Probable Cause Of Failure Research Articles

Comparing tensile, bending and interlaminar shear performance of GFRP composites fabricated using recovered and virgin glass fibers: Optimization of the microwave assisted chemical recycling technique

AbstractGlobal glass fiber reinforced plastic (GFRP) recycling provides an effective solution to the end‐of‐life wastes and industrial scrap, by which we can construct a closed‐loop system that reduces environmental impact while increasing sustainability. This study reports the tensile, flexural and shear properties of GFRP composites fabricated from reclaimed fibers from the waste GFRP. A hybrid recycling technique that is, microwave assisted chemical recycling has been used for recovering the glass fiber fabrics. The quantity of solvents (a mixture of 30% H2O2 and CH3COOH in 1:1 ratio) required (in mL/g) for degrading the polymer is optimized with respect to the amount of microwave irradiation time. The microwave irradiation duration was varied at constant power of 900 W for optimizing the quantity of solvent used. SEM analysis of both virgin and reclaimed fiber surfaces indicate an almost complete degradation of polymer from the waste composites. RGFE laminates, fabricated from reclaimed glass fiber fabrics, exhibited marginally higher tensile strength (7%–8%) and significant lower tensile modulus (~29%). On the other hand, RGFE composites demonstrated a greater strain to failure of ~44% compared to VGFE composites during tensile testing, consequently leading to a subsequent increase in tensile toughness by ~28%. The ILSS values obtained from SBS tests and storage modulus and loss factor curves from DMA tests showed almost similar values. SEM studies revealed the probable causes of failures of the samples for tensile and flexural tests.Highlights Hybrid recycling technique using microwave irradiation is optimized. Amount of solvent used is optimized by varying the irradiation times. Tensile and flexural strengths exhibit a marginal increase of 7%–8%. Significant rise in strain at failure by 44% and tensile toughness by 28%. Fractography studies have been performed for analyzing failures.

Enhanced susceptibility of high-strength fastener nuts to hydrogen-induced stress corrosion cracking

Abstract High-strength HV-fastener sets of dimensions M48 and M64 with property class 10.9 were employed in offshore wind turbine frameworks. The M64 were used in coupling flanges within monopiles. The M48 were employed in another offshore wind farm and encountered natural weathering. In both installations, time-delayed fractures of the nuts were observed. Owing to the presence of macroscopically visible corrosion products, hydrogen-induced stress corrosion cracking (Hi-SCC) was established as the probable cause of failure. However, a nut fracture in a properly pre-tensioned bolt assembly is atypical since the stresses in the bolt threads are higher than those in the nuts. Based on the Hi-SCC theory, the fracture should occur at the most stressed component, which is the bolt. During the root cause analysis, extensive examinations were conducted to determine the cause of the nut fractures. The focus was on investigating whether the nut material was more prone to Hi-SCC than the bolt material. The examination program included scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM-EDS) analysis of the fracture surfaces, optical microscopy of microspecimens, mechanical tests, and stress rupture tests of hydrogen-charged specimens. While the results suggest that the tested nuts comply with the requirements of the applicable standards regarding material properties, they also reveal that the nut material is, despite its lower tensile strength, significantly more susceptible to Hi-SCC than the bolt material. Therefore, a direct relationship between material susceptibility to Hi-SCC and the tensile strength, as standards and guidelines imply, is not given.

Evaluation of welded joints of austenitic stainless steels at high temperatures in the presence of SO2, SO3, and O2

This study undertakes a comprehensive examination of crack formation in welded joints of austenitic stainless steel 304, particularly in high-temperature corrosive environments prevalent in sulfuric acid production units. Initially, an investigation was conducted on a steam superheater that had been operational for about 19 years, where a crack formation was discovered. This unit, subjected to a working temperature of approximately 620 °C and exposure to gases composed of SO2, SO3, and O2, allowed for the analysis of corrosion products formed during the crack propagation. Building on the initial findings, a more controlled study was undertaken, focusing on the cracks formed in welded joints using the coated electrode E308L for joining 304H stainless steel plates under similar corrosive conditions. The specimens, constructed using materials typically utilized in sulfuric acid production units, were designed based on the double-beam principle, enabling exposure to both tensile stresses and a corrosive environment at high temperatures. Over a span of 122 days, or roughly 3000 h, microstructural analyses were conducted, revealing that the formation and propagation of cracks preferentially occurred through fragile microconstituents, notably the sigma phase. These findings mirrored the sigma phase formation observed in the initial superheater study and point to a stress corrosion process acting synergistically with sigma phase development, and consequently seen as a probable cause of failure. This comprehensive evaluation, therefore, indicates a significant role of the sigma phase and corrosive environments in influencing crack formation and propagation in welded joints of austenitic stainless steels, which require further studies for preventative strategies in industrial setups.

