焊材进行了镍基合金焊缝的焊接,并对焊缝和Incoloy 825母材在质量分数为3.5%的NaCl溶液、6%的FeCl_3溶液中进行电化学试验,并对其耐蚀性进行了对比分析。结果在质量分数为3.5%的NaCl溶液中,不同温度下母材自腐蚀电位均高于焊缝,自腐蚀电流密度均小于焊缝,随着温度的升高,母材的自腐蚀电位和焊缝的自腐蚀电流密度均增加,母材的自腐蚀电流密度变化不明显;在质量分数为6%的FeCl_3溶液中,母材与焊缝的自腐蚀电位整体较高,母材的自腐蚀电流密度高于焊缝,不同温度下焊缝极化曲线均存在明显的钝化平台。结论 Incoloy 825母材和焊缝在两种溶液中的耐蚀性存在一定差异;在质量分数为3.5%的NaCl溶液中,母材腐蚀对温度不敏感,焊缝的腐蚀敏感倾向性随着温度的升高而增大,腐蚀敏感性高于母材;在质量分数为6%的FeCl_3溶液中,不同温度下的焊缝极化曲线均存在明显的钝化平台,腐蚀敏感性低于母材。     

Failure analysis of an A333Gr6 pipeline after exposure to a hydrogen sulfide environment

The analysis of an A333Gr6 pipeline failure was conducted after exposure to high H₂S partial pressure for several hours. Chemical composition, metallurgical structure, steel pipe hardness, and the welding joint near the broken position were studied. The chemical compositions of corrosion products inside the steel pipe were also analyzed. Results show that corrosion products consist of Fe₃O₄ and FeOOH without ferrous sulfide. Stress analysis was obtained through the finite element analysis method. The failure analysis and calculation results show that spontaneous ferrous sulfide combustion in a high H₂S environment leads to high temperature and pressure in the pipe, resulting in pipeline breakage.     

Location and Sizing of Defects in Coated Metallic Pipes Using Limited View Scattered Data in Frequency Domain

The inverse problem of reconstructing the location and size of defects in a coated metallic pipe from single frequency limited view electromagnetic scattered field is considered. Specifically, the paper addresses the problem of assessing shape changes in the shadow region entailed by limited view data in 2D by operating in an intermediate size parameter (ka) range. The inverse scattering problem is formulated as a non-linear optimization problem solved through genetic algorithm that seeks to minimize in the least-squared sense the difference between measured data and simulated data through iterations of the solution to a forward problem. The hybrid finite element boundary integral formulations were used to solve the forward problem of coated metallic pipe with defects. The proposed inversion methodology was applied for shadow region shape change assessment to determine whether a metal pipe is coated or not, and to reconstruct the location and size of corrosion-like defect, over a range of size parameters. The study is carried out using transverse electric and transverse magnetic polarized fields. To understand the effect of coating on backscattered fields, parametric studies are conducted using numerical data. A range for size parameter \(2.0\le ka\le 4\) was found to produce the highest contrast between defect free pipe and coated metallic pipes with defects in the deep shadow region. The experiments are carried out using vector network analyzer in an anechoic chamber. The inversion results obtained using measured data were found be in good agreement with inversion results obtained using synthetic data. Estimated extent of corrosion in deep shadow region of a coated metallic pipe was found to be within 9 % of actual extent of corrosion.     

A review of surfactants as corrosion inhibitors and associated modeling

Surfactants have been commonly used as corrosion inhibitors for the protection of metallic materials against corrosion. The amphiphilic nature of surfactant molecules creates an affinity for adsorption at interfaces such as metal/metal oxide–water interface. The adsorption of surfactant on metals and metal oxides creates a barrier that can inhibit corrosion. The properties of surfactant and the interaction of surfactant with metal or metal oxide and the surrounding solution environments determine the level of adsorption and corrosion inhibition. Understanding and modeling the behavior of surfactants in corrosive environments is critical to optimal utilization of surfactants as corrosion inhibitors. This review of surfactants as corrosion inhibitors is designed to provide systemic evaluation of various physical and chemical properties of surfactants, surfactant behaviors in corrosive environments, and their influence in corrosion inhibition, which can be used to improve the effectiveness with which surfactants are used as corrosion inhibitors in a variety of environments. Progress in the development of various predictive models, including semi-empirical models, mechanistic models, and multiphysics models, are reviewed for the evaluation and prediction of surfactant properties and surfactant corrosion inhibition efficiency. Applications of these models to experimental design and analysis, surfactant design and selection, and lifetime prediction are also discussed.     

