Tube Damage Research Articles

Axial compressive residual ultimate strength of circular tube after lateral collision

The tubes which are applied in jacket platforms as the supporting structure might be collided by supply vessels. Such kind of impact will lead to plastic deformation on tube members. As a result, the ultimate strength of tubes will decrease compared to that of intact ones.In order to make a decision on whether to repair or replace the members, it is crucial to know the residual strength of the tubes. After being damaged by lateral impact, the simply supported tubes will definitely loss a certain extent of load carrying capacity under uniform axial compression. Therefore, in this paper, the relationship between the residual ultimate strength of the damaged circular tube by collision and the energy dissipation due to lateral impact is investigated. The influences of several parameters, such as the length, diameter and thickness of the tube and the impact energy, on the reduction of ultimate strength are investigated.A series of numerical simulations are performed using nonlinear FEA software LS-DYNA. Based on simulation results, a non-dimensional parameter is introduced to represent the degree of damage of various size of tubes after collision impact. By applying this non-dimensional parameter, a simplified formula has been derived to describe the relationship between axial compressive residual ultimate and lateral impact energy and tube parameters. Finally, by comparing with the allowable compressive stress proposed in API rules (RP2A-WSD A P I, 2000), the critical damage of tube due to collision impact to be repaired is proposed.

Combating hot corrosion of boiler tubes – A study

Abstract The premature failure of boiler tubes, especially in coal fired boilers poses serious threat to the efficiency of the Indian boilers. In coal fired thermal power plant boilers, hot corrosion and erosion is the primary reason behind downtime, which leads to huge economic losses. So the consolidated results of the various researchers working in the area of combating hot corrosion of boiler tubes, especially in context with Indian boilers (both actual and simulated environment) are presented in this article. These results help the researchers in selecting an appropriate and accurate coating material composition, coating process and parameters for a particular boiler steel to improve the life of boiler tubes. So, that, any unwanted damage of boiler tubes due to hot corrosion could be minimized.

Evaluation of Stress Relaxation Cracking on 800HT Pigtails of the Steam Reformer

Stress relief cracking occurs when susceptible alloys are subjected to thermal stress after welding to reduce residual stresses and improve toughness. Cracks were observed on the external surface of the outlet pigtails of a steam reformer. The failures (cracks) occurred at the toe of the socket weld connecting the pigtail to the catalyst tube. Design parameters are 900 °C and 22 barg; the actual operating conditions are 875 °C and 20 barg. The material of construction is Alloy 800HT, which is an iron–nickel–chromium alloy. The outlet pigtail was used to transfer the process fluid of the steam reformer which is connected to a manifold header. It was requested to conduct a failure analysis on damage in the outlet pigtail tubes that occurred in the form of cracks. The failure analysis study is described in detail in this paper, and the mechanism of the crack is identified and proper recommendation is given to avoid such issues in future operations.

Pulsed Eddy-Current Detection of Loose Parts in Steam Generators

Flow-induced vibration of loose parts located on steam generator (SG) tube sheets can result in SG tube damage and eventual loss of SG efficiency. Regular inspection of SG tubes at support structures can help extend SG life by detecting and monitoring flaws as well as identifying accumulation of loose parts. Application of conventional eddy-current technologies in this case, however, is limited when magnetite fouling is present or when loose parts are resting directly on the SG tube sheet. Pulsed eddy current (PEC) combined with a modified principal components analysis (MPCA) was investigated as a method of detecting and identifying a variety of loose part materials in close proximity to 15.9-mm outer diameter Alloy-800 SG tubes and surrounding steel support structures. Loose parts were found to be detectable for varying axial positions along the SG tube and when in contact with the tube sheet. When offset radially from the SG tube, 1.6-mm-diameter carbon steel parts with a strong magnetic component allowed detection up to 3.2 mm away, while nonferromagnetic stainless steel parts of the same size could only be detected up to 1.5 mm away. Signal variation in the presence of loose parts was attributed to differences in amplitude of transient response and in relaxation times for diffusion of transient magnetic fields through various materials. The ability to accurately detect and identify loose parts located in close proximity to SG tubes establishes PEC combined with MPCA as a potential candidate for SG inspection.

