Offshore Applications: The Future Is Now
The composites industry seems to be waiting for "the big one" — the killer application requiring vast quantities of materials that will propel composites into the material mainstream. Offshore oil has been recognized as one arena with that kind of potential. For some time, composites have slowly and steadily replaced topside (above water-level) metal on a growing number of offshore facilities, in both new installations and retrofits of existing structures. But today, large-scale applications, such as carbon composite riser pipe for deepwater drilling, are on the brink of commercial success, bringing the market, for the first time, very near to "big one" status.
Factors fueling market growth include the dramatically lower weight and far greater corrosion resistance of composites, compared to conventional offshore materials, and the increasing acceptance of composites by regulatory and materials-certification agencies. Weight reduction is a major driver — less weight means the structure costs less to build and allows for more drill pipe and production equipment for oil production. Jerry Williams of Petroleum Composites (Houston, Texas, U.S.A.) points out that when comparing composites with steel, "The cost differential narrows when installed costs are compared, and shifts in favor of composites when life-cycle costs are considered. We've seen life-cycle savings of up to 70 percent for fiber-reinforced plastic pipe."
In contrast to steel, which seawater quickly corrodes, composites are virtually corrosion-free when made with chemical-resistant resins. For platform components such as column pipe (pipe that extends from the platform down below the water surface to supply seawater) and firewater systems (strategically placed pipes for fighting potential fires), this corrosion resistance translates to years of maintenance-free service. One Gulf Coast fabrication facility reports that steel pipe installations are often severely corroded after just two or three years of service, while thousands of composite column pipes are still in service, several more than 25 years old.
Key regulatory developments over the last five years also have encouraged the use of composites. In late 1998, the U.S. Coast Guard approved the use of fiber-reinforced plastic (FRP) piping and glass/phenolic gratings on offshore platforms and drill ships (USCG Policy File Memoranda [PFM] 1-98 and 2-98). The International Maritime Organization (IMO) has approved composite piping for use in platform fire-fighting systems carrying water, as specified by its Level 3 Fire Endurance standards (A.753 ), which include jet fire endurance standards. ("Jet fire" refers to the release of burning hydrocarbons under high pressure.) However, IMO regulations do not allow the use of composite pipe for flammable liquids like hydrocarbons or diesel fuel (Level 1 Fire Endurance), and such certification is probably unlikely to occur. ISO (International Organization for Standardization) regulation ISO 14692 recommends a performance-based risk assessment for composite piping applications. Det Norsk Veritas, a Norwegian-based organization that certifies seagoing vessels and structures, recently released two standards related to composites: Draft Offshore Standard OS-C501 provides requirements and recommendations for composite component structural design and structural analysis procedures. Recommended Practice DNV-RP-F202 describes performance-based guidelines for composite riser certification. Both signal a growing acceptance of composites in offshore oil platform design and construction.
COMPOSITE PIPING SAVES TOPSIDE WEIGHT AND COST
Composites are considered standard equipment for some types of topside facility piping. Since its first installation in 1974 on the Trinmar Ltd. Platform 9 near Trinidad, fiberglass pipe has been specified in hundreds of offshore platform projects (e.g., the topside fire pipe installation on the Shell Mars platform, covered in "Inside Manufacturing," CT July/August 1998, p. 16).
Today, with phenolic resins, fire-retardant additives and intumescent coatings, composite pipe can be designed to survive even the most extreme jet fire conditions. While standard fiberglass composite pipe is non-conductive, there is some disagreement within the industry as to whether conductivity is required on an open deck of a platform. For applications where operators request or require electrical conductivity, most manufacturers offer electrically conductive versions of their piping products.
Fred Landry of J. Ray McDermott, a well-known offshore platform fabricator in Morgan City, La., U.S.A., says that composites are less expensive than the copper/nickel alloy often used for fire pipe and can be fabricated in fewer pieces to fit into unusually shaped or tight quarters. Its lower modulus gives composite piping some elasticity and flexibility in configurations that might not be possible with more rigid metal. Plus, bonded joints eliminate the need for hot welding, which can be a potential fire source on a platform filled with flammable hydrocarbons.
Composites must be handled differently than metal during installation because they can be damaged if dropped or struck by a heavy object, says Landry. He typically installs composite pipe at the end of a job, to minimize the risk. The thermal and pressure behavior of composites is different than metal, and is accounted for in pipe hanger design, which allows for pipe movement and includes protective wear pads to protect the pipe from abrasion.
