Mercury Embrittlement Crack Initiation in 5083 Aluminum Alloys--the Role of the Oxide Film

Mercury Embrittlement is a significant problem in natural gas processing facilities that use aluminium cold boxes and has led to a number of major plant incidents.  It has been postulated that the natural passive layer on aluminium provides an effective barrier between droplets of mercury and the underlying aluminium and this prevents mercury embrittlement.  However, under certain circumstances this barrier is breached and embrittlement can occur.  In this paper the condition of the mercury-aluminium interface is measured using ac impedance techniques and the effects of film aging conditions on the stability of the interface are studied.  The film was modelled as a constant phase element and resistor in parallel and it was found that the resistance of the film increased with aging, although the effective film thickness only changed slightly.  The paper finds that galvanic corrosion between the mercury droplet and underlying aluminium is likely to be a major cause of the breakdown of the mercury-aluminium interface.