Treatment of feline pyothorax: A report of two spontaneous cases

Two cases of feline pyothorax, presented in severe respiratory distress, were treated successfully by applying intermittent drainage and daily lavage of the pleural space with warm normal saline. Before that an indwelling thoracostomy tube had been fixed on the thoracic wall and left in place from 5 to 10 days. The only complication noticed was a symptomatic pneumothorax due to either tube malpositioning or damage to the tube wall. In both instances, the inspiratory dyspnea decreased or disappeared as soon as the tube was removed. Systemic and long term (6-9 weeks) treatment with antibiotics, combined with supportive measures and good nursing care, had a positive effect to the successful outcome in both cases.

Optical Fiber Demodulation System with High Performance for Assessing Fretting Damage of Steam Generator Tubes.

In order to access the fretting damage of the steam generator tube (SGT), a fast fiber Fabry-Perot (F-P) non-scanning correlation demodulation system based on a super luminescent light emitting diode (SLED) was performed. By demodulating the light signal coming out from the F-P force sensor, the radial collision force between the SGT and the tube support plate (TSP) was interrogated. For higher demodulation accuracy, the effects of the center wavelength, bandwidth, and spectrum noise of SLED were discussed in detail. Specially, a piezoelectric ceramic transducer (PZT) modulation method was developed to get rid of the interference of mode coupling induced by different types of fiber optics in the demodulation system. The reflectivity of optical wedge and F-P sensor was optimized. Finally, the demodulation system worked well in a 1:1 steam generator test loop and successfully demodulated a force signal of 32 N with a collision time of 2 ms.

The application of compressive sampling in rapid ultrasonic computerized tomography (UCT) technique of steel tube slab (STS).

This paper explores a new method for rapid structural damage inspection of steel tube slab (STS) structures along randomly measured paths based on a combination of compressive sampling (CS) and ultrasonic computerized tomography (UCT). In the measurement stage, using fewer randomly selected paths rather than the whole measurement net is proposed to detect the underlying damage of a concrete-filled steel tube. In the imaging stage, the ℓ1-minimization algorithm is employed to recover the information of the microstructures based on the measurement data related to the internal situation of the STS structure. A numerical concrete tube model, with the various level of damage, was studied to demonstrate the performance of the rapid UCT technique. Real-world concrete-filled steel tubes in the Shenyang Metro stations were detected using the proposed UCT technique in a CS framework. Both the numerical and experimental results show the rapid UCT technique has the capability of damage detection in an STS structure with a high level of accuracy and with fewer required measurements, which is more convenient and efficient than the traditional UCT technique.

Experimental Investigation on the Deformation and Fracture of Steel Square Tubes under Double‐Explosion Loadings

The experimental investigations on the square tubes with various stand‐off distances and wall thickness were helpful to understand the dynamic response of metal shell under single and double explosion. Therefore, the effect of stand‐off distance, wall thickness, and amounts of explosion on the deformation and damage of the square tubes and the regular pattern of the fracture development was analyzed by dimensions of local plastic deformation, volume of the depression area, and crack type. The result reveals that the deformation and fracture mode of steel square tubes gradually transform from local deformation to rupture with the decrease of wall thickness and stand‐off distance. Besides, the failure degrees of square tubes under a double explosion were relatively higher than those of square tubes under a single explosion. In addition, the experiment indicates that the side corners of the square tube are very vulnerable, and they are damaged easily by the stress concentration and shear effect. The conclusion provides an important scientific basis for the structural design of square‐tube structures and calculation of engineering protection.

Fiber Fabry-Perot Force Sensor with Small Volume and High Performance for Assessing Fretting Damage of Steam Generator Tubes.

Measuring the radial collision force between the steam generator tube (SGT) and the tube support plate (TSP) is essential to assess the fretting damage of the SGT. In order to measure the radial collision force, a novel miniaturized force sensor based on fiber Fabry-Perot (F-P) was designed, and the principle and characteristics of the sensor were analyzed in detail. Then, the F-P force sensor was successfully fabricated and calibrated, and the overall dimensions of the encapsulated fiber F-P sensor were 17 mm × 5 mm × 3 mm (L × W × H). The sensor works well in humid, high pressure (10 MPa), high temperature (350 °C), and vibration (40 kHz) environments. Finally, the F-P force sensors were installed in a 1:1 steam generator test loop, and the radial collision force signals between the SGT and the TSP were obtained. The experiments indicated that the F-P sensor with small volume and high performance could help in assessing the fretting damage of the steam generator tubes.

