Wall Thickness Loss Research Articles

Failure analysis of an oil refinery sour water stripper overhead piping loop: Assessment and mitigation of erosion problems

This study investigated the integrity of the outlet nozzle and elbow of the piping system downstream the finfan cooler in sour water stripping unit. The piping system in these locations experienced severe thinning and occasional leaks. The unit was modelled using process simulation software with the use of the appropriate thermodynamic methods for electrolyte models to accurately estimate the flow rates, properties in vapour and liquid phases in the piping system. The results from the process simulation were subsequently used in the Computational Fluid Dynamics (CFD) simulation. The CFD simulation results matched the erosion pattern that caused the loss of wall thickness. The eroded nozzles were also visually and optically examined using scanning electron microscopy (SEM) and Energy Dispersion X-ray (EDX). The results have indicated that the erosion is inevitable regardless of the fluctuation in the throughputs to the unit. Iron sulfide, indicative of the synergy between erosion and corrosion, was observed in the pipes elbows. For mitigation, an option has been recommended to change the operating mode of the finfan cooler so as to alleviate alloy change.

The Underoil Droplet Corrosion Behavior of X100 Pipeline Steel

Canadian natural bitumen production will reach a peak of 112 million barrels per day in 2078 [1]. Pipelines are primarily used to transport this bitumen. Bitumen must be diluted in order to be pumped through a pipeline effectively because it is otherwise too viscous to flow [2]. Underoil droplet corrosion of diluted bitumen (dilbit) pipelines may lead to the loss of pipe wall thickness, which deteriorates the structural reliability and increases the risk of leaking of pipelines. The current models for atmospheric droplet corrosion, where no limitation to oxygen access is imposed, cannot be applied to underoil droplet corrosion in dilbit pipeline conditions. In this study, a NaCl droplet on X100 pipeline steel covered by paraffin oil is used to simulate the corrosive environment encountered in diluted bitumen pipelines. A new distinctive corrosion mechanism is proposed to explain the corrosion of X100 pipeline steel beneath an underoil salty droplet. This mechanism accounts for the depleted oxygen levels in the droplet environment. In the initial stage (1 h), the distribution of corrosion pits was heterogeneous with one area under the droplet presenting a higher pit density. As the corrosion proceeded (24 h), the localized corrosion was governed by pH development due to initial pit density. Regions of initially higher pit density switched to general corrosion, while regions with lower pit densities continued pitting. The effects of droplet volume, chloride ion concentration, and temperature on the underoil droplet corrosion behavior of X100 pipeline steel were also studied by scanning electron microscopy, Raman spectroscopy, and profilometry. At 23 °C, lepidocrocite and hematite were observed in the region where pitting was initially prevalent. However, as this region switched to uniform corrosion, goethite, lepidocrocite, and hematite were formed. The same distribution of crystal structures was identified for the droplets with varying volume and chloride ion concentration. When the temperature was increased to 60 °C, hematite was detected in both regions. Decreased droplet volumes, increased chloride concentration, and raised temperatures increase corrosion penetration when uniform corrosion is prevalent. This study provides important findings to better understand the mechanisms behind droplet corrosion underoil and informs future predictions of the corrosion rate of pipeline steels.

Data-Enabled Quantitative Corrosion Monitoring using Ultrasound

Corrosion is the most pervasive degradation mechanism of engineering infrastructure. It has caused numerous disastrous events that resulted in devastating societal, environmental and financial consequences. There exist numerous standard techniques for corrosion monitoring. Among these techniques, ultrasonic testing stands out as a non-intrusive and straightforward approach. Component wall-thickness loss rate (WTLR) is an intrinsic parameter of corrosion processes. Accurate and rapid determination of WTLRs from continuous ultrasonic wall-thickness loss (WTL) measurements is a critical aspect of effective corrosion control. In this paper, a statistics-based method that enables automatic detection of changes in WTLR will be introduced. The detection method further extends the application of ultrasonic corrosion monitoring to more sophisticated corrosion processes that involve multiple rates. Statistical analysis of ultrasonic WTL measurements that were acquired by a state-of-the-art laboratory setup shows that changes in WTLR of 0.1–0.2 mm/year can be determined within 1–2 h.

