FIBER GLASS PIPE EFFECTIVE FOR OFFSHORE WATER HANDLING

Stephen P. Turnipseed
Chevron Research & Technology Co.,
Richmond, Calif.

Excellent corrosion resistance, weight savings, ease of construction, and reduced maintenance make fiber glass pipe attractive for water-handling service on offshore platforms.

This article covers guidelines for fiber glass pipe installations and presents a number of case histories from the industry and Chevron Corp.

FIBER GLASS PIPE

The oil and gas industry has widely installed fiber glass piping in low-pressure, nonhazardous services. Fiber glass is attractive because it provides superior saltwater corrosion resistance, reduced maintenance costs relative to carbon steel systems, and lower capital costs relative to alloy systems.

Typical fiber glass pipe applications include:

Seawater treating lines
Supply lines for water injection systems
Seawater cooling lines
Fire water systems
Produced water systems
Potable water systems
Sewage and drain lines.

To ensure reliable performance, the piping design must provide adequate support and minimize the risks of water hammer and mechanical damage. Piping must be installed by a contractor experienced with fiber glass. A manufacturer's representative should be on site at the beginning of the job to provide training and ensure that the work is being done correctly.

In appropriate services, fiber glass can provide superior corrosion resistance, improved reliability, and reduced maintenance costs relative to carbon steel systems, and lower capital cost relative to alloy systems.

Low-pressure, saltwater piping is one of the main offshore fiber glass pipe applications. Alternatives to fiber glass for saltwater service include bare carbon steel, steel lined with cement or polypropylene, and stainless and copper-nickel alloys.

Unlined carbon steel is an option only if the salt water is stagnant. In flowing, aerated seawater, steel will rapidly corrode.

Alloys such as 6-Mo stainless steel (such as AL-6XN) and 90-10 CuNi will resist flowing salt water but are generally more expensive than a fiber glass system.

SERVICE ENVIRONMENT

Fiber glass piping offshore typically transports water and brine at operating temperatures below 200 F. (95 C.) and pressures below 300 psi (2 Newton/sq m). From a corrosion viewpoint, fiber glass is an excellent choice in salt-water because it will not corrode and it is resistant to marine growth.

Offshore applications include both epoxy and vinyl ester fiber glass pipe. Epoxy resins are common in fire water and potable water systems. Generally, epoxy resin is stronger than vinyl ester but has less chemical resistance.

Epoxy resins are acceptable in services with less than 50 ppm chlorine and/or hypochlorite. Vinyl esters are used in services where chlorine and/or hypochlorite levels exceed 50 ppm, such as seawater treatment piping

and water injection supply lines. Both vinyl ester and epoxy resins provide external corrosion resistance to humid, salt air.

Fiber glass pipe is sometimes manufactured with a resin-rich liner to improve chemical, erosion, and temperature resistance. For the Takula water injection platform in Cabinda, Angola, an epoxy fiber glass pipe with a 20-mil (500-u) internal resin-rich liner was specified. While not essential, the liner provides chemical resistance to occasional upsets in the hypochlorite levels and erosion resistance to sand and particulate matter.

UV (ultraviolet) stabilizers are recommended to prevent accelerated degradation of the resin from sunlight. As an alternative, conventional coatings may be applied to the pipe after the installation.

COST

Considering both materials and installation costs, fiber glass piping systems are often cost competitive with carbon steel systems. Material costs for fiber glass are competitive with coated steels and alloys, while installation costs are generally much lower. Fiber glass systems also offer the advantage of low maintenance costs.

Overall, fiber glass pipe is most economical in small sizes and offers some initial cost savings up to 12 in. OD. Chevron in Hobbs, N.M., found that fiber glass pipe costs less than cement-lined pipe in the 4-10 in. range. A study showed that the total materials and installation cost of 4 and 12 in. OD fiber glass systems was less than T-304L or T-316L stainless steel.2

Because larger fittings increase cost and installation time is longer, cost savings were less for the larger pipe sizes.

APPLICATIONS

Applications where Chevron and the industry have used fiber glass pipe on offshore platforms include seawater treating and water injection systems, drain systems, and firewater systems. Fiber glass is also used in seawater cooling, produced water, and potable water Systems.

SEAWATER TREATMENT

Generally, the industry reports good experience with FRP (fiber glass-reinforced plastic) pipe in seawater treatment plants and as supply lines for water injection systems. Fiber glass offers the advantages of relatively low cost, light weight, and excellent resistance to saltwater. Typically, FRP pipe sizes for these applications range from 2 to 30 in.

