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The failure of a bellow expansion joint of 304 stainless steel has been analysed. Stress corrosion cracking (SCC) caused by wet hydrogen sulfide was responsible for the failure. Observation of metallographic sections indicated that the crack is transgranular SCC (TGSCC) with cracking in a direction perpendicular to axial stress. Scanning electron m...
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... pressure-time curve shows no signature of abrupt increase of pressure of the system (Fig. 3). This showed that the cracks are responsible for the explosion. The main crack was opened and the fracture sur- face examined. The schematic diagram of the burst crack surface is shown in Fig. 4 and 5. The crack surface is uneven and steps are found on the surface. There were some crack branches close to the inner surface. There were several crack initiation sites on this fracture surface. At least two obvious points are observed in Fig. 4, i.e., two groups of radiating ...
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... and the fracture sur- face examined. The schematic diagram of the burst crack surface is shown in Fig. 4 and 5. The crack surface is uneven and steps are found on the surface. There were some crack branches close to the inner surface. There were several crack initiation sites on this fracture surface. At least two obvious points are observed in Fig. 4, i.e., two groups of radiating ...
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... pieces, taken from three different locations of the failed region of the expansion joint were prepared for optical metallography using conventional techniques. Three samples were cut numbered 1, 2, and 6 cor- responding to Fig. 4. Sample 1 contains base and weld material, sample 2 contains crack tips, and sample 3 delamination structure of raw material. Polished specimens were viewed under light optical microscope (LOM) to study crack ...
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... analysis of crack surface at the edge, middle and tip positions are carried out. Fig. 11 is initiation point corresponding to Fig. 4, 1 point. It is clear that a pit is the originator of the cracks. Fig. 12 site shows of 5# crack. No pit is found at this site. Another site (4 # corresponding to Fig. 4) also showed no pit (Fig. 13). The facets do not belong to cleavage fracture, but fine cleavage steps are present on small flat ...
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Citations
... Guo et al [3] analyzed the reasons for the cracking of the bellows, and the results showed that the bellows trough would fail due to excessive deformation. Guan et al [4] analyzed the failure reasons of the bellows expansion joint, mainly due to the brittle fracture caused by stress corrosion. M. Sujata et al. [5] analyzed the failure reasons of the bellows expansion joint, mainly due to the brittle fracture caused by stress corrosion. ...
... Many authors have written extensively about axisymmetric problems. EJMA, on the other hand, appraises angular and lateral rigidities using the principles of equivalent axial rigidities [6]. Zhu et al. [7] present general solutions for stresses and angular movement of overall bending problems (pure bending moments) in a meridional plane using slender ring shells. ...
Process industries typically utilize bellows expansion joints (compensators), which offer both axial flexibility and circumferential strength on convolutions. These components are utilized in pipe structures as well as their connections to vital process equipment’s, such as boilers, fixed tube heat exchangers, pressure vessels, pressure relief equipment, pulsation dampeners, etc. The expansion-contraction operation of the compensators attached to the pipes produces different thrusts and stresses, rendering process equipment vulnerable to catastrophic failure if there is an axial misalignment or lateral offset in connection. For the purpose of maintaining structural integrity, it is essential to determine the meridian stresses generated on bellows compensator under various operating conditions. This study examines the quantitative effects of combined lateral shift and angular rotational misalignment on meridional stress levels for the heat exchanger shell bellows. Mainly the generation of the stresses on the U-shaped convolution profile is multifaceted and difficult to evaluate. An experimental setup has been designed to make it easier to see the combined angular rotation and offset at various levels and to improve evaluating the stress levels for analysis purposes. The paper presents the results pertaining to meridional deflection-based stresses. The analysis process signifies the assessment of structural integrity to enable designers to implement mitigating measures regarding the installation of bellows compensators and adequate support conditions.
... Fig. 14e showed microstructure at higher magnification away from failure location and confirmed the presence of shear bands. The shear bands could be attributed to cold deformation in the failed exchanger tube [33]. ...
The reformer effluent is serially cooled down to produce hydrogen in the hydrogen unit of an oil refinery. The process heat from effluent is effectively utilized for low pressure steam generation using heat exchanger. This exchanger shell and tube side fluids were boiler feed water and process gas, respectively. Several tubes of this heat exchanger were failed especially within tube sheet after 4 years of useful service. Therefore, failed exchanger tube was subjected to engineering failure analysis to determine the cause of failure. Initially visual inspection was conducted using videoscopy in heat exchanger dry condition and evidenced circumferential crack. Subsequently, all failed tubes were separated from U tube bundle. Selected tube was subjected to visual inspection, dye penetrant and dimensional measurement. No evidence of visual deformation and thickness loss observed in the failed tube. Further investigated tube was subjected to chemical analysis and confirmed the required metallurgy as per design specification. The fracture surface was subjected to elemental analysis, fractographic, metallographic and hardness investigations. The micro hardness of an exchanger tube at failure location was higher than specified hardness value. Investigation also revealed that exchanger tubes were expanded from tube inner surface to establish tube to tube sheet joint according to specified design drawing. Tube expansion was done prior to start of service and attributed to residual stress within tube material. The results revealed that presence of chloride in the accumulated deposits within tube to tube sheet joint favored conducive environment for chloride stress corrosion cracking. Recommendations were suggested for failure prevention. Achievement in this paper may supplement the similar heat exchanger tube failure database and mitigation of failure will be possible by good engineering practices.
