Jemena has completed the construction of one of the most unique and innovative projects of its kind in Australia – the Colongra Lateral Pipeline – Australia’s largest ever gas storage bottle.

Designed and built by Jemena, the Colongra Lateral Pipeline project will deliver gas to Delta Electricity’s new 660 MW gas-fired peaking power station through the largest diameter onshore gas pipeline constructed in Australia.

Delta chose Jemena to develop a new high pressure 42 inch lateral to provide a gas storage and transportation service to meet the needs of the peaking plant. The pipeline will have a dynamic storage capacity of five hours and was built because the existing Sydney to Newcastle gas supply could not meet the peak demand of the station.

Jemena and Delta together developed a design for the lateral pipeline to be pressurised over a 24-hour, off-peak period and held at pressure until the power station is brought online during peak periods.

Route restrictions late in the project complicated the project, requiring Jemena to find a way to store over one third of the 9 km of fully-pressurised gas pipeline in a 1 km stretch of land. The innovative solution was to use the largest diameter onshore gas pipeline ever used in Australia and double loop it to create the required storage capacity.

Construction was completed in January 2009 and at the time of writing Jemena’s project team was about to start commissioning.

Jemena Project Manager Mario Bavaro said the Jemena team was proud of its achievement in meeting the diverse and unique challenges of constructing Australia’s largest diameter onshore gas pipeline.

Complex design a first

This complex looping design is a first for Australia. The loop allows the pipeline to remain piggable and also minimises the need for additional 42 inch ball valves, thereby delivering significant cost savings to the project.

The lateral pipeline connects Jemena’s Sydney to Newcastle pipeline at Wyee to the Colongra Power Station near Doyalson on the New South Wales central coast. It consists of a compressor station, 3.5 km of 10 inch feeder pipeline, 9 km of looped 42 inch storage pipeline and a let -down station.

The Colongra lateral will play dual roles of high-pressure gas pipeline and pressure vessel with cycling of gas pressure between 3.4 to 13 MPa during operation of Delta’s peaking power station.

Subsidence: a challenge

Another major challenge that Jemena successfully met was to build the storage pipeline in a designated mine subsidence area. This means that the pipeline, designed as a ‘zero rupture pipeline’ and engineered and constructed to AS2885, had to withstand both the fatigue stresses from its pressure cycling and the potential shear stresses from mine subsidence.

Most components of the lateral are designed to withstand the high fatigue and potential mine subsidence stresses through extremely fine tolerances in design, procurement and construction activities, such as welding. For example, the constructed pipeline cannot deviate from the designed alignment by more than 500 mm in any horizontal direction.

Many of the project suppliers had to redesign their equipment and develop special testing procedures to ensure that their components met the required fatigue strength. Adding to the challenges the whole project, from design and approvals to commissioning, had to be completed over an approximately two-year period.

Construction was completed over a four-month period ending in December 2008 allowing for operation to commence at the end of the first quarter of 2009.

Innovative project

The innovative project drew on expertise from across Jemena – including business development, engineering, project planning and operations. A major factor in the Colongra Lateral Project’s success was Jemena’s proven capability of delivering similar projects, such as the Sydney Primary Loop and the recently completed Mila Compressor Station.

Jemena General Manager of Business Development Adrian Hall said that one of Jemena’s major strengths in winning the Delta Electricity contract to construct and own the Colongra lateral was Jemena’s ability to leverage existing knowledge, expertise and reputation.

“Supporting the depth of operational expertise is our in-house project management capability to liaise with authorities for design and project approvals,” he said.

Mr Bavaro said that rarely a week went by without the project team experiencing and solving Australia-first challenges.

He recalls a time during the front-end engineering and design when the Australian Nuclear Science and Technology Organisation was called upon to undertake specialised computer modelling to confirm that it was possible to manufacture line pipe that would meet the unique strength requirements for this project.

“Another example was the need to locate the 10 inch feeder to 42 inch storage pipeline interconnect below ground for security reasons,” said Mr Bavaro.

“This created difficulties with the stress analysis associated with five adjacent pipelines, two 42 inch ball valves and four 10 inch valves all being located below ground, within a relatively narrow envelope, in a designated mine subsidence area.

“To deal with the stress at the interconnection station, an additional below ground expansion loop was required along with stabilised sand approximately 400 m upstream of the interconnect.”

