Failure prediction analysis for polyethylene flawed pipes

Through this paper limit load analysis and the EPRI/GE procedure were applied to predict instability conditions for medium density polyethylene flawed pipes. Predicted values for internally pressurized cylinders with axial cracks and cylinders with circumferential cracks under remote tension were compared to experimental results obtained from tests conducted on full scale structures. For the pipes under internal pressure, both schemes led to critical pressure values in agreement with actual burst pressures, despite plastic collapse having been observed in the failure of these structures. For the pipes with circumferential internal cracks subjected to remote tension, the predicted loads from the EPRI procedure do not agree with experimental values whereas limit load predictions are quite satisfactory. On the other hand, for the circumferentially externally cracked pipes both predictions reasonable agree with experimental data.     

CFD analysis of gas explosions vented through relief pipes

Vent devices for gas and dust explosions are often ducted to safe locations by means of relief pipes. However, the presence of the duct increases the severity of explosion if compared to simply vented vessels (i.e. compared to cases where no duct is present). Besides, the identification of the key phenomena controlling the violence of explosion has not yet been gained. Multidimensional models coupling, mass, momentum and energy conservation equations can be valuable tools for the analysis of such complex explosion phenomena. In this work, gas explosions vented through ducts have been modelled by a two-dimensional (2D) axi-symmetric computational fluid dynamic (CFD) model based on the unsteady Reynolds Averaged Navier Stokes (RANS) approach in which the laminar, flamelet and distributed combustion models have been implemented. Numerical test have been carried out by varying ignition position, duct diameter and length. Results have evidenced that the severity of ducted explosions is mainly driven by the vigorous secondary explosion occurring in the duct (burn-up) rather than by the duct flow resistance or acoustic enhancement. Moreover, it has been found out that the burn-up affects explosion severity due to the reduction of venting rate rather than to the burning rate enhancement through turbulization.     

钻杆的失效分析

对某油井连续发生12次刺穿断裂事故进行了调查,用力学试验、化学分析、金相、扫描电镜、能谱分析等手段并结合现场实际情况对刺穿钻杆进行了失效分析.结果表明.由空气钻井改用泥浆钻井时,由于只改变了钻井方式和钻头,未改变钻具组合而导致钻具与井壁之间的间隙过大,从而导致钻杆的疲劳断裂.     

Failure analysis of an exploded gas cylinder

This paper reports the major activities carried out during the failure analysis of an exploded cylinder containing hydrogen. The general cracking pattern of the cylinder, the fractographic features, and the stress analysis results were all indicative of an internal gaseous detonation. Accordingly, several specific characteristics of detonation-driven fracture of closed-end cylindrical tubes were identified. These characteristics were analyzed through detailed examinations of the fracture surfaces, cracking patterns, and dynamic stress analysis of the cylinder using a transient analytical model. Based on the size and location of special markings found on the shear lips, and using the time duration of flexural waves, the crack growth increments and speed were computed. Consequently, the basic features of the gaseous detonation and the composition of the original gas mixture were identified. The results indicated that the detonation of a low-pressure oxygen-rich mixture of hydrogen and oxygen was the cause of this failure. The presence of oxygen was attributed to an improper usage of an oxygen cylinder for hydrogen storage.     

Failure analysis of natural gas buried X65 steel pipeline under deflection load using finite element method

A 3D parametric finite element model of the pipeline and soil is established using finite element method to perform the failure analysis of natural gas buried X65 steel pipeline under deflection load. The pipeline is assumed to be loaded in a parabolic deflection displacement along the axial direction. Based on the true stress–strain constitutive relationship of X65 steel, the elastic–plastic finite element analysis employs the arc-length algorithm and non-linear stabilization algorithm respectively to simulate the strain softening properties of pipeline after plastic collapse. Besides, effects of the soil types and model sizes on the maximum deflection displacement of pipeline are investigated. The proposed finite element method serves as a base available for the safety design and evaluation as well as engineering acceptance criterion for the failure of pipeline due to deflection.     