Radiant tubes lifetime prediction in steel processing lines using fluid–structure interaction modelling

One of the limiting factors for processing steel lines performances is the radiant tubes damage. This damage results from a combination of many parameters such as operating conditions (combustion performances, depending on burner design and control, furnace control, fuel quality and stability…) and radiant tube design (material selection, geometry, and manufacturing). Current operating conditions lead to upper temperature limit for radiant tubes, which are then exposed to several mechanisms, such as hot corrosion, creep, and thermal fatigue that ultimately may result to their failure. To improve equipment lifetime subject to severe thermal stresses it is essential to know precisely the radiant tube temperature distribution. The common approach to evaluate radiant tube lifetime is usually limited to thermal stresses calculations on the hypothesis of linear elastic behavior, based on calculated or measured temperature distribution. However, at high temperature, creep behavior implies large deformations that could change the fluid flow inside the radiant tube. A coupled analysis of fluid dynamics and thermomechanical behavior could lead to a more precise evaluation of thermal operating conditions and lifetime for radiant tubes. Thus, a development has been carried out by Fives to increase lifetime of W-shape NiCr cast radiant tube operating at temperatures up to 1000 °C. Combustion and heat transfer inside the tube are simulated using Computational Fluid Dynamics with RANS approach, for fuels including Natural Gas, Coke Oven Gas and residuals Mixed Gases from the steel production. Creep behavior is simulated using a Nonlinear Structural model with Norton’s creep law model, using parameters from the literature. The deformation resulting from creep combined with material selection, tube design and tube supports contributes to evaluate radiant tube lifetime. Our results are satisfactory compared with radiant tubes surface temperatures and observed deformation after several years of operation, obtained in Fives test center and during industrial operation.

Probable causes of damage of heat-exchange tubes of low-pressure-exchanges of PND-3 type and repair methods

The structures of low-pressure heaters (LPH), which are installed at nuclear power plants with the K-1000-60/1500 type turbine plants are considered. It was revealed that only the PND-3 type low-pressure heaters have the damages of the heat exchange tubes. For a short operation life, the number of the damaged heat-exchange tubes of PND-3 is approximately 50 pcs for Kalinin NPP and 100–150 pcs for Balakovo NPP. The low-pressure heaters were manufactured at AO Ural Plant of Chemical Machine-Building “Uralkhimmash,” OAO Taganrog Boiler-Making Works “Krasny Kotelshchik,” and Vitkovice Machinery Group, but the damage nature of the heat-exchange tubes is identical for all PND-3. The damages occur in the place of passage of the heat exchange tubes through the first, the second, and the third partitions over the lower tube plate (the first path of the turbine condensate). Hydraulic shocks can be one of the possible causes of the damage of the heat-exchange tubes of PND-3. The analysis of the average thermal and dynamic loads of the tube systems of PND-1–PND-4 revealed that PND-3 by the thermal power are loaded 1.4–1.6 times and by the dynamic effects are loaded 1.8–2.0 times more than the remaining LPHs. Another possible cause of damage can be the cascaded drain of the separate into PND-4 and then through the drainage heat exchange into PND-3. An additional factor can be the structure of the condensate drainage unit. The advanced system of the heating steam flow and pumping scheme of the separate drain using the existing drainage pumps of PND-3 for K-1000-60/1500 turbine plants for Balakovo and Kalinin NPPs were proposed. The considered decisions make it possible to reduce the flow rate of the heating steam condensate from PND-3 into PND-4 and the speed of the heating steam in the tube space of PND-3 and eliminate the occurrence of hydraulic shocks and damages of the heat exchanger tubes.

