Abdulla I. Almazrouee

Role of Welding Parameters Using the Flux Cored Arc Welding Process of Low Alloy Steels on Bead Geometry and Mechanical Properties

Welding parameters have direct effects on the bead geometry, microstructure, and mechanical properties of low alloy steels. A series of experiments have been carried out to examine some of these parameters using the flux cored arc welding process (FCAW). In this article, an experimental study was conducted to investigate the influence of welding parameters in FCAW process particularly welding voltage and travel speed on weld bead dimensions. The study also includes the effects of bead overlap and deposition sequence on the parent material and the heat-affected zone (HAZ) properties. It was found that an increase in the welding voltage leads to an increase in the weld bead width, and the increase in the welding traverse speed leads to a decrease in the weld bead width. When studying the bead overlap percentages, it was found that the 50% bead overlap can be considered to be practically a better option than the higher percentages of bead overlap (i.e., 70-90%). The experimental investigation of studying the deposition sequence showed that there were no significant differences in the microstructure, hardness, and the size of the refined HAZ between the two proposed deposition sequences. However, a significant improvement in the microstructure and the size of the refined HAZ, and a reduction in the hardness were achieved after depositing the second welding bead, irrespective of the depositing sequence.

High Temperature Oxidation of Cr-Mo Steels in the Context of Accelerated Rupture Testing for Creep Life Prediction

Accelerated creep rupture testing is used to aid in assessing the remaining life for components such as pipes and tubes used in high temperature plants. At the high temperatures, oxide growth can affect the creep results by diameter reduction and, thus, increase the stress. This paper includes the study of oxide-scale growth and diameter reduction kinetics during air oxidation of two Cr-Mo steels used in the manufacture of boiler tubing. Tests were at 500–700°C for times up to 1000h for 1.25Cr-0.5Mo and 2.25Cr-1Mo steels (using cylindrical specimens similar to those used for creep testing). At 500–600°C, 2.25Cr-1Mo steels showed a superior oxidation resistance than 1.25Cr-0.5Mo steels. However, at 700°C, the oxidation resistance of 1.25Cr-0.5Mo and 2.25Cr-1Mo steels was similar. Multilayer oxide formation was observed to occur in 1.25Cr-0.5Mo and 2.25Cr-1Mo steels, involving oxides with various compositions. It is suggested that inaccuracies in creep data may arise as a result of the cross-sectional losses of the specimens. This inaccuracy may also cause discrepancies in life assessment.

Cracking of a Cobalt-Based Hardfacing of a Gate Valve Disk in a Desalination Power Plant

Cobalt-based alloys of the Stellite family are used as hardfacing for sealing surfaces of valves operating in desalination and power plants because of their excellent low friction and anti-galling properties in high-load sliding contact under the prevailing conditions. However, insufficient control of pressure and temperature during operation can degrade the integrity of the hardfaced material thus leading to its premature failure. This article presents a failure investigation carried out on the disk of a main stop gate valve that was used in a desalination plant. The disk was manufactured from X20 as a substrate material and a cobalt-based alloy for hardfacing. The cobalt-based hardfacing suffered from many surface and subsurface cracks that degraded its integrity. It was concluded that high-pressure steam flowing against the disk had tilted it and, thus, disturbed the alignment between the surfaces of the disk and the seat, leading to wear and large frictional heat that resulted in the degradation of the microstructure of the hardfacing layer and formation of the observed cracks.

Weld repair procedures of aged components in the refineries and power plants: Kuwait and Australia

Abstract Petroleum refineries and power plants seek to extend the life of their aging components through weld repairs. Some of the repairs require stress relieving using post weld heat treatment (PWHT). However, PWHT is a cost and time consuming process. This paper provides a brief description of different alternative techniques for PWHT: half-bead welding, temper-bead welding and cold repairs. It presents a short survey about the different repairs techniques with or without the PWHT and their use in refineries and power plants in Kuwait and Australia. Some of these repairs now have had a successful life of over a decade; the oldest is nearly 20 years old. Details of the methods used are described and recommendations made concerning the alternative techniques. The availability of skilled labour turns out to be a decisive issue.