V. Linton

Laser diagnostics of welding plasma by polarization spectroscopy

The application of polarization spectroscopy (PS) to detect atomic species in an atmospheric pressure welding plasma has been demonstrated. PS spectra of Na atoms, seeded in the shielding gas flow of a gas tungsten arc welding (GTAW) plasma, are presented at different pump beam energies. The nature of the PS technique was found to be very efficient in suppressing the high background emission associated with the welding plasma. The PS spectral profiles appear to be Lorentzian and Lorentzian cubed for high and low pump beam energy, respectively. The effect of beam steering, due to the thermal gradient in the interaction plasma zone, was addressed. It was found that there is 2% unavoidable error in the detectable PS signal.

Fatigue Crack Growth Comparison Between Sleeved and Non Sleeved Pipeline

A section of gas pipeline containing dormant stress corrosion cracks was removed from service and pressure cycled, and the crack growth from fatigue was measured. Crack growth was able to be conservatively calculated by BS7910. Parts of the pipeline section had composite repair sleeves placed over it in order to compare fatigue crack growth of sleeved and unsleeved cracks. Sleeved cracks consistently showed less crack growth than unsleeved cracks; this is believed to be due to reduced hoop stresses in the pipe under the composite repair sleeve and reduced crack opening. A simple model of the sleeve repair was developed which was consistent with the measured strains in the pipe. The application pressure of the sleeve repair affects the amount of stress reduction in the pipe and the amount of crack growth experienced. Two possible methods of repair of SCC affected pipelines were validated by this work.

Compositional aspects of cellulosic electrodes used for welding pipelines

The mechanical properties and compositional limits of line pipe for all major pipeline projects are subject to stringent project specific specifications and have substantial user input. The standards for welding electrodes do not have the same level of user involvement and permit significant latitude in terms of alloy design despite the fact that it is known the original electrode design can be markedly altered by elemental transfer as a result of changes in welding parameters and also the condition of the electrodes prior to welding. Several commercially available E8010 consumables have been evaluated under simulated field welding conditions. In addition, the influence of welding arc length and electrode conditioning were investigated. Significant variations in microstructure, hardness and Charpy impact toughness were noted and appear to be primarily related to the final chemical composition of the deposited weld metal. The weld metal carbon equivalent values ranged from 0.20 to 0.42 and all consumables contained additions of Ti and B in the flux coating which resulted in significant levels of B in the final deposited weld metal. It is recommended that the appropriate standards relating to the production and performance of cellulosic consumables be addressed to ensure complete disclosure of consumable formulations to the end user.Copyright

Laser scattering for particulate fume measurement

Abstract This paper investigates the use of laser light scattering to determine fume concentration generated by gas metal arc welding (GMAW). The effect of transfer mode on the intensity of scattered laser light was measured to compare the results with those generated by fume box measurements. Good correlation was found between previously measured fume formation rates and scattered light intensity across a range of transfer modes for two wire feed rates. Thus it is proposed that laser light scattering is a viable measurement technique for welding fume and demonstrates several advantages over traditional methods.

Residual Stresses in High Strength, Thick Section Steel Welds

The conservative assumption of residual stress in highly restrained steel structures can lead to unnecessary repairs of defects in welded joints. This applies particularly with respect to high restraint, high yield strength thick sections welds because the assumption of yield strength residual stress is used in integrity assessments. By analysing the stress within components both before and after welding it is anticipated that a greater understanding of the residual stress field as a product of both the welding residual stress and the pre-welding residual stress can be made. This paper discusses a series of experiments designed to build up such a model of the changing stress field within a T-butt weld. Neutron strain scanning has been performed on unwelded flat and curved steel sections and a curved T-butt weld. To complement this, surface X-ray measurements have been carried out in order to gain a quantitative measure of the changing surface stress during welding and sectioning. The findings were that welding stresses dominate close to the weld, bending stresses dominate further from the weld.