Wall Thickness Loss Research Articles

Auxiliary Particle Filter–Based Multisensor Data Fusion for Quantification of Corrosion in Aerostructures

Abstract The identification of structural flaws and subsequent management is significant for health monitoring of aviation structures. Wall thickness loss can occur because of corrosion in exposed aerostructures, thereby reducing the strength of the structure. This may impose prolonged downtimes for repair and replacement activities if not detected at early stages. Eddy current testing (ECT) is a viable technique to detect such anomalies. Fusing multifrequency data produces better results because of complementary features of each contributing mode. Particle filter–based methods have already been proposed to detect and quantify flaw profiles of corrosion damage to an aircraft structure using a multifrequency ECT data fusion technique. However, to address the associated drawbacks, an auxiliary particle filter (APF) method is proposed here. In APF, the proposed importance density is a mixture of the prior state and the latest measurements, yielding focused estimation into a high-likelihood region. Simulation results are presented to demonstrate effectiveness of the proposed technique to quantify damages in aerostructures.

Influence of bend geometry on flow accelerated corrosion under neutral pH conditions

Flow accelerated corrosion (FAC) is an unavoidable problem in the integral part of the pipe line systems of Nuclear Power Plants worldwide. This has a significant influence on the thickness loss of the pipe line which affects the operation and maintenance of the plants. During the prolonged operation of the plants, FAC leads to inside wall thinning, rupture and catastrophic failure of the pipeline systems and ultimate shutdown of the reactor system for maintenance. Qualitative coupon based chemical off-line analysis techniques were only followed earlier for the prevention of untoward incidents. With the introduction of ultrasonic nondestructive thickness measurements viz., pre-service, in-service and inspection during shutdowns, the possibility of accidents have been reduced to a maximum extent. However, detailed understanding of FAC and wall thinning of pipes due to different plant operation conditions such as flow velocity, different pH, different temperature and pressure values etc., are not available even today. The present experimental study is aimed to throw light on the parameters that have more impact on FAC. Also it is aimed to identify the vulnerable locations and wall thickness loss along the clock positions. The output of this study will gain currency while dealing with FAC code, and plays a critical role in the establishment of safe and reliable and continuous plant operations. According to existing literature, one of the most important parameters that affect FAC is the piping configuration i.e., geometry of flow path. Hence, the present study is aimed towards the understanding of FAC with respect to the bend angle and bend radius of the carbon steel piping. In this study, carbon steel pipes as per ASTM A106 Gr‘B‘ material with two bend angles viz. 58° and 73° with bend radius 2D and 4D, where D denotes the outer diameter of the pipe, have been chosen. These parameter ranges are available in the existing reactor and hence four different pipe bend specimens have been undertaken. Therefore, the four different pipe specimen holders of ASTM A106 Gr ‘B‘ materials having 15NB (Nominal Bore) pipe bends were designed and fabricated. Under the similar experimental conditions, using the Computational Fluid Dynamics (CFD) studies, the velocity distribution, the wall shear stress and the turbulent kinetic energy were simulated and correlated with the corresponding measured wear rate. Basic parameters like pipe material, bend angle, bend radius, etc. have been used for the simulation studies. Comparison of the simulated flow rate with the experimental values of wall thickness obtained through the ultrasonic measurements indicate that the bend angle and bend radius of the geometry play a crucial role on FAC.

Loss Prevention Mitigation in Sour Water Stripper (SWS) Cooler Using Process and Computational Fluid Dynamics (CFD) Modelling

Sour water stripping (SWS) units are similar to other process units that can bring many operational challenges to meet target stripped water specifications. Failure of any equipment in the unit leads to unplanned shutdown and hence increases the downtime of the unit. In this study we investigated the outlet nozzle and elbow downstream the finfan cooler as they occasionally leak due to apparently metal thinning. Process simulation using appropriate electrolyte thermodynamic package to predict vapour liquid equilibrium and streams flow rates was used. Subsequently, Computational fluid dynamics (CFD) simulation was use to predict the erosion patterns. To mitigate and prevent unit upset, many option have been recommended to change the operating mode of the finfan cooler so as to circumvent alloy change. The CFD simulation results matched the erosion pattern that caused the loss of wall thickness. Different cases were investigated addressing elbow size, flow regime and elbow angle. The results, however, have indicated that the erosion is unavoidable irrespective of the fluctuation in the throughputs to the unit.