Feasibility investigation regarding evaluation of external wall-thickness loss in nonmagnetic tubes using a bobbin-typed electromagnetic acoustic transducer

ABSTRACTDuring fabrication and practical service, nonmagnetic tubes are prone to the External Wall-thickness Loss (EWL) which leaves the tubes vulnerable to structural failure. In this paper, a bobbin-typed electromagnetic acoustic transducer is proposed for tube inspection. The feasibility of EWL evaluation by using the proposed transducer is investigated via simulations and experiments. In order for efficient simulations of Electromagnetic Acoustic Transduction (EMAT), the hybrid modeling integrating the analytical modeling and finite element modeling is established. Closed-form expressions particularly regarding the EMAT-related field quantities of electromagnetics are formulated via the Extended Truncated Region Eigenfunction Expansion (ETREE) modeling. Simulations by using the hybrid model indicate that the proposed transducer is capable of evaluating EWL in nonmagnetic tubes. In parallel, experiments with the fabricated transducer have been carried out. The experimental results are supportive of the conclusion drawn from simulations. From simulations and experiments, it can be found that EWL evaluation with the proposed bobbin-typed electromagnetic acoustic transducer is feasible, which could benefit the real-time and in-situ nondestructive evaluation of nonmagnetic tubes.

Modelling casing wear at doglegs by incorporating alternate accumulative wear

In some situations while drilling through severe doglegs, drill strings are inevitably touching the inner wall of casing, which may wear casing harshly. For instance, this is a frequent problem in wells drilled in Bohai Bay basin in East China. In large dogleg sections of the well, casing is subjected to a dual-wear accumulation contributed by the tool joint and drill pipe (alternate wearing). Nonplanar geometry of the hole and complex geometry of the rotating drill pipe may add to the complexity of the wear process. Here, we propose a mathematical model to calculate the loss of wall thickness of the casing due to the dual wear. A finite element model is developed to incorporate wearing of the casing alternating between the tool joint and the drill pipe. Arbitrary Lagrange-Eulerian (ALE) adaptive meshing and remapping technique is utilized to specify the ablation velocity vectors at the inner casing surface. Our numerical results show that the dual wear contributions and ever changing contact geometry in alternate wearing intensifies the rate of the casing wear 150% faster than that of the single wear models. Additionally, the curvature at point with maximum wear depth has been found to significantly impact the maximum stress of worn casing. This paper provides an accumulative wear model for accurate prediction of the casing wear and its residual strength before running the casing through the dogleg section.

On quantitative corrosion rate monitoring with ultrasound

Wall-thickness loss rate (WTLR) is an important parameter that defines a corrosion process. The speed at which a WTLR can be determined is directly related to how quickly one can intervene in a process that is heading in the wrong direction. Ultrasonic testing has been widely used as a convenient and efficient technique for online corrosion monitoring. One of the key performance parameters of ultrasonic corrosion monitoring is detection speed. While WTLRs can be determined by fitting linear lines to wall-thickness loss (WTL) measurements, the presence of noise in the measurements makes it difficult to judge the confidence levels of the slopes that are calculated this way. In this paper, a statistics based approach for assessing the detection speeds that are achievable by ultrasonic corrosion monitoring systems is presented. Through the statistical analysis of experimental data, a state-of-the-art laboratory setup is shown to be able to detect both WTLRs and changes in WTLR that are of interest to industry (i.e. 0.1–0.2 mm/year) within 1–2 h.

