Tasmanian Gas Pipeline Offshore Environment Plan
|Activity type||Operation of a petroleum pipeline|
|Submitted by||Tasmanian Gas Pipeline Pty Ltd|
|Submission date||02 October, 2019|
|Status||Under assessment (with NOPSEMA)|
|Link to previously accepted EP|
Phone: 03 9044 1123
The Tasmanian Gas Pipeline (TGP) is a natural gas transmission pipeline system that extends from Longford in Victoria, across Bass Strait to Bell Bay in north-east Tasmania. Additional onshore pipelines extend from Bell Bay to Port Latta in north-west Tasmania and to Bridgewater in the south. The TGP offshore section commences at the high-water mark along Ninety Mile Beach, Seaspray and crosses Bass Strait to the low water mark at Five Mile Bluff, Tasmania where it continues onshore. The Offshore TGP is approximately 301 km in length, with maximum water depth along the route of approximately 77 metres. The Offshore TGP route was selected to minimise pipeline length and avoid adverse seafloor conditions and on bottom obstructions.
There are two drilled crossings where the pipeline meets the Victorian and Tasmanian landfalls, which were constructed using horizontal directional drilling (HDD). The Victorian HDD section is 1080 m long, exiting the seabed at approximately 10 m water depth. The Victorian shore approach was trenched and backfilled naturally. The Tasmanian HDD section is 859 m long entering the seabed in 10.5m water depth. The rest of the offshore component of the TGP was installed on the Bass Strait seabed but has self-buried to various extents along parts of the route. The seabed along the Offshore TGP route across Bass Strait is mostly flat and featureless.
There are no daily activities on the pipeline itself apart from continuous monitoring of pipeline flows and pressures. The SCADA system monitors flow in the pipeline and provides information on, and remote management of, the CP system, pressures, temperatures, valve status, metering selections, alarms, gas quality, flow rates, condition monitoring and site entry monitoring. The SCADA system includes alarms on all key operational parameters, ensuring appropriate response to any adverse conditions.
ROV surveys of the pipeline, to assess pipeline integrity and any maintenance requirements, are undertaken on a periodic basis and occur approximately every 5 to 8 years. Consequently, temporary facilities are only on location during subsea survey and emergency repair works if, and when, they arise. In line inspections (ILI) are performed with an intelligent pig on a risk-based frequency.