Remote Monitoring Digitizes Asset-Integrity Management

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 197168, “Digitalize Asset-Integrity Management by Remote Monitoring,” by Mohamed Sahid, ADNOC, prepared for the 2019 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 11-14 November. The paper has not been peer reviewed. Monitoring of corrosion in process pipelines has always been of paramount importance in ensuring plant-asset integrity. Similarly, steam traps play an important role in ensuring steam quality and, thus, the integrity of critical assets in the plant. The complete paper discusses these two aspects of monitoring asset integrity - real-time corrosion monitoring and real-time steam-trap monitoring - as implemented by the operator. The authors highlight the importance of digitization by means of implementing wireless technology and making data available in remote work stations in real time. Real-Time Corrosion-Monitoring System Corrosion coupons and electrical resistance probes are among the most-tried and -tested methods to monitor corrosion, but the authors detail shortcomings of these systems, focusing their efforts on the option of using nonintrusive ultrasonic sensors for corrosion monitoring. Fixed ultrasonic thickness (UT) monitoring systems measure a localized thickness of vessel wall or pipe through the use of sound waves. They are the fastest method to measure wall thickness and wall loss reliably. The wall thickness is calculated from the reflection of the ultrasonic signal at both external and internal surfaces. UT systems normally include a transducer and a pulser/receiver. The type of transducer used for this application is the ultrasonic transducer, which can be either piezoelectric or variable-capacitive. The pulser generates short electric pulses of energy at a constant rate, which are converted by the transducer into short, high-frequency ultrasonic sound pulses. These pulses are then directed into the material. Any discontinuation or impurity in the path of the ultrasonic sound wave will be reflected and received by the transducer, transformed into an electric signal, and amplified by the receiver to be projected onto the display (in the case of portable UT instruments). Depending on the intensity shown on the display, information about the impurity or discontinuity, such as size, orientation, and location, can be derived accurately. The shortcomings of using portable UT sensors have been overcome by the introduction of permanent UT sensors, which provide wall-thickness measurement continuously at one location in real time. Because these sensors remain fixed at one location for years, it is possible to analyze corrosion at a single point over time, thus detecting early corrosion onset. Real-Time UT Gauging. The operator installed the real-time corrosion-monitoring system in its offshore associated gas (OAG) unit. A UK-based vendor provided UT sensors along with data-management and -viewing software to support data interpretation. Twenty locations were identified in various plants of the OAG unit on the basis of criticality and previously recorded corrosion levels.

Failure Analysis of Heat Exchanger Using Internal Rotary Inspection System (IRIS)

Retubing of a heat exchanger always plays a critical role in oil and gas plants. Normally, many end-users prefer to do full retubing rather than partial retubing during maintenance or shutdown in order to achieve more efficiency. But in case of alloy steel tube-based heat exchanger, partial retubing is preferred because cost of alloy steel tubes is ten times higher than that of the carbon steel tubes. In this research, low-efficiency heat exchanger was selected since it requires full retubing (maintenance) due to severe in-service tube thickness loss and low efficiency as per end-user. Tube material was Inconel SB 163-800H, and the quantity of tubes was 286. Among numerous advanced NDT strategies used to minimize downtime arising from catastrophic failures induced by erosion/corrosion or mechanical loss sustained during the operating period, internal rotating inspection was chosen. This approach identifies a lack of wall thickness reduction arising from deterioration, wear, pitting (ID & OD) and corrosion. After IRIS inspection method was carried out, it was easy to categorize how many tubes are exactly defective and exchanger requires partial retubing or full retubing which finds huge savings and reduction in maintenance cost and time. IRIS inspection method also provides the distribution of tubes by wall thickness loss of total 286 tubes in the heat exchanger and retubing of heat exchanger will be further continued to achieve more efficiency.

Corrosion induced failure of the ductile iron pipes at micro- and nano-levels

Corrosion induced failure of buried ferrous pipelines causes significant economic losses to the world. Many of the existing buried water pipelines are made of ductile iron in most of the developed countries. Literature shows that the research on the corrosion-induced degradation assessments of ductile iron pipelines is limited and mostly deals with the physical deterioration i.e., loss of wall thickness determined by short-term research. This paper addresses this gap and presents a comparatively long-term study on the corrosion and its subsequent effect on the composition and nanomechanical properties of buried ductile iron pipelines in the accelerated corrosive environment. For experimentation, ductile iron specimens were immersed in the acidic simulated soil solution for 365 days. Physical deterioration assessment over the time was carried out in terms of corrosion rates measured at intervals of 180 and 365 days. A significant change in the percentage composition of key elements and phases were quantified. Furthermore, the mechanical properties of the grains were found to be considerably reduced after 365 days of immersion in the acidic environment by the nanoindentation technique. The results revealed an alarming increase of structural degradation at nano scale for some of the grains due to chloride induced localised corrosion. The significance of the current research is its in-depth analysis of the corrosion-induced degradation of ductile iron pipes which enhances the knowledge related to the failure of these pipelines.

