Professor Hongbiao Dong, Department of Engineering, Leicester University

Effect of Post-Weld Heat-Treatment on Hydrogen Embrittlement
When Nov 03, 2014
from 02:00 PM to 03:00 PM
Where LR8, IEB Building, Engineering Science
Contact Name
Contact Phone 01865-283302
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Dissimilar welds, such as those between ferritic and austenitic materials, are commonly employed in various industrial applications.  In the petrochemicals sector, subsea low alloy steel hubs are joined to micro-alloyed steel linepipes using nickel alloy fillers. The forging assembly is commonly given a post weld heat treatment (PWHT) to temper hard heat affected zones and redistribute residual stresses that form in the as-welded condition.  Whilst PWHT is successful in returning some ductility to the HAZ, a number of in-service failures warrant further investigation.

Whilst in-service, structures of this kind are subjected to cathodic protection (CP) via aluminium based anodes - a common method of mitigating corrosion of the ferritic parts.  CP has, however, been associated with the evolution of hydrogen on metallic surfaces, wherein diffusion, followed by hydrogen embrittlement (HE), may occur.  As a result, a programme of mechanical performance testing under CP, followed by fractographic examination has been designed.  Dissimilar weld specimens were given various PWHTs, and ranked according to resistance to embrittlement.  In this presentation, recommendations on forging chemistry and PWHT are made, based on phase evolution during PWHT and its effect on resistance to fracture.