The use of decision trees to identify the causes of failures in a medical enterprise - a case study

The large amount of historical data contains information about events that occur along an industrial production line. Having a set of historical data about emergency events and their causes makes it possible to automate decision-making processes based on a data-driven approach. Data-driven approaches, particularly machine learning (ML), are attracting attention. Due to its visualization and interpretability characteristics, the decision tree (DT) model is an important ML tool for decision analysis. This paper aims to present the possibility of using DT to increase the efficiency and effectiveness of maintenance activities by identifying the probable cause of failure based on historical data. Based on the research conducted, we have shown that the use of machine learning techniques can improve the accuracy of decisions regarding the type of maintenance work that should be carried out to efficiently and effectively remove failures and reduce losses caused by machine downtime.

Effect of GNP coating on carbon fibers on the deformation modes of composites under flexural loading

AbstractGraphene nanoplatelets (GNPs) are extremely useful nanofillers in epoxy in carbon fiber‐reinforced polymer (CFRP) composites as they make CFPRs sustain higher loads before failure in different kinds of loading for example flexural, tensile and fatigue. The current study aims to investigate the effect of GNP coating on carbon fibers on the deformation modes of CFRPs under flexural loading. Laminates have been fabricated using vacuum‐assisted resin transfer molding (VARTM) after spray coating GNPs on unidirectional carbon fiber fabrics. One set of flexural tests were carried out where the strain was recorded using DIC and the other set had in‐situ deformation while recording optical images to monitor deformation. Since, the most probable causes of failure under flexural loading are local compression, shear or contact stresses due to a sharp ram, other mechanical tests like compression test and nano‐indentation were also carried out on the composites. Compressive stress–strain response was ascertained using combined loading compression (CLC) fixture and digital image corelation (DIC) while contact response was evaluated using nanoindentation. GNP‐coated CFRPs were shown to have an increase in compressive modulus of 16% and failure strain of 6%, respectively. Axial and transverse strains measured through DIC were more than two times higher in GNP‐coated CFRPs. Nano‐indentation tests across the entire composite showed some data with intermediate modulus (~10–45 GPa) and hardness (~1–5 GPa) between the epoxy and the fiber and this corresponded to an interphase region which was thicker in 0.4GNP laminate compared to pristine laminate. Flexural strength, flexural modulus and strain at maximum stress improved by 10%, 8%, and 9% respectively in GNP‐coated CFRPs compared to uncoated CFRPs. In addition, while pristine laminates showed non‐uniform distribution of strains during flexural loading, the distribution of strains was much more uniform in GNP‐coated laminate. However, in both kinds of laminates, the failure initiation was in the region of compressive bending stresses.Highlights GNP‐added laminate showed an intermediate modulus and hardness interphase through a nanoindentation test. Digital image correlation analysis has been performed to obtain the strain maps during compressive and flexural loading. GNP‐added laminates showed higher failure strains compared to pristine laminates under the compressive loads. GNP‐added laminates performed well under flexural loading.

Transient Analysis of Fluid Flow through a Closing Blowout Preventer Using Coupled Domain Computational Fluid Dynamics

Summary Erosion and forces on rams may prevent a blowout preventer (BOP) from sealing a well. Analyzing the flow field throughout a BOP may provide insight into these flowing effects on the inability of a BOP to seal the well. 3D transient simulation of fluid flow throughout closing BOP fluid domains is demonstrated using computational fluid dynamics (CFD). Simulation may be used to analyze the transient stress, pressure, and velocity fields throughout a BOP domain as it is closing. Many challenges exist in simulating a closing BOP using CFD, including boundary conditions and treatment of dynamic meshing. Solutions to those challenges are presented in this work. CFD simulations are carried out using ANSYS Fluent v19.2 (ANSYS, Canonsburg, Pennsylvania, USA). For inlet boundary conditions to the CFD domain, the CFD simulations are explicitly coupled with a 1D wellbore simulator. The 1D wellbore simulator provides a connection between the BOP and constant pressure reservoir. Numerical instability is present during this coupling process. An implementation for dealing with this instability is presented. An example validation case is presented to demonstrate the accuracy of CFD for pressure fields throughout valves. A second 2D axisymmetric case is shown to demonstrate the meshing and coupling simulation process. A third case, simulation through a 3D shear geometry is then presented to show the applicability of the process to a more complex geometric design. Velocity and stress fields are plotted to show the practicality of CFD in analyzing the probable causes of failure in BOP closures.

