Tube Failure Research Articles

Bending Failure Behavior of Thin-walled Composite Tube Structures

Abstract The bending failure, failure load and failure mode of thin-walled circular tubes made of carbon fiber reinforced resin matrix composites were investigated by experiments and numerical simulation. Three typical failure modes of circular tubes under bending load were observed in experiments, and the characteristics and mechanisms of different failure modes were analyzed. The results show that interlaminar shear induces the generation and propagation of microcracks at the interface of circular tubes, which accelerates the failure of circular tubes. In the bending failure process, because the interlayer performance of the round pipe is relatively low, it is the weak link of the structure, and the pipe wall is the first to produce interlayer delamination and splitting failure under the action of shear stress, resulting in structural instability and premature fracture failure. The lay-up and initial defects of thin-walled round pipe have great influence on the bending failure mode and failure load.

Stub column behaviour of high strength steel square hollow sections with semi-circular stiffeners

This paper proposes a novel high strength steel square hollow section with semi-circular stiffeners, aiming to delay or eliminate premature local buckling failure of the steel tube and lead to improved compressive performance. A total of 9 stiffened and unstiffened stub columns were tested to investigate the failure modes and compressive responses. The test results showed that the stiffened sections achieved significantly higher compressive strength with delayed local buckling failure compared to the unstiffened counterparts. Tensile coupons were extracted from flat, corner and curve portions of the steel tubes in order to determine the corresponding material properties. Finite element (FE) models were established to numerically simulate the tested stub columns, in which both failure modes and load-end shortening curves could well replicate the test results. Parametric studies were then implemented using the validated FE model to extend the dataset. The obtained test and numerical results were used to assess the applicability of existing design standards and methods. It was found that EC3, ANSI/AISC 360-22, AS 4100 and Direct Strength Method (DSM) could be safely adopted in cross-section classifications and cross-section capacity predictions.

Improved Early Detection of Tube Leaks Faults in Pulverised Coal-fired Boiler Using Deep Feed Forward Neural Network

Boiler tube leaks significantly reduce the operational availability of power units, yet their early detection and prediction have not been fully realised in the industry. This paper introduces a novel approach employing deep feedforward neural networks for early detection of boiler tube leaks in pulverised coal-fired boilers. Early detection enhances repair planning, minimising downtime and production losses. It also improves monitoring and control of boiler tube failures, thereby optimising power plant operations and revenue. Diverse deep neural network models were developed and rigorously tested by leveraging 9 years of operational data (2012–2020). Exhaustive hyper-parameter optimisation, involving seven parameters, substantially improved predictive accuracy. By achieving training and testing accuracies of 82.8% to 99.3%, the study assessed their ability to detect boiler tube leaks over the same 9-year span, providing insights into leak detection capabilities. The models notably predicted all 12 identified tube leak events, averaging a 14-day lead time before boiler shutdown. In addition to leak prediction, a leak detection matrix was devised to analyse residual behaviour and reduce the likelihood of false alarms. However, the models’ predictive performance was observed to be limited to the following year, with satisfactory results for 2021 only. Incorporating the 2021 data into retraining significantly improved the predictions for 2022. The study concludes that while the models demonstrate robust short-term prediction capabilities, they require continuous retraining to maintain accuracy and relevance. This ongoing refinement is essential for keeping the models up-to-date and reliable in predicting future boiler tube leaks.

Impact of oxide layer on performance and creep life of a superheater tube in a coal-fired power plant

The failure of a superheater tube in a coal-fired power plant, designed to resist creep damage at high temperatures and pressures, was investigated after it ruptured following 115,360 h of operation, which was significantly shorter than its expected 200,000-hour life. An oxide layer measuring 106 µm was discovered on the inner side of the tube, which acted as a thermal insulator, raising the tube’s temperature and reducing its thickness. This led to increased stress, decreased creep resistance, and a shortened tube life. The oxide layer’s growth, tube temperature, and stress were estimated. After 115,360 h, at a flue gas velocity of 22 m/s, the oxide layer reached an estimated thickness of 120 µm. The outer and inner tube surface temperatures were 522 °C and 510 °C, respectively, and the stress was estimated at 79.9 MPa. To extend tube life to the designed 200,000 h, it was determined that reducing the flue gas velocity to 15.8 m/s or lower would be required. At this velocity, the tube’s creep life was estimated at 200,070 h when accounting for tube thinning. Without accounting for the reduction in thickness, the estimated life was 210,650 h, which was approximately 1.2 years longer.