Failure analysis of an HCl gas cylinder valve

The fouling failure of an anhydrous HCl gas cylinder valve was investigated after the failure led to an accidental release of HCl gas. It is surmised that water penetrated into the valve by improper purging or valving, and created a severely corrosive environment. The aluminum bronze valve body underwent general corrosion. The corrosion products, primarily nantokite (CuCl), built up within the valve and led to the fouling failure. Dezincification was observed in a leaded nickel silver component of the valve. The Monel 400 valve stem was intact. The cylinder and valve testing procedures that led to the gas release incident are also examined.     

客车空调压缩机排气管路失效分析与结构改进

采用ANSYS Workbench软件对客车空调压缩机排气管路进行失效分析和结构改进。以3种典型管路为研究对象,在压缩机端施加位移载荷进行管路失效分析,模拟结果与管路实际断裂位置一致。通过添加弯头、调整管路角度以及增加不锈钢波纹管长度等改进措施,可以降低管路的最大等效应力,延长管路的使用寿命。     

Failure analysis of gas blower shaft of a blast furnace

Failure of a gas blower shaft of a blast furnace was analyzed. Investigation showed that the loosening of the lock plate was responsible for the shaft fracture. Examination revealed that the dislodgement of the lock plate resulted in constant rubbing of this component against the shaft leading to formation of grooves and loss of material from the shaft in localized regions. The fractographic features were completely obliterated due to post fracture rubbing and hence the micro mechanism of fracture could not be determined. However, analysis suggests that the failure of the shaft had occurred most probably by fatigue. The shaft failure was secondary in nature and had resulted subsequent to the primary failure, i.e., dislodgement of the lock plate from its position.     

Failure analysis and prediction of pipes due to the interaction between multiphase flow and structure

Frequently found in piping, erosion failures may lead to the leakage of pipes and even damage the whole system. Erosion is a form of material degradation that involves electrochemical corrosion and mechanical wear processes encountered on the surface of metal pipes. Research on the erosion–corrosion mechanism indicates that the erosion mainly results from the interactions between the pipe surface and the fluid traveling along the surface. This paper studied multiphase flow induced erosion–corrosion in pipes, mainly focusing on the interactions between the multiphase flow and the structure. In order to evaluate the erosion effects caused by the flow and the coupled dynamics, the multiphase flow regimes, flow dynamics parameters and the distribution of phases on different positions of the boundary layer in REAC pipe inner surface were analyzed. The CFD simulation results proved that the location, rate and the extent of erosion failures on the pipe surfaces can be well predicted, as compared with actual instances. Practically, this method can be used in optimizing the design of the inner sleeves of pipes.     

Hydrate formation during gas flow in pipes

The problem of crystalline hydrate formation during nonisothermal stationary flow of an ideal gas in a circular inclined pipe is studied. A model is proposed for the growth of the hydrate layer on the pipe walls.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 1, pp. 94–98, July, 1973.     

液化天然气铁路罐车罐体的有限元分析

依据TB/T1335—1996《铁道车辆强度设计及试验鉴定规范》及70 t级铁路货车的强度考核要求,采用ANSYS有限元方法对中国北车集团所设计的、拥有自主知识产权的中国首个液化天然气铁路罐车罐体进行静强度计算。计算结果表明,罐体高应力区主要集中在水平拉杆组件和玻璃钢支撑位置。其中,玻璃钢支撑位置内罐加强圈最大应力879 MPa,外补强板最大应力460 MPa,均超出材料的许用应力。对超出许用应力部分进行结构改进,对加强圈添加翼板,外补强板添加14 mm厚筋板。改进结构后,内罐加强圈厚度为16 mm时,加强圈结构最大应力246 MPa;外补强板筋板间隔角度为30°时,外补强板及筋板结构的最大应力为276 MPa。改进后的罐体结构满足强度考核要求。     

