Santos announced on Friday that the January 1 fire at the Moomba plant was caused by a chemical reaction between aluminium and mercury. The gas release that led to the fire was caused by the failure of a heat exchanger (cold box) inlet nozzle in the liquids recovery plant. This is the final stage of liquids processing in the plant.
The findings from an initial independent metallurgical laboratory study have been released. The study was commissioned by Santos and based on analysis of samples taken from the affected area. It states that the failure of the inlet nozzle was due to liquid metal embrittlement (LME) of the train B aluminium cold box by elemental mercury.
Santos is investigating whether additional factors contributed to the explosion, but these investigations are expected to take some weeks to complete.
LME is a rare instantaneous phenomenon. It is a complex metal fracture mechanism that occurs without warning. It is understood that, to date, the Moomba incident is the first known occurrence of a gas release and fire due to LME. While LME occurs with aluminium, it does not occur with steel and therefore does not affect the strength of steel pipes and valves. At the Moomba Plant, the cold box is the only major piece of aluminium equipment. The remainder of the processing equipment is predominantly constructed of steel.
Natural gas from subterranean reservoirs in Australia and South East Asia typically contains minute levels of elemental mercury. Central Australian raw natural gas contains approximately 30 parts per billion of elemental mercury.
Santos has in place a management plan for dealing with elemental mercury in the Plant, including susceptible aluminium components. This plan reflects accepted industry practice.
Santos claims it has decided to implement a plan to eliminate the possibility of a similar failure recurring. This plan includes the procurement of new cold boxes and associated facilities.