Simulation of Corrosion Process for Structure with the Cellular Automata Method

In this paper, from the mesoscopic point of view, under the assumption of metal corrosion damage evolution being a diffusive process, the cellular automata (CA) method was proposed to simulate numerically the uniform corrosion damage evolution of outer steel tube of concrete filled steel tubular columns subjected to corrosive environment, and the effects of corrosive agent concentration, dissolution probability and elapsed etching time on the corrosion damage evolution were also investigated. It was shown that corrosion damage increases nonlinearly with increasing elapsed etching time, and the longer the etching time, the more serious the corrosion damage; different concentration of corrosive agents had different impacts on the corrosion damage degree of the outer steel tube, but the difference between the impacts was very small; the heavier the concentration, the more serious the influence. The greater the dissolution probability, the more serious the corrosion damage of the outer steel tube, but with the increase of dissolution probability, the difference between its impacts on the corrosion damage became smaller and smaller. To validate present method, corrosion damage measurements for concrete filled square steel tubular columns (CFSSTCs) sealed at both their ends and immersed fully in a simulating acid rain solution were conducted, and Faraday’s law was used to predict their theoretical values. Meanwhile, the proposed CA mode was applied for the simulation of corrosion damage evolution of the CFSSTCs. It was shown by the comparisons of results from the three methods aforementioned that they were in good agreement, implying that the proposed method used for the simulation of corrosion damage evolution of concrete filled steel tubular columns is feasible and effective. It will open a new approach to study and evaluate further the corrosion damage, loading capacity and lifetime prediction of concrete filled steel tubular structures.

Simulation of corrosion process for concrete filled steel tubular columns with the cellular automata method

Abstract In this paper, from the mesoscopic point of view, under the assumption of metal corrosion damage evolution being a diffusive process, the cellular automata (CA) method was proposed to simulate numerically the uniform corrosion damage evolution of the outer steel tube of concrete filled steel tubular columns subjected to corrosive environment, and the effects of corrosive agent concentration, dissolution probability and elapsed etching time on the corrosion damage evolution were also investigated. It was shown that corrosion damage increases nonlinearly with increasing elapsed etching time, and the longer the etching time, the more serious the corrosion damage; different concentration of corrosive agents had different impacts on the corrosion damage degree of the outer steel tube, but the difference between the impacts was very small; the heavier the concentration, the more serious the influence. The greater the dissolution probability, the more serious the corrosion damage of the outer steel tube, but with the increase of dissolution probability, the difference between its impacts on the corrosion damage became smaller and smaller. To validate the present method, corrosion damage measurements for concrete filled square steel tubular columns (CFSSTCs) sealed at both their ends immersed fully in a simulating acid rain solution were conducted, and Faraday's law was used to predict their theoretical values. Meanwhile, the proposed CA mode was applied for the simulation of corrosion damage evolution of the CFSSTCs. It was shown by the comparisons of results from the three methods aforementioned that they were in good agreement, implying that the proposed method used for the simulation of corrosion damage evolution of concrete filled steel tubular columns is feasible and effective. It will open a new approach to study and evaluate further the corrosion damage, loading capacity and lifetime prediction of concrete filled steel tubular structures.

The energy absorbing properties of bamboo-based structures

A series of quasi-static and dynamic tests on bamboo-based honeycomb and bamboo-reinforced foam structures were carried out to investigate their energy absorbing characteristics and the related failure modes. Here, the tube damage shows the typical buckling (bulging) and top surface splitting failure. The results on the individual tubes show that the energy absorbing capacity increases as the diameter-to-thickness ratio decreases. Simple analytical models were also developed to predict the peak load and the corresponding displacement, with reasonably good correlation to the experimental results, in spite of the inherent variability of the bamboo tubes. It was found that different dynamic responses of the individual bamboo tubes and grouped bamboo tubes in the honeycomb cores affect their energy absorbing capabilities. The composite structure made from bamboo and foam shows that the embedded tube exhibits a higher energy absorption capacity than the sum of the individual foam and bamboo, due to the constraint offered by the foam.

