Circumferential Crack Research Articles

1747 Rare Case of Esophagitis Dissecans Superficialis Mimicking Eosinophilic Esophagitis Treated With PPI

INTRODUCTION: Esophagitis dissecans superficialis (EDS) is a rare condition characterized classically by sloughing of the esophageal mucosa. EDS is a benign condition that usually resolves without lasting pathology. EDS can be associated with medications, chemical irritants, hot beverages, autoimmune diseases. Here we present a case of EDS which mimicked Eosinophilic esophagitis on endoscopy. CASE DESCRIPTION/METHODS: 76 y old male with PMH of CAD on ASA presented with chief complain of dysphagia to solid food underwent EGD that revealed mucosal friability, non-obstructing Schatzki ring, faint mucosal rings. The esophagus was dilated with 18 Fr savory dilator. Biopsies from mid and distal esophagus showed nonspecific inflammation with no intramucosal eosinophils. EGD was repeated 3 months later while he was taking PPI BID. Repeat EGD showed esophagus with circumferential rings, congestions, friability and a thin white membrane lifting from the mucosa. Biopsies from mid and distal esophagus showed splitting of squamous mucosa, focal lymphocytic infiltration and diffuse parakeratosis consistent with EDS. He was continued with PPI BID with the improvement of symptoms. DISCUSSION: Classical EDS has been characterized by stripped, whitish mucosa with or without bleeding, vertical fissures and circumferential cracks. EDS is associated with medications such as bisphosphonates or NSAIDs, chemical irritants, celiac disease, hot beverages, autoimmune bullous dermatoses or idiopathy. Commonly presents as dysphagia, anemia, pain, and heartburn. It is unclear if 81 mg ASA taken by our patient is a culprit, as he did not have any other known risk factor. Treatment includes PPI and discontinuing precipitating factors and medications. In this case, endoscopic findings initially mimicked EoE, however, repeat EGD with biopsies revealed underlying EDS.

Numerical Analysis of the Effect of External Circumferential Elliptical Cracks in Transition Thickness Zone of Pressurized Pipes Using XFEM

The present work investigates the effect of the elliptical three-dimensional (3D) cracks on a pipe with thickness transition, considering internal pressure. Level sets were defined using the extended finite element method (XFEM), the stress intensity factors (SIFs) of 3D cracks were investigated and compared between straight pipes and pipes with thickness transition. The results show that the XFEM is an effective tool for modeling crack in pipes. A pressurized pipe with thickness transition is more sensitive to the feature compared to the straight pipe. Parameters of the transition zone have an influence on stress intensity factors. Quantification of the SIFs associated with cracks in the transition zone of pipes with thicknesses is performed.

Cracking failure analysis of convection tube of heat recovery steam generator

The failure causes of cracks on a convection tube of heat recovery steam generator were analyzed by the optical microscope and scanning electron microscope analysis. The results show that the circumferential crack of the convection tube belongs to fatigue fracture. The micro-crack defect on the surface of fracture promotes the fatigue crack propagation.

A strain-controlled fracture assessment for submarine thin-walled pipes with V-groove welds and circumferential embedded cracks

Abstract In the offshore industry, oil and gas are commonly transported with thin-walled clad pipes. Reel-lay is a widely used method to install clad pipes. During the installation and service process, engineering critical assessment (ECA) is usually required to guarantee safety. Most of the ECA methods pertain to surface cracks. The DNV-RP-F108 standard indicates that an embedded crack can be transformed into a surface crack in evaluation, and the result is still conservative. However, the evaluation can be over-conservative at times, meanwhile, the effect of the weld material as well as groove shape is not considered. In this work, a more direct assessment of welded clad pipes with a circumferential embedded crack is proposed based on a modified reference strain approach. A strain-controlled boundary condition is applied, and various pipe and weld geometrical shapes are considered in the analysis matrix. Two plugins based on Python script are developed to circularly create a lot of numerical models. Hundreds of regression analyses based on the linear relationship between normalized J integral and nominal strain are implemented. An analytical solution of the peak J integral of the embedded crack is proposed, and the solution is proved to be close to FEA.

