Experimental studies on the failure of oil pipes with inner surface corrosion defects

The results of experimental studies on the failure of oil pipes with defects on their inner surfaces are presented. It has been found that in predicting the residual life of an oil pipe the criteria of corrosion-and-mechanical and corrosion-erosion wear should be used.     

Pitting corrosion failure analysis of a wet gas pipeline

This paper presents corrosion failure analysis of an underground natural gas pipeline. The pipeline material grade is API 5L X65 with 10-in ID. The pipeline transfers multiphase fluid (gas, condensate, and water) from a gas well to a gas gathering plant, located 4200 m away from the well site. A portion of the line failed due to pitting corrosion under unknown circumstances. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are employed to characterize the scales and/or corrosion products near the failed portion. Based on visual and microscopic analyses and reviewing the background information, the following pitting corrosion sequences were identified: the oversized pipeline changed the dominant flow regime to “stratified”. In the stratified flow regime, the accompanying water phase accumulated in the pipelines' low points. Considerable concentration of calcium ions along with high pH in CO₂ media favored precipitation of calcium carbonate. The relatively thick scales adhered to the pipe surface were partially loosened and removed by the regional turbulent flow. This exposed the fresh steel surface to the corrosive media. The uncovered areas acted as the preferential anodic sites coupled with nearby large cathodic sites which were covered by scales and/or corrosion products. Under such conditions, pits emerged on the steel surface until one of them grew faster and failed the gas pipeline.     

Stress corrosion failure of high-pressure gas pipeline

Incidents of failure due to corrosion/stress corrosion cracking of high-pressure gas pipelines in Pakistan have been observed to occur after about 15–20 years of service. The present paper constitutes the failure analysis of an 18-inch diameter electric resistance-welded gas pipeline. The failure was characterized, on the basis of all the available evidence and the metallurgical examination carried out on the ruptured pipe, as a stress corrosion failure that had initiated at a longitudinal ‘stress raiser’. This stress raiser, which was essentially a manufacturing defect, constituted a longitudinal ‘step’ on the pipe surface that had resulted from the faulty trimming/shaving of the weld flash. The findings of this study, thus, emphasize the need for the care that must be taken during the shaving-off of the weld flash.     

Multiple failures of API 5L X42 natural gas pipe: Experimental and computational analysis

Multiple failures of API 5L X42 (X42) coal–tar coated natural gas feeder line due to vertical jetting of high pressure erosive slurry was studied experimentally and computationally. Computational Fluid Dynamic (CFD) was used as the simulation tools to study the flow pattern, velocity distribution and strain rates on pipe surface. Experimental work was performed to determine the erosion pattern. Three different diameters of jetting sources produced three distinct impact patterns were clearly identified. These patterns were frequently referred in the experimental study. A CFD simulation result shows that the highest shear strain rate area coincides with the leakage point. These results thus support the hypothesis that it is very likely that the failure of the gas pipeline was caused by the high pressure water jet gusting from the failed welded joint of the water pipeline.     

Experimental and numerical studies on a bubble-induced inverse gas-liquid-solids fluidized bed

Hydrodynamics in a newly invented bubble-induced inverse gas–liquid-solids three-phase fluidized bed has been studied via both experimental and numerical methods. With experiments in a 3.0 m column of 0.153 m in diameter, four fluidization regimes including a fixed bed regime, a bed expansion regime, a complete fluidization regime, and a freeboard regime have been identified with the increase in the superficial gas velocity. A three-phase Eulerian-Eulerian CFD model was developed to simulate the hydrodynamics in the inverse three-phase fluidized bed and the simulation results have a good agreement with the experimental data. The effects of the particle property and solids loading on the transitions across the flow regimes were numerically studied. A higher solids loading and/or a larger particle density are reported to contribute to an easier fluidization and a faster flow development to the complete fluidization regime. The radial flow structure becomes less uniform with increased inner circulation of the liquid after introducing more bubbles into the column.     

Experimental studies on CO2 corrosion of rubber materials for packer under compressive stress in gas wells

The corrosion performance of rubber materials exposed to high temperature high pressure CO₂ environment has been investigated under a compressive state. The dissimilarity of attack was compared in two exposure conditions i.e. gaseous CO₂ and liquid CO₂ under different compressive stress by mechanical properties testing and morphology analysis. Experimental comparisons showed that rubber samples exposed to liquid CO₂ exhibited greater reactivity as compared to gaseous CO₂. The existence of compressive stress would aggravate the corrosion of CO₂ to rubber materials. Factors that affect the corrosion process have been discussed to evaluate corrosion behavior of the packer rubber materials.     

