Analysis of internal corrosion in subsea oil pipeline

AbstractFailure of a subsea crude oil API 5L X52 steel pipeline which led to oil leakage has been reported to occur after 27 years in service. Some leaks were found to form at the bottom of the horizontal API 5L X52 steel pipeline near an elbow section which connected the pipeline to a riser. The present investigation aims to analyze the main cause of failure by conducting standard failure analysis methods including visual examination, chemical and mechanical characterizations, metallurgical examinations using optical microscopy in combination with scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analysis and corrosion test using a three-electrode potential technique. Results of this investigation suggest that the cause of failure is electrochemical corrosion combined with mechanical process known as flow-induced corrosion. The failure mechanism is discussed with specific attentions are paid to fluid flow rate and chloride-containing water phase

Assessment of Nugget Size of Spot Weld using Neutron Radiography

Resistance spot welding (RSW) has been widely used for many years in the fabrication of car body structures, mainly due to the cost and time considerations. The weld quality as well as the nugget size is an issue in various manufacturing and processes due to the strong link between the weld quality and safety. It has led to the development of various destructive and non-destructive tests for spot welding such as peel testing, ultrasonic inspections, digital shearography, and infrared thermography. However, such methods cannot show spot weld nugget visually and the results are very operator’s skill dependent. The present work proposes a method to visualize the nugget size of spot welds using neutron radiography. Water, oil and various concentrations of gadolinium oxide-alcohol mixture were evaluated as a contrast media to obtain the best quality of radiography. Results show that mixture of 5 g gadolinium oxide (Gd2O3) in 25 ml alcohol produces the best contrast. It provides the possibility to visualize the shape and size of the nugget spot weld. Furthermore, it can discriminate between nugget and corona bond. The result of neutron radiography evaluation shows reasonable agreement with that of destructive test. Received: 13 October 2010; Revised: 25 August 2011; Accepted 26 August 201

Characteristic Evaluation of Brake Block Material

This paper reports on a comparison of the frictional characteristics of three different samples of brake block materials. Two commercial brake blocks (composite and grey iron/metallic) and a non-commercial composite brake block were extracted to form pins (specimens), and then their frictional properties were evaluated using a pin-on-disc apparatus. The non-commercial composite brake block that was investigated in this work was developed as a substitute for the grey iron brake block. The results revealed that the composite brake blocks had a higher wear resistance and were more stable in terms of their coefficient of friction at various contact pressures and sliding speeds compared to the grey iron brake block. The non-commercial composite brake block that was developed in this research had a coefficient of friction that was close to that of the grey iron brake block, and hence, it can be considered as a substitute for the grey iron brake block

Investigation of Friction Behaviors of Brake Shoe Materials using Metallic Filler

Some vehicles use brake shoe made from semi-metallic materials. Semi-metallic brake shoes are made from a combination of metallic and non-metallic materials. Metallic particles are added in the formulation of brake shoe material to improve composites characteristics. In this paper, friction behaviors of brake shoe material using metallic filler were investigated. Machining chips of cast iron and copper wire of electric motor used were incorporated in composite as metallic fillers with amount 0, 2, and 4 vol. %. Friction testing was performed to measure coefficient of friction by pressing surface specimen against the surface of rotating disc. The results show that cast iron chip and Cu short wire have effect on increasing coefficient of friction of brake shoe material. They form contact plateau at contact surface. At contact surface, the Cu short wires which have parallel orientation to the sliding contact were susceptible to detach from the matrix

Assessment of Nugget Size of Spot Weld using Neutron Radiography

Resistance spot welding (RSW) has been widely used for many years in the fabrication of car body structures, mainly due to the cost and time considerations. The weld quality as well as the nugget size is an issue in various manufacturing and processes due to the strong link between the weld quality and safety. It has led to the development of various destructive and non-destructive tests for spot welding such as peel testing, ultrasonic inspections, digital shearography, and infrared thermography. However, such methods cannot show spot weld nugget visually and the results are very operator’s skill dependent. The present work proposes a method to visualize the nugget size of spot welds using neutron radiography. Water, oil and various concentrations of gadolinium oxide-alcohol mixture were evaluated as a contrast media to obtain the best quality of radiography. Results show that mixture of 5 g gadolinium oxide (Gd2O3) in 25 ml alcohol produces the best contrast. It provides the possibility to visualize the shape and size of the nugget spot weld. Furthermore, it can discriminate between nugget and corona bond. The result of neutron radiography evaluation shows reasonable agreement with that of destructive test

Enhanced fatigue performance of tandem MIG 5083 aluminium alloy weld joints by heat sink and static thermal tensioning

In this work, tandem metal inert gas (MIG) welding using double torches with each torch contained a single wire feed was conducted to join AA5083 aluminium alloy plates. In order to minimise excessive welding distortion and residual stress and hence fatigue crack propagation rate due to high heat input, two methods for minimisation of welding distortion and residual stress, namely heat sink and static thermal tensioning (STT) treatments were applied during welding. The tandem MIG processes were conducted by locating two torches at a distance of 100 mm from each other with and without the treatments. Furthermore, welding distortion, residual stress, microstructure, hardness distribution, tensile strength and fatigue crack propagation were characterised and evaluated. Results showed that the use of heat sink effectively reduced fatigue crack propagation rate of the tandem weld, especially at low ΔK below 6 MPa√m. This fatigue crack propagation inhibition in the heat sink treated weld could be linked to its fine grained equiaxed structure and compressive residual stress. However, in term of welding distortion reduction, heat sink treatment seemed to be less effective compared to STT treatment. The beneficial effect of heat sink and STT in minimising welding distortion and residual stress was attributed to thermal tensioning due to temperature gradient and it is discussed in the present study

Tensile and fatigue properties of friction stir AZ31B-H24 magnesium alloy welded joints under the influences of pin geometry and tool rotation rate

Friction stir welding (FSW) is an innovative joining technology suitable for manufacture of magnesium welded lightweight structures. This paper presents tensile and fatigue crack growth rate (FCGR) behaviors of friction stir AZ31B-H24 magnesium alloy welded joints produced using two different pins, namely cylindrical and square pins at varying tool rotation rates of 910 rpm, 1500 rpm and 2280 rpm. Experiments conducted in this study included microstructural observations, Vickers microhardness measurements, tensile tests, residual stress measurements and FCGR tests. The results showed that increasing tool rotation rate increased ultimate tensile strength (UTS) of the welded joints and the highest values of UTS were achieved at 2280 rpm giving 229.0 MPa for the cylindrical pin and 200.3 MPa for the square pin. In the middle tension M(T) fatigue specimens, FCGR of FSW joint fabricated using the square pin at 2280 rpm was lower in comparison to the weld produced by the cylindrical pin. Subsequently, in single edge crack tension (SECT) specimens, the higher FCGRs were observed as the crack propagated across heat affected zone (HAZ) followed by the crack growth retardation in the weld nugget zone (WNZ). These fatigue crack growth rate behaviors were likely dictated by the weld microstructure and residual stresses