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Pipelines confront new extremes

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Asle Venås Asle Venås
Senior Principal Pipeline Specialist
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Pipeline
Contractors are investing in responses to ever more challenging demands on pipelines and pipelay

Demands on subsea pipelines are increasingly complex as they operate in remote and harsh environments, and transport increasingly aggressive products across longer and/or deeper sealines.

Lay vessels must align wider and heavier pipelines, and new concepts such as pipe-in-pipe (PIP), to specified routes in difficult conditions such as steep slopes, narrow corridors, rough seabeds and harsh metocean. Critical inline structures must meet stringent targets.

“Such demands require high capacity equipment to handle, hold and protect pipelines during installation and to monitor lay parameters in real-time,” said Roberto Bruschi, vice president of advanced engineering services and innovation technology projects at leading international contractor Saipem SpA, Italy.

Continuous investment in new and upgraded vessels is a key part of Saipem’s strategic response to offshore market needs.

The art of smart

The Castorone dynamically positioned (DP) deepwater laying ship for operations in extreme environments, and the Saipem FDS 2 (DP) field development ship, illustrate this. Castorone monitors lay progress. It displays easy-to-read charts and data generated by integration of instrumentation and advanced calculation, such as real-time configuration of pipelines on the stinger and along the lay span.

“The stinger is really smart, not just a steel truss,” Bruschi said. The stinger tip can extend up to about 40 metres (m) aft (rear) of Castorone, and more than 90m below the sea in steep lay configuration, to guide pipelines carefully. This, and skilful operators, maintains the working level of the pipe within allowance limitations, right up to seabed touch down.

Stress on pipelines at points along the stinger and, after exit, along the lay span is continuously controlled. “Monitoring the working level of each part of the equipment can be quite crucial during the most demanding operations and therefore for the laying season.” This enhances control of pipe-laying operations and schedule, and allows speedy responses to unexpected events that cannot be excluded in open sea.

Powerful computing underpins Bruschi’s belief that future challenges can be met: “I started in the industry in 1980, and computers are now doing things 100 or even 1,000 times faster.”

Applications include numerical simulation of most conditions and scenarios. Examples include the pipe and the lay vessel position near seabed targets under a specific setting for laying parameters, and for dynamic conditions under wave-induced oscillations and slow drift counteracted by DP.

Design for safe life

On the mechanical design, Bruschi noted “a general consensus” around reliability based design criteria and load-resistance factor design, and on continuous upgrading of design to reflect research and development.

However, he argued that for environmentally sensitive and remote locations, criteria for applying design to new applications should include assessment of consequences to health, property and environment across the widest range of factors and for the pipeline’s lifecycle. “It is not a case of just modelling the capacity of the actual material to perform in normal conditions,” Bruschi said. Numerical modelling should anticipate and verify line pipe capacity to handle realistic demands under severe environmental events such as wave storms, geohazards or ice gouging, he explained.

“It is about safe life rather than fail safe. The most important consideration for Saipem is safety. This applies to every element of planning, design and pipelaying operations, and across all our people and levels of management. We have put a lot of effort into training and competency throughout the organisation.”

Robustness is the key

For pipelines to be safe, cost-effective and efficient 20 to 50 years on, the key is “robustness” throughout the lifecycle, Bruschi stressed.

“With pipelines in shallow to medium depths, across crowded and near-to coast offshore basins, you have the possibility to intervene. You have a state of preparedness that can maybe accept a minor fail where it is not jeopardising the structural integrity and carrying capacity in the short-term, without the need to intervene quickly.”

If intervention is needed, then vessels and other resources can be lined up in good time. Experiences in the North and Mediterranean Seas help to understand criticality. “But what do you do if you have a winter season incident at Sakhalin or in the Barents Sea?” he asked. “Then you have to do something involving a huge spread of very specific working vessels in a very short time, and vessels are in short supply. Would you not prefer to have a robust solution from the beginning?”

An increasingly integrated multidisciplinary approach across surveying, design and installation is inevitable in hi opinion, as is collaboration between industry, academia and others. His view of DNV GL’s role in this ecosystem is that it has “a big ear” to what is happening worldwide through clients, and through DNV GL’s joint industry projects (JIPs) and the Pipeline Committee and Innovation Forum.

Standardisation, along the lines of the DNV-OS-F101 Offshore standard for submarine pipeline systems, can help to raise quality, reduce risk and lower cost. However, Bruschi also pointed out that responses to needs in deep waters off Brazil, for example, may be very different to those off West Africa.

Saipem's deepwater laying ship Castorone operates in extreme environments