Experimental and numerical study of heavy gas dispersion in a ventilated room

In order to better evaluate the consequences of an accidental release of heavy gas, such as uranium hexafluoride (UF(6)), in some installations in the nuclear fuel cycle, an experimental and numerical study was conducted by IRSN on heavy gas dispersion in a ventilated room. This study was based on about 20 injection configurations of a large quantity of a heavy tracer gas, sulphur hexafluoride (SF(6)), inside two ventilated rooms of different sizes. Stratification of the tracer gas was detected in all the configurations studied, even at low concentrations. Numerical simulations performed with the multidimensional CFX code enabled the stratification and the concentration levels reached in the rooms to be predicted overall, and the higher the air flow rate, the more satisfactory the comparison between simulation and experiment.     

Propagation of steel corrosion in concrete: Experimental and numerical investigations

This paper focuses on experimental and numerical investigations of the propagation phase of reinforcement corrosion to determine anodic and cathodic Tafel constants and exchange current densities, from corrosion current density and corrosion potential measurements. The experimental program included studies on RC specimens with various binder compositions, concrete cover thicknesses, and concrete cover crack widths. Modelling and fitting of experimental data using an electrochemical model allowed for the determination of parameters, which are key parameters for electrochemical modelling tools. The numerical model was, furthermore, used to identify electrochemical parameters, which are independent of concrete cover thickness and crack width and at the same time allow for determination of the corrosion current density and corrosion potential of concrete structures within an acceptable error.Very good comparisons between the experimentally measured and numerically simulated corrosion current densities and corrosion potentials were found for the various RC specimens. Anodic and cathodic Tafel constant between 0.01 and 0.369 V/dec and 0.01 and 0.233 V/dec, respectively, were found in the present study through numerical simulations of the experimental data. Anodic and cathodic exchange current densities ranged from 1.0E–12 to 1.0E–09 A/mm² and 1.0E–12 to 1.1E–09 A/mm², respectively.     

Hot corrosion failure in the first stage nozzle of a gas turbine engine

First-stage nozzles of gas turbines, which are the first elements after the combustion chamber, encounter hot gases from the combustion process and have the task of directing the fluid path and increasing the velocity of combustion products. This paper reports on the incidence and failure of the first-stage nozzles of a gas turbine in September 2013 at a seaside pump-house located in the South-West of Iran. The nozzle was made of nickel-based superalloy Nimonic105. Due to nozzle failure, the turbine was damaged severely. The cause of nozzle failure was investigated. The results of visual inspection, XRD analysis of deposits on the blade airfoil, SEM images and EDAX analysis showed the characteristics of hot corrosion. Finite-element analysis (FEM) revealed that the cause of blade trailing edge failure was thermal stress leading to thermal fatigue, which accelerated nozzle blade failure in addition to the hot corrosion.     

Experimental and numerical studies of the J-integral for a surface flaw

Applied J-integral values for a surface cracked tensile panel are experimentally evaluated by measuring strain and displacement quantities along an instrumented contour located on the longitudinal symmetry plane. Nonlinear, 3-D, finite-element analyses are employed to obtain corresponding estimates of the contour and area integral contributions to a 3-D J-integral. Finite element results indicate that the area integral contribution is negligibly small on the symmetry plane; the fracture driving force is thus adequately characterized by the experimental contour values. Detailed comparisons of the experimental and numerical results (crack mouth opening displacement, J-values, and strains along the contour) reveal that the one-quarter symmetric, finite element model accurately predicts the panel response for overall (gauge length) strains approaching 1.6 times the material yield strain, beyond which the observed deformation patterns exhibited globally asymmetric shear bands.

---

Résumé On évalue expérimentalement les valuers de l'intégrale J dans un panneau en traction fissuré en surface, en mesurant les dilatations et les déplacements suivant un contour instrumenté localisé le long du plan de symétrie longitudinale. On utilise une analyse non linéaire par éléments finis à trois dimensions afin d'obtenir des estimations de la manière dont les intégrales de contour et de surface contribuent à l'intégrale J à 3D.Les résultats par éléments finis indiquent que la contribution de l'intégrale de surface est négligeable suivant le plan de symétrie; le déterminant de la rupture peut done être adéquatement décrit par les valeurs expérimentales relatives au contour.Des comparaisons sur le détail des résultats expérimentaux et numériques révèlent qu'un modèle par éléments finis quart-symétriques peut prédire de manière sûre la réaction de la pièce par rapport à des dilatations globales de près de 1,6 fois la dilatation à la limite élastique du matériau, valeur au-delà de laquelle les configurations de la déformation observées font état de bandes de glissement globalement asymétriques.