Circular concrete filled steel tubular (CFST) columns under cyclic load and acid rain attack: Test simulation

Concrete filled steel tubular (CFST) structure attracts increasing engineering applications in earthquake prone regions due to its high section modulus, high strength, and good seismic performance. However, the seismic resistance of CFST columns may be affected by the environmental corrosions, such as acid rain attack. This paper makes an attempt to investigate the performance of CSFT columns with circular sections under both a cyclic load and an acid rain attack. First, the tensile mechanical properties of steel plates with various corrosion rates were tested. Second, a total of 12 columns with different corrosion rates were tested subjected to a reversed cyclic load. It was found that the corrosion leads to not only a loss in wall thickness but also an evident decrease in yield strength, elastic modulus, and tensile strain capacity of the steel coupons, and also to a significant deterioration in the load carrying capacity, ductility, and energy dissipation of the CFST columns. The larger the axial force ratio, the severer deterioration of deformation capacity of the columns.

Compressive characteristics of damaged circular hollow section (CHS) steel columns repaired by CFRP or grout jacketing

An experimental study was conducted to evaluate the compressive behavior of damaged circular hollow section (CHS) steel columns repaired by carbon fiber-reinforced polymer (CFRP) or high-strength grout. A total of 22 specimens, including bare steel specimens, CFRP repaired specimens and grout repaired specimens were tested under axial compression loading. The design parameters are the amount of loss in wall thickness, extent of damage along tube height, and the damage angle around the circumference. Two promising retrofit techniques, external wrapping of CFRP and grouted jacket, were adopted here. The repairing efficiency was assessed in terms of the above-mentioned retrofit techniques and design parameters. A finite element (FE) analysis was also performed and analyzed with test results. The failure modes are presented together with load-shortening and load-strain behavior of specimens. The results indicate that the behavior of damaged CHS steel columns can be effectively rehabilitated by either CFRP or grout jacketing. The local buckling of the internal steel tube was either delayed by fibers or suppressed by the surrounding grout, leading to an improvement both in compressive strength and deformation capacity. It was also found that grouted jacket repair generally shows an overwhelming strength enhancement over the CFRP wrapping method except for specimens with 90° damage around circumference, which shows a delay of the restraining effect. A parametric study was eventually undertaken to fully understand the influences of design parameters on columns' compressive characteristics.

Effect of Sandblasting on Tensile Properties, Hardness and Fracture Resistance of a Line Pipe Steel Used in Algeria for Oil Transport

Transport of oil and gas through pipelines in the harsh conditions of the Algerian desert, results in erosion of the pipeline materials. Erosion is a mechanical process that causes a loss of wall thickness, damage and residual stresses on the surface of a pipe due to shocks between sand particles and structure surface. Damage manifests by spalling craters of different shapes and depths. The evaluation of tensile properties and hardness after sandblasting for different durations has been performed on API 5L X70 pipeline steel. Particular attention has been paid to fracture resistance after sandblasting to provide the necessary data for defect assessment, specially the effect of sandblasting on the Material Failure Master Curve (MFMC). The results demonstrated that the sandblasting has slightly increased the yield stress, the ultimate strength and the fracture toughness and, at the same time, had an adverse effect on elongation, young’s modulus, hardness and thickness of the tested pipeline.

Sand erosion measurements under multiphase annular flow conditions in a horizontal-horizontal elbow

Gas-liquid annular flow is commonly observed in natural gas transmission and offshore horizontal pipelines. The presence of sand particles in such flows can cause severe equipment degradation of piping elements. The most vulnerable parts of pipeline systems tend to be components in which the flow direction changes suddenly such as elbows and tees. This paper presents the results of an experimental study on erosion in an elbow under gas-liquid-sand flow conditions. Firstly, erosion patterns and mass loss measurements were obtained in a test cell with paint erosion approach and aluminum elbow specimen. Secondly, a non-invasive Ultrasonic Technology (UT) device was employed to achieve erosion patterns in a 76.2mm ID stainless steel standard elbow. The wall-thickness loss was measured at 16 different locations on the elbow using dual element ultrasonic transducers. Experiments were performed with superficial gas velocities ranging from 27m/s to 49m/s at nearly atmospheric pressure. Superficial liquid velocities varied from 0.005m/s to 0.457m/s. In all cases examined, the orientation of the elbow was horizontal-horizontal. Three different sand sizes (20, 150 and 300μm sand) were used for performing the tests. Experimental results showed different erosion behaviors with variations of flow patterns in the horizontal-horizontal elbow (H-H). The data were also compared to some erosion data previously obtained in a vertical-horizontal elbow that shows erosion in H-H elbow is much smaller than V-H elbows for some of the multiphase flow conditions. In summary, the effects of different parameters such as sand size and liquid viscosity on measured erosion rates were investigated.