A semi-analytical prediction model for fluid elastic instability in the streamwise direction of a normal triangular tube array

Fluid elastic instability (FEI) is widely regarded as the most destructive mechanism of flow-induced vibration. Numerous failures of heat exchanger tubes have been attributed to this phenomenon. This paper focuses on a normal triangular tube array and develops a semi-analytical time-domain solving model to address FEI in the streamwise direction. Utilizing computational fluid dynamics simulations and image processing techniques, a comprehensive set of tube-in-channel model parameters is derived, including the area perturbation amplitude, phase difference, mean area along the flow channel, and steady-state term of flow velocity. Tube motion in the streamwise direction generates a disturbance distinct from that caused by transverse flow, leading to revisions in the expressions of relevant model parameters. Furthermore, variations in these parameters across different positions and velocities are quantitatively analyzed through function fitting, yielding specific mathematical formulas. Ultimately, the derived tube-in-channel model parameters applicable to streamwise FEI are validated against experimental data, affirming the model's accuracy.

Analysis of cracking failures in water-cooled wall fins and thermal peaking unit mitigation strategies

Abstract The causes of leakage in the submitted superheater tubes were analyzed using the analysis of macroscopic morphology, chemical composition, and metallography. The analysis results indicate that the chemical composition of the failed superheater tube is within the standard range, and the metallographic structure is ferrite + pearlite, with no abnormalities in the metallographic structure. The main reason for the failure of water-cooled wall tubes and superheater tubes may be the formation of fatigue cracks on the inner and outer walls of the superheater tubes under cyclic stress. As the two fatigue cracks grow and converge, penetrating cracks form, ultimately leading to the initial leakage of the superheater tubes. In addition, the excessive depth of the weld pool in the fins of the superheater tube is another crucial factor that promotes accelerated cracking of the superheater tube. It is recommended that power plants reasonably regulate the temperature difference fluctuation rate of boilers to prevent similar failure accidents from occurring.

Group resistances of tensile-loaded anchored-bolted connections with CFST columns: Tests, simulations, and theoretical models

The performance of the connections in concrete-filled steel tubular (CFST) columns fabricated with a group of two anchored blind-bolts under tensile forces is evaluated. Based on the bolt group arrangement, two sets of experiments, comprising eight full-scale specimens, were tested. Test parameters include the presence of concrete, bolt anchorage length, pitch distance, and gauge distance. Further, numerical models were developed, which, after validation, were used for parametric studies. Key findings indicate that bolt gauge distance, anchorage length, concrete grade, and column cross-section slenderness significantly influence the connection behaviour, but pitch distance has the least influence. Tube and concrete failure modes, as well as critical gauge and pitch distances, are identified, which govern tube deformation and concrete crushing zones. Finally, a bi-linear theoretical model is developed that can provide a fair prediction of the connection strength and stiffness.

Ear diseases due to diving with an aqualung

Due to the growing popularity of diving, more and more people suffer from injuries related to this activity and ear injuries are among the most common ones. During diving, dysfunction of both the external, middle and inner ear are likely to occur. Inflammation is the most common disease of the external ear, which, in most cases, requires only local treatment with ear drops. Barotrauma of the middle and inner ear may occur due to Eustachian tube failure and difficulties in equalizing underwater pressure, also manifested as hearing loss and dizziness. In most cases, conservative treatment is applied, however, under specific conditions such as perforation of the tympanic membrane or the presence of persistent perilymphatic fistulas, surgical treatment may be necessary. In the case of severe dizziness or hearing loss during ascent after diving at great depths, a preliminary diagnosis of inner ear decompression sickness should be made and the patient should be placed in a hyperbaric oxygen chamber as a matter of urgency.

Comparative study of heat exchanger tubes failure analysis using ECT and IRIS

Comparative study of heat exchanger tubes failure analysis using ECT and IRIS

Two functionally interchangeable Vps9 isoforms mediate pollen tube penetration of style.

Style penetration by pollen tubes is essential for reproductive success, a process requiring canonical Rab5s in Arabidopsis. However, functional loss of Arabidopsis Vps9a, the gene encoding for guanine nucleotide exchange factor (GEF) of Rab5s, did not affect male transmission, implying the presence of a compensation program or redundancy. By combining genetic, cytological, and molecular approaches, we report that Arabidopsis Vps9b is a pollen-preferential gene, redundantly mediating pollen tube penetration of style with Vps9a. Vps9b is functionally interchangeable with Vps9a, whose functional distinction results from distinct expression profiles. Functional loss of Vps9a and Vps9b results in the mis-targeting of Rab5-dependent tonoplast proteins, defective vacuolar biogenesis, disturbed distribution of post-Golgi vesicles, increased cellular turgor, cytosolic acidification, and disrupted organization of actin microfilaments (MF) in pollen tubes, which collectively lead to the failure of pollen tubes to grow through style.

