Fracture Failure Analysis of the Blowout Preventer Ram in an Oilfield

This paper gives a thorough investigation on the fracture failure of the blowout preventer (BOP) ram. Through appearance inspection, magnetic powder inspection, physicochemical inspection, metallographic inspection and scanning electron microscope (SEM), the main fracture reason of the BOP ram is that there was some original cracks in the BOP ram before fracture, during the service process the bop ram is subjected to impact load, therefore brittle fracture occurs due to the high brittleness of the gate material (which is caused by large internal structure) and low anti-crack propagation ability. Key words: Blowout preventer (BOP) ram; Fatigue break; Brittle fracture; Failure analysis

Failure Analysis of a Diesel Engine Crankshaft

A six-cylinder crankshaft in a 12L diesel engine was locked after testing for about 840 hours in the bench test. The fractography investigation indicates that fatigue is the dominant failure mechanism of the crankshaft. It is found that the fatigue crack mainly initiated at the fillet of the crankweb between the 6th main journal and 6th crankpin. The fatigue crack initiation area lies outside the induction surface hardened zone. From detailed metallographic inspection, abnormal microstructure containing Widmannstatten was found in the fatigue crack initiation area and the 5th main journal, while that was not found at the severely deformed crankweb. Since the region containing Widmannstatten has lower hardness, the root cause of the failure may be that the abnormal microstructure lowered the fatigue strength at the stress concentrated fillet. The crankshaft prematurely fractured under the complex stress condition in the bench test.

Repair of Aluminum 6061 Plate by Additive Friction Stir Deposition

The deposition of new alloy to replace a worn or damaged surface layer is a common strategy for repairing or remanufacturing structural components. For high-performance aluminum alloys common in the automotive, aerospace, and defense industries, however, traditional fusion-based deposition methods can lead to solidification cracking, void formation, and loss of strength in the heat affected zone. Solid state methods, such as additive friction stir deposition (AFSD), mitigate these challenges by depositing material at temperatures below the melting point. In this work, a solid state volumetric repair was performed using AFSD of aluminum alloy 6061-T6 to fill grooves machined into the surface of a plate of 6061-T651. The groove-filling process is relevant to replacement of cracked or corroded material after removal by localized grinding. Three groove geometries were evaluated by means of metallographic inspection, tensile testing, and fatigue testing. For the process conditions and groove geometries used in this study, effective repairs were achieved to a depth of 3.1 – 3.5 mm. Below that depth, the interface between the substrate and AFSD filler exhibited poor bonding associated with insufficient shear deformation. The mechanical properties of the filler alloy, the depth of the heat affected zone, and areas for further optimization are discussed within the context of precipitation hardened aluminum alloys.

Leakage Failure Analysis of the ERW Steel Pipeline

This paper provides a thorough investigation on the leakage reason of the ERW steel pipeline in an oil field. Through appearance inspection, physicochemical inspection, metallographic inspection and scanning electron microscope (SEM), it was found that the main reason of corrosions was caused by residual liquid at the bottom of the pipeline and O2 and CO2 in the air pressure test. The corrosion medium was large volume of O2 and CO2 forming continuously saturated corrosive aqueous solution in small volume of residual liquid, and the corrosion type was the under-deposit corrosion. It is recommended to conduct hot air purging on the pipelined before pressure test for building pipelines in the future, and if the pipeline is not put into use in time, it is recommended to use nitrogen to maintain pressure.

Metallographic Investigation on Solder Creep Phenomenon

Solder bulging is detected on the exposed paddle of Device A after burn-in causing the affected units to fail the coplanarity criteria. The affected units show up at random burn-in board socket locations and occur with varying frequency. Potential causes are plotted through an Ishikawa diagram which reveal fusion and creep as the potential mechanisms behind the solder bulging phenomenon. This paper seeks to determine the mechanism behind the solder bulging phenomenon via a 2-step metallographic investigation through (i) material deformation characterization and (ii) deformation mechanism simulation. In material deformation characterization, visual inspection on affected units show that the solder bulge is generally circular and is located on the center of the exposed paddle. Moreover, SEM/EDX analysis reveal that the solder bulge is not caused by a foreign contaminant or a compositional anomaly in the solder plating. On the other hand, deformation mechanism simulation involves the metallographic comparison between controlled simulations of fusion and creep versus the actual unit with solder bulge. Metallographic inspection reveal that the grain size and grain shape of the solder bulge possess the characteristics of creep phenomenon. Additionally, investigation on the burn-in (BI) process conditions also supports creep over fusion as the mechanism behind the solder bulging phenomenon. The static stress induced by the socket on the package at elevated temperature caused the solder plating to creep towards the free area which is the hole on the bottom of the socket.

Shrinkage Pores and Fatigue Behavior of Cast Al-Si Alloys

The fatigue strength of cast Al-Si alloys is strongly sensitive to the presence of casting defects. Extensive rotating bending fatigue testing of cast AlSi7Mg alloy at room temperature and 50 Hz is reported showing that shrinkage pores are the critical casting defect. The porosity of selected fatigue specimens extracted from castings is characterized with metallography using different pore sizing criteria. Data are fitted to EVS distributions and used for critical size prediction. Fatigue fracture surfaces are inspected in the SEM and the critical pores originating the fatigue cracks identified and measured according to criteria used in the metallographic inspection.

The Analysis on Causes of Rupture of a HP-Nb High Temperature Alloy Radiant Furnace Tube

An explosion accident occurred in a HP-Nb high temperature alloy radiant furnace tube. Twenty one lengths of furnace tubes were broken and cracked during this explosion. This paper investigates the explosion accident. The broken furnace tubes were investigated by fractographic observation and metallographic inspection and with mechanical performance test and analysis to determine the cause of the explosion. The results of the analysis indicated that the failure of the furnace tube was caused by high temperature creep. In order to determine the temperature of the furnace tube failure, some heat simulation tests from 900°C to 1200°C were carried out, the results of which confirmed that the failure of the furnace tube was primarily due to creep fracture because of the high temperature.

An EBSD Study on Orientation Effects during Recrystallization of Coarse-Grained Niobium

The recrystallization behavior of coarse-grained niobium depends on the nature of its deformation microstructure. In this regard, a longitudinal section of a high-purity coarse-grained niobium ingot was cold rolled to a thickness reduction of 96% followed by annealing in vacuum at 800°C for 1 h. Metallographic inspection in cold-rolled and annealed specimens was carried out in a field emission gun scanning electron microscope (FEG-SEM). Microtexture was determined by electron-backscattered diffraction (EBSD) coupled to the FEG-SEM. The use this technique has evidenced details of the boundary character and subgrain structure found in partially recrystallized regions. The early stages of primary recrystallization are associated to the presence of high-angle lamellar boundaries found in the cold-worked state. Abnormal subgrain growth has been evidenced as a viable mechanism for nucleation of recrystallization.