Case studies in engineering failure analysis最新文献

Incident involving failures of ASTM A53 carbon steel (CS) pipe, connected to pressure safety valve (PSV) and carrying raw gas has caused serious supply disruption. This study was performed to identify the most probable cause of the pipe failure. It was conducted by reviewing the existing design, construction data and pipe material analysis using non-destructive techniques such as VT, PT, MT and UT along with metallographic, hardness and microscopic analysis. The investigation revealed that excessive material loss has occurred in both failure and its adjacent regions due to abrasive grinding, resulting in the formation of a through thickness flaw. These grindings were performed to accommodate the pre-installed piping spool to avoid alteration in the pipe position. RCA demonstrated that this rapid thinning of the steel pipe body later led to its failure. Metallurgical study using photomicrograph shows that the morphology of the steel material was consistent and did not show any evidence of internal corrosion or micro fractures. Further damage to the surface of already excessively reduced thickness occurred due to nominal pipe vibration and atmospheric effect during service. The research work described in the paper has a significant meaning to recognize the root cause of such failures in CS pipes and through given recommendations to eliminate future such happenings.

Internal angles are used to strengthen Aircrafts center box corners where the wing is attached to the airframe. There are 16 angles in Airbus A300s wing box. On the right side, rear spur, and lower flange area of the center wing box, one of these angles had been cracked with a length of 28 mm. This crack has decreased residual strength of the part under allowed values and resulted to a rupture in the rear spur lower cap. Several reports of the same occurrences in other Airbus A300 air crafts, highlight the importance of finding the causes of this failure. Detailed optical and SEM, plus 4 other metallurgical tests were conducted on the failed angle. Finally, it was concluded that corrosion fatigue was the main reason which itself comes from manufacturing, maintenance, metallurgical, and geometric reasons as were discussed in this study.

This paper presents the results of a failure analysis investigation conducted in a connecting rod from a diesel engine used in the generation of electrical energy. The investigation included an extensive analysis of the con-rod material as well as the fracture zone. The investigation involved the following experimental procedures and testing techniques: visual inspection, fractography, magnetic particle inspection, chemical analysis, tensile and hardness testing, metallography, and microanalysis. The connecting rod was fabricated from an AISI/SAE 4140 low alloy steel; chemical composition, mechanical properties and microstructure were appropriate for the application. The connecting rod fractured at the body in a section close to the head; the origin of the fracture was located at the con-rod lubrication channel. The lubrication channel exhibited an area containing a tungsten based material, presumably from a machining tool, embedded in its surface as a result of a deficient manufacturing process. This area acted as nucleation site for cracks that propagate through the connecting rod section by a fatigue mechanism, reducing its section and finally producing its catastrophic failure.

During the inspection of a North Sea oil and gas platform a crack was identified on the crankshaft of a compressor.

Subsequently, the component was decommissioned and a failure examination undertaken to determine the mechanism of failure. The crankshaft was analysed using a range of inspection, measurement and fractographic techniques.

Magnetic particle inspection (MPI) indicated that the crack extended for the majority of the shaft's length, rotating through approximately 225 degrees of the shaft's circumference. Laser scanning verified the dimensions and concentricity of the crankshaft were in accordance with the manufacturer's specifications. On sectioning the crack and forcing it open, complex fracture features were revealed. Optical and scanning electron microscopy were used to examine these features as well as the surface of the crankshaft.

The investigation determined that the mechanism of failure of the crankshaft was probably corrosion fatigue, initiating from localised corrosive attack on the crankshaft's surface.

A choke bean used in an oil–gas field has catastrophically failed during operation. It is shown that that the damage has been caused by leakage of the corrosive and abrasive drilling fluid. The choke bean adapter made of carbon steel has been corroded and embrittled by hydrogen ingress leading to its fracture in the presence of stresses created by the pressure of accumulated fluid at the bottom section. On the other hand, the choke corner body made of stainless steel has been damaged by abrasive wear of its outer surface.

The failure of the induced draft fan's shaft in a power boiler was been analyzed. The performances of material applied satisfied the design requirement. The order torsional vibration showed anomaly at the shaft's smallest diameter for the design condition and the actual radius of that chamfer less than the design radius caused more significant stress concentration. The additive effect of the abnormal torsional vibration and the higher stress concentration induced the microcrack's initiation along the network pearlite's interface. The vibration and the alternating torsional loading in the induced draft fan's service led to crack growing along the different direction and fracture presenting the typical ratchet-like characteristic.

A failure analysis investigation was performed on a fractured heavy duty truck frame rail obtained during endurance track testing. The fracture observed was on the frame web within the torque rod connection to the rear drive axle of the vehicle. This section of frame experiences multi-axial loading conditions including out-of-plane bending, twisting and shear under road loads. Metallographic examination revealed micro-cracks on the edges of an open hole located in an area of high stress concentration. This manufacturing defect acted as a stress raiser and resulted in fatigue crack initiation. Simulation of crack growth on frame rail using dynamic loads from a full vehicle model was completed. After careful analysis it was concluded that the failure occurred due to an aggressively drilled open hole which created small crack initiations in a high stress-state location of the frame. This resulted in extensive curvilinear crack growth under dynamic loads of the vehicle.

In this paper, a case of severe strip breakage in rolling mill of Thin Slab Casting and Rolling (TSCR) shop of TATA Steel, Jamshedpur is presented. Visual observation revealed complete splitting with material missing along the central axis of the strip. Presence of defects in form of white stringers, white patches and holes were observed along the same axis just ahead of split location. Metallurgical analysis revealed association of these defects with slag type foreign materials in the rolled strip. The entrapments of un-deformable materials like slag in slab resulted in the formation of surface discontinuities on the strip on account of differential rolling. The discontinuities manifested in form of holes at lower strip thickness in the later stands of the mill. Inhomogeneous deformation about such holes also resulted in material overlapping. In summary, the breakage of the strip was found to have a strong correlation with the presence of heavy chunk of foreign inclusions from secondary steelmaking sources.

Cracks were analysed at the root of the third blade row of low-pressure steam turbine blades of different natural frequencies. The root cause of the fatigue crack initiation was pitting corrosion of the forged ferritic/martensitic X20Cr13 material. Metallographic investigations, finite element analysis and fracture mechanics analysis combined with experimental data from the literature are used to evaluate crack propagating stresses to discuss the operating conditions. The calculations show that corrosion pits at the root of the turbine blade increase the local stresses above yield strength. Excitation of natural frequencies by changing the rotor speed is not responsible for the crack propagation. The centrifugal load and superimposed bending load caused by unsteady steam forces are responsible for the crack propagation.

In Jam petrochemical complex (JPC), Iran, the plates (ASTM A.240 Type.316) of some heat exchangers have been damaged due to the occurrence of cracks at the sitting place of gaskets. A comprehensive failure analysis including the chemical analysis, visual inspection, optical microscopy and scanning electron microscopy (SEM) of the cracks spread over the plates together with the energy dispersive X-ray spectroscopy (EDS) of the corrosion products and the measurement of chloride and sulfide ions content of the process water were employed for the examination of the failure mode and its causes. The obtained results indicate the building-up of the chloride and sulfide ions at the crevices between plates and gaskets at high temperature leads to stress cracking corrosion (SCC) of the plates. Moreover, the simultaneous presence of chloride and sulfide in the media hastens the SCC failure in the heat exchanger plates.