Connection to oilfields
Despite all of these advantages, flexible pipes have encountered challenges as they have developed. Like all major oil and gas infrastructure, corrosion and degradation mean integrity management is an area of significant focus and development for customers.
Flexible pipes used for large volume gas export and gas injection can cause flow induced pulsations (FLIP) to occur, which can lead to excessive vibration of small-bore topsides and subsea pipework. Excessive vibration can lead to failure and loss of containment if not caught early. The phenomenon is caused by the interaction of the gas with the cavities of the carcass layer of the flexible and onset occurs above some critical flowrate.
Until recently, operators would have to accept this as a fact of life and manage the consequences through subsea and topside modifications or place limitations on the flow rate. These conditions, and recent advances in research and development in this area have led to the development of a system called Flex-Insert. In this case the internal carcass is manufactured with an additional, internal layer within the pipe which effectively removes the cavities and prevents FLIP from occurring, saving time and cost in the process.
Despite the significant leaps forward in the technology applied to new flexible pipes, there remains the challenge of how best to manage existing, older flexible pipelines. Lines in operation, in almost all cases, have steel components and are afflicted by the age-old issue of sea water corrosion.
The annular space is the key point for integrity, and for inspection/management strategies. This is the volume between the internal barrier polymer sheath and the outer cover polymer sheath containing the steel wires of the pressure and tensile armour layers. Damage to the outer sheath is one of the main causes of sea-water entering the riser, causing corrosion of the armour wires.
An added complication in pre-salt fields with high carbon dioxide (CO2) levels, is that the water turns to vapour then mixes with the CO2 before entering the annular space by permeation. This creates a highly acidic, highly corrosive solution in close contact with the armour wires.
Both situations can lead to a flooded annulus. Given the potential consequences of flexible pipe failure, the need for a clear and efficient understanding of the integrity of this outer sheath is critical.
For new pipe projects, Baker Hughes has developed SPIRE, a new system that allows operators to monitor whether there is water in the pipe annulus, and even determine whether it is a result of gradual permeation or sudden damage to the outer sheath. The SPIRE system contains three hardware components: an in-pipe sensor (FlexSensor) incorporated as part of the pipe construction in the tensile armour wire layer, a connection at the topside end-fitting (smart bolt) and; either a control room rack (for monitoring) or a portable measurement instrument (for inspection).
The sensors are wrapped around the outside of the pipe, incorporated in the tensile wire layer, before the outer sheath is applied, resulting in a small change to the manufacturing process. The system allows continuous monitoring of the pipework integrity, meaning early intervention is made not only feasible, but highly efficient.
An outer sheath breach puts the tensile armour wires at risk from corrosion and corrosion-fatigue. Amongst a range of solutions for integrity management that Baker Hughes has, the MAPS technology is designed to provide information about the integrity of the tensile armour wires, making it ideal for cases where there is an outer sheath breach. The underlying MAPS technology - a non–destructive, non-contact technique for the measurement of stress in steel materials – also has ‘reach’, which is the ability to sense the effect of a wire defect many metres from the actual damage site. This gives it a significant advantage over other inspection techniques as it allows critical areas, such as underneath a bend stiffener, to now be inspected.
It is clear that operators are increasingly looking to suppliers who can offer the best overall value across an entire project lifespan. Choosing a product is just one part of the total cost; transportation, installation and management of integrity make up a significant part of the rest. Today, operators are looking at the bigger picture, how can infrastructure, like flexible pipe, help get the most out of a field, in the most efficient way. Baker Hughes are focused on reducing TOTEX, across the full range of subsea infrastructure throughout its life, these products form a family named Aptara, meaning fit-for-purpose.
Reduced operational, safety and environmental risks while curbing maintenance costs and extending the life of equipment is the optimum solution. With increased speed, flexibility, and performance, these increasingly adaptable systems boost productivity over the expected full life of the field.
This is part two of a two-part article. Part one can be read here: https://www.oilfieldtechnology.com/special-reports/25022020/why-the-oil-and-gas-industry-needs-flexible-pipe-dreams--part-one/.
Read the article online at: https://www.oilfieldtechnology.com/offshore-and-subsea/26022020/why-the-oil-and-gas-industry-needs-flexible-pipe-dreams-part-two/
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