Nonlinear finite element analysis of short and long reinforced concrete columns confined with GFRP tubes

This paper presents three-dimensional nonlinear finite element models to understand the uniaxial behavior of concrete-filled fiber reinforced polymer tubes. A stress–strain confined model was introduced for the concrete, a damage criteria based on Hashin's failure model was used to model damage and failure of GFRP tubes, and steel bars were modeled based on classic metal plasticity model. A comparison between experimental results found in the literature and the finite element model was conducted regarding the load-deflection curves and the failure pattern of different test specimens. The model was found to be efficient in capturing the loads and deformations of slender concrete-filled fiber reinforced polymer tube columns. It was then used in a parametric study to understand the effect of different parameters (including fiber orientation, number of layers of (glass-fiber reinforced polymer) and steel reinforcement ratio) on the behavior of concrete-filled fiber reinforced polymer tube under axial compressive loading. It was observed that the behavior of the columns was greatly affected by the investigated analysis parameters.

No.25 微粉炭燃焼における灰付着および伝熱管損傷機構(灰・微量元素(3))

No.25 微粉炭燃焼における灰付着および伝熱管損傷機構(灰・微量元素(3))

Magnetic detection technique for double-layer steel tubing and casing damage

Magnetic detection technique for double-layer steel tubing and casing damage

Experimental study on cross-flow induced vibrations in heat exchanger tube bundle

Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can lead to the tube damage, tube leakage, baffle damage, tube collision damage, fatigue, creep etc. In the present study, vibration response is analyzed on single tube located in the centre of the tube bundle having parallel triangular arrangement (60°) with P/D ratio of 1.44. The experiment is performed for two different flow conditions. This kind of experiment has not been reported in the literature. Under the first condition, the tube vibration response is analyzed when there is no internal flow in the tube and under the second condition, the response is analyzed when the internal tube flow is maintained at a constant value of 0.1 m/s. The free stream shell side velocity ranges from 0.8 m/s to 1.3 m/s, the reduced gap velocity varies from 1.80 to 2.66 and the Reynolds number varies from 44500 to 66000. It is observed that the internal tube flow results in larger vibration amplitudes for the tube than that without internal tube flow. It is also established that over the current range of shell side flow velocity, the turbulence is the dominant excitation mechanism for producing vibration in the tube since the amplitude varies directly with the increase in the shell side velocity. Damping has no significant effect on the vibration behavior of the tube for the current velocity range.

Analysis of the Break Size Influence on the Damage Accident of Single Heat Transfer Tube of Ship Nuclear Power Steam Generator

In view of the problem that the breakage size is not enough to analyze the damage of the heat transfer tube of the ship nuclear power steam generator under the condition that the breakage loop cannot be isolated, this paper analyzes the damage safety analysis model based on the MELCOR program, Damage of heat transfer tubes at different break sizes (2 mm and 6 mm) to reactor power, primary loop pressure, regulator water level, core water level, vapor pressure, break flow, fuel element cladding breakage, etc. The influence of the breakage size on the damage effect of the heat transfer tube has improved the analysis and handling capacity of the damage of the heat transfer tube, and improved the reactor accident handling capacity under the condition of the damage of the heat transfer tube.

Experimental Study on Ultrahigh Strength Concrete Filled Steel Tube Short Columns under Axial Load

Based on the project of Modaoxi Bridge, an experimental study on the compressive behavior of ultrahigh strength concrete filled steel tube (UHSCFST) short column was conducted. A total of 9 UHSCFST specimens were tested, and the cube strength (fcu) of the core concrete reached 115.4 MPa. Main parameters were the confining factor (ξ=0.608, 0.919, and 1.015), steel ratio (α=14.67%, 20.02%, and 21.98%), and steel strength (fy = 349 MPa, 352 MPa, and 427 MPa). The axially loading test results showed that the visible damage of steel tube occurred under the ultimate load. The higher the confining effect, the less the damage features. And all specimens basically presented a drum-type failure mode. The confining effect of steel tube effectively changed the brittle failure mode of ultrahigh strength concrete (UHSC) and tremendously improved the load bearing capacity and ductility of specimens. Moreover, the higher the steel ratio and steel strength of the specimens, the stronger the confining effect. Meanwhile the excellent mechanical properties will be obtained. Also it is recommended that the UHSCFST prefers Q345 or above strength steel tube to ensure sufficient ductility, and the steel ratio should be more than 20%. Furthermore, the confining effect of steel tubes can improve the ultimate bearing capacity of the ultrahigh strength CFST short columns.