Metrological aspects of natural gas analysis by the chromatographic method

We consider the metrological characteristics of the chromatographic method for determination of the component content of natural gas according to GOST 23781- 87. We note the disadvantages inherent in the calibration method recommended by the GOST standard. We present the results of measurements of the composition of natural gas obtained on the high-precision chromatographic system at the All-Union Scientific-Research Institute of Metrology, which makes it possible to solve problems of certification of natural gas samples at the level of primary standards and to transfer the concentration scale for the components in natural gas from the standard chromatographs to working chromatographs. We establish that the figures of merit for the precision of the Institute's apparatus are not inferior to those for the apparatus of the US National Institute of Standards and Technology.Translated from Izmeritel'naya Tekhnika, Vol. 38, No. 4, pp. 62–65, April, 1995.     

Failure analysis of gas turbine blades in a thermal power plant

A case study of failure analysis of a 40 MW gas turbine blade made of Udimet 500 is presented. The cause of failure is found to be intergranular cracks which started during exposure to high temperature. The cracks initiated from the grain boundaries and propagated to the critical length to result in catastrophic fracture. In many locations M₆C type secondary carbides were found agglomerated on grain boundaries. Also micro-cavities were found on fracture surfaces which served as an origin of creeping failure mechanism.     

Classification of ruptures of gas pipes according to length

On the basis of an analysis of the kinetics of rupture and data on breakdown of gas pipes the article suggests a classification of ruptures. This makes it possible to classify each special case of rupture either as local-type or as global avalanche-type rupture.Translated from Problemy Prochnosti, Nos. 5–6, pp. 136–142, June, 1995.     

Failure analysis of a second stage blade in a gas turbine engine

The failure of a second stage blade in a gas turbine was investigated by metallurgical and mechanical examinations of the failed blade. The blade was made of a nickel-base alloy Inconel 738LC. The turbine engine has been in service for about 73,500 h before the blade failure at 5:50 PM on 14 August 2004. Due to the blade failure, the turbine engine was damaged severely. The investigation was started with a thorough visual inspection of the turbine and the blades surfaces, followed by the fractography of the fracture surfaces, microstructural investigations, chemical analysis and hardness measurement.

The observation showed that a serious pitting was occurred on the blade surfaces and there were evidences of fatigue marks in the fracture surface. The microstructural changes were not critical. It was found that the crack initiated by the hot corrosion from the leading edge and propagated by fatigue and finally, as a result of the reduction in cross-section area, fracture was completed.

An analytical calculation parallel to the finite element method was utilized to determine the static stresses due to huge centrifugal force. The dynamic characteristics of the turbine blade were evaluated by the finite element modal and harmonic analyses. Finally according to the log sheet records and by using a Campbell diagram there was a good agreement between the failure signs and FEM results which showed the broken blade has been resonated by the third vibrational mode occasionally before the failure occurred.     

Failure analysis of Ti6Al4V gas turbine compressor blades

The failure mechanism of Ti6Al4V compressor blades of an industrial gas turbine was analysed by means of both experimental characterisations and numerical simulation techniques. Several premature failures were occurred in the high pressure section of the compressor due to the fracture of the blade roots. Metallurgical and mechanical properties of the blade alloy were evaluated. A 2D finite element model of the blade root was constructed and used to provide accurate estimates of stress field in the dovetail blade root and to determine the crack initiation in the dovetail.

The results showed no metallurgical and mechanical deviations for the blade materials from standards. SEM fractography showed different aspects of fretting fatigue including multiple crack initiation sites, fatigue beach marks, debris particles, and a high surface roughness in the edge of contact (EOC). The numerical model clearly showed the region of highest stress concentration at the front EOC of the blade root in the dovetail region, correlated closely with the experimentally characterised fatigue crack region. It was concluded that this failure has occurred due to the tight contact between the blade root and the disk in the dovetail region as well as low wear resistance of the blade root.