The company said that the project is a showcase of Jemena’s engineering and delivery expertise to the industry.

Co-operation the key

Mr Bavaro attributed the success of the project not only to his team but also to Jemena’s close working relationships with its contractors and consultants.

“The commitment, professionalism and capability of all concerned was outstanding,” he said.

“Delivery of the project was in every way a team effort and it required team members to work extremely closely and effectively with each other. Having a positive and constructive working relationship with contractors was critical to our success in overcoming obstacles and challenges as they occurred during construction, with minimal impact on the delivery schedule and cost.”

Detailed project management systems and principles were applied to the project execution and have been a fundamental part of the team’s ability to systematically and promptly address the project challenges as they arise.

Major pre-construction challenges

Even before construction began, Jemena’s construction team faced a number of major challenges.

Jemena Site Manager Craig Fuller said “The project schedule was compressed because of a number of reasons outside of Jemena’s control. These reasons included a route change, which delayed construction and resulted in the pipeline redesign that produced the loop; line pipe delivery delays; and Delta’s need to maintain the original start date of the pipeline’s operation.”

To maintain the schedule, Jemena had to run a number of key activities in parallel that would normally have been completed sequentially. These activities included route selection, procurement, detailed design and contractor selection.

For example, lead times required the 42 inch line pipe induction bends to be ordered before the new route with loop was finalised. This meant that as well as the more common restrictions, the final route was also limited by the pre-ordered bends.

“Finalising arrangements with contractors was difficult due to continuous scope changes,” Mr Fuller said.

Describing the relationship Jemena had with the construction contractor over the duration of the project, Mr Fuller said “The relationship with all contractors on the project was excellent. A key criterion in contractor selection was having a track record in successfully working with Jemena. Interfaces with contractors were managed co-operatively to the considerable benefit of the project.”

Jemena’s major contractors on the project included GHD, designing and engineering the pipeline and loop; Diona Pty Ltd, constructing the 42 inch storage pipeline; Codmah Pty Ltd, constructing the 10 inch feeder pipeline; and Enerflex, engaged as the engineering, procurement and construction contractor for the compressor and let-down.

Compressor design

According to Andrew O’Neill, Jemena’s Engineering Manager, the compressor design basis required a very wide suction and discharge pressure range.

“Such a wide range of operating pressures proved difficult for the compressors to operate across, given the station is designed to be unmanned.”

To simplify the compressor controls Jemena added station suction and discharge control valves to limit the suction and the discharge pressure; to limit the operating hours at less than the minimum recommended duty; and, to allow remote operation of the station.

“The compressor station is also located within 250 m of a residential property,” said Mr O’Neill.

“In order to meet noise requirements design measures were adopted including additional exhaust silencers, unit enclosures and electrically driven air cooled heat exchangers. Being electrically driven, the cooler fans were able to be controlled by variable speed drives, allowing turn down during night time operations.”

Ecological services

During construction, Jemena engaged two ecologists to provide a range of services including the construction of nesting boxes placed in trees along the construction corridor, the encouragement of native fauna consolidation in the area, and the development of revegetation programs.

Ecologists were present to supervise the clearing of habitat trees and inspect tree hollows for native fauna. A number of ringtail possums, feather-tailed gliders, skinks, tree frogs and a tawny frogmouth owl were identified and safely relocated to adjacent bushland. No animals were harmed during the vegetation clearing or other construction activities.

Around 30 specially-constructed nesting boxes were placed in trees along the construction corridor to provide additional habitat and encourage native fauna colonisation in the area.

The scale and complexity of the construction as well as the tight construction window meant that safety was the most critical success factor of the project.

Safety challenges

Specific safety challenges of the project included high voltage power lines, narrow easements, heavy lifting operations, swamps, snakes, major roads and the excessive wet weather.

To manage these challenges as well as other general construction challenges, Jemena implemented a comprehensive safety management plan. The plan included initiatives such as ensuring Jemena and each of its contractors had a full-time safety manager on site at all times and ensuring Jemena construction team members attended all contractor daily pre-start meetings to provide toolbox talks and talk about safety.

Jemena’s Safety Manager for the project David Milutin said “As a safety manager with 20 years experience in major construction, I am proud to be associated with the Colongra Lateral Pipeline project management team. This is the first time in my working career that I have been privilege to work with an entire team so proactively committed to the safety of people working on their project, reflected from the project manager down!”