... Post failure analysis of metal bellows was done by various researchers to study the metallurgical investigations of the bellows of different materials. Effect of stress corrosion cracks was inspected by the scanning electron microscopy (SEM) [6,7]. Subsequently, various investigations were conducted in relation to residual stress, droplet erosion, pitting, sulphur attack in the corrosive medium, etc. [8,9]. ...
The aim of this paper is to investigate the effect of angular rotational misalignment in pipe structure on the deflection based convolution stresses. Such stresses are generated in the thin walled unreinforced bellows compensators during the expansion-contraction function. On the convolution geometry, the most vulnerable stress type is meridional deflection stresses under the internal pressure. Therefore, it’s critical to check the structural integrity of pipe systems with bellows expansion joints, which typically connected to the process equipment’s including boilers, pressure vessels, reactors, heat exchangers, refineries, and so on. The findings of theoretical and experimental investigations of thin-walled unreinforced conditioned bellows subjected to different angular rotations are presented in this paper. The meridional deflection stresses are investigated for the different operating pressures when bellows subjected to angular rotations of 1°, 1.5° and 2° in the flexural plane. In addition, the testing is performed along various longitudinal lines across the periphery of the bellows to determine the maximum induced stress points on the convolution profile. The higher meridional stress is seen to be the bending stress at the bottom curved toroidal section of the convolution, which approaches towards the elastoplastic regime at 1° to 2° of angular deviation in flexural plane. These extreme stress points may prove the risky areas at the root of the convolution for the fatigue failures. Further, the results of the maximal convolution stress assessment are useful in predicting the structural integrity of bellows in elastic regime, when prone to the angular shift.
... The average hardness value is measured to be 185HV and no variation noticed on convolution crest and valley. An expansion bellow supplied in cold deformed + solution treated condition can have 187HV as maximum hardness value [12]. The two tensile specimens with 6.90 mm (width) × 30 mm (gauge length) of available thickness were prepared and tensile results shown in Table 2. ...
... It was reported that combinations of both hydro forming & roll forming can improve bellow fatigue life [1,7]. The collected samples were further probed in microanalysis to identify deformation induced martensite (if any) as reported by several other researchers, however, no such indications were present [1,12,13]. The absence of deformation induced martensite can be due to final solution annealed at 1040 • C and oil quenched. ...
... The absence of shear band and deformation induced martensite indicates that bellow was cold deformed and solution heat treatment in final stage of manufacturing. The aim of cold deformation during last stage can exhibit high fatigue resistance; however, it can also lead to stress corrosion cracking in corrosive service if bellow was not solution annealed [12]. Furthermore, other reported failure mechanisms such as carbide precipitation and sigma phase embrittlement were absent. ...
The bellow is a flexible component which compensates an expansion allowance imposed by axial strain during high temperature service. The bellow failure during turbine operation of boiler unit has been systematically investigated. The metallurgy of bellow was AISI 316L stainless steel. The comprehensive laboratory investigation includes visual inspection, chemical analysis, mechanical tests, metallographic and fractographic studies. Visual inspection in the field revealed multiple cracks in the bellow and failed debris were collected for laboratory investigation. The mechanical tests of the expansion bellow confirmed to material property specification. The microstructure revealed austenitic structure and fracture surface revealed striation marks. The striation marks attributed to fatigue failure. Finite element analysis revealed that maximum stress induced in the trough region and stress could be higher as compared to ASME VIII Div 1 design equations. It can be concluded that actual operating pressure range could resulted in sufficient stress cycles to initiate fatigue cracks from surface of the bellow. The large number of stress cycles owing to actual varied pressure range attributed to fatigue failure. It is recommended to reduce many intermittent operating conditions by good operational practice and installation of strain gauges at critical locations of the bellow. It is further proposed to increase the existing ply thickness and install reinforced expansion bellow & sandwich/layered plies for prevention of fatigue failure.
... A relevant experimental result, described by [40], is the appearance of the strain-induced martensite, transformed from austenite during the cold working process that can be observed in Figure 4. Which could be related with the appearance of corrosion points, since the formation of micro-pitting occurs preferentially in areas where the tensile residual stresses are the highest [41]. ...