In 1974, Dubai Petroleum Co. along with five other companies, specified fiber glass piping for a joint seawater treatment unit in the Arabian Gulf. The unit filters saltwater through gravel and sand beds in a series of nine 15-ft diameter vessels.

Over 4,000 It of fiber glass pipe, up to 16 in. OD, along with fiber glass fittings, were installed. To withstand saltwater corrosion and the humid coastal atmosphere, Dubai chose fiber glass pipe

with a vinyl ester resin. The fiber glass piping has required minimum maintenance and repair.

Fiber glass pipe has performed reliably since 1984 in a seawater treatment plant in Prudhoe Bay, Alaska. Arco Alaska Inc.'s plant, which was constructed on a 610-ft barge, required 53,700 ft of 1-18 in. OD fiber glass pipe and 16,500 fittings. Three epoxy resin fiber glass products from one manufacturer were used: two unlined and one resin-lined.

WAR INJECTION

Chevron (CUSA) used epoxy resin FRP piping for a water-injection system on the GI-37 Yankee, a platform built in 1965. The GI-37 Yankee may be the oldest water injection platform in the Gulf of Mexico. The FRP piping, which was up to 12 in. OD, operated at a maximum pressure of 150 psi.

CUSA reported problems with weeping from pipe walls just downstream of the lift pump; however, the leaks were repaired successfully with a "stamp-type" patch. Overall, FRP performed well enough that it was used again when the system was redesigned to increase volume capacity.

In the late 1980s, Chevron installed epoxy-resin fiber glass pipe for low-pressure, aerated saltwater piping on the Takula water injection platform, offshore Cabinda. FRP pipe, with a 20-mil resin-rich liner provided extra chemical resistance. Epoxy resin was acceptable for this service because the design hypochlorite level was low (2-5 ppm). Epoxy resin is also less expensive than the vinyl ester alternative.

SEWAGE AND DRAINS

Fiber glass pipe has been used as a replacement for carbon steel in seawater services and open nonhazardous drain systems. Because of corrosion and plugging, steel drain systems are high maintenance. The drains plug when foreign objects get snagged on the rough, corroded metal surfaces. Fiber glass pipe solves both the corrosion and plugging problems.

DELUGE FIRE WATER

The industry commonly uses deluge systems on wellheads and process areas of offshore platforms. Typically, most of the piping in these systems is dry. Dry piping is generally small, about 2 in., with pipe sizes ranging up to 8 in. When a fire is detected, deluge valves open to flood the dry piping and pour water through the sprinklers.

Dry deluge piping has traditionally been constructed from bare steel. Because the systems often use salt water, steel piping corrodes at high rates, particularly if it does not drain well. The thinned pipe must be replaced every few years.

An even bigger problem with steel deluge systems is plugging. Corrosion products plug nozzles and sprinkler heads, leaving fire water Systems inoperable.

By eliminating corrosion and plugging problems, fiber glass piping reduces maintenance costs and improves fire water system reliability. Chevron has plans to use fiber glass piping for two deluge systems on two new deepwater platforms offshore West Africa.

The design of a fiber glass deluge system should address two issues: the potential for water hammer and the need for fireproofing.

The piping design and support system should minimize the impact of water hammer from pressure surges, such as opening deluge valves. Fireproofing is also an important consideration for both dry and wet systems. If the piping is dry, fiber glass manufacturers recommend fireproofing on both the pipe and fittings. Wet piping needs fireproofing only on the fittings.

HOSE PEEL FIRE WATER

Hose reel systems are "wet" when the piping is continuously filled with seawater. Branching off of the main piping are runs that lead to heavy-duty rubber hoses with large nozzles.

In 1992, Chevron retrofitted manual hose reel systems with fiber glass piping on two Gulf of Mexico platforms. Chevron's EI-361 A platform (Fig. 1)

in the Gulf of Mexico is one of the platforms retrofitted with fiber glass fire water piping. Although some companies use fiber glass piping for an entire hose reel system, in these two cases Chevron used fiber glass only below deck where puncture resistance was not critical. Above deck, galvanized steel was used for about 3 ft of piping to the hose reel connection (Fig. 2).

SEAWATER COOLING

FRP is sometimes used in piping to and from seawater cooled heat exchangers. Chevron has had good experience with FRP in this service.