Effect of particle size on erosion measurements and predictions in annular flow for an elbow

Sand production is a flow assurance challenge in oil and gas condensate wells. Solid particles entrained in multiphase during production can severely affect the integrity of fluid transportation structures such as pipelines, elbows, and reducers. Traditionally, sand management techniques such as sand screens and gravel packs are used to control sand. However, small particles can pass through these controls. Furthermore, small particles can block a portion of the sand screen, causing high velocities in other sections which can promote erosion of the sand screen openings allowing larger particles to pass through which in turn cause more erosion. Furthermore, these small particles are susceptible to highly turbulent regions of flow and can cause severe erosion in these regions. Hence, it is critically important to understand the erosion caused by small particles. This study investigates the effect of small particles on erosion. Small particle erosion is more severe in gas dominated multiphase flows such as annular and mist flows than liquid dominated bubbly and slug flows. Experiments are conducted in vertical upward annular flow for different particle sizes as well as different superficial gas and superficial liquid velocities for pipe sizes of 3-inch (76.2 mm). Flow visualization and paint-removal studies are performed to visualize the flow and paint-removal pattern. Erosion patterns are measured with multiple sensors attached to the outer walls of elbows in multiphase flows. Elbow wall thickness losses are measured using state-of-the-art ultrasonic measurement techniques, and the effects of particle size on erosion ratio and its distribution in pipe bends are discussed. Erosion patterns are also compared with Computational Fluid Dynamics (CFD) simulations of multiphase flows using the VOF Model. Current CFD results generally over-predict erosion compared to experimental data.

Neuronal Parasitism, Early Myenteric Neurons Depopulation and Continuous Axonal Networking Damage as Underlying Mechanisms of the Experimental Intestinal Chagas' Disease.

There is a growing consensus that the balance between the persistence of infection and the host immune response is crucial for chronification of Chagas heart disease. Extrapolation for chagasic megacolon is hampered because research in humans and animal models that reproduce intestinal pathology is lacking. The parasite-host relationship and its consequence to the disease are not well-known. Our model describes the temporal changes in the mice intestine wall throughout the infection, parasitism, and the development of megacolon. It also presents the consequence of the infection of primary myenteric neurons in culture with Trypanosoma cruzi (T. cruzi). Oxidative neuronal damage, involving reactive nitrogen species induced by parasite infection and cytokine production, results in the denervation of the myenteric ganglia in the acute phase. The long-term inflammation induced by the parasite's DNA causes intramuscular axonal damage, smooth muscle hypertrophy, and inconsistent innervation, affecting contractility. Acute phase neuronal loss may be irreversible. However, the dynamics of the damages revealed herein indicate that neuroprotection interventions in acute and chronic phases may help to eradicate the parasite and control the inflammatory-induced increase of the intestinal wall thickness and axonal loss. Our model is a powerful approach to integrate the acute and chronic events triggered by T. cruzi, leading to megacolon.

Effects of Carvedilol and Thyroid Hormones Co-administration on Apoptotic and Survival Proteins in the Heart After Acute Myocardial Infarction.