Quality of Life and Motor Function in Children with Spina Bifida and Hydrocephalus: Impact on Family Functioning in Indian Rural Population

Background & Purpose: Spina Bifida means “open spine”, and refers to a common congenital birth defects involving a failure of the neural tube to close or to remain closed during early embryogenesis. A significant complication for infants born with myelomeningocele is the onset of hydrocephalus. In rural Indian populations, where socioeconomic constraints and healthcare accessibility are significant challenges, the correlation between motor function and QoL becomes a critical area of investigation. Thus, the purpose of this study is to explore quality of life and motor function in children with spina bifida and hydrocephalus… its impact on family functioning in Indian rural population. Methodology : 20 Subjects with spina bifida and hydrocephalus, age 6 –10 years, both male and female with mean age of 47.30 months were assessed for their demographic profile according to selection criteria. They were assessed for quality of Life by using PedsQL Infant scoring Scale, Family functioning by using PEDSQLFIS, Motor function by using Gross Motor Function Measure (GMFM), socioeconomic status using Modified Kuppuswamy Socioeconomic Scale. The data was collected and computed in a systematic way and then analysed by using SPSS 20. Results : Correlational analysis was done. Statistically significant correlation was found in duration of operation and GMFM, PedsQL Infant scoring Scale and GMFM. Conclusion : This study shows that children with spina bifida and hydrocephalus in rural India benefit from better quality of life when they have improved motor skills. However, the impact of family dynamics, socioeconomic status, and the length of surgery on their quality of life was less clear. Overall, while good motor function is strongly linked to a better quality of life, other factors also play a role.

A cumulative damage model for tubes in nuclear power plants subject to continuous degradation and multi-effect shocks under dynamic environments

Continuous degradation and shocks are two vital damage mechanisms for tubes under dynamic environments in nuclear power plants (NPPs). In this work, we presented a cumulative damage model to evaluate the reliability of tubes in NPPs, which accounts for continuous degradation and random shocks. The dynamic environments were assumed to obey a homogenous Markov process. Continuous degradation was described as a general stochastic process with independent increments. A multinomial distribution was used to depict the multiple effects of Poisson-distributed shocks on tubes. The influence of dynamic environments on the cumulative damage process of tubes was also explicitly modeled. Closed-form reliability measures were derived, such as reliability functions and mean time to failure (MTTF) of tubes. Drawing upon a case study from the existing literature, the analytical solution was validated through a comparative analysis with the outcomes of Monte Carlo simulation (MCS) and other methodologies referenced in the literature. As a practical engineering application, the reliability of steam generator tubes made of Alloy 690 within pressurized water reactors (PWRs), which are susceptible to primary side stress corrosion cracking (PWSCC) and the effects of water hammer, was calculated. The findings indicate that the probabilities of steam generator tube rupture (SGTR) as estimated by the model and those inferred from operational experience have the same order of magnitude.

Corrosion of Waste Heat Boiler Tubes in Methanol Plant

A thorough failure investigation was conducted into a failure of waste heat boiler tubes in a methanol plant to determine the failure mechanism, and contributing factors. The investigation was performed utilizing different characterization techniques, including optical light microscopy, scanning electron microscopy, mechanical testing and chemical analysis techniques. The investigation findings showed that the tubes failure is attributed to corrosion under deposit. Details of the failure’s contributing factors, and recommendations to avoid similar failures, are discussed in this article.

Numerical and Experimental Study of Flow-Induced Vibrations in Micro-Tube Heat Exchangers

Abstract Thermal management presents an increasing challenge in future engineering systems, especially in applications like combined cycle precooling, waste heat recovery, and innovative propulsion systems. These systems face a growing demand for managing higher heat loads while coping with limited heat sink. Central to these thermal management systems is the heat exchanger, with micro-tube heat transfer emerging as a promising solution for future technologies. Micro-tube heat exchangers are becoming popular owing to their ability to significantly enhance the heat transfer surface area while maintaining a compact core volume. As the demand for high-performance, lightweight heat exchangers escalates, micro-tube heat exchangers are being designed to be increasingly compact yet highly loaded. This trend poses significant challenges to their structural integrity, particularly under harsh operational conditions. Flow-induced vibrations, a critical concern in the design of tubular heat exchangers, can lead to tube failures, compromising the safe operation of engineering systems. While the flow-induced vibrations of conventional-sized heat exchangers have been extensively studied, there is a noticeable gap in the research on similar phenomena in micro-tube heat exchangers. This paper details ongoing research at Reaction Engines Ltd to aid the design of safe and robust heat exchangers, focusing on the flow-induced vibrations in micro-tube heat exchangers and utilizing a cutting-edge laser vibrometry test facility. A predictive model, employing an unsteady flow simulation approach and eigenvalue analysis, has been formulated.