EDO Specialty Plastics (Baton Rouge, La., U.S.A.) has manufactured its FIBERBOND composite pipe for hundreds of offshore installations. The company's licensee in Malaysia, Dialog Systems SDN BHD, recently completed a project for the Tapis B and Irong Barat A platforms, operated by EMEPMI (ExxonMobil E&P Malaysia), replacing metal piping for firewater headers and deluge systems. Because the piping carries only seawater, no special corrosion liner was necessary, but specified design pressure was 290 psi/20 bar. "The Malaysian platforms have traditionally used a lot of copper/nickel piping, so we were successful in finally convincing them to use composite materials for this high-pressure application," says EDO Specialty Plastics' engineering manager Kevin Schmit.
Pipe ranging from 2-inch to 12-inch diameter was constructed as follows. Two plies of fiberglass surfacing veil, supplied by the Nicofibers division of Hollinee Corp. (Shawnee, Ohio, U.S.A), were layed up on a mandrel to form a 0.5-mm/0.02-inch thick liner, over which E-glass roving was filament wound at an angle of ±54.75° relative to the longitudinal (0°) axis. For most applications, this fiber architecture satisfies stress loads in both hoop and axial directions. Winding angles are often modified for installations requiring greater strength, such as long unsupported spans, in which ±20° and ±70° winding angles are used. The liner and roving was wet out with Dow Chemical Co.'s (Midland, Mich., U.S.A.) Derakane corrosion-resistant epoxy vinyl ester resin, optimized by EDO with proprietary additives for fire endurance. Final wall thickness was 6 mm/0.25 inch to 14.5 mm/0.58 inch. Piping was produced in 12.2m/40 ft lengths and cured at room temperature.
On the platform, pipe was joined by the patented FIBERBOND composite butt-welding technique. Similar to steel butt welding, the plain ends of the composite pipes are simply butted together. The "weld" is accomplished by wrapping the seam with resin-wet layers of chopped-strand mat and woven E-glass roving, using the same epoxy vinyl ester resin used in the pipe bodies. The joint cures without heat, so no hot work permits are required.
McDermott's Morgan City facility is currently fabricating a SPAR platform for BP's Holstein field, destined for installation in 1,311m/4,300 ft of water in the Gulf of Mexico before 2004. Designers specified conductive composite piping supplied by Ameron International, Fiberglass Pipe Division (Houston, Texas, U.S.A.) for the fire system, says Ameron's director of product marketing services Joie Folkers.
"Because the spar platform will sit high above the water surface, more pressure is needed to lift the seawater up to the facilities area," says Folkers. "So the piping has a fairly high-pressure rating of 250 psi/17 bar and it is all conductive to meet the requirements for use in a hazardous area." The fire system features Ameron's Bondstrand Series 7000M and PSX-L3C piping for the ring main piping, together with PSX-JFC for the dry deluge piping downstream from the ring main. Dry pipe contains seawater only when the system is activated, which reduces topside weight and helps prevent corrosion of the system's metallic valves and nozzles. The JFC product name stands for jet fire conductive, which means the pipe is approved for jet fire conditions.
Fabrication of the 7000M piping begins by filament winding glass roving, typically supplied by Johns Manville (Denver, Colo., U.S.A.) and 3K carbon tow, wet out with an amine-cured epoxy resin from Dow Chemical. The carbon fiber makes up about 10 percent of the hybrid laminate, spaced such that it forms a grid. "The carbon fibers contact each other and provide through-the-wall conductivity as well as end-to-end conductivity," Folkers explains, noting that the stiffer, stronger carbon fiber also increases the pipe's structural performance.
Ameron's PSX (polysiloxane-modified phenolic) resin matrix tackles the traditional processing challenges posed by phenolics. Phenolic gives off water and formaldehyde during cure and has a tendency to be brittle. Ameron modifies the base Cellobond phenolic resin supplied by Borden Chemical Inc. (Louisville, Ky., U.S.A.) by adding siloxane in a proprietary manner, which improves processibility, bond strength and impact resistance of the finished piping.
Fire resistance also is enhanced with the PSX piping's heat barrier design. The pipe incorporates 10 to 12 plies of polypropylene veil tape and glass roving in the outer laminate. The veil vaporizes under extreme jet fire conditions, leaving an air gap in the laminate. This gap works in combination with the phenolic (which chars when it burns) and the glass rovings to create a heat barrier that helps keep the pipe intact.
