Various tools were applied to simulate heat affected zone microstructures, and identify the inherent anodic and cathodic behaviour of different phases during environmental exposure.
First, procedures were defined to produce representative, simulated heat affected zones, equivalent to a range of heat inputs in 2205 duplex stainless steel pipe (38mm wall thickness), using a GLEEBLE 3500 thermo-mechanical simulator. This included the formation of third phases and precipitates that might accompany the reduction in austenite content, compared with the starting parent material. A range of techniques was applied including electron backscatter diffraction, scanning Kelvin probe force microscopy, and high-resolution energy-dispersive X-ray microanalysis.
The simulated heat affected zones were then characterised, and the effects of the thermal cycles on the austenite morphology investigated. The effects of elemental partitioning on the electrochemical properties of a simulated heat affected zone were also investigated.
A multi-pass TIG/GTA weld was made in the form of a girth weld in a 2205 DSS pipe (406mm OD, 9.2mm wall thickness), and used to assess the influences of different austenite morphologies on the hydrogen-induced stress cracking (HISC) behaviour.