Since 1980, FRP saltwater piping has been installed on five offshore California platforms: Gail, Grace, Edith, Hermosa, and Hidalgo.

PRODUCED WATER

FRP works well in produced water service because it is resistant to corrosive H2S and CO2 in the water.

Onshore, the industry has installed FRP to handle produced water for about 20 years. Offshore, FRP is used for transporting produced water from separators to drains in several locations, including The Netherlands.

POTABLE WATER

An oil industry survey indicated that many offshore platforms use fiber glass for potable water systems. Field operators reported good experience with fiber glass in this service.

Several fiber glass manufacturers have products that are approved by NSF, (National Sanitation Foundation), for use in potable systems. NSF addresses health and safety issues with FRP, but NSF-certified resins are rarely requested.

USAGE GUIDELINES

For offshore applications, one manufacturer recommends a filament-wound fiber glass-reinforced epoxy pipe with a nominal 0.020-in. resin-rich liner. Internal pressure ratings, using a cyclic test, range from 165 to 450 psi 0.1 to 3.1 Newton/sq m), depending on pipe sizes.

These ratings are valid for sustained use up to 200 F. (93 C.). At higher temperatures, up to 250 F. (120 C.), the pipe may be used at lower pressures.

This manufacturer supplies piping up to 16 in. OD as a standard item, and up to 42 in. OD with longer lead times. In most cases, pipe dimensions conform to iron pipe sizes for 1-36 in. ODs and to marine cast iron ODs for 14-42 in. sizes. Standard pipe lengths are 10, 20, 30, or 40 It, depending on the pipe OD.

Another manufacturer supplies two epoxy fiber glass products for small diameter, less than 16 in. OD, piping. One of these products is an unlined, filament-wound epoxy fiber glass pipe. It has a cyclic pressure rating up to 300 psi and a maximum operating temperature of 210 F. Pipe and fittings are available in 2-16 in. ODs.

Another product is an epoxy fiber glass pipe with an epoxy liner for improved chemical resistance. This pipe is designed for pressures up to 300 psi, and temperatures up to 225 F. and comes in standard sizes from I to 16 in. OD.

Fittings from different manufacturers' piping are generally not interchangeable. One manufacturer supplies 1-16 in. sizes with adhesive-bonded bell and spigot joints. The design features a pipe stop inside the bell and a 0.5 taper on the bell, which centers the pipe. A competing product has tapered bell and spigot joints for 8-16 in. sizes and threaded and bonded joints for 2-6 in. OD. The taper angle varies from 1 to 2, depending on the pipe size.

Fig. 3

shows fiber glass pipe joints before being installed in a fire water system.

JOINTS

Joining is a critical step of FRP pipe installation. Adhesively bonded joints must be assembled correctly or they will leak.

Chevron reported that vibration on a water injection platform caused FRP joint failures just downstream of the seawater lift pump and just upstream of the injection pump at elbows and tees. An FRP firewater system on Chevron's SMI-78 platform also had leaking FRP joints.

For successful installation, one should have a contractor experienced with FRP and have a manufacturer's representative available on site to provide training. The contractor should practice on several joints before starting the job. The contract should include a guarantee clause in case of problems and the FRP piping should be hydrotested following installation.

FREEZE CRACKS

A fiber glass system should be designed to prevent water from freezing inside the pipe and cracking it.

On Chevron's Main Pass platforms, 0.5-in. bell valves were installed at each dead end in the hose reel systems to maintain a constant flow through the fiber glass piping. In the event that generator power was lost, valves were also installed at low points in the piping to drain stagnant water.

UV DEGRADATION

Fiber glass is susceptible to ultraviolet degradation after long-term exposure to sunlight. Over time, the resin at the pipe surface breaks down, exposing glass fibers. Adding stabilizers to the resin will enhance the pipe's UV resistance, but manufacturers do not always add stabilizers unless it is specified. Coating fiber glass pipe will also prevent LN damage.

In rare circumstances, an external coating may be recommended for fiber glass pipe. One manufacturer advises coating its 2-3 in. pipe in two cases: if the pipe is left empty for extended periods of time or if the fluid inside the pipe operates at a temperature greater than 120 F.

External coating is not essential for other sizes of the same product line or the company's other products.

MECHANICAL DAMAGE

Fiber glass should only be used in areas where the risk of mechanical damage is low. A review of FRP line pipe in oil and gas production found that mechanical damage was the main cause of FRP failures.

