Understanding the Differences Between Flexible and Rigid Flow Lines in Subsea Applications
Updated: Jul 22
Akrake Petroleum Benin S.A. (Akrake), an indirect subsidiary of Rex International Holding (Rex), is using the Rex Group’s tried-and-tested production system comprising a Mobile Offshore Production Unit (MOPU) and a Floating Storage and Offloading unit (FSO) linked by a flow line, for the upcoming production operations in the Sèmè Field in Benin, for which it is the operator. Naturally, the choice of the right type of flow line is critical to field production.
Flow lines transport unprocessed oil and water from the MOPU to the FSO, the design and implementation for which require careful planning, with consideration for the high pressure, temperature, and volume handled, as well as for the environment and preservation of material quality.
Did You Know?
Flow lines can be flexible or rigid and each option presents specific advantages and challenges, technically and economically.
Technical Considerations
Flexible flow lines are designed to adapt to a wide range of underwater conditions. Made from advanced materials such as carbon fibre composites, they are lightweight and resistant to corrosion. These flow lines can endure extreme conditions, handling deep-water pressures over 10,000 psi and temperatures above 130°C1[1]. This flexibility makes them ideal for deepwater operations, where space and structural constraints are common.
In contrast, rigid flow lines – typically constructed from carbon steel or corrosion-resistant alloys – are known for their strength and reliability, especially in stable environments. They offer greater structural integrity over long distances, though installation is often more complex and requires additional support structures. Rigid pipes are most suited to shallow waters or stable seabed, where they can be securely installed.
Economic Factors
There are also economic considerations when choosing between flexible and rigid flow lines. While flexible flow lines tend to have higher upfront costs per metre, they can ultimately reduce overall project expenses. Their lighter weight allows for smaller installation vessels and faster deployment times, which lowers operational costs. For example, hybrid composite flexible pipes reduce riser weight by up to 30%, simplifying transportation and installation[2]2.
Conclusion
Choosing between flexible and rigid flow lines in subsea applications requires balancing technical requirements, environmental conditions, and economic considerations. Each option offers distinct advantages – the adaptability and resilience of flexible flow lines in extreme conditions, versus the strength and durability of rigid flow lines.
At Akrake, which is operating in the dynamic offshore environment of the Sèmè Field, selecting the right subsea technological solutions, down to the type of flow lines used, is vital to ensuring safe, efficient, and cost-effective production. Stay tuned for more operational updates from Akrake in the months ahead.
[1] Offshore Magazine, High-pressure flexible pipe, the next frontier, 1 May 2007
[2] Oilfield Technology, Why the oil and gas industry needs (flexible) pipe dreams – part one | Oilfield Technology, 25 February 2020