Electromagnetic Testing of Rod Cluster Control Assemblies in Pressured-Water Reactor Power Plants

This paper presents an electromagnetic testing system for rod cluster control assemblies used in pressurized-water reactors. The system uses several encircling-type magnetic cameras equivalent to a number of the control rods; each sensor probe composes of an encircling Hall sensor array (EHaS) and a bobbin coil. The EHaS has 16 Hall sensor elements that measure the electromagnetic field distribution in the radial direction of the control rod induced by the bobbin coil for defects. Experiments are performed on artificial defects on the cladding tube of real control rods to simulate short-circumferential grooves (SCGs), sliding wears (SWs), and circumferential cracks (CCs). The system can inspect the artificial SCGs, SWs, and CCs with depths up to 20%, 30%, and 40% of the cladding tube thickness (0.47 mm), respectively. Furthermore, the shape and depth of the defects could be estimated. The standard deviations of depth estimation are 18%, 5.8%, and 6.0% for CCs, SCGs, and SWs. The SCGs and SWs have a small and similar estimation error, but the CCs have the highest error of estimation, and have a small width of 0.2 mm.

Electromagnetic Nondestructive Testing Model and Surface Magnetic Field Analysis for Circumferential Cracks on Metal Rod

AbstractIn this paper, an analytical model for a metal rod with a coating layer is proposed to evaluate circumferential crack from the signals of the surface magnetic field. In the proposed model, magnetic vector equations for four regions of space were built, and series expressions of the magnetic field were proposed by the truncated region eigenfunction method. The calculation results can show the three-dimensional distribution of axial and radial magnetic induction intensities on the surface of a metal rod clearly. In addition, the analytical model is verified by using comsol finite element simulation, which also demonstrates that induced eddy currents on the inner surface of the metal rod with cracks appear to be propelled toward the inner layer of the metal rod and the presence of a circumferential crack directly causes a decrease in the induced eddy current on the inner surface of the rod. The results calculated from the analytical model indicated that the model is capable of providing an accurate variation in the magnetic field due to circumferential cracks at different depths. The analytical results showed that the radial magnetic induction intensity increases by 0.16 × 10−3 T, while the axial magnetic induction intensity decreases by 0.3 × 10−3 T as the crack depth increases from 0 to 3 mm.

Limit load solutions for elbows with circumferential through-wall crack under the pressure-induced bending restraint effect

Abstract A typical pipe finite element model is made by assuming there is internal pressure with a single crack located in the middle of the pipe where both ends are constraint-free. In reality, however, both ends are constrained by their connections to components such as the pressure vessel or pump. Furthermore, due to the complexity of the pipe system, it also experiences a self-constraint effect. This is called the pressure-induced bending restraint effect, and is known to affect the fracture mechanics parameters at the crack tip. Some studies exist on the pressure-induced bending restraint effect of straight pipes, but none have focused on elbow pipe and junction between straight pipe and elbow. This study suggests limit load solutions for elbow and their jointing regions with circumferential through-wall cracks under the pressure-induced bending restraint effect. The relevant equations can be used to estimate the maximum withstand load evaluation of a highly ductile pipe, and can also be used to estimate the elasto-plastic fracture mechanics parameters using the reference stress method.

A Study on the Failure of AISI 304 Stainless Steel Tubes in a Gas Heater Unit

This paper investigates a failure in convection section tubes of a gas heater unit in a petrochemical plant. Tubes are made of AISI 304 stainless steel. The failure is reported after 5 years of service at working temperature 500 °C. The failure is in the form of circumferential cracks in the vicinity of the weld. Various characterization techniques, including optical and electron microscopes as well as energy-dispersive X-ray spectroscopy (EDS), were used to study the failure. Results showed that that the damage has initiated in the heat affected zone (HAZ) area parallel to the weld/base metal interface. Cracks have propagated alongside grain boundaries, resulting in an intergranular fracture. The main cause of failure was concluded to be attributable to the grain boundary sensitization and intergranular grain boundary attack due to improper welding and long time exposure of tubes to high temperature. Possible mitigation strategies to minimize similar failures will be discussed.

Analytical Solution for Free Vibration of Annular Mindlin Plate with a Circumferential Open Crack

Mindlin plate theory is employed to obtain the free vibration response of an annular moderately thick plate with a circumferential open crack with fixed-free boundary conditions. To model the crack, a set of continuously distributed rotational springs are employed at the crack location. The corresponding spring stiffness value is a function of the crack depth and is given as a closed-form function. To obtain the vibration behaviour, the eigenvalue problem is solved to obtain the natural frequencies and mode shapes. The current method is verified by comparing the results with those obtained from finite element analysis. Through a parametric study, the effects of the crack depth and its radial location on the natural frequencies and mode shapes are investigated. The results show that for a constant crack depth, the reduction in natural frequency is a strong function of the radial location of the crack.