     

Experimental studies on an indigenous coconut shell based activated carbon suitable for natural gas storage

Experimental studies are carried out to characterize an indigenous, coconut shell based, activated carbon suitable for storage of natural gas. Properties such as BET surface area, micropore volume, average pore diameter and pore size distribution are obtained by using suitable instruments and techniques. An experimental setup is developed to estimate the equilibrium methane adsorption capacity and adsorption/desorption kinetics. The experimental isothermal uptake data is used to fit four different isotherm models. Using the constants obtained for the D–A isotherm model the variation of heat of adsorption and adsorbed phase specific heat with equilibrium pressure and temperature are obtained. Similarly Henry’s Law coefficients, important at low pressure and low uptake regime are also obtained. Finally using the kinetic data and a linear driving force model, constants in the kinetic equation are obtained. Results show that the indigenous material used in this study offers reasonably high natural gas storage capacity and fast kinetics and is suitable for adsorbed natural gas (ANG) applications. It is expected that this study will be useful in the design and development of ANG systems based on this indigenous material.     

Experimental and numerical studies in model composites Part I: Experimental results

Results on strength, apparent toughness, fatigue crack growth and fiber debonding on specially made composite materials are reported. The compact tension composite specimen used consisted of an epoxy matrix and layers of long aligned glass or kevlar fibers that were equally spaced. The experimental data on crack initiation strength showed that for a range of fiber spacing , the composite's strength _A , scaled with the fiber spacing in the form of % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaOqaaiabeo8aZnaaBa% aaleaaieGacaWFbbaabeaakmaakaaabaGaeq4UdWgaleqaaOGaeyyp% a0JaeqOUdSgaaa!3EB5!\[\sigma _A \sqrt \lambda = \kappa \]. The apparent toughness of the composite specimens increased with a decrease in fiber spacing. Two sets of fatigue crack propagation experiments were performed. The first one was on specimens with the same fiber spacing and under different applied loads. The second set was on specimens with different fiber diameter and the same loading conditions. While crack arrest was observed in the first set, crack arrest was seen in the second set for the relatively large diameter fibers and specimen fracture for the relatively thin fibers. A method, based on fracture mechanics principles and crack opening displacements, for evaluating bridging tractions is outlined. Using this method, simulations for the bridging tractions and stress intensity factor were carried out using a linear crack opening profile. The total stress intensity factor was found to decrease with crack length. The debonding in the bridging zone, on specimens with different fiber spacing, was evaluated using a one dimensional debonding analysis. The model was calibrated with the debonding on the first fiber and consequently used to describe debonding on the bridging zone of specimens with different fiber spacing. In spite of the assumptions adopted in the present studies, the model seems to describe debonding well.     

Understanding the effect of soil particle size on corrosion behavior of natural gas pipeline via modelling and corrosion micromorphology

The effect of particle size on the electrochemical corrosion behavior of natural gas pipeline steel in a 1.5 wt% NaCl sandy soil corrosive environment was investigated by standard quartz sand. A mathematical model of gas/liquid/solid three-phase boundary (TPB) zone and the soil particle size was developed, and then the theoretical calculation indicated that a critical particle size corresponded to 1.2 mm radius. The laboratory experiments indicated that the corrosion rate of natural gas pipeline steel increased with decreasing soil particle size to < 1.0 mm and was mainly determined by a cathodic reaction. Whereas the corrosion rate of pipeline steel increased with increasing soil particle size exceeding 1.0 mm and the dominant reaction was metal dissolution in the bulk zone and the corrosion rate was determined by anodic reaction. The modelling result is in good agreement with experimental data.     

Experimental and numerical study of fastener pull-through failure in GFRP laminates

A methodology to design and analyze multi-material bolted joints in hybrid train structures is presented. This methodology enables the prediction of the response of a multi-material bolted joint in a short amount of time and it is suitable to be used for large structures, where the number of bolts can be very high. The method developed is applied to a real industrial case which consists on the connection between the roof and the side of a carbody shell train structure. Experimental tests are performed on a full-size sub-component. The comparison between the experimental data and the numerical results confirms the accuracy of the method.     

