A rising tide

Riser technology is one of the most challenging areas for the offshore industry as it deals with the problems associated with undertaking cutting-edge field developments with increasingly difficult reservoir environments and ultra-deepwater conditions. When it comes to flexible risers, oil companies and contractors are fully focused on evolving this complex area of technology as rapidly as possible so that one of the offshore sector’s most well-established production solutions can safely deliver the goods from the seabed to the surface. As with nearly all evolving technologies at this present time, the driver for advancing the pace of flexible riser solutions is the industry’s push into water depths of 3,000 m (9,850 ft) and beyond. Flexibles are not the only choice, of course. Various innovative rigid steel catenary and hybrid options also are available and are being regularly employed – the use of Technip’s free-standing hybrid risers for Petrobras in the Gulf of Mexico on its now-producing Cascade/Chinook field development is a recent outstanding example. But many within the industry see flexible risers and all their emerging variants as one of the key enabling technologies when the booming number of planned floating production around the world is considered (at least 233, according to the latest figures from International Maritime Associates).

Why is so much attention being lavished upon flexibles? The contractors involved all have their eyes on the sizable prize – the global flexible pipe market is estimated at around 1,200 km (730 miles) per year (measured in theoretical length of standard 8-in. pipe). Convert that into market value, and it equates to more than US $1.5 billion per year, according to information from NKT Flexibles (bought earlier this year by National Oilwell Varco).

NKT also points out that Brazil is undoubtedly the largest single market for flexibles, accounting for more than 50% of global consumption, with other important markets in the North Sea, West Africa, and the Far East.

High-growth market

According to industry analysts at Douglas-Westwood, deepwater flexible pipe demand (driven primarily by demand for risers and flowlines) is a high growth market. Global expenditure for this year is forecast to be more than $700 million, with $478 million of that to be spent in Brazil, while by 2016 those figures are expected to soar to more than $3 billion per year, with more than $2.2 billion of expenditure in Brazil alone (and nearly $500 million in Africa).

Going back to where flexible risers have their roots, it is impressive to see how far they have come. Pioneering work back in the early 1970s saw them initially used in relatively benign and shallow water areas such as West Africa, the Far East, and the Mediterranean. Fast-forward to today, and flexible dynamic production and export risers, flowlines, and jumpers are in common use in up to nearly 1,900 m (6,235 ft) water depth for challenging field developments in the North Sea, West Africa, and Brazil, in configurations including the “steep S” and “lazy S” (using anchored buoyancy modules) as well as the “steep wave” and “lazy wave” (incorporating buoyancy modules), able to withstand severe vertical and horizontal motions in adverse weather conditions.

Flexible risers comprise a varying number of layers of different materials in the pipe wall fabrication such as an inner flexible metal carcass; leakproof thermoplastic barriers; and spiral wound, corrosion-resistant steel or “armor” wires, all of which essentially are free to slip past each other when experiencing external and internal loads. The steel wires give the structure its high-pressure resistance and good bending characteristics.

The ability to deploy them in a variety of configurations, depending on the water depth and field development conditions, means that each layer can be made fit-for-purpose and independently tuned to best meet the operator’s requirements. The most complex flexible pipes may have up to 19 layers.

Pushing back the boundary

Traditionally, bonded and unbonded flexibles have been limited by diameter and water depth, but that is a boundary constantly being pushed back by the industry. Designs are available for ultra-deep water, with qualification carried out for up to 3,000 m (9,850 ft) water depth, while higher temperatures (up to 150°C, or, 302°F) and higher pressures of up to 7,200 psi for a 9-in. inside diameter (ID) pipe and 10,000 psi for a 7.5-in. ID also have been achieved.

Riser expert Patrick O’Brien from Wood Group Kenny pointed out that one of the most encouraging trends in the market is the number of new or enhanced products and solutions arriving on the scene. “One of the main things for me is the number of products and players coming to the party with answers or potential answers,” he said. “Some have different approaches, some sticking with larger traditional pipe, others going for flexible composite pipe, while more are looking at composite bonded pipe.

“To a large extent this is being driven by a few major players. Petrobras is one that is very much driving the market. It is very aware of the need to have competition and get the best price, and it has been very encouraging to flexible pipe manufacturers. Petrobras is pushing the technology boundaries but also is driven very strongly by the need to have competition.”

Petrobras is one of the world’s biggest users of flexible pipe, and manufacturers are queuing up to make it for Brazil’s booming presalt province. The presalt presents some severe challenges, with aggressive bore environments, severe water depths, CO, and more. This is why the Brazilian state-owned major has signed several large deals within the past year or so with suppliers and other organizations, signaling its commitment to the technology and enabling the winning manufacturers to proceed with their own necessary plans for setting up manufacturing bases and appropriate R&D facilities to tackle the challenge.

Presalt studies

A technical feasibility study on flexible pipes for presalt oil production is presently underway and due for completion by December 2014 after Petrobras signed an agreement last year with the Japan Oil, Gas, and Metals National Corp. The cooperation agreement enabled a Japanese consortium including Furukawa Electric to proceed with the development of a flexible pipe design for oil production in Brazil’s presalt cluster.

Qualifying a new generation of flexible risers is one of the many technical challenges Petrobras is trying to overcome as it increases its efforts to develop its presalt riches. The presence of relatively high rates of COand HS in the natural gas mix demands a more corrosion-resistant riser for the fields, and the operator also has been cooperating with key existing suppliers including Technip and Wellstream (the latter now owned by GE Oil & Gas) to qualify a new range of more resistant flexible risers.