Experimental investigation of a circumferential crack in a PMMA cylindrical shell using caustics

Abstract In this paper, the optical method of transmitted caustics is extended to study the stress singularity at the tip of a circumferential crack in a PMMA cylindrical shell. First, a new theoretical analysis of light path is presented based on local deformations around the circumferential crack tip and geometry condition of the cylindrical shell. Second, governing equations of transmitted caustics are established, and the effects of material properties, radius of curvature, shell thickness and crack length on the shape and size of caustic patterns are analyzed. Finally, the stress intensity factors in cracked cylindrical shells under axial tension are evaluated using a simple and reliable optical measurement setup. It is shown that the stress intensity factors obtained by using the optical caustics agree well with the already existing theoretical solutions and the numerical results of finite element analysis.

Microstructure Evolution and Failure Behavior of Stellite 6 Coating on Steel after Long-Time Service

The microstructure evolution, elements diffusion and fracture behavior of the Stellite 6 weld overlay, deposited on 10Cr9Mo1VNbN (F91) steel by the tungsten inert gas (TIG) cladding process, were investigated after long-time service. Obvious diffusion of Fe occurred from the steel and fusion zone to the Stellite overlay, resulting in the microstructure evolution and hardness increase in the coating, where hard Co–Fe phases, σ phases (Fe–Cr metallic compounds) and Cr-rich carbides (Cr18.93Fe4.07C6) were formed. Besides, the width of the light zone, combined with the fusion zone and diffusion zone, increased significantly to a maximum value of 2.5 mm. The fracture of the Stellite coating samples mainly occurred in the light zone, which was caused by the formation and growth of circumferential crack and radial crack under high temperature and pressure conditions. Moreover, the micro-hardness values in the light zone increased to the maximum (470–680 HV) due to the formation and growth of brittle Co–Fe phases. The formation of these cracks might be caused by formed brittle phases and changes of micro-hardness during service.

Initial-contact-induced bending failure of a semi-infinite ice sheet with a radial-before-circumferential-crack pattern

Abstract Ice loadings induced by the bending failure of a semi-infinite ice sheet have been investigated extensively for ice-capable vessels or sloping offshore structures in the arctic regions. In recent years, real-time simulators of ice-sloping structure interactions are rapidly gaining traction due to their potential applications. For such purposes, analytical or semi-analytical bending failure models are required to achieve reasonable levels of efficiency and accuracy. Motivated by this need, the current paper focuses on the bending failures of a semi-infinite ice sheet, with a breaking pattern of radial before circumferential cracking. Departing from existing work done in literature, the proposed framework does not assume a large initial radial crack length, nor associate the maximum ice load with the initiation of a circumferential crack. Instead, the proposed framework tracks the competition between component forces for the initiation and propagation of radial cracks, as well as that for the initiation of the circumferential crack, to determine the maximum ice load. For sea ice with large fracture energy, it is shown that the maximum ice load does not occur at the initiation of the circumferential crack, as commonly assumed in literature. The research methodology and conclusions presented herein thus facilitate a more accurate real-time description of ice-sloping structure interactions.

Distribution of Mode I Stress Intensity Factors for Single Circumferential Semi-Elliptical Crackin Thick Cylinder

In this paper, mode I stress intensity factors (SIFs) are calculated numerically by finite element software ANSYS, for a single semi-elliptical circumferential crack on a thick cylinder. The examined cracks were located either on the external or internal surface of the cylinder and subjected to two different types of loadings, tension and internal pressure, applied separately. To present results in a more comprehensive form, dimensionless analysis is used, and a wide variation limit of parameters that define the crack geometry is considered. The ratio of crack depth to crack length ranging between 0.4 to 1.2, the ratio of crack depth to cylinder wall thickness vary between 0.2, 0.5 and 0.8, and the ratio of the cylinder wall thickness to the cylinder internal radius 0.25. Based on the obtained results, distributions of SIFs found to be symmetric along the crack front. The location where the maximum SIFs on the crack front attained is strongly affected by the change of aspect ratio, and external cracks generally exhibit a higher SIFs than those of internal cracks. It is also found a significant effect for the relative depth of the crack on SIFs value, which could accelerate the fracture process.