Investigation of Fluidelastic Instability in Parallel Triangular Tube Arrays Subjected to Air Flow

Abstract One of the major considerations in the design and operation of heat exchangers is the flow-induced vibration (FIV). While there are multiple FIV excitation mechanisms, fluidelastic instability (FEI) is by far the most crucial mechanism as it can significantly compromise the structural integrity of the tube arrays. Traditionally, it was assumed that FEI could only happen in the transverse direction. However, recent tube failures in replacement steam generators have demonstrated that FEI can occur in the streamwise direction and be equally devastating. This new phenomenon has sparked intensive research to uncover its nature. An intensive experimental research program was launched to investigate the geometrical impact of various tube array types on the FEI in both the transverse and streamwise directions. To that end, the stability of a single flexible tube and multiple flexible tubes in tube arrays was tested. The study will focus on the stability behavior of parallel triangular arrays at pitch ratios in the range of 1.25–1.70. A comparison between the available experimental data and the current results was presented. The current results reveal that the stability threshold is sensitive to the pitch-to-diameter ratio of the array and the number of flexible tubes, especially in the streamwise direction.

Cause Analysis and Improvement Measures for Superheated Platen Tubes Failure of a 580 t/h CFB Boiler

Superheaters are crucial components of boilers operating under high temperatures and pressures. Understanding potential damages, especially in components like superheaters, is essential for enhancing boiler, turbine, and overall power plant productivity. This paper highlights a study for the failure investigation of platen superheater tube in Unit 2 of a 2x150 MW coal-fired power plant in South Sumatra. Various tests including chemical composition, hardness, tensile, metallography, SEM fracture surface examination, and XRD compound analysis were conducted to assess the failure of the platen superheater tube. The investigation revealed that the failure of platen superheater tube was initiated by the plugging of the tube elbow due to deposits and ashes adhering to the tube's interior. This obstruction prevented saturated steam flow inside the tube, leading to overheating and a subsequent drop in mechanical strength. Overheating was confirmed by the presence of spheroid particles in the ferrite matrix. Prolonged overheating resulted in the formation of microvoids, leading to creep failure and crack formation in the tube. Following improvements made during Unit 2 maintenance outage, which involved adding refractory material inside the furnace on the platen superheater panel, positive results were observed. The platen superheater tubes, which previously exceeded temperature limits, now operate within normal range temperatures. This improvement also reduced spray water consumption and significantly increased boiler efficiency from 83.19% to 83.54%.

Experimental investigation of the behavior of UHPCFST under repeated axial tension

A ultra-high performance concrete filled steel tube (UHPCFST) is a composite structural component that extends the performance of both steel and concrete. It is a promising component to be used in a diagrid structure to further reduce self-weight. Compared with the research on compressive performance of UHPCFST, there is a lack of knowledge on the mechanical behavior of UHPCFST under axial tension. This paper fills this knowledge gap by carrying out experiments on UHPCFST subjected to monotonic and repeated tension. The test parameters are steel tube thickness and volume fraction of ultra-high performance concrete (UHPC). The failure modes, load-strain curves, tensile strength and tensile stiffness are studied in detail. Stiffness degradation is also studied. The test results show that: (1) under axial tension load, a UHPCFST typically experiences fracture failure of the outer steel tube, followed by section fracture of the UHPC, and notable deformation before a final ductile failure; (2) tensile strength increases with the increase of the thickness of the steel tube, while it is less obvious in a UHPCFST with a higher steel ratio; (3) the force-strain curve of a UHPCFST under monotonical axial tension is close to that of the UHPCFST under repeated axial tension, suggesting that the accumulated damage during unloading and reloading is limited. An exponential decay formula is proposed to predict stiffness degradation observed in the repeated axial tensile tests. It is found that the design codes from Europe, USA, and China underestimate tensile strength and stiffness of UHPCFST. Finally, a three-phase empirical model is proposed for the load-strain curve of UHPCFST under tension.

Symptoms and Factors Associated With Eustachian Tube Dysfunction Among the Population of Qassim, Saudi Arabia.