High accuracy ultrasonic monitoring of electrochemical processes

Ultrasonic testing (UT) can be used for non-intrusive corrosion monitoring. In this paper, we firstly show that UT is not only capable of monitoring wall-thickness losses, but can also be exploited for tracking electrodeposition processes. All ultrasonic measurements reported are in agreement with analytical predictions and optical surface profile measurements. Since UT is highly sensitive to the coupling conditions and the relative acoustic properties of substrates and deposited materials, it can become an effective tool for studying the interface phenomena in which dissolution and deposition compete. Examples of these include passivation layer formation and scale deposition which are corrosion-inhibiting electrochemical processes.

Exogenous GDF11 induces cardiac and skeletal muscle dysfunction and wasting.

Growth differentiation factor 11 (GDF11), a TGF-beta superfamily member, is highly homologous to myostatin and essential for embryonic patterning and organogenesis. Reports of GDF11 effects on adult tissues are conflicting, with some describing anti-aging and pro-regenerative activities on the heart and skeletal muscle while others opposite or no effects. Herein, we sought to determine the in vivo cardiac and skeletal muscle effects of excess GDF11. Mice were injected with GDF11 secreting cells, an identical model to that used to initially identify the in vivo effects of myostatin. GDF11 exposure in mice induced whole body wasting and profound loss of function in cardiac and skeletal muscle over a 14-day period. Loss of cardiac mass preceded skeletal muscle loss. Cardiac histologic and echocardiographic evaluation demonstrated loss of ventricular muscle wall thickness, decreased cardiomyocyte size, and decreased cardiac function 10days following initiation of GDF11 exposure. Changes in skeletal muscle after GDF11 exposure were manifest at day 13 and wereassociated with wasting, decreased fiber size, and reduced strength. Changes in cardiomyocytes and skeletal muscle fibers were associated with activation of SMAD2, the ubiquitin-proteasome pathway and autophagy. Thus,GDF11 over administration in vivo results in cardiac and skeletal muscle loss, dysfunction, and death. Here, serum levels of GDF11 by Western blotting were 1.5-fold increased over controls. Although GDF11 effects in vivo are likely dose, route, and duration dependent, its physiologic changes are similar to myostatin and other Activin receptors ligands. These data support that GDF11, like its other closely related TGF-beta family members, induces loss of cardiac and skeletal muscle mass and function.

Structural failure assessment of buried steel water pipes subject to corrosive environment

It is essential to predict the lifetime of buried pipelines since they are not easily accessible for inspection. In this study a time-dependent, non-linear state model has been introduced for the structural analysis of corrosion affected steel water pipes, stressed by external forces. Using limit state concept, the simultaneous effect of externally applied loading and material corrosion are considered through failure modes. A non-linear corrosion model is used to simulate the loss of pipe wall thickness during the operation period. In order to take the uncertainty associated with the design and environmental variables into account, a Monte Carlo simulation technique has been adopted using MATLAB. A parametric sensitivity analysis is also carried out to measure the effectiveness of each parameter on the probability of pipe failure. Results obtained for a steel water pipeline in Eastern Sydney are presented and discussed.

Possibility of detecting wall thickness loss using a PZT based structural health monitoring method for metal based pipeline facilities

Wall thinning effect for pipeline related facilities are one of the major issues when maintaining the structural integrity of facilities. Degradation of pipe by corrosion from the outer environment or the erosion from the products flowing within the pipe can reduce the wall thickness, weakening the structure. In this study, an attempt using the electromechanical impedance (EMI) method for detecting the wall thickness reduction is investigated. The main part of the study consists of analyzing how the resonance frequency range shifts as the wall thickness is reduced. The fact that a resonance frequency can either increase or decrease depending on how the property of a total system changes was taken into an account in this study. Since the EMI method heavily relies on signature variations, selecting a suitable frequency range was vital for detecting the reduction in wall thickness. The results from the investigation show a possibility of using the EMI method for detecting wall thickness reduction of metal structures.