After heat curing, Ameron's piping is adhesively bonded by fitting the slightly tapered end of the pipe joint into the mating end of the adjacent joint and bonding with PSX-60 two-part polysiloxane-modified epoxy adhesive. For composite-to-metal pipe attachments, Ameron bonds filament-wound flanges onto the pipe that can be bolted to corresponding flanges on the metal pipe.
MORE TOPSIDE INSTALLATIONS
Offshore use of composite gratings, handrails, ladders and other topside hardware has expanded significantly since Petrobras' wide-scale use of gratings in 1994 and the breakthrough installation in 1995 of 215 tons of glass/phenolic grating on Shell's Mars tension leg platform in the Gulf of Mexico. U.S. Coast Guard acceptance of phenolic grating as a Level 2 fire-retardant has opened the door for numerous platform installations that previously weren't possible. (Level 2 areas include those where groups of people would assemble for safe refuge and/or lifeboat embarkation.)
Pultruded products have the highest fiber-to-resin ratio (typically about 70:30) and, therefore, the highest load-bearing capacity with the least deflection. A 38-mm/1.5-inch deep pultruded grating, at one third of the weight of steel, supports more than 4,882 kg/m2 (1,000 lb/ft2) of uniform load over a 1.2m/4 ft clear span. Because pultruded grating has a high fiber content, its surface resin layer is relatively thin, which impacts its corrosion resistance. Molded gratings and parts, on the other hand, have a fiber-to-resin ratio of about 35:65, which provides less strength, but gives greater corrosion resistance than pultruded products. Molded gratings, stairs and railings are especially well-suited to the splash zone, where resistance to seawater corrosion is more critical.
Fiberline Composites A/S (Kolding, Denmark) makes composite topside products, including pultruded gratings, handrails, ladders and stairs, as well as customized products. The company recently completed an installation consisting of over 1,000m2/10,600 ft2 of glass/phenolic gratings that meet USCG Level 2 fire performance (with a minimum glass content of 60 percent) on an Amoco platform in the British sector of the North Sea. The customer specified composites to replace stainless steel, which had corroded in the marine environment. The composite products weighed less than one-third of the steel installation, saving significant topside weight and improving the overall platform balance.
Fiberline also recently installed a 21.8m/71-ft long connection bridge between two platforms in the Danish sector of the North Sea, operated by Maersk Oil and Gas. The 2.3m/7.5-ft high by 1.2m/4-ft wide bridge was assembled from pultruded flat and tubular profiles that were machined and bolted together with stainless steel fasteners at Fiberline's Kolding facility. The 2,000 kg/4,400 lb assembled bridge was barged to the North Sea site and lifted into place with the larger platform's crane — possible only because of the bridge's low weight.
THE "BIG ONE?"
"Topside composite technology is maturing fast," says one oil industry insider. "We're now moving on to higher-risk components like risers which have to withstand subsea conditions." Composites have been envisioned as a breakthrough material for deepwater subsea tubulars ever since initial development of 15,000-psi, 102-mm/4-inch diameter composite choke and kill lines by the Institut Franç1ais du Pétrole (IFP) two decades ago. (Choke and kill lines are auxiliary pipes that are attached to the exterior of the drilling riser pipe, used to control shear rams at the wellhead in the event of a catastrophic blowout.) Yet because of the enormous risk involved, full-scale use of an all-composite riser string or choke and kill lines has never materialized. "Deepwater developments are physically, technically and economically unforgiving as there is no room for failure in any area," notes Turid Storhaug of Deepwater Composites AS, a joint venture of ConocoPhillips, Houston, Texas, U.S.A. and Kvaerner Oilfield Products, KOP, Oslo, Norway.
The hesitancy to use composite tubulars may be changing, based on the success of the CompRiser project, spearheaded by Deepwater Composites. After initial design and development efforts by General Dynamics Advanced Technical Products, Lincoln Operations (formerly Lincoln Composites, Lincoln, Neb., U.S.A.), Spencer Composites Corp. (Sacramento, Calif., U.S.A.) has fabricated several full-scale, high-pressure drilling riser joints that have been successfully field tested in the North Sea.
