Suraj Joshi

Hardness, Microstructure, and Residual Stresses in Low Carbon Steel Welding with Post-weld Heat Treatment and Temper Bead Welding

This paper investigates the effects of post-weld heat treatment (PWHT) and temper bead welding (TBW) on hardness, microstructure and residual stresses in multi-layer welding on low carbon steel specimens made with two different weld geometries, viz. (1) smooth-contoured and (2) U-shaped. It was found that the PWHT technique gave overall lower hardness than the TBW technique, but the hardness values in both techniques were acceptable. Microscopy analysis showed that the TBW technique was more effective in tempering the heat affected zone as the grain size decreased slightly at the fusion line in spite of the higher temperature at the fusion line. Residual stresses measured using the hole-drilling method showed that the residual stress is not reduced below yield stress near the last bead solidified in TBW. Only PWHT gives low residual stress results in this area. High tensile residual stresses may result in sensitivity to fatigue loading.

Structural health monitoring of a dragline cluster using the hot spot stress method

‘Hot spot stress’ is an approach often used to consider fatigue loadings in heavily welded tubular joints. This article reports the determination of hot spot stresses in mining dragline booms, which are often ≥100 m in length, using strain gage measurements and finite element analysis (FEA) modeling as part of a structural health monitoring concept. Strain gages were installed on a typical A11 cluster for estimating hot spot stresses, as recommended in the existing fatigue design guidelines by the International Institute of Welding (IIW) and the International Committee for the Development and Study of Tubular Construction (CIDECT). The results from the experimental measurements and the FEA were found to be comparable to a large measure. It was concluded that while hot spot stresses were high enough at the weld toes to cause cracking, they could not explain the cracking that occurs at the welds in the main chords on their own. Issues in comparing theoretical and experimental measurements are discussed.

Investigation on Preferential Corrosion of Welded Carbon Steel Under Flowing Conditions by EIS

Carbon steels are used extensively in construction of oil and gas pipes but they exhibit poor corrosion-resistance properties because of internal corrosion. In this research, a rotating cylinder electrode apparatus was designed so that electrodes machined from the weld metal, heat-affected zone, and parent material of a welded X65 pipeline steel could be tested in high shear stress conditions using electromechanical impedance spectroscopy. The aim was to investigate the cause of the severe localized corrosion that sometimes occurs at welds in carbon steel pipelines carrying hydrocarbons and inhibited brine solutions saturated with carbon dioxide. It was concluded that the surface films play an important role in effective inhibition, and this inhibition is more effective on a clean surface rather than on a precorroded one.

Identification of Motive Forces on the Whole Body System during Walking

Motive forces by muscles are applied to different parts of the human body in a periodic fashion when walking at a uniform rate. In this study, the whole human body is modeled as a multidegree of freedom (MDOF) system with seven degrees of freedom. In view of the changing contact conditions with the ground due to alternating feet movements, the system under study is considered piecewise time invariant for each half-period when one foot is in contact with the ground. Forces transmitted from the body to the ground while walking at a normal pace are experimentally measured and numerically simulated. Fourth-order Runge-Kutta method is employed to numerically simulate the forces acting on different masses of the body. An optimization problem is formulated with the squared difference between the measured and simulated forces transmitted to the ground as the objective function, and the motive forces on the body masses as the design variables to solve.

Numerical Simulation of Welding Induced Residual Stresses in a Circular Hollow Section T-Joint

Heavily welded circular hollow cross sections (CHS) are a common feature in civil structures such as draglines used in the mining industry and other off-shore structures. The sheer mass of the weldment and the application of intense heat generated during the welding process give birth to significant residual stresses in the structure. Often, residual stresses are high enough to act to accelerate factors such as corrosion, crack growth and fatigue. The objective of this research investigation was to predict welding generated residual stresses in a typical CHS T-Joint using Sysweld+, a welding Finite Element Analysis software. The T-joint is the first of the four lacings welded on to the main chord of a BE 1370 mining dragline cluster (designated All) of a type which is often used in the mining industry in Australia. This work examines a massive 3-dimensional geometry, which is on a much larger scale than those examined in existing studies. The paper presents the results of the simulation of residual stresses generated during the welding process in a single weld pass and compares them with the approach used in the commonly used document R6-Revision 4, Assessment of the Integrity of Structures Containing Defects.Copyright