The scattering of torsional guided waves from Gaussian rough surfaces in pipework.

In older sections of industrial pipework there are often regions of general corrosion that typically have a Gaussian thickness distribution. During guided wave inspection this corrosion causes an increase in the background noise and a significant attenuation of the inspection wave. These effects are investigated in this paper through finite element modelling of the interaction of torsional guided waves with rough surfaces in pipes. Pipes of different diameter and rough surface profile are modelled and it is found that the attenuation of waves is explained by significant mode conversion and scattering within the rough surface. This mode conversion is greatest when the non-axisymmetric modes to which energy is scattered are close to the cutoff frequency or when the ratio of surface correlation length to wavelength is around 0.2-0.25. Mode conversion increases with increasing surface roughness and is a strong function of frequency-diameter product, with larger pipes causing more mode conversion. When this mode conversion occurs the energy is lost mostly to those waves with a displacement profile closest to the original torsional inspection wave. Resulting attenuation of the inspection signal can be severe; for example a mean wall thickness loss of 28% can cause 2.7 dB/m attenuation in a pulse-echo configuration.

Second-order analysis of an imperfect corroded tubular member on a two-parameter elastic foundation

This paper presents a method for the second-order elastic and stability analyses of a corroded tubular member with initial geometric imperfections, resting on a two-parameter elastic foundation. It is assumed that the member is a simply supported Euler–Bernoulli beam-column with a corroded, yet compact cross section. Corrosion is modeled as symmetric loss of wall thickness that varies in magnitude along the member length. Moreover, the member is loaded both axially, transversely and simultaneously subjected to internal and external pressures. Despite all the effects considered herein, this model neglects the effects of thermal loads and torsion, as well as shear and axial deformations along the member. The fourth-order boundary value problem that governs the second-order elastic behavior of the tubular member is solved using the Galerkin method. The proposed method and corresponding equations are used to obtain the second-order transverse deflections, as well as the bending moment and shear force diagrams. This method is also used to estimate the buckling load and compressive strength of the tubular member, which play an important role in the design of tubular structures. The accuracy and effectiveness of the aforementioned formulation are evaluated using four comprehensive examples. The results from the examples demonstrate that the proposed method can be used in the analysis and design of submerged or non-submerged tubular members at a low computational cost.

Effects of uniformly distributed side corrosion on thin-walled open cross-section steel columns

Compressive capacity of the thin-walled steel columns, corroded uniformly over their entire side surface length is analysed in this paper. The thin-walled profile steel columns are often used for bridges, rail and road building constructions. Loss of the profile mass that appears due to corrosion growth reduces the cross-sectional area and influences column compressive capacity. Computational models of the structure are assumed based on the observation of existing corroded columns. The theory of thin-walled profiles is taken for the analysis. Models simulating the walls weakening due to corrosion growth are considered on the example of three thin-walled steel profiles: semi-closed channel section, two semi-closed channel section connected by webs and HKS profiles. Different patterns and degrees of corrosion growth were considered and, as a result, changes of the profile cross-sectional geometry were observed. Theoretical considerations of thin-walled compressed corroded steel columns stability are illustrated by bearing capacity calculations. Geometric cross-sectional characteristics are determined and the system of stability equations is solved. The calculation results are presented in the form of graphs illustrating the effects caused by the geometry change due to corrosion defects. The reduction of column compressive strength in each of the considered case is observed. Moreover a variation of the buckling mode from flexural one into warping is noticed in one of the analysed items. It has been found that more dangerous corrosion growth pattern appears when asymmetric loss of the profile wall thickness arises. That may change the form of buckling from flexural one into warping.

