When three strong earthquakes shook Tennant Creek in theNorthern Territory on 22 January 1988, local welder Laurie Atkins had no idea that he would soon be called in to work on one of the most interesting and challenging pipeline repair jobs in Australian history.
The region had previously been considered seismically stable, but the quakes – escalating to 6.8 on the Richter scale – were strong enough to cause unexpected damage to the Amadeus Basin to Darwin natural gas pipeline.Laurie worked as part of a team of site managers, engineers and other personnel to weld and repair a section of the pipeline located above a reverse slip fault, which transgressed the line at right angles.
Assessing the damage
The approximately 1,600 km long pipeline traverses the length of the Northern Territory from the Amadeus Basin to Darwin principally of 12 and 14 inch diameter pipe.
The January 1988 shocks displaced a section of the mainline’s grade 5L X60 steel pipe, telescoping the pipeline so that it flowed in a concertina-type formation.
Operator NT Gas spearheaded the process of checking the pipeline system for faults, and when the compression failure was discovered near Tennant Creek, Laurie and his team were rushed in to ensure that it could return to supplying gas to Darwin and several other power stations in the region.
“It was all new to everybody and very new to me, it was the first time it had happened in Australia I think, so no one had a lot of experience with it or knew what to expect,”? says Laurie.
Laurie and his welding partner Tony Blew arrived on the site and met with NT Gas to establish a work plan for getting the pipeline back online as quickly and easily as possible.
At the site the pipeline was being progressively exposed toward the fault line in order to relieve the stress in the pipe. As this was relieved the pipe snaked all over the place, meaning the repair involved cutting out approximately 100 m of the stressed pipe and replacing it with pre-hydrotested thicker wall emergency pipe.
Laurie undertook preparatory work, and settled on a method for cutting the 14 inch diameter pipe at the location of the concertina-type failure.
“Because it was in a concertina shape,nobody actually knew which way the pipe was going to swing or move when we cut it,”? Laurie says.
“We had to drill a hole in it and light it up and then cut it live with oxyacetylene cutting equipment, and as the flames were coming out, I got in the bucket of a backhoe to be lowered into the hole to cut the pipe.
“Cutting the bottom of the pipe was the hardest, because we had no idea which way it was going to go – if it went left and I was standing there it would squash me.”?
Laurie and Tony cut the pipe on a taper, which allowed it to swing away from the taper side and away from themselves.
The race to repair against all odds
It was a difficult job in a tiny trench, completed under “one hell of a time strain,”? according to Laurie.
“We had a caravan onsite, and we caught a little bit of sleep whenever we could,”? he says.
Searing heat of up to 45 degrees during the day, flies by the millions and over 2 inches of rain on the second night caused much discomfort.
Laurie recalls that an amazing support network helped the job to run reasonably smoothly.
“People put in a lot of help, from the workers’ wives who retrieved water, to the helicopter pilot who made sandwiches for us all. It was a team effort.
“I remember one of the blowdown stack valves got chewed out in 45 seconds. This happened during the blow down of the pipe section which was necessary to be able to perform the repair and was caused by erosion of the steel by sand granules left in the pipeline from construction. I fabricated a new blow-down stack, and a guy flew to Darwin and got a valve, and at midnight that night I was putting it back in.
Laurie credits Site Engineer Steve Dykes and Site Superintendent John Oxtoby for helping the repair job to reach a quick conclusion. From the time it was blown down to the time the gas was back on, it took just under 72 hours. He says Steve and John thoroughly
consulted the welders before tackling repair tasks that had never been seen before in Australia.
“I learnt a hell of a lot from it – the challenges were different. Nothing went wrong, nobody was hurt, and it went back online well without the lights going out in Darwin.
“I also heard later that an operator in Darwin had put in a huge effort constantly changing the filters at the city gate station. As the gas velocity increased in the pipe, the gas picked up all the dust from construction and blocked the filters in a matter of hours. Ronnie would just have finished replacing the cartridges in one filter and the other one was choked. NT Gas flew in a charter jet full of filter cartridges just to keep the gas flowing to the Channel Island power station.
The final x-ray passed, and gas was slowly brought back online via the now repaired mainline block valve bypass. Brian’s Pub in Tennant Creek was in full swing for a night.
“NT Gas flew in seafood from Darwin for the crew that night,”? says Laurie.
A total of 93 m of thin wall pipe was removed and replaced with heavy wall, and the new section of the Amadeus Basin to Darwin pipeline was 970 mm shorter than the original. The pipeline resumed normal operations on 30 January 1988, and Laurie resumed normal life as Managing Director of A&B Welding.