September 25, 2018 marks 20 years since an explosion at the Longford gas plants occurred. The explosion led directly to two deaths and total interruption of gas supplies to the state of Victoria for nine days. The full supply of gas to Victoria was re-established after 19 days but other services such as crude oil production from the Bass Strait oil fields remained interrupted for many months.
We were closely involved with the Longford gas plants and held one of the retrofit projects contracts with Esso in joint venture with ABB. We knew the plant well and the people involved in running it.
Longford gas plants
The Longford gas plants comprise three gas plants and a crude stabilisation plant to process crude oil and natural gas from Bass Strait. The plant is located in the east of Victoria, in the south-east corner of Australia. The gas was supplied to the state of Victoria in Australia. At the time of the explosion, Longford had been supplying gas to Victoria for almost 30 years without a single day of interruption of supply.
Gas Plant 1 is a lean oil gas plant which uses a cryogenic lean oil solvent to recover ethane and LPGs from the gas stream.
The incident
The incident occurred in Gas Plant 1. The plant had been suffering from operational upsets following pigging of the upstream gas pipelines. On the day, the lean oil recovery system which extracts LPGs from the gas stream had tripped and the plant operators were struggling to restart production. Some of the most senior plant operations personnel were in attendance to try to restart the lean oil circulation pumps.
The lean oil worked in a complicated circuit of heat recovery heat exchangers with the rich oil and one of the cross exchangers was called GP 905. With the loss of the warm returning lean oil through the heat exchanger it had cooled to an estimated -48°C, far below its design metal temperature.
When warm lean oil circulation was restarted this caused uneven warming of the very cold heat exchanger. The high stresses at the junction between the warm shell of the heat exchanger and cold head led to failure of the head which failed completely. The failure initiated at a defect in a weld from the original construction of the heat exchanger in 1969.
The catastrophic failure of GP905 was estimated to have released 10 tonnes of volatile rich oil, rich in natural gas and LPGs. The gas migrated as a cloud until it found an ignition source. A series of explosions followed, along with massive fire balls.
Immediate impacts of the explosion
Two people died and a further eight people were injured in the explosions and subsequent fires. I knew both of the dead – I knew John Lowery in passing from project reviews we had conducted with the plants, but Pete Wilson I had known for over a decade in his role as a plant superintendent and had only spoken to him a month earlier.
The explosion left the state of Victoria without any gas supply for nine days. The explosion occurred close to the junction of the main north-south piperack in Gas Plant 1 with the main east-west piperack that connected the gas plants and the crude stabilisation plant. The junction was known as Kings Cross. While Gas Plant 2 and Gas Plant 3 were not damaged they could not transfer their condensate from the gas plants to the export path through the crude stabilisation plant.
For Victorians, the impact was pronounced. The State is highly dependent of gas supply for both domestic and industrial use. Gas was seen as readily available and a cheap energy supply. Therefore, industry used natural gas for heating including curing of paint for automobiles, for supply to the kitchens of the hospitality industry and for commercial heating. For domestic users, the gas was used for hot water services and ovens and hobs in the kitchen.
In direct response to the explosion, all industrial users were interrupted. All domestic users were asked to stop using gas and turn off their hot water systems. Gas was reserved for essential services such as hospitals. The public responded immediately and the essential services were never at risk of losing gas supplies – substantial pressure remained in the gas network at the end of the crisis when gas supplies were restored.