Cellular death and survival signaling plays a key role in the progress of adverse cardiac remodeling after acute myocardial infarction (AMI). Therapeutic strategies, such as co-treatment with beta-blocker carvedilol and thyroid hormones (THs), give rise to new approaches that can sustain the cellular homeostasis after AMI. Therefore, we sought to investigate the effects of carvedilol and TH co-administration on apoptosis and survival proteins and on cardiac remodeling after AMI. Male Wistar rats were distributed in 5 groups as follows: sham-operated group (SHAM), infarcted group (MI), infarcted plus carvedilol group (MI+C), infarcted plus TH group (MI+TH), and infarcted plus carvedilol and TH co-treatment group (MI+C+TH). Echocardiographic analysis was performed, and hearts were collected for western blot evaluation. The MI group presented systolic posterior wall thickness loss, an increase in the wall tension index, and an increase in atrial natriuretic peptide tissue levels than the SHAM group. However, in the MI+C+TH group, these parameters were equally to the SHAM group. Moreover, whereas the MI group showed Bax protein expression elevated in relation to the SHAM group, the MI+C+TH group presented Bax reduction and also Akt activation compared with the MI group. In addition, the MI+TH group revealed beta-1 adrenergic receptor (β1AR) upregulation compared with the MI and MI+C groups, whereas the MI+C+TH group presented lower levels of β1AR in relation to the SHAM and MI+TH groups. In conclusion, we suggest that carvedilol and TH co-administration may mediate its cardioprotective effects against adverse cardiac remodeling post-AMI through the Bax reduction, Akt activation, and β1AR decrease.

High-Frequency Guided Waves for Corrosion Thickness Loss Monitoring

Abstract Adverse environmental conditions result in corrosion during the life cycle of marine structures such as pipelines, offshore oil platforms, and ships. Generalized corrosion leading to the loss of wall thickness can cause the degradation of the integrity, strength, and load bearing capacity of the structure. Nondestructive detection and monitoring of corrosion damage in difficult to access areas can be achieved using high-frequency guided waves propagating along the structure. Using standard ultrasonic wedge transducers with single-sided access to the structure, specific high-frequency guided wave modes (overlap of both fundamental Lamb wave modes) were generated that penetrate through the complete thickness of the structure. The wave propagation and interference of the guided wave modes depend on the thickness of the structure and were measured using a noncontact laser interferometer. Numerical simulations using a two-dimensional finite element model were performed to visualize and predict the guided wave propagation and energy transfer across the plate thickness. During laboratory experiments, the wall thickness was reduced uniformly by milling of one steel plate specimen. In a second step, wall thickness reduction was induced using accelerated corrosion for two mild steel plates. The corrosion damage was monitored based on the effect on the wave propagation and interference (beating effect) of the Lamb wave modes in the frequency domain. Good agreement of the measured beatlengths with theoretical predictions was achieved, and the sensitivity of the methodology was ascertained, showing that high-frequency guided waves have the potential for corrosion damage monitoring at critical and difficult to access locations.

Corrosion of cast iron pipelines buried in Fraser River silt subject to climate-induced moisture variations

Experiments were carried out to characterise the influence of soil water retention properties on the corrosion of a cast iron specimen buried in Fraser River silt. The corrosion rates were measured at different degrees of saturation using standard corrosion tests, along with separate water retention tests for the Fraser River silt. Building on previous work on this topic, a numerical model solving moisture flow, oxygen diffusion, electrical conductivity and their coupled influence on metallic corrosion in unsaturated soil was developed. The experimental data and preliminary numerical modelling results were then used as inputs to a field-scale numerical model to examine climate-induced moisture migration around a pipeline and the resulting levels of corrosion. The time-dependent corrosion mass loss and the resulting loss in pipe wall thickness of a buried pipeline were modelled, and it was demonstrated that the cyclic climatic variations predominantly perturb the corrosion rates during the initial cycles, and subsequently a gradual corrosion rate arises depending on general climatic conditions. Further analysis of the influence of electrical resistivity on the levels of corrosion revealed that a decrease in resistivity due to effects such as seawater intrusion or naturally saline soils may result in a significant increase in the levels of localised corrosion.

Metallurgical investigation of a heat-exchanger tube of 70/30 cupronickel failed by fretting corrosion

The present paper describes a failure investigation of a tube that had shown leakage in a shell and tube type heat-exchanger with 70/30 cupronickel tubes and mild steel baffles (13 nos.). Corrosion damage or thinning of the failed tube was found to have occurred from the outer surface at all the baffle locations. Further examination of the failed tube was done using an optical microscope, a scanning electron microscope equipped with energy dispersive spectroscopy, Raman spectroscopy and an instrumented microhardness indentation machine for hardness measurement. Based on the results, it was concluded that the failure and the loss in wall-thickness of the tube at locations where it was in contact with the mild steel baffles were caused by fretting corrosion. The focus of this investigation is to bring out the metallurgical changes and the surface conditions (including changes in microstructure and microhardness, mode of corrosion attack and type of oxides/corrosion products) of the tube material undergoing fretting corrosion at micro level. Recommendations to avoid such a failure are also suggested.