Hydrogen-Assisted Crack Growth in the Heat-Affected Zone of X80 Steels during in Situ Hydrogen Charging.

Herein, the hydrogen embrittlement of a heat-affected zone (HAZ) was examined using slow strain rate tension in situ hydrogen charging. The influence of hydrogen on the crack path of the HAZ sample surfaces was determined using electron back scatter diffraction analysis. The hydrogen embrittlement susceptibility of the base metal and the HAZ samples increased with increasing current density. The HAZ samples have lower resistance to hydrogen embrittlement than the base metal samples in the same current density. Brittle circumferential cracks located at the HAZ sample surfaces were perpendicular to the loading direction, and the crack propagation path indicated that five or more cracks may join together to form a longer crack. The fracture morphologies were found to be a mixture of intergranular and transgranular fractures. Hydrogen blisters were observed on the HAZ sample surfaces after conducting tensile tests at a current density of 40 mA/cm2, leading to a fracture in the elastic deformation stage.

Peridynamic investigation of stress corrosion cracking in carbon steel pipes

Abstract Stress corrosion cracking (SCC) is the nucleation and propagation of crack due to a combined effect of mechanical stress and chemical corrosion, which may lead to unexpected failure. Specially, pitting corrosion is an extremely localized corrosion style, where micro cracks are easily formed. Experiments and traditional computational methods suffer when dealing with materials failure in such a complex dynamic process. To this end, we present a numerical study of SCC in corrosion pits based on recently developed peridynamic method. The simulation is implemented based on carbon steel pipes with different corrosion types and loading conditions. Circumferential and Longitudinal crack patterns are observed due to bending and internal pressure, respectively. We also find the critical loads to initiate macroscopic crack and compare the process of dynamic growth due to different corrosion pits and loads. The results provide guidance for structural design and engineering practice.

Movable hood tube in LD convertor: Failure analysis and coating solution

Abstract An assembly of movable and fixed hood tubes provide safe passage to LD gas produced during primary steel making process. These water-cooled tubes, made up of ASTM A106 : Grade B steel are exposed to most extreme environment involving severe thermal cycling, corrosion from hot LD gas as well as cooling water, wear and erosion from lime and slag splashing, etc. Current work analyzed the failure of movable tubes that led to generation of multiple cracks on the outer surface of the tube facing the LD gas. Analysis revealed cracks parallel to each other in circumferential direction of the tubes. Most of the cracks originated from outer wall of the tube and propagated inwards, however, some of the cracks emanated from inner wall which was in contact with cooling water as well. Elemental analysis revealed the presence of calcium, potassium and sulphur in the oxide scale along the cracks. The nature of scale was confirmed using Energy Dispersive Spectroscopy and Raman Spectroscopy. Presence of these elements are known to reduce the thermal conductivity of the scale and thus can make the cooling inefficient and promote greater thermal stresses. A number of circumferential and longitudinal cracks were observed in tube-to-tube weld zone as well and these were related to microstructural abnormality therein. Overall failure analysis suggested that “thermo-mechanical corrosion fatigue” resulted in premature failure of the hood tubes. Based on detailed laboratory study and field trial, Inconel 625 coating using twin wire thermal spray method has been proposed as a viable techno-economic solution for improved reliability of these tubes.

Influence of heating and cooling rate on the stress state of the brick lining in a rotary kiln using finite element simulations

Rotary kilns for iron-ore pellets production are highly dependent on a well-functioned refractory brick lining. To improve the long-term capability of the lining, in-situ observations of the bricks' performance are desired, however, the harsh environment inside the rotary kiln makes it difficult or nearly impossible to study the lining during operation. By using numerical simulations as a tool, some of the problems encountered by the brick lining can be studied without limitation of the extreme conditions. In this work, stress state of the lining was studied under the influence of different heating and cooling rates, and different brick compaction cases. A finite element model was created for conducting the numerical simulations. The numerical model was calibrated for transient heat transfer. Temperature dependent material properties of the bricks and casing were used as input. The heating and cooling was controlled by temperature prescription on the boundary of the brick lining, while brick lining compaction by defining relative position of the bricks in axial and radial directions. The conducted numerical simulations showed that considerable tensile stress may appear in a large area of the brick during initial heating stage. The large tensile area corresponds well with the typical circumferential cracks experienced by the bricks. It was demonstrated that the compressive stresses counteract the development of tensile stresses. However, the compressive stresses may become very large in the initial stage of heating. The positive effect of lower heating rate was considerable on the tensile stresses, while influence on the compressive stresses was almost unnoticed. The hypothetical cooling rates showed that very high tensile stresses may occur on the surface of the bricks, potentially leading to surface spalling. Furthermore, it was demonstrated that axial compaction is highly important on the stress development in the lining, which, may not always be followed in practice. As a general conclusion, it is recommended to always achieve a tight compaction of the brick lining and to take measures for lowering the heating and cooling rates. The conducted work exemplifies behaviour of the brick lining for realistic heat transfer and material properties. The insight into the behaviour gives possibilities to make adjustments and directed investments for lowering risk of brick lining failure.