The CompRiser's layup consists of about 40 alternating, low-angle helical and hoop plies of 12K carbon fiber tow supplied by Grafil Inc. (Sacramento, Calif., U.S.A.), wet out with epoxy resin from Resolution Performance Products (Houston, Texas, U.S.A.) and wound over a thin titanium liner protected with a hydrogenated nitrile rubber coating. (A liner is critical for a drilling riser to avoid damage from tools and other pipes that are placed inside during drilling operations.) The riser's end fittings are massive 24-bolt titanium flanges from Oil States (Aberdeen, Scotland) with traplock (i.e., grooved) flange extensions. Special attention was given to winding over the traplocks to ensure the carbon fibers were locked into the grooves, thus forming a solid composite-to-metal bond, without adhesives. The outer surface of the joint was protected with a layer of rubber as well as fiberglass wet out with epoxy and carbon black filler. Winding of each joint took about five days and consumed approximately 682 kg/1,500 lb of fiber.
The bending stiffness of the composite joint — 195 MNm2/6.79 x 1010 lb-in2 — had to be the equivalent of the titanium drilling joints normally used on the Heidrun Platform, where the field test took place. Minimum design burst pressure was 12,000 psi/827 bar and axial load capacity had to be 1.361 million kg/3 million lb. Risers were inspected ultrasonically, then subjected to impact and bending fatigue loads that simulated a 150-year loading spectrum. Several joints were tested to failure in a burst pressure test. All tests confirmed that the CompRiser performs above its design specifications. The Heidrun operator is so comfortable with the composite joint that it has incorporated the riser into several riser strings used to drill additional wells from the platform.
Since the 2001 Heidrun tests, Spencer has continued to develop other composite tubulars, including choke and kill lines with steel liners. The 165-mm/6.5-inch OD (114-mm/4.5-inch ID), 15,000-psi tubulars are made with the same materials as the larger risers, with traplock composite-to-metal joints and "pin-and-box" end connectors. The company has tentative plans to field test the choke and kill lines on a Petrobras platform off the coast of Brazil.
Spencer is gearing up for commercial production of both risers and choke and kill lines through its spin-off company C4PO (Composites for Producing Oil) and has tentative plans for a manufacturing facility in the Gulf of Mexico coastal region. President Brian Spencer says talks are underway with several oil companies. "We're very close to signing deals on several applications."
IFP has taken an approach similar to Spencer's, and has produced its version of a hybrid choke and kill tubular designed to reduce overall riser weight for deepwater projects. Prototype tubes have been fabricated by Composites Aquitaine (Salaunes, France) with a steel liner, overwrapped with carbon fiber/polyamide (nylon) thermoplastic ribbon and cured on the fly. IFP's Emmanuel Laval says that the thermoplastic overwrap design can accommodate 15,000 psi with a smaller 12-mm /0.5-inch steel liner, rather than a 24-mm/1-inch thick steel liner, which reduces the tubular's weight by 50 percent. The prototypes have been extensively tested in the laboratory and are undergoing field tests initiated in April 2002, on a drill ship in the Gulf of Guinea off the Nigerian coast.
"If you consider a 7,500-ft long, 21-inch diameter drilling riser, outfitted with two 15,000-psi choke and kill lines and a third 5,000-psi booster line, the mass of that riser is approximately 4,800 kips/4.8 million lb-force," says Laval, "Substituting composite choke and kill and booster lines for steel lines reduces the riser mass by 1,000 kips." Another advantage is existing riser strings can be upgraded with higher-pressure composite choke and kill lines without increasing overall weight or top tension.
Other composite riser projects are close to fruition, including ABB Vetco Gray's (Houston, Texas, U.S.A.) drilling riser and a spoolable catenary riser under development in Norway by ABB Offshore Systems (Billingstad, Norway). Another tubular product that's already commercially available is small-diameter bonded spoolable pipe made with carbon fiber, produced by Fiberspar Corp. of West Wareham, Mass., U.S.A. (Risers, spoolable pipe and other products mentioned in the article are examined in detail in Composites in Offshore Oil: A Design and Application Guide.)
Performance Composites' Jerry Williams points out that while composites might be making inroads into the retrofitting of existing platforms, simple material substitution to gain immediate weight savings or corrosion resistance doesn't exploit the full advantages of composites. "If you retrofit, you're not taking advantage of all of the benefits of composites," he explains. "Composites will really come into play in reducing overall platform system costs at the design stage." Given the range of proven composite products now available, platform engineers have significant motivation to design with composites in mind.
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