This paper analyzes pitting corrosion at the weld zone and at the heat affected zone (HAZ) in AISI 304 rolled stainless steel welds. As the aforementioned material is one of the most frequently used types of stainless steel, it is needful to be aware of the mechanisms that lead to its deterioration, like corrosion, since it can cause failures or malfunction in a wide variety of products and facilities. For the experimental tests 1.5 mm thick AISI 304 stainless steel plates were welded and rolled to different thicknesses and after, the samples were subjected to mechanical and corrosion tests and to a micrograph study. Deformation stresses and other intrinsic metallurgic and physic-chemical transformations that occur during cold rolling and welding, and that are key factors in the anti-corrosion behavior of AISI 304 rolled stainless steel, have been observed and analyzed. A correlation has been found between cold work levels in test samples and number of pits after corrosion tests.
... The low-cycle fatigue life of bellows using elastic-plastic analysis was predicted by Hamada and Tanka [11]. The failure of bellows expansion joint of 304 stainless steel was analyzed by Guan et al. and they found that the stress corrosion cracking caused by the flowing medium was responsible for the failure [12]. A number of cracks were also found originating from weld fusion lines [13]. ...
Bellows joint is a critical part of an underground pipeline system, which can undergo severe damage such as breaking, crushing, and bending under a strong earthquake. In our research work, finite element analysis (FEA) of the bellows joint was studied using LS-DYNA. Single convolution and multi-convolution bellows joints applied with different loadings were investigated. Force – displacement curve, plastic strain distribution and bending moment – angular displacement curve were obtained. Furthermore, low frequency cyclic experiment on 4-convolution bellows joints was conducted and the results from the experiment were compared with the results from FEA. The load capacity of the multi-convolution bellows joint was almost the same as the single convolution bellows joint, and the energy absorption increased with the number of the convolution linearly.
... Any alloy susceptible to corrosion is also vulnerable to corrosion fatigue. Martensitic stainless steels are known to be susceptible to failure in the presence of S and Cl contamination [6][7][8][9][10][11]. Cracking can initiate on the blade surface at pits or other surface defects and irregularities of very small surface size [10] and rapidly propagate through a martensite microstructure [12]. ...
A multi-stage low-pressure centrifugal air compressor used in the utility section of a manufacturing plant tripped. An increase in vibration was recorded prior to the breakdown. Subsequent inspection revealed that a small part of one blade had fractured and separated from the impeller body. The failure occurred in the 3rd stage impeller blade employed in a three-stage compressor with two inter-stage cooling tanks. The air compressor had been in service for 18 years while the current impeller had been used for 18 months. Impeller was made of 17-4 PH steel. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and Vickers hardness testing were used to metallurgically evaluate the broken blade and corrosion deposit obtained from cooling tank. Experimental results indicated that the mode of failure of the impeller blade was corrosion fatigue. Hardness of impeller material was also found to exceed the upper limit required to use it in sulfur bearing environment. Cause of failure can be attributed to intense vibrations in the compressor system responsible for the generation of stresses that led to the fatigue failure of impeller blade already embrittled due to improper heat treatment and exposed to an environment made corrosive due to the presence of sulfur.
In view of the fact that the small-diameter thin-walled stainless-steel bellows are easy to break at the trough and have a vague failure mechanism, this paper adopts the method of combining finite element simulation, bending experiment, and microscopic characterization to conduct a detailed study on the bending deformation characteristic and fracture failure mechanism of bellows. Results show that the repeated bending deformation process of the bellows is a reciprocal loading/unloading process, in which the amplitude of plastic stress gradually increases, and the amplitude of stress change in the trough is significantly higher than the peak. The large variations in stress and wall thickness are found to be major factors in the fracture of the trough. Due to the influence of molding and heat treatment processes, the microstructure differences are the internal causes for the fracture of the trough, such as the larger grain size, the insufficient uniformity of grain and the higher content of martensitic phase ratio. The Analysis on crack failure mechanism shows that the refinement and homogenization of grain could change the fracture morphology of bellows from quasi-dissociation fracture to ductile fracture, the secondary cracks become thinner and more numerous, and the crack boundaries change from straight to serrated, which significantly reduces the crack expansion rate and improves the bending resistance of bellows.
Metal bellows used in the flexible connection of metallurgical converter oxygen lance compensates for pipeline displacement through its bending deformation, and adjacent waveforms in the concentrated deformation area are squeezed, resulting in premature fracture. The bending geometric model of U-shaped metal bellows is established in this paper, and the geometric relationship between waveform structure parameters and ultimate bending radius is derived. Moreover, a mathematical model of bending moment (M) with bending angular displacement (θ) about wave height H and wave crest fillet radius Rc is established. Then, combined with Fe-safe fatigue life analysis software, the fatigue life and failure location of metal bellows are obtained. The optimal waveform parameter design range of DN80 metal bellows with high repeated bending fatigue life under large bending is determined. Finally, the bending performance and fatigue life of bellows are tested on a bending fatigue testing machine. The distribution law of fatigue life and the propagation law of cracks at the wave trough of metal bellows under different bending angular displacement amplitudes are obtained. The crack propagation mechanism and fracture mechanism under different displacement amplitudes are revealed by a scanning electron microscope. In the engineering application of large bending, the pipeline failure caused by the ultimate bending deformation of metal bellows can be avoided according to the prediction results of fatigue life.
