Commercial Marine Group has delivered a complex subsea pipeline in South-East Queensland.
Pipeline construction is an incredibly nuanced area, with different situations calling for different methodologies. At a glance, this might look like overland pipes running through a vast landscape, or microtunnelling beneath an urban environment. But when you can’t go over it and you can’t go under it, sometimes there’s no choice but to go through it.
And that’s where Commercial Marine Group (CMG) comes in.
With its origins in diving operations, CMG has grown over a decade to become a marine construction company 66 people strong, with teams of engineers, mariners and divers all over the country.
The business boasts engineering and project management capabilities, allowing it to offer crafted and innovative marine construction services from the design and feasibility stage, right through to delivery and inspection.
One of its most recent efforts was the construction of a nearly 1km underwater sewer pipeline along the riverbed of a busy Queensland waterway.
“The project was for the construction of a 630mm diameter pipeline that ran through the river,” CMG Engineering Director Nick Ayres told The Australian Pipeliner.
“Our installation approach adapted specialist offshore techniques to a high-flow, turbid river environment in a congested urban area. The result was a robust pipeline design paired with a cost-effective efficient installation method.”
To deliver the project, CMG utilised the S-lay method, where lengths of pipe are welded, inspected, and collared with concrete blocks on board a pipelay barge. As the barge moves forward, the welded pipe gradually feeds through a specialised ramp, called a stinger, into the river. CMG’s team of divers inspected each section of pipe as it was submerged, ensuring a seamless installation.
At the same time, CMG constructed and floated 80m lengths of pipe on each side of the river which served as connection points for the underwater pipeline.
In addition to the challenges associated with this delivery method, the project had tides, current, and river traffic to contend with.
“We were initially asked to design to a high flowing current. We put our own current flow measuring device in to collect real-time data and were able to adopt much lower flows in the temporary works design,” Ayres said.
“So instead of designing for six knots, we could design for one and a half knots, which is what the current is. This made the construction process a lot simpler.
“To work around river traffic, the barge progressed in 40m movements supported by five anchor points. The barge’s position could be adjusted in relation to these anchors with the winch systems. We progressed section by section, which meant other vessels were able to pass by without issue.”
Another benefit of this method was that it allowed the CMG team to be incredibly accurate with the pipeline’s installation.
“GPS navigation system on the barge allowed us to monitor position and tolerance as we progressed and make any necessary adjustments to our position. This meant that even in maximum flows in the current, we were still able to continue progressing without compromising alignment,” Ayres said.
CMG Project Engineer Oliver Beechener, who was out on the barge every day, described the excitement on deck.
“As each day progressed, you’d have moments where it was quite relaxed while we were moving anchors and putting blocks on – and things like that,” he said.
“There were three critical moments in each day, which were bringing the pipe on board, and then the two movements of the pipeline.
“During those moments we were all on radio comms – it was quite a high-pressure situation. And then after that, while we were completing the welds, people were able to catch their breath again, and then we would ramp up again for the next movement.
“One thing that stuck out to me was that everyone on the barge had a role. Everyone was delivering their task and was critical to moving forward each day.”
This degree of precision didn’t materialise overnight, it was the product of a meticulous design and engineering process that took place long before the barge hit the water.
Ayres said the team utilised workshops, animations of methods, scale models of equipment and processes, and leveraged expert pipe installation and vessel stability analysis to explore and refine installation options.
“This process led to the development of a bespoke pipelay barge and stinger, specifically designed for the project,” he said.
“These techniques allow us to better engage with our partners and work crew, find the optimal solution for any project, and show exactly how it will work before we get to site.”
For the CMG team, seeing their hard work pay off always makes for a memorable moment.
“The first manoeuvre we made with the pipe was quite a challenging one, but we knew the methodology was tested,” Beechener said.
“The first time the block moved on the stinger was a bit like ‘Okay, this works. We’ve got a working methodology, and the barge is handling how we expect’. It was a very exciting day.”
In early December, the CMG team successfully handed the completed pipeline over to the asset owner after hydrotesting.
Close collaboration among stakeholders allowed the project to be completed within 11 months and only eight weeks on the river. The project was completed without incident, and with no disruption to river users, the local community, or the asset owner.
“If the project is deemed difficult or complex – technically or environmentally – then it’s exactly the sort of project that CMG is keen to take on,” Ayres said.
“We’re here to solve these difficult problems for our clients. Challenge is our competitive edge. CMG prides itself in mastering the complexities of marine and coastal construction solutions.”
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