Flexible future off Brazil

Technip is one company that has seen the benefits of investing in the long-term future of flexibles offshore Brazil, having earlier this year been awarded a five-year frame agreement by Petrobras for the supply of around 1,400 km (850 miles) of flexible pipe. Supplies will start next year, and orders are guaranteed for at least 50% of the total value, estimated at around $2.1 billion. It is a challenging contract workscope – the deal covers the manufacture of more than 150 types and diameters of high-end, technologically advanced risers, flowlines, and associated equipment and accessories. Technip will produce flexibles at both its existing manufacturing site in Vitoria and also at its new manufacturing facility being built in Acu, Brazil.

Frederic Delormel, executive vice president and COO, Subsea, stated in a press release at the time of the award that the agreement “demonstrates the great potential of flexible pipe solutions to facilitate the development of deeper and more complex offshore oil and gas fields worldwide.”

An example of the highly technical nature of the work came just three weeks later, when Technip was awarded a lump sum contract by the operator for the Guara and Lula Nordeste presalt fields in the Santos Basin, located in a water depth of 2,250 m (7,380 ft). Technip is manufacturing 24 km (15 miles) of 6-in. gas injection flexible lines rated for 7,850 psi design pressure, including 2-m by 200-m (6.5-ft by 650-ft) top risers designed using Technip’s Teta-Clip pressure vault technology, 4-m by 1,400-m (13-ft by 4,600-ft) intermediate and bottom risers, and 18 km (11 miles) of flowlines.

Delormel said at the time of the award that it will take Technip significantly further along the road towards meeting corrosion and fatigue requirements that increase with presalt field developments as well as dealing with the high internal pressure and high tension requirements.

Another beneficiary of the momentum in flexibles generated by Petrobras is NKT Flexibles, which last year also received a framework agreement from Petrobras for four years worth an estimated $1.9 billion for the supply of flexible pipes between 2012 and 2015. The agreement specifically covered risers in 1,500 m to 2,000 m (4,920 ft to 6,560 ft) water depth, including up to 694 km (423 miles) of flexible pipe structures.

As part of the deal, NKT also is establishing a new dedicated flexible pipe plant in Brazil, expected to come into operation by mid-2013.

Future challenges

The aspects of deeper water and riser corrosion and fatigue were cited by O’Brien, who said there was no doubt where the challenges are. “Deepwater capabilities and more severe environments are putting challenges on flexible pipe, and the industry is trying to push the boundaries in terms of temperature.” He listed some of the challenging areas of focus as follows:

• Flexible riser fatigue;
• Analysis of “birdcaging” in flexible risers;
• Smooth-bore flexible pipe technology;
• Anti-HS layers for flexible pipes; and
• Composite armors in flexible pipe.

Corrosion is a serious concern, specifically the metallic degradation mechanisms in the risers that generally occur due to the highly corrosive environment in the annulus region. Corrosive gases such as COand HS can permeate from the bore through a riser’s polymer internal sheath to the annular space due to the high pressures of the product in the bore, creating a corrosive environment in the annulus. Mechanical damage of the outer sheath of the flexible riser can then take place, leaving a hole that will allow seawater to enter.

This, in combination with the COand/or HS that has permeated from the bore, will create a corrosive environment for the riser’s armor wires. That in turn can cause hydrogen pressure-induced cracking or stress corrosion cracking of the armor wires.

However, O’Brien said there is not one particular issue that needs to be tackled above all others – no showstopper waiting in the wings.

“Flexible pipe has been in the industry for some time now, and there is a lot of day-to-day business going on,” he said. “We still continue to push the boundaries all the time. The only thing I would mention is the need to find out more about what is going on inside the flexible riser itself, the ability to better monitor in service a range of things going on inside the pipe related to its integrity.”

He added that, as an industry, the offshore business still struggles to predict the remaining life of flexibles and tends to err on the side of caution. “We are pretty good at analyzing stresses, but it seems that we do not have a good handle yet on the environment inside the annulus and the bore of the pipe,” he said. “There is no single piece of kit out there that is properly able to inspect inside. So we need to further evaluate the annulus environment. But most likely we are conservative in our fatigue predictions.”

SureFlex JIP

Industry cooperation is of course key to overcoming current challenges such as these, and the flexibles sector is building up an encouraging track record in this regard.

An industry survey was conducted to gather data (see chart above) with statistics based on 1,900 risers, 1,400 static lines, and more than 130 production facilities worldwide. Some of its main findings on flexibles damage and failure indicated that external sheath damage/flooded annulus remains the most common damage mechanism and that general wire corrosion due to intermittent exposure in the splash zone is a concern.

O’Brien added that the SureFlex findings also revealed that vent system anomalies and carcass collapse failure were showing significant increases over previous data. Some key conclusions from the survey were:

• There is a lack of coherent strategy detailing all design and operational data to be monitored and recorded. Follow-up on recording and assessing is still found wanting;
• Handover from project execution to operations has improved since 2002 but still needs to be better, and there were numerous failures to correctly commission gas venting systems;
• There has been a significant uptake in annulus testing since 2002, including improvement in procedures and assessment capability and new techniques developing. Initial testing followed by annual testing is now accepted practice;
• The limited number of retired riser dissections so far implies predictions are too conservative. Corrosion fatigue assessments need improvement; and
• The principal cause of damage remains to be external sheath breach. The focus now is on global corrosion in the splash zone.

Other conclusions that O’Brien highlighted as important as the industry moves forward are that it has now made a “definitive step up” in its ability to model the complex cross-section of flexible risers. This in turn contributes toward improved prediction of flexible riser fatigue life, armor wire disorganization, and birdcaging (with the latter two points important for deepwater application).

The industry also needs continued efforts to rationalize fatigue life predictions with a consistent, transparent approach, he added.