Microstructure engineering for high productivity welding of pipeline steels

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There are currently a number of significant proposals for expansion of the North American oil and natural gas pipeline system including the Mackenzie Valley, the Alaska North Slope and Keystone XL pipelines. These projects will involve the use of new higher strength steels (X80 and X100) and new welding techniques (tandem and dual torch gas metal arc or laser hybrid) to lower construction costs. It is critical for the integrity of these pipeline systems that the welds have well understood mechanical behaviour. There are further challenges for northern pipelines due to the low temperatures and the probable melting of significant regions of permafrost. These considerations have led to new strain based design performance criteria. This project has the objective to model the microstructure and mechanical properties of the critical region adjacent to the fusion zone, the heat affected zone (HAZ). The material in this region undergoes a complex thermal history and is usually found to be the weakest link in the system. The objectives of this project are i) to measure the temperature-time history for a number of welding procedures (gas metal arc, laser hybrid and submerged arc welding), ii) to develop microstructure evolution models for the HAZ which account for its spatial variation and iii) to examine the mechanical properties of the weld considered the HAZ as a graded structure. This will be done through a combination of experimental and modelling activities with a strong collaboration with our partners, Evraz NA Inc. and TransCanada PipeLines Ltd. The results from this project will be i) an increased knowledge base for the microstructure/mechanical properties in the heat affected zone for advanced steels and high productivity welding procedures, ii) transfer of this knowledge to our industry partners and iii) the education of 6 high qualified personal (2 Ph.D., 2 M.A.Sc and 2 PDFs).