Early failure of a highly cross-linked polyethylene inlay after total hip arthroplasty probably due to insufficient irradiation.

Highly cross-linked polyethylene (XLPE) is a major advance in total hip arthroplasty (THA), as it suffers from less wear and thus is associated with lower revision rates than standard ultra-high molecular weight polyethylene. Early failures are reported rarely, and associated with specific design or manufacturing issues. We report a case requiring early revision due to adverse reaction to polyethylene particles. Investigations identified insufficient irradiation as the most probable cause of failure. Here are reported the features of a clinical case with determination of the material properties of the retrieved XLPE liner and establishment of the appropriate calibration curves as reference. Periprosthetic joint infection could be ruled out with appropriate sampling as cause for the inflammatory periarticular tumour. Histology identified a massive macrophagic reaction to micrometric polyethylene particles. No component malposition was present, nor any third-body wear. The trans-vinylene index (TVI) indicated insufficient and potentially detrimental irradiation of the polyethylene, while gel content, crystallinity, melting temperature and oxidation index remained within expected ranges. Histologically proven failure of a XLPE THA liner was identifiable despite correct implantation of the components. The cause of failure most probably was an inadequate irradiation, as indicated by determination of the TVI. This case underscores the importance of histologic workup even in aseptic revisions, and of detailed analysis of retrievals. The calibration curves provided are essential for analysis of other retrievals.

Analiza grešaka putničkih obrtnih postolja vagona iz železničkog sistema Republike Bugarske

This paper is based on a review of a study of damage to passenger bogies on railway vehicles. The results of the research of the reliability of the passenger bogies from the park of the Bulgarian State Railways (BDZ) are analyzed. The constructions of passenger bogies type swing in the operation of the Republic of Bulgaria are presented - YT72, Görlitz V and GP200. The most common faults of the passenger bogies are indicated. The general failures, the probable causes of failures and the ways to minimize them have been successfully identified.

Design Failure Mode and Effect Analysis – Case Study

Design-Failure mode and effect analysis (D-FMEA) is very important tool used in industries to detect failure during design stage. D-FMEA is a technique to find out causes of failure and their effects on the performance of a system(parts) during design phase. In this paper, the D-FMEA of critical components of designed automatic tilting mechanism trolley is carried out. The critical components of automatic tilting mechanism trolley are identified and analyzed by the D-FMEA tool. This paper provides risk priority number of components of trolley. The component with higher risk priority number has higher chances of failure. The risk priority number of critical components is reduced by incorporating corrective actions. This paper provides probable causes of failure, effects of failure and corrective actions to be undertaken during design phase of Automatic tilting mechanism trolley. The D-FMEA tools helps in reducing accidents.

Intelligent Steam Power Plant Boiler Waterwall Tube Leakage Detection via Machine Learning-Based Optimal Sensor Selection.

Boiler waterwall tube leakage is the most probable cause of failure in steam power plants (SPPs). The development of an intelligent tube leak detection system can increase the efficiency and reliability of modern power plants. The idea of e-maintenance based on multivariate algorithms was recently introduced for intelligent fault detection and diagnosis in SPPs. However, these multivariate algorithms are highly dependent on the number of input process variables (sensors). Therefore, this work proposes a machine learning-based model integrated with an optimal sensor selection scheme to analyze boiler waterwall tube leakage. Finally, a real SPP test case is employed to validate the proposed model’s effectiveness. The results indicate that the proposed model can successfully detect waterwall tube leakage with improved accuracy vs. other comparable models.