Microbially induced rupture of a heat exchanger shell

Abstract Microbially induced corrosion (MIC) has been identified as the main cause of the rupture of a key heat exchanger shell at a local refinery. The failure occurred at the 6 o'clock position, close to the girth weld, halfway along the length of the carbon steel shell. An ultrasonic survey revealed up to 90% wall thinning in the ruptured zone. Despite extensive crystallization at the external cooling seawater inlet of the cooling system tubing, there was no evidence of internal leakage of seawater into the shell compartment. The total dissolved solids in the condensate dropout sample were found to be 262 mg/L. The investigation also confirmed that the girth weld had been satisfactorily conducted, including post heat treatment, and that the failure occurred outside the heat affected zone (HAZ). Quantitative polymerase chain reaction (qPCR) analysis of the dry surface film from a crack in the ruptured area confirmed the suitability of the operating environment for prokaryotic growth and the presence of both groups of highly corrosive acid producing bacteria (APB) and denitrifying bacteria (DNB) in moderate numbers (1.92 × 10 3 APB/g and 1.81 × 10 5 DNB/g respectively). The colonization of different groups of corrosion-causing bacteria of a sour system resulted in the localized generation of highly aggressive metabolic by-products causing substantial loss of wall thickness of the heat exchanger shell. The localized wall thinning by over 90% of its original thickness led to the loss of pressure retention capacity of the shell and the rupture of the wall.

Guided Wave Tomography of Pipe Bends.

Detection and monitoring of corrosion and erosion damage in pipe bends are open challenges due to the curvature of the elbow, the complex morphology of these defects, and their unpredictable location. Combining model-based inversion with guided ultrasonic waves propagating along the elbow and inside its walls offers the possibility of mapping wall-thickness losses over the entire bend and from a few permanently installed transducers under the realm of guided wave tomography (GWT). This paper provides the experimental demonstration of GWT of pipe bends based on a novel curved ray tomography algorithm and an optimal transducer configuration consisting of two ring arrays mounted at the ends of the elbow and a line of transducers fixed to the outer side of the elbow (extrados). Using realistic, localized corrosion defects, it is shown that detection of both the presence and progression of damage can be achieved with 100% sensitivity regardless of damage position around the bend. Importantly, this is possible for defects as shallow as 0.50% of wall thickness (WT) and for maximum depth increments of just 0.25% WT. However, due to the highly irregular profile of corrosion defects, GWT generally underestimates maximum depth relative to the values obtained from 3-D laser scans of the same defects, leading in many cases to errors between 3% WT and 8% WT.

Predicting Oxidation-Limited Lifetime of Thin-Walled Components of NiCrW Alloy 230

Using alloy 230 as an example, a generalized oxidation lifetime model for chromia-forming Ni-base wrought alloys is proposed, which captures the most important damaging oxidation effects relevant for component design: wall thickness loss, scale spallation, and the occurrence of breakaway oxidation. For deriving input parameters and for verification of the model approach, alloy 230 specimens with different thicknesses were exposed for different times at temperatures in the range 950–1050 °C in static air. The studies focused on thin specimens (0.2–0.5 mm) to obtain data for critical subscale depletion processes resulting in breakaway oxidation within reasonably achievable test times up to 3000 h. The oxidation kinetics and oxidation-induced subscale microstructural changes were determined by combining gravimetric data with results from scanning electron microscopy with energy dispersive X-ray spectroscopy. The modeling of the scale spallation and re-formation was based on the NASA cyclic oxidation spallation program, while a new model was developed to describe accelerated oxidation occurring after longer exposure times in the thinnest specimens. The calculated oxidation data were combined with the reservoir model equation, by means of which the relation between the consumption and the remaining concentration of Cr in the alloy was established as a function of temperature and specimen thickness. Based on this approach, a generalized lifetime diagram is proposed, in which wall thickness loss is plotted as a function of time, initial specimen thickness, and temperature. The time to reach a critical Cr level at the scale/alloy interface of 10 wt% is also indicated in the diagrams.