Year

2003

Degree Name

Master of Engineering

Department

Faculty of Engineering

Abstract

There are numerous cases of premature and often catastrophic failure of pressure equipment. Too often the poor performance of welded joints in the component is the cause of such failures. It is therefore of critical importance to understand what dictates the performance of welded joints operating at elevated temperature and pressure. The microstructure of welded joints is fundamental to understanding how they will perform. The microstructure of heat affected zone (HAZ) sub-zones of a multipass 2.25Cr1Mo steel weld were simulated using a Gleeble 3500 thermal simulator for both 'high' and 'low' heat input welding conditions. The heat affected zone (HAZ) structure has been characterised in terms of twelve sub-zones, which have been investigated by microstructural analysis and hardness measurements. The HAZ structure was found to be complex and variable, with the structure depending on the local thermal history. In particular, post weld heat treatment (PWHT) has a significant influence on the structure and hardness of the sub-zones, exerting a strong normalising effect on the HAZ for both the 'high' and 'low' simulated heat input conditions.

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