Microstructural Analysis of Corroded Copper Pipes Used in Water Distribution Network

A network of three copper piping systems has been used to distribute cold, warm and hot waters to a healthcare complex. The pipes have been hard-drawn using phosphorus-oxidized copper grade. However, water leakage from the three pipes has been detected after less than 2 years in service. It is shown that the three pipes have been degraded by pitting corrosion due to the relatively high sulfate-to-chloride ratio in the water. The corrosion product formed at the inner surface of each pipe is found to consist of an outermost discontinuous and non-protective layer of copper oxide followed by an intermediate chloride layer, and an inner sulfate layer forming the major component. It is concluded that the most probable cause of failure is sulfur contamination of water at the source.

Thermal Fatigue Failure of Low-Pressure Turbine Blade in a Low-Bypass Turbofan Engine

Failure of low-pressure (LP) turbine rotor blade in a low-bypass turbofan engine is analyzed to determine its root cause. Forensic and metallurgical investigations are carried out on the affected blades. High surface oxidation on damaged blade is found to be the reason for crack initiation in blades. Thermal fatigue is the probable cause of failure in the blades due to prolong operation at maximum condition and malfunction of engine control system.

Failure investigation of a secondary super heater tube in a 140 MW thermal power plant

This article describes the findings of a detailed investigation into the failure of a secondary super heater tube in a 140MW thermal power plant. Preliminary macroscopic examinations along with visual examination, dimensional measurement and chemical analysis were carried out to deduce the probable cause of failure. In addition optical microscopy was a necessary supplement to understand the cause of failure. It was concluded that the tube had failed due to severe creep damage caused by high metal temperature during service. The probable causes of high metal temperature may be in sufficient flow of steam due to partial blockage, presence of thick oxide scale on ID surface, high flue gas temperature etc. rupture.

Failure analysis of fire resistant fluid (FRF) piping used in hydraulic control system at oil-fired thermal power generation plant

This is a case study regarding frequent forced outages in an oil-fired power generating station due to failure of fire resistant fluid (FRF) piping of material ASTM A-304. This analysis was done to find out the most probable cause of failure and to rectify the problem. Methods for finding and analyzing the cracks include nondestructive testing techniques such as visual testing (VT) and dye penetrant testing (PT) along with that periodic monitoring after rectification of problem. The study revealed that pitting and pit to crack transitions were formed in stainless steel piping containing high pressure (system pressure 115 bars) fire resistant fluid. However, after replacement of piping the pitting and cracking reoccurred. It was observed that due to possible exposure to chlorinated moisture in surrounding environment pitting was formed which then transformed into cracks. The research work discussed in this paper illustrates the procedure used in detection of the problem and measures taken to solve the problem.

Back analysis of an ancient rockslide at Lake Fundudzi, Limpopo Province, South Africa

A massive rockslide occurred in the Soutpansberg Mountains of the Limpopo Province ~20,000 years ago that blocked the course of the eastern flowing Mutale River forming Lake Fundudzi, which is the only known true inland lake in South Africa. The landslide occurred in the northwestward dipping and highly jointed Fundudzi Formation of the Soutpansberg Group. The failed slope was observed to be a homogenous jointed sandstone rock slope which is quartzitic in places. Cluster analysis, which uses fuzzy clustering in Rocscience Dips, revealed three major joint sets (JS1, S0 and JS3) in the rock mass with an average dip and dip direction of 85°/237°, 15°/283° and 73°/157°, respectively. The main failure plane best correlated with JS3, which dips towards the lake. The kinematic analysis also revealed that the mechanism of failure was planar which is in agreement with site observations. The strong rock material classification of the sandstone from a laboratory index and mechanical tests was one of the indicators that failure could have been mostly structurally controlled. The technique of back-analysis was employed using RocPlane in order to investigate the geotechnical conditions that may have resulted in failure. The results obtained from the sensitivity analysis in RocPlane showed that the joint roughness coefficient (JRC) followed by the residual basic friction angle (ϕ r) were the main influential shear strength parameters on the factor of safety, F, as opposed to the joint wall compressive strength (JCS) which has very little impact on F for the range of values considered. Results from back-analysis show a range of possible combinations of JRC and ϕ r values under different groundwater and seismic conditions. Whilst the groundwater shows more impact than the seismic coefficient, the field evidence points to seismic activity as a more plausible trigger than groundwater. This study shows the usefulness of back-analysis techniques in assessing various conditions of failure that may have resulted in ancient rockslides. Although it may not result in a unique set of geotechnical parameters that may have resulted in failure, it, however, gives an insight into probable causes of failure and, thus, can be useful in mitigation of future failures.