Hydrothermal corrosion of 2nd generation FeCrAl alloys for accident tolerant fuel cladding

As part of an effort to develop advanced fuel cladding for use in light water reactors, several FeCrAl alloys have been developed at Oak Ridge National Laboratory. A second generation of these alloys bearing additional alloying elements over the previously tested model alloys were tested in boiling water reactor (BWR) conditions to determine their resistance to hydrothermal corrosion. Coupons with alloy compositions Fe–10Cr–6Al–2Mo, Fe–13Cr–5Al–2Mo, Fe–13Cr–6Al–2Mo, Fe–13Cr–7Al–2Mo, and Fe–13Cr–5Al–2Mo–1Nb were tested in normal water chemistry (NWC) and hydrogen water chemistry (HWC) for 9 months in continuously refreshing autoclaves. Commercial FeCrAl alloy APMT and Zircaloy-2 were also tested for comparison. Among samples exposed to HWC, Fe–13Cr–7Al–2Mo performed worst with an average mass loss of 1.3 mg/cm2 over 9 months. This mass loss represents an estimated thickness loss of approximately 60 μm over 6 years. Samples exposed to NWC had very small mass losses of less than 0.15 mg/cm2 or mass gains up to 0.05 mg/cm2. Based on the results of this testing, the 2nd generation FeCrAl alloys tested exhibit low wall thickness loss and are suitable in terms of corrosion resistance for use as LWR cladding in BWR-HWC and BWR-NWC under normal operating conditions.

A wall-thinning measuring method based on magnetic permeability perturbation

In the determination of metal thickness by traditional electromagnetic nondestructive testing methods, the material’s electrical conductivity and magnetic permeability are required but practically unavailable or inexact. In this paper, a wall-thinning measuring method based on magnetic permeability variation of steel pipes is proposed. The direct current magnetization is applied to the ferromagnetic material, the internal magnetic field perturbation caused by the wall-thinning brings the permeability perturbation in the surface layer and be sensed by eddy current probe. The simulation results show that the permeability perturbation is closely related to wall thickness loss. The experiment results show that the signal amplitude increases with the thickness of the wall-thinning and the new method can measure the 10% wall-thinning of pipe. Finally, theoretical range of magnetization current values are discussed. The new method takes advantage of the changes in permeability and is not limited by thickness of object to be detected.

Failure analysis of superheat tube 2.25Cr-1Mo in biomass power plant

The understanding of microstructures, their influences, and failure mechanisms are of necessary for determining lifetime and failure behaviors of metal parts being used in some severe environments. This research aims to study the failure causes and mechanisms of superheat tube used in a power plant. The tube examined in this experiment was 2.25Cr-1Mo (SA213 Grade T22) with a diameter of 33.5 mm and 4.33-mm wall thickness. This tube had been in-service for 7.5 years in a 9.9-MW biomass power plant. Visual inspection, chemical analysis with an optical emission spectrometer, optical microstructure, scanning electron microscope (SEM), energy dispersive X-ray (EDS), hardness measurement and tensile were employed to investigate the causes of superheat tube failure. The results showed that the damaged tube was subjected to the non-uniform loss of outer wall thickness due to erosion and presence of ferrous oxide at the outer tube surface. The hardness of outer and inner tube surfaces was found to be less than that of the mid-wall section. In addition, carbide particles were observable and uniformly dispersed throughout the microstructures. Regarding the SEM result, the tube failure was relevant to the bursting with ductile fracture.

Compressive strength of corroded special-shaped welded hollow spherical joints based on numerical simulation

Special-shaped welded hollow spherical joints (WHSJ) are increasingly used in several important spatial grid structures. The corrosion of WHSJ is inevitable and can eventually threaten structural safety. There is no research or comparison on the compressive strength of corroded special-shaped WHSJ. Therefore, through the simulation and analysis of the corrosion depth, corrosion mode, corrosion size, joint size, and steel material, the compressive strength of three types of special-shaped WHSJ after corrosion was studied, and the corresponding evaluation method for compressive strength was established. Results indicated that the loss of wall thickness (Tc/T) and the ratio of grooving corrosion (2Wc/D) were the key factors affecting the compressive strength of the special-shaped WHSJ after corrosion. The effect of corrosion on the bearing capacity was related to the size ratio (d/D). WHSJ connected by the H-beam were most affected by corrosion; the failure mode was basically buckling failure, but punching failure might occur in the H-beam WHSJ. The results obtained could form the basis for the selection of the WHSJ shapes and the evaluation of the bearing capacity of the space grid structure with special-shaped WHSJ after corrosion.