To minimize this risk, one should prepare handling and installation procedures for all field jobs and adequately support aboveground pipe. In locations where the FRP contacts steel, such as at supports or flat bar brackets, the FRP should be protected with an abrasion-resistant material.

Water hammer is another consideration for designing a fiber glass pipe system. If necessary, pressure surges can be minimized by installing surge tanks and using valves that open and close slowly. Expansion joints placed in longer runs and anchor piping at each change in direction can be included if pressure surges are sufficient to flex the pipe.

SUPPORT SYSTEMS

In general, the manufacturer's recommendations should be followed for support design and spacing." A few basic guidelines are outlined below:

Provide circumferential support

A support cradle should provide 180 of circumferential support. Although a 120 design has been used, it does not fully alleviate bending stresses.

To provide adequate support, the cradle must closely match the OD of the pipe. Because FRP pipe sizes are based on a standard inside diameter, pipe ODs will vary depending on the thickness of a liner, (if present), and the structural wall thickness.

The ODs do not necessarily meet iron pipe size standards. Manufacturers state that in many cases standard steel pipe supports can be used with FRP pipe, if they meet other design requirements.

Use adequate support dimensions

The support must be long enough to avoid point loading and to resist lateral loads and bending. Supports not meeting the manufacturer's specified minimum dimensions should be supplemented with a protective sleeve.

Protect against mechanical damage

An abrasion-resistant material should be placed between the pipe and the metal support. Recommended materials include FRP saddles and elastomeric liners, such as rubber or neoprene.

In noncorrosive environments, galvanized sheet metal may be bonded or banded to the pipe. FRP saddles are bonded directly to the pipe, while elastomeric materials may be bonded or held by the force of the support.

Valves and heavy equipment should be independently supported from the FRP pipe in both vertical and horizontal installations. The support should be designed to withstand the maximum design load of the pipe without significant deflection and provide adequate support for vertical piping runs.

FIREPROOFING

Based on fire tests, fiber glass manufacturers strongly recommend fireproofing some or all of a fiber glass piping system.

If the system is dry, both the pipe and fittings should have fireproofing. Wet systems need fireproofing only around the fittings, where leaks are most likely.

Tests showed that dry fiber glass pipe, without fireproofing, leaked after 6-7 min at a furnace temperature of 1,800 F. (980 C.).9 If the leaks did not relieve the internal pressure buildup, the pipe exploded. However, under flowing conditions, bare pipes weeped at low rates but survived the 5-hr tests.

Special epoxy coatings are sometimes used for fireproofing fiber glass pipe. The coatings will swell during a fire, forming a hard material that insulates the substrate and delays structural damage. Two common products are a high-build, single-application coating and a mesh-reinforced coating. Both meet the requirements of Underwriters' Laboratories 1709 rapid temperature rise fire test.

One manufacturer has developed a method of preapplying a fireproofing to fiber glass pipe and fittings at the factory. The coated pipe costs

about 2.5 times as much as the uncoated pipe.

In a dry system, this product can withstand at least 10 min of exposure to 2,000 F. (1,090 C.), while in a wet system under full-flow conditions it will remain functional for at least 3 hr.

Laboratory tests have shown that 5-8 mm of this fireproofing is sufficient to obtain these results. The same manufacturer also sells a molded half-shell fireproofing cover for flanges.

Fiber glass pipe with preapplied fireproofing has been purchased for dry deluge firewater systems on two offshore platforms: Amoco Trinidad Oil Co.'s Immortelle field offshore Trinidad and Arco China Inc.'s Yacheng 131 gas field offshore China.

The Intmortelle started operating in 1993. The Arco project is in the construction phase with production slated to start in late 1995. In both cases, because the systems are dry, fire protection was specified for both piping and fittings.

INSTALLED SYSTEMS

Chevron has used fiber glass piping in the firewater systems in both the Gulf of Mexico and offshore Angola. In the Gulf of Mexico, the fiber glass piping was installed during system retrofits. But in Angola the piping was placed on new platforms.

MP-133 C

Almost all of Chevron's platforms in the Gulf of Mexico have wet firewater systems with carbon steel piping. Some deluge systems have been tried, but problems with water delivery when needed prompted a return to traditional designs.

Carbon steel piping is widely known to suffer from severe internal corrosion because of continuous flow of oxygenated seawater. Systems are designed to minimize the length of the wet loop and maximize the length of deadleg runs. Partial replacement of pipe is made on an as-needed basis.

