February 2020, Vol. 247, No. 2


Why Industry Needs to Keep Its Pipe Dreams Flexible

By Ray Burke, Flexible Pipe Systems Product Management Director, Baker Hughes

The first flexible pipes were used in the offshore oil and gas industry in 1972. These early models were built and applied as a “kill and choke” line and formed with a bonded type of material, usually vulcanized rubber and armoring. 

Since then, the demands for this technology have grown steadily and diversified. Today, they are found in every major production basin worldwide and are used for everything from risers, flowlines, fluid transfer lines and jumpers, all designed to keep production flowing efficiently.

The development of flexible pipe technology has accelerated in recent years. Of course, the clear trend across the oil and gas industry has been operators looking for operational efficiencies wherever possible. Marginal gains in operational efficiency have become the order of the day. 

However, implementing this is trickier than it may sound given that many new fields are in some of the most challenging environments with which the industry has ever had to contend. Deeper water, higher temperatures, higher pressure, aging infrastructure and complex chemistry all stack up to create ever more intense conditions for flexible pipe to withstand.

In short, more and more fields are pushing the boundaries of existing technology. So, is it feasible to expect even more from flexible pipe technology? 

Why Go Flexible? 

Every project, at some point, must choose between rigid or flexible pipeline. The simplicity of the rigid carbon steel, welded together on a barge or at a spool base and then laid on the seabed, has been overshadowed in some cases by the more sophisticated mechanism of a flexible pipe – where installation and operation are simplified by design, before the pipes are constructed and shipped. 

The choice of subsea pipeline technology is often based on local conditions, technical requirements, installation vessel availability, operator preferences and cost efficiency. 

The ability to apply flexible pipe in the most challenging environments is a significant part of its appeal. High performance in water depths beyond 2,500 meters (8,202 feet), pressure reaching beyond 10,000 psi (689 bar), and high temperatures above 130 C (266 F), as well as the ability to withstand large vessel motions in adverse weather conditions, point toward why flexible pipelines have increased in popularity in recent times.

For floating production, flexible risers are often the only option that solves the geometric constraints of water depth, fluid pressure, vessel motions due to environmental loading and the consequent fatigue degradation of steel. 

Of course, these operating conditions are set against their own challenging backdrop. Even five years after the downturn hit, almost every operator continues to encourage supplier-led solutions to reduce cost and standardize and simplify subsea system installation and operation.

Deeper, Higher, Hotter 

Today, frontier markets such as Latin America, Brazil, in particular, and West Africa, epitomize the need for enhanced flexible pipe technology. Operations here typically involve negotiating extremely deep waters, high pressures and very high temperatures with production to a floating production storage and offloading (FPSO). It’s because of this that Brazilian projects have often been at the cutting edge of technology developments.

Increased project activity in such complex environments has led to incremental improvement in product capabilities. To date, flexible pipeline has been manufactured from a combination of materials, including steel pressure armor.

This gives the designers high stiffness to provide strength, geometric compliance to provide flexibility, and it incorporates polymer sealing layers with low stiffness for increased fluid integrity. With the addition of further strength-bearing armor layers, this traditional structure is what gives the product its intrinsic properties; however, new operating and economic environments have called for more – deeper, hotter, faster, larger, cheaper… 

Therefore, Baker Hughes has developed new designs for flexible pipe, moving from purely metallic strength to a carbon fiber composite pressure armor layer, marking a major step change in the industry.

By developing a composite pressure armor layer, the weight of the riser is reduced by up to 30%, making it easier and less expensive to transport and install – using smaller vessels or reduced vessel time, fewer ancillaries, and giving the operator a simpler riser configuration to manage. This hybrid composite flexible pipe allows a significant reduction in overall system complexity, allowing operators to move into deeper waters while lowering operational expenditure (opex) and operational risk. 

Furthermore, the composite replaces metallic layers that are susceptible to carbon dioxide corrosion, something increasingly encountered in deepwater basins, which may cause stress corrosion cracking unless properly managed. This hybrid riser design, proven with full life-cycle testing, adopts aerospace-type materials to significantly reduce permeated gas flow rate through the pipe, reducing operational risk and adding cost benefits over the field life cycle. 

Field Connections 

Despite all 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 our 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. 

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 that 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 seawater 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 armor layers. Damage to the outer sheath is one of the main causes of seawater entering the riser, causing corrosion of the armor wires.

An added complication in presalt fields with high O2 levels is that the water turns to vapor 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 armor 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 system contains three hardware components: an in-pipe sensor (FlexSensor) incorporated as part of the pipe construction in the tensile armor 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). 

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.

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