Characterization of microstructure,chemical composition,corrosion resistance and toughness of a multipass weld joint of superduplex stainless steel UNS S32750

The superduplex stainless steels have an austeno-ferritic microstructure with an average fraction of each phase of approximately 50%. This duplex microstructure improves simultaneously the mechanical properties and corrosion resistance. Welding of these steels is often a critical operation. In this paper we focus on characterization and analysis of a multipass weld joint of UNS S32750 steel prepared using welding conditions equal to industrial standards. The toughness and corrosion resistance properties of the base metal, root pass welded with gas tungsten arc welding, as well as the filler passes, welded with shielded metal arc welding, were evaluated. The microstructure and chemical composition of the selected areas were also determined and correlated to the corrosion and mechanical properties. The root pass was welded with low nickel filler metal and, as a consequence, presented low austenite content and significant precipitation. This precipitation is reflected in the corrosion and mechanical properties. The filler passes presented an adequate ferrite:austenite proportion but, due to their high oxygen content, the toughness was lower than that of the root pass. Corrosion properties were evaluated by cyclic polarization tests in 3.5% NaCl and H₂SO₄ media.     

Degradation of properties of the metal of welded joints in operating gas mains

Mechanical and electrochemical properties of individual zones of a welded joint of 17H1S pipe steel are investigated. It is established that long operation causes decreases in the plasticity and impact toughness, especially of the metal of the heat-affected zone. For the operated metal, we observe a general regularity of the shift of the potential for all zones of the welded joint in the direction of negative values, which is the weakest for the base metal. With increase in the operation time of main pipelines, corrosion may be localized on the weld metal.     

低碳钢的激光除锈机理及表面性能研究

激光除锈技术是一种新型、绿色环保的除锈方法。对一些在极易生锈的工作环境中的低碳钢构件,采用激光除锈技术代替传统除锈方法,有广阔的发展前景。激光除锈技术主要利用辐射在锈蚀表面的激光能量高、脉冲短的特点,使锈蚀温度很快达到熔点以上。但在除锈的同时,会有部分激光透过锈蚀层直接与金属基底作用,以及辐射在锈蚀表面的激光也会通过热传导将部分能量传递到金属基底表面。本文采用实验分析手段,对金属基底表面的微观组织、力学性能、硬度等进行对比研究。结果表明,所采用的激光除锈工艺在获得良好的除锈效果情况下,对金属基底没有造成损伤,对金属基底表面性能没有产生显著影响.     

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 th...     

CFD analysis of the dynamic behaviour of a pipe system

An unsteady flow of viscous-compressible fluid through a pipe system induced by a transient disturbance at the pipe intake is studied by means of ANSYS-CFX Navier-Stokes code. The disturbance is predefined as a time-dependent boundary condition at the pipe inlet. The flow through the pipe is calculated using a system of RANS equations combined with various turbulence models. Based on data obtained by analysing a single straight, circular pipe, advanced systems of three and seven pipes are modeled and systematically analysed. The pressure responses of complex, periodically excited systems are observed under various boundary conditions. Time-domain results are transformed into the frequency-domain in order to determine the frequency content of the dynamic response for each simulation. Considering relevant criteria, an approach is presented for the determination of crucial parameters to enable the evaluation of system operation. An original diagram of such parameters is proposed, which allows convenient evaluation of the performance of various pipe systems.     

流体横掠泡沫金属中等温光管的流动与传热分析

基于Brinkman-Forchheimer-extended Darcy流动模型和局部热平衡传热理论建立了流体横掠泡沫金属中等温光管的对流传热控制方程组,运用Runge-Kutta法和"打靶法"对方程组进行了数值求解,依据数值计算结果对流体流动与传热性能进行了分析,并得出了对流传热的Nusselt数关联式。结果表明,泡沫金属的孔隙率和孔密度(ppi)对强化传热起着至关重要的作用,但它的存在同时也增大了压力降,这为泡沫金属在换热器等化工设备上的实际应用提供了理论依据。