Guided ultrasonic wave tomography of a pipe bend exposed to environmental conditions: A long-term monitoring experiment

Continuous monitoring of corrosion damage in pipelines requires sensor systems that can achieve high precision (repeatability) to detect and size subtle wall thickness (WT) losses. In fact, corrosion typically progresses at a rate of 1 mm per year or less which poses very demanding performance requirements if the state of the pipe has to be assessed on a weekly or even monthly basis. Guided ultrasonic wave tomography (GUWT) has emerged as an attractive approach for continuous monitoring owing to its ability to map WT losses over an extended pipe section. This is possible because GUWT employs ultrasonic waves that are guided by the pipe wall to travel a large distance from the source transducer. Defects along the path of the guided wave cause a perturbation of the signal which is then interpreted by model-based inversion schemes to determine the WT loss. In addition to damage, there is a vast number of time-dependent operational and environmental (O & E) factors that can perturb the signal also when damage is not present. To achieve high precision, it is therefore essential that GUWT can detect the changes in the signal due to damage and suppress those caused by other benign factors such as temperature variations. Although numerous studies have been conducted to estimate the accuracy of various implementations of GUWT, precision has received less attention due to the challenges associated with reproducing realistic O & E conditions in the lab. This work focuses on the effect of temperature and presents the results of a continuous monitoring experiment conducted on a pipe bend kept outdoors and exposed to weather conditions for a period 21 months. It is shown that the pipe undergoes a relatively severe temperature cycling with typical daily peak-to-trough variations of 20∘C that cover the range from -15∘C to +51∘C as the seasons alternate. The effect of temperature is suppressed by exploiting the spatial diversity of array measurements and combining multiple datasets measured during the monitoring period. The maximum WT loss is estimated with high precision exhibiting a standard deviation not exceeding 0.4% of the nominal WT.

Experiments and CFD simulations of erosion of a 90° elbow in liquid-dominated liquid-solid and dispersed-bubble-solid flows

Pipeline erosion in the production of oil and gas often occurs in elbows, tees, valves, pipes, chokes and other pipe geometries that cause a rapid change in flow direction. Liquid-dominated flows are of importance in mining and many oil fields and transportation lines carrying oil and gas including those in deep water subsea flowlines. In this study, experimental data for wall thickness losses were measured with an ultrasonic transducer in a 50.8 mm standard elbow. Experiments were conducted with multiphase flows with water, air and 300 µm average sand particles and with liquid-sand flows. Wall thickness losses were measured on the outer radius of elbows at 63 locations and for several different flow conditions. Computational Fluid Dynamics (CFD) simulation was performed using the Euler-Lagrange approach with the Reynolds Stress Model (RSM) for turbulence and Eulerian Multiphase model for multiphase flow cases. Different flow regimes were investigated in liquid-sand and multiphase flows. It was observed that maximum erosion increases as the mixture velocity increases. In addition, for liquid-sand and dispersed-bubble-sand flows the Euler-Lagrange and Euler-Euler-Lagrange approaches used in the CFD simulations were able to predict the observed maximum erosion rates, erosion locations and erosion patterns.

Behaviour of square CFST beam-columns under combined sustained load and corrosion: FEA modelling and analysis

This paper presents a numerical investigation on concrete-filled steel tubular (CFST) beam-columns with square sections subjected to combined sustained load and corrosion. A general numerical method is used for the simulation of the time dependent behaviour of the core concrete, while the wall-thickness loss of the outer steel tube induced by corrosion is considered in this model simultaneously. The established finite element analysis (FEA) modelling is verified with test data and used for further investigations of the load-deformation relationship, load-transfer mechanism, stress and strain development, failure modes and ultimate states on CFST beam-columns when suffering combined sustained load and corrosion. Parametric studies are conducted to reveal the effects of key parameters, based on which simplified design method is suggested for square CFST beam-columns under combined sustained load and corrosion.

Model for remaining strength estimation of a corroded pipeline with interacting defects for oil and gas operations

Remaining strength estimation of corroded pipelines is a major consideration in pipeline integrity management. The loss of pipe wall thickness due to corrosion inevitably leads to a reduction in th...