Introduction The Eustachian tube regulates middle ear functions such as ventilation and pressure normalization. Eustachian tube dysfunction (ETD) is defined as the failure of the Eustachian tube to maintain one or more of its functions. It is a common condition that is associated with other middle ear disorders such as cholesteatoma, tympanic membrane atelectasis, and otitis media with effusion (OME). This study aims to assess ETD prevalence and risk factors in the Qassim region. Methodology This cross-sectional study was conducted in the Qassim region of Saudi Arabia during the period from September 20 to October 10, 2023. Data were gathered via a validated, self-administered electronic questionnaire that encompasses socio-demographic information, the prevalence of ETD, and the prevalence of its various symptoms, as assessed by the Eustachian Tube Dysfunction Questionnaire (ETDQ-7). Results Our study in Qassim, Saudi Arabia, with 467 participants reveals a high prevalence of ETD at 12.2%. The 18-25 age group dominates (50.1%), with a majority of females (66.2%). Symptom analysis using the ETDQ-7 questionnaire shows varied prevalence, with severe pain (7%) and muffled hearing (29.8%) notable. Logistic regression identifies significant predictors, including hearing loss history (odds ratio = 28.2) and smoking (odds ratio = 3.70). Specific symptoms, such as feeling blocked or underwater, significantly correlate with more severe ETD symptoms (odds ratio = 1.73). Conclusion Our study highlights a notable prevalence of ETD. Significant predictors, including hearing loss history and smoking, were identified. Specific symptoms, such as feeling blocked or underwater, were associated with more severe ETD symptoms.

Patterns and short term neurosurgical treatment outcomes of neonates with neural tube defects admitted to Felege Hiwot Specialized Hospital, Bahir Dar, Ethiopia

BackgroundNeural tube defects (NTDs) account for the largest proportion of congenital anomalies of the central nervous system and result from failure of the neural tube to close spontaneously between the 3rd and 4th weeks of in utero development. Prognosis and treatment outcome depends on the nature and the pattern of the defect. The nature of treatment outcomes and its pattern associated with grave prognosis is not well known in the study area.ObjectiveThe aim of study was to determine the patterns and short term neurosurgical management outcomes of newborns with neural tube defects admitted at Felege Hiwot Specialized Hospital.MethodsInstitutional based retrospective cross-sectional study among neonates, who were admitted at Felege Hiwot Specialized Hospital with neural tube defects from January 1st to December, 30th, 2018 was conducted. All Charts of Neonates with confirmed diagnosis of neural tube defects were included as part of the study. Trained data collectors (medical interns) supervised by trained supervisors (general practitioners) collected the data using a pretested data extraction format. Data were coded, entered and analyzed using SPSS version 23 software. Frequency and cross tabulations were used to summarize descriptive statistics of data, and tables and graphs were used for data presentation.ResultAbout 109 patients had complete documentation and imaging confirmed neural tube defects. Myelomeningocele was the commonest pattern 70 (64.2%). Thoracolumbar spine was the commonest site of presentation 49(45%). The most common associated impairment was hydrocephalus 37(33.9%). Forty-five (41.1%) had multiple complications. The mortality rate was 7.3%, 44% were discharged with sequalae and 36.7% were discharged without impairment. The significant causes of death were infection 66.7% and Chiari crisis 33.3%.ConclusionMyelomeningocele was the most frequent clinical pattern of neural tube defect and thoracolumbar spine was the commonest site. Isolated neural tube defect was the commonest finding. There were multiple complications after surgery accompanied with meningitis and hydrocephalus. The mortality rate among neonates with neural tube defects was considerably high. The commonest causes of death were infection and Chiari crisis.

Analysis of the causes of waste heat boiler leakage in large-scale chemical plants

A waste heat boiler is a kind of high-temperature and high-pressure heat exchanger in a large chemical plant, and its safe operation is directly related to the production efficiency and safety risk of a chemical plant. In this paper, the leakage failure analysis of a waste heat boiler in an ethylene plant is carried out, and the analysis methods such as field observation, macro observation of fracture, metallographic analysis, micro observation of fracture, phase analysis, and energy spectrum analysis are adopted respectively. The results show that the direct cause of the leakage of the waste heat boiler is the thinning of the wall thickness of the heat exchange tube caused by alkali corrosion, which leads to the overload and fracture of the heat exchange tube. The pits on the outer surface of some heat exchange tubes are caused by mechanical reasons, which are related to this leakage and closure. The corrosion failure of heat exchange tubes is widespread, which has a great influence on safety production and serious consequences. Through this comprehensive analysis, the failure mechanism is clarified, which can provide a reference for the maintenance of similar equipment. At the same time, preventive measures are put forward from the aspects of technology, structure, and detection to reduce the occurrence of similar accidents.