Detection of cracks with arbitrary orientations in a metal pipe using linearly-polarized circular TE11 mode microwaves

Abstract This study proposed a long-range non-destructive pipe inspection approach using linearly-polarized circular TE11 mode microwaves, enabling rapid detection of both axial and circumferential cracks on the inner surface of a metallic pipe. The applicability of the TE11 mode microwaves for crack detection was discussed in the light of the currents induced on the inner surface of a pipe due to the propagation of the TE11 mode microwaves. A dual-bend structured mode converter was designed to propagate linearly-polarized TE11 mode microwaves inside a pipe with a certain inner diameter, based on the theoretical and numerical analysis of mode conversion due to a bend. A 3.5 GHz working bandwidth of the mode converter was achieved with a conversion efficiency of the TE11 mode of over 90%. Experimental verification was conducted using stainless-steel pipes with an inner diameter of 23 mm and a total length of 7 m. An axial and a circumferential slit were introduced to simulate cracks. The experimental results confirmed reflections from both the axial and circumferential slits, indicating that the TE11 mode microwaves are applicable to crack detection. The results also confirmed the correlation between TE11 mode polarization and its detection sensitivity toward slits with different orientations along the circumferential direction. Furthermore, the axial and circumferential slits situated at different longitudinal and circumferential locations in the pipe were successfully detected by orthogonally deploying the mode converter to change the polarization of the TE11 mode by 90°.

Averaged strain energy density estimated rapidly from the nodal stresses by FEM for cracks under mixed mode loadings including the T-stress contribution

The present contribution reviews a recently proposed method to rapidly estimate the averaged SED at the tip of short as well as long cracks under in-plane I+II and long cracks under out-of-plane I+III mixed mode loadings. Short cracks are distinguished from long cracks by considering that the stress fields within the control volume of short cracks are no longer governed solely by the stress intensity factors (SIFs), but the contribution of higher order terms, and primarily the T-stress, becomes significant to estimate the averaged SED. According to the proposed method, the averaged SED is calculated using the linear elastic nodal stresses evaluated by FEM either at the crack tip, to account for the SIFs contribution, and at selected FE nodes of the crack free edges, to include the T-stress contribution. The advantage of the proposed approach is two-fold: coarse FE meshes can be adopted; moreover, geometrical modelling the control volume is no longer necessary. To validate the approach, cracked plates subjected to in-plane I+II mixed mode loading as well as bars weakened by circumferential outer cracks subjected to out-of-plane mixed mode I+III loading have been analysed. A comparison between approximate values of the averaged SED according to the nodal stress approach and those derived directly from the FE strain energy adopting very refined FE meshes has been successfully performed.

Analysis and Study on Crack Characteristics of Highway Tunnel Lining

Lining cracks are one of the most common diseases in highway tunnels, and the existence of lining cracks directly affects the overall stability and durability of tunnels, which has an important impact on the safe operation of tunnels, and it is necessary to analyze and study the characteristics of tunnel lining cracks. Combining with the detection data of multiple highway tunnels in the field, the different types of tunnel cracks are divided, and the classification numerical statistics method is used to obtain that the number and length of annular cracks in highway tunnel cracks are significantly higher than those of the other two kinds of cracks, and the longitudinal cracks in tunnel crack cracking degree are greater than the circumferential cracks and the inclinded cracks. The influence degree of cracks on the safety of tunnel structure longitudinal cracks are relatively the largest, the inclinded cracks are second only to longitudinal cracks, and the influence of cyclic cracks is relatively small. It provides reference for tunnel engineering design, construction, operation management and comprehensive improvement work.