Experimental and numerical studies on orifice spillway aerator of Bunji Dam

ABSTRACT

In this study, hydraulic design of the aerators of steep slope orifice spillways (26°–32°) was evaluated using physical and numerical modeling techniques. The Bunji Dam spillway, which is proposed to be constructed on the Indus River in Pakistan, was selected for physical and numerical modeling of the aerators. Extensive experimentation was carried out on a physical model of the Bunji Dam spillway by changing the air vent size and ramp angle of the aerator. Three air vent sizes and five ramp angles were constructed to assess the hydraulic performance of the aerator. The numerical model was formulated using Computational Fluid Dynamics (CFD)—FLOW 3D. The air vent size showed a significant impact on the dimensionless performance indicators of the aerators. Empirical equations were developed based on the outputs of physical and numerical models of the aerator. It is believed that the proposed equations will be useful for the estimation of nondimensional cavity length and air entrainment coefficient of the orifice spillway aerators having a short horizontal stretch leading to a convex curvature with slope varied from 26° to 32°.     

Experimental and numerical study of fastener pull-through failure in GFRP laminates

An experimental and numerical study of the fastener pull-through failure mode in glass–fiber reinforced plastic (GFRP) laminates using both phenolic and vinylester resins is presented. It is shown that the type of resin does not affect the mechanical response of the joint when a pull-through test is performed because similar values of the sub-critical initial and final failure loads are obtained. Moreover, considering that the joint is considering to fail when the sub-critical failure load is reached, a methodology to predict the pull-through failure mode is proposed. It is observed that the main failure mechanism is the delamination of the plies; therefore, the prediction of the sub-critical initial failure load is performed using a three-dimensional finite element model where cohesive elements are used to simulate delamination. The predictions agree remarkably well with the experimental results.     

The main mechanisms of stress corrosion cracking in natural gas trunk lines

Stress corrosion cracking in a pipe material presents a most critical hazard to natural gas trunk lines. The paper addresses the causes (mechanism) of crack formation and growth. Understanding of these issues will enable a proper implementation of methods for early identification, diagnostic, and prediction of this type of failure. A most comprehensive explanation of a joint influence of internal and external factors on the corrosion cracking can be provided by means of the probabilistic local electrochemical corrosion theory. It is based on the probabilistic nature of initiation of a local corrosion damage. A probabilistic approach is used to develop a concept of stress corrosion cracking. The factors responsible for the formation of local damage nuclei have been determined. The pipe manufacturing operations are shown to have a certain effect on the pipeline susceptibility to stress corrosion cracking. Modeling has been performed for the corrosion processes that may occur in a gas trunk line section subjected to a stress corrosion cracking hazard.     

油气田天然气流量计量系统的校准

介绍油气田天然气孔板流量计量系统的校准方法。根据实际情况,提出在油气平台现场进行天然气流量计量系统整体校准的新方法。操作过程简单,可以得到系统在结算状态下的误差,并能快速发现系统产生误差的主要原因。     

Experimental and numerical studies on size and constraining effects in lead-free solder joints

The durability and reliability of lead‐free solder joints depends on a large number of factors, like geometry, processing parameters, microstructure and thermomechanical loads. In this work, the nature and influence of the plastic constraints in the solder due to joining partners have been studied by parametric finite element simulation of solder joints with different dimensions. The apparent hardening due to plastic constraints has been shown to strongly depend on the solder gap to thickness ratio with an inversely proportional evolution. Due to interaction of several parameters, the macroscopic stress–strain constitutive law of lead‐free solder materials should be determined in the most realistic conditions. In order to identify the elasto‐plastic constitutive law of Sn–Ag–Cu solders, a sub‐micron resolution Digital Image Correlation technique has been developed to measure the evolution of strain in solder joints during a tensile test. Experimental results of the stress–strain response of Sn–Ag–Cu solder joints have been determined for several solder gaps. The measured load–displacement curves have been used in an inverse numerical identification procedure to determine the constitutive elasto‐plastic behaviour of the solder material. The effects of geometrical constraints in a real solder joint with heterogeneous stress and strain fields are then studied by comparing the apparent (constrained) and constitutive (non‐constrained) stress–strain relationships. Once the size dependant constraining effects have been removed from the stress–strain relationship, the scale effects can be studied separately by comparing the constitutive elasto‐plastic parameters of joints with a variable thickness. Experimental stress–strain curves (constrained and unconstrained) for Sn–4.0Ag–0.5Cu solder in joints of 0.25–2.4 mm gap are presented and the constraining and the size effects are discussed.