English

Design FMEA is structured method of identifying potential failure modes and providing corrective actions before first production run occurs. This paper aims to provide probable causes of failure, levels of effects of failure and corrective actions to be taken in the design phase for Bevel- Planetary Vertical Roller Mill Gearbox. Keywords—DFMEA, Bevel-Planetary Gearbox, Vertical Roller Mill, Risk Priority Number I. In tro d uct io n 1) Vert ica l Ro ll er M il ls: Vertical roller mills (VRM) are well accepted as most effectual means for grinding raw material in cement and power generation industry. These mills are driven by heavy duty gearboxes with horizontal input shaft and vertical output shaft (i). Generally, Bevel-Helical or Bevel-Planetary gearboxes are used for VRM. The gearbox is integral component of VRM as its output flange is rigidly connected with the mill grinding table. Fig. 1 shows the general arrangement of VRM with gearbox located at its bottom.

Investigation on Failure of a Drilling Rig Mast Structure

A drilling rig that was used for exploration of gaseous fuels was inspected. During its operation the rig mast suddenly collapsed and the structure got twisted from the middle. The failure investigation was carried out to determine the probable causes of failure in the rig. Estimation of mechanical properties, optical microscopic analysis along with scanning electron microscopy examinations were necessary supplements to this investigation. Detailed stress analysis of the structure for different conditions of loads and anchors was examined. It was ultimately concluded that non-functioning of record-o-meter was responsible for rapid increase in operating load and one or more cables/anchoring points did not have sufficient strength to withstand the operating load. The anchoring cable broke with a jerk and the mast structure collapsed under its weight.

Experimental and Analytical Investigation of Steel Bolts Failed After Isothermal Heat Treatment

In the present study, ultra high-strength steel bolts declared unqualified in the magnetic particle testing (MPT) after isothermal heat treatment have been investigated to find out the probable cause of failure. The material was characterized by scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, tensile testing, hardness, and chemical analysis. It has been revealed that the magnetic flux leakage in MPT was due to the presence of sub-surface non-metallic inclusions. Finite element analysis (FEA) had been carried out to approximate the ensuing stress state due to non-metallic inclusions in the steel during the heat treatment process. Radial (σ xx), axial (σ yy), shear (σ xy), and von-Mises stresses were determined, and their peak stress values were evaluated to assess the probable mode of failure. FEA results showed significantly high stresses arising from thermal expansion mismatch between steel and inclusions; however, the peak stress value did not exceed the yield strength of the material.

Analysis of a Failed Primary Superheater Tube and Life Assessment in a Coal-Fired Powerplant

The paper presents results of failure analysis of a primary superheater tube in a steam powerplant boiler. The boiler has been in service for around 52,000 h (6 years) and failure occurred on one of the primary superheater tubes in the form of a wide-open burst with appreciable wall thinning. The location of failure was first determined by on-site visual examination. Subsequently, specimens were taken from a region near the fracture surface for chemical analysis, microstructural examination using optical microscopy, and scanning electron microscopy equipped with energy-dispersive X-ray analysis to determine the probable cause of failure; whereas the lifetime of the superheater tubes was assessed using stress rupture test. Results suggest that the cause of failure was overheating due to deposit buildup inside the superheater tube which acted as thermal barrier and wall thinning resulted from direct impingement of flue gases. The lifetime of the superheater tubes is estimated and is discussed in the present investigation.

Failure Investigation of a Final Super Heater Tube in a 140 MW Thermal Power Plant

This article describes the findings of a detailed investigation into the failure of a final super heater tube in a 140 MW thermal power plant. Preliminary macroscopic examinations along with visual examination, dimensional measurement, chemical analysis, evaluation of mechanical properties, and oxide scale thickness measurement were carried out to deduce the probable cause of failure. In addition, optical microscopy was a necessary supplement to understand the cause of failure. It was concluded that the tube had failed due to stress rupture. The tube metal had been exposed to a temperature above the safe operating limit for a long duration. As a result the tube metal had lost its strength, suffered creep deformation and failed to support the working stress resulting in final rupture. The adherent scale, particularly on internal surface formed due to exposure at high temperature. It had acted as an insulating blanket in view of its much lower thermal conductivity than that of the tube metal. The progressive build-up of scale had greatly affected heat transfer and raised the tube metal temperature above A1 for a short duration before bursting of the tube. The overheating in this case may be due to poor circulation over the localized area.