The joint presentation, “Possibilities for Aboveground Pipelines” was given by Peter Tuft & Associates director Peter Tuft and Santos principal mechanical engineer Russell Schulz.

Tuft and Schulz said that following changes to the AS 2885.1-2007 standard there were now circumstances where aboveground gas pipelines could be installed and operated safely, giving a variety of cost and environmental benefits.

“It is also clear that these circumstances are quite restricted and we do not expect to see large numbers of aboveground gas pipelines, except as flowlines in very remote areas where the benefits can be maximised,” they said.

“A key finding of the recent work is that the risks associated with aboveground gas pipelines are quite manageable, but they do require particular attention during both design and operation.”

The biggest areas of risk are: third party and environmental protection, lighting protection, and pipe behavior in the event of rupture, according to Tuft and Schulz.

“The event of full bore rupture and separation resulting in violent pipe whip is now better understood,” they said.

“The likelihood of pipe whip is extremely small if the pipeline is properly built and managed, and design tools are being developed which are expected to provide means of establishing designs to control whip in the unlikely event that rupture occurs.”

Before the recent release of AS 2885.1-2007, Australian pipeline standards mandated burial for all cross-country pipelines carrying gas.

“The reason was not stated explicitly but would appear to be related to the hazard of pressure-volume energy which could lead to devastating pipe whip if an aboveground gas line were to rupture,” the joint presenters said.

“Nevertheless, the fact that such failure may have serious consequences is not a reason for mandatory burial provided that the risks are understood and managed.

“As there are circumstances in which aboveground gas pipelines can offer significant benefits while posing relatively low risks, some gas producers are interested in application of aboveground gas lines so that they could have this option available for production flowlines in remote areas.”

Consideration by Standards Australia Committee ME38-1 and the APIA Research & Standards Committee led to the new provisions in AS 2885.1-2007, as well as a research project to investigate the key risk issues associated with aboveground gas pipelines.

Tuft and Schulz said installing gas flowlines aboveground could reduce capital cost and facilitate development of stranded reserves that might otherwise be uneconomic.

It could also reduce environmental impact by minimising ground disturbance and right-of-way width, and would facilitate abandonment, reclamation and re-use of pipes at short-life fields.

But the 2007 revision of AS 2885.1 makes it clear that pipelines may be installed aboveground or with reduced cover only in exceptional circumstances.

Aboveground installation not permitted if the location class is other than R1 (broad rural) or the line contains high-voltage power lines or dense phase fluid.

Liquids pipelines may be aboveground if the safety management study does not identify any threats requiring burial for protection.

Gas pipelines may be aboveground if there is no surrounding population and negligible public access, and if the safety management study finds no risks exceeding low ranking.

The standard also lists several issues that must be considered in the design of aboveground pipelines.

Tuft and Schulz cited the concept development for the recently announced Bonaparte Pipeline in the Northern Territory, which they said briefly considered aboveground installation through a long section of very rocky and remote terrain.

“However in this case, the risk of lightning strike was considered to be unacceptable, partly because of the high frequency of lightning in the area but mainly because of the effects of supply interruption on a transmission pipeline which at some stage may be the sole source of gas to the power station for Darwin,” they said.

Planning for this pipeline also had to consider attempted vehicle crossings, bushfire, temperature variations, pipe movement due to transient flows or slugging, intentional damage from gunshot, and injury to stockmen who could collide with the pipe if it was partly obscured by vegetation.