The Main Pass 133 C platform required a total fire water piping replacement. The carbon steel lines had been severely restricted with corrosion by-product. The deposits caused unacceptable pressure drops in the wet firewater system. Delivery of required flow rates to the hoses became impossible.

After thoroughly researching the available pipe material alternatives, fiber glass was selected for the project. The retrofit was completed in 1993 and declared a success.

Because this was Chevron's first use of fiber glass pipe in offshore service, a number of precautions were taken. The joints and fittings were insulated with calcium silicate to provide extra protection during a fire (Fig. 4).

After installation, a coat of paint was applied to the pipe for protection against ultraviolet degradation.

During winter, freezing temperatures can be encountered. The flow loop was designed to keep water moving through as much of it as possible. Ball valves were also installed at the ends of the hoses and all dead-legs to allow an operator to keep water moving in all parts of the system during cold periods.

Valves such as the steel control valve in Fig. 5

were independently supported.

The ease of handling fiber glass pipe more than compensated for the extra material cost. The lightweight material made movement of pipe from the boat to and around the platform easier and safer. Consequently, installation went much faster than would have been possible with carbon steel. The engineer in charge of the project now recommends fiber glass pipe as the "material of choice" for water-handling services on offshore platforms.

EI-381 A

Eugene Island-361 A was another Chevron project on which the firewater system was retrofitted with fiber glass pipe.

Based on the experiences gained with MP-133 C, confidence was higher in the capabilities of fiber glass. No thermal insulation was used on the joints or couplings. No paint was used to protect against UV degradation.

Fig. 6

shows how one of the steel valves in the fiber glass piping was independently supported on the platform. On EI-361 A, to minimize pipe length with no flow, distances between the hose reel and main piping were kept short (Fig. 7).

NEMBA AND LOMBA

Two new deep-water platforms being designed for offshore West Africa call for a deluge firewater system with fiber glass pipe.

The South Nemba platform will be an eight-leg manned structure in 386 If of water. Lomba will be a four-leg "minimum facilities" production platform in 425 It of water. Launch dates are scheduled for 1997.

An intumescent (swelling and charring when exposed to flames) fire protective coating will be used on all nonmetallic surfaces in dry fire water systems, downstream of the deluge valves. Only joints, fittings, and flanges will receive fire protection in the wet firewater systems.

Fire protection for flanges includes molded intumescent-coated, half-shell covers. No conventional coating will be used for preventing UV damage.

ACKNOWLEDGMENTS

The bulk of this article is a summary of a Dec. 31, 1993, report by W.S. Putnam.10 Details of the case histories were provided by R.B. Atkinson, J.E. Price, N. Nielson, and P.K. Myint.

REFERENCES

1. Slining, J.R., and Niccolls, E.H., "Oilfield Fiberglass Technology Development," Chevron internal report, Feb 3,1989, P 16.

2. Britt, F., "Stainless Steel vs. Fiber glass Pipe," Chemical Engineering, February 1990.

3. Ciaraldi, S.W., Alkire, J.D., and Huntoon, G.G., "Fiber glass Fire water Systems for Offshore Platforms," Paper No. OTC 6926, 24th Annual Offshore Technology Conference, Houston, May 4 7, 1992.

4. Williams,J.G,,"Oil Industry Experiences with Fiber glass Components," Paper No. OTC 5380, 19th Annual Offshore Technology Conference, Houston, Apr. 27-30,1987.

5. Chiu, A.S., and Franco, R.J., "FRP Linepipe for Oil and Gas Production," Paper No. 232, NACE Corrosion 89 Conference in New Orleans, Apr. 17-21, 1989.

6. Engineering and Design Guide, Manual No. E5000, Smith Fiber glass Products Inc., 1992.

7. Bondstrand Engineering, Guide for Suspended Pipe, Ameron, 1992.

8. Britt, W.F., "Providing, Proper Supports for Reinforced Thermoset and Non-Reinforced Thermoplastic Process Pipe," Paper No. 92, NACE Corrosion 83 Conference, Anaheim, Calif., Apr. 18-22,1983.

9. Anderson, E.L., and Wenzel, A.B. "SWRI Project No. 01-2602-407 Final Report," Feb. 7,1989, F. 3.

10. Putnam, W.S., Use of Low-Pressure Fiber glass Piping on Off shore Platforms, Chevron internal report, Dec. 31, 1993.