Production Technology

Uses for corrosion-resistant, high-pressure, spoolable, carbon-composite line pipe

Operators show that this technology can have benefits – including costs – when installed in areas where jointed pipe would be difficult, or where environmental and corrosion effects are a concern

David Poshard, Hydril Advanced Composites, Houston

Operators must continuously seek new ways to reduce costs and risks, and improve safety and operating efficiencies. Conventional thinking and products are not always the best solution. Corrosion-resistant jointed pipe has been widely used for decades in various product configurations such as coated steel, wrapped steel, lined steel, fiberglass, plastic, CRA's, etc. Joints not only increase installation costs and reduce operating efficiencies, but they also increase long-term risks and man-hours, therefore reducing safety.

A new alternative is Spoolable Carbon Composite (SCC). SCC has been used successfully in many line-pipe applications since 1999. These applications primarily include crude and gas production lines, injection lines and supercritical CO 2 injection. Several techniques have been used to install SCC. These include conventional trench and backfill, inserting/ relining steel (pulling with a wire line), plowing, or lying above ground.

SCC is available in 15,000-ft. lengths, pressure ratings to 7,500 psig and diameters up to a 4.5-in. ID. Since SCC is available in long lengths, once the pipe is in place, the only joints to put together are the end connections. These are installed by a certified installer. Primary end connections include ANSI flanges, 8-round or NPT threads.

SCC line pipe uses a three-element design. The outer surface consists of a damage-resistant layer and is not part of the pressure design. An intra-laminar hybrid laminate provides the structural strength. This laminate comprises carbon and glass fibers in an enhanced, amine-cured epoxy-resin system. An inner thermoplastic liner serves as a pressure barrier, but is not used in the pressure-related structural design. The internal liner selection is determined by operating conditions. The liner can be any round, extruded plastic. High density polyethylene (HDPE) is widely used and is inexpensive. HDPE is ideal for water lines and other fluids up to 140°F. A relatively new product on the market is a crosslinked HDPE called XLPE or PEX, which is suitable for fluids and gases up to 200°F.

SCC offers advantages over conventional line pipe:

1. Up to 95% fewer connections per mile
2. Installation in up to 75% less time
3. Higher pressure ratings
4. Greater impact resistance
5. Bending radius similar to HDPE
6. Internal and external corrosion resistance
7. Longer life than glass products.

The following case studies illustrate the unique characteristics of spoolable carbon composites.

EXAMPLE 1: WESTERN US

In June 2000, ChevronTexaco was forced to replace production lines in a remote area. The rocky terrain was not friendly for heavy equipment, and the blasting and trenching were very expensive. Steel lines, which had been run on the surface, had begun to develop leaks, and fluids were running into drainages.

The operator decided to replace the steel in these areas with a corrosion-resistant product. After reviewing various options, engineers decided that SCC would solve their problem. Two and three-inch SCC was selected to replace the existing steel lines in environmentally sensitive areas. According to Chevron-Texaco engineers, “Because of the carbon fiber construction in SCC, the pipe can be operated above ground with minimal concerns about damage from external sources. Laying extreme amounts of SCC line pipe while using only a two-man crew the majority of the time is a normal operating procedure. A backhoe was needed only to string out pipe, which took a few hours at the most, Fig. 1. The only time a welder was needed was to connect the Hydril pipe to the steel flowline, which took an hour. In a lot of cases, SCC was flanged in the yard, placed on a trailer and delivered to location by a gang truck, eliminating the need for a backhoe.”

Fig. 1. Replacing a leaking steel flowline with SCC.

EXAMPLE 2: ALBERTA, CANADA

By January 2002, ConocoPhillips had several corroded steel production lines that were failing. Due to the cost of paying the land owner for surface damages, it did not want to cut a ditch. By selecting 18,000 ft of 3-in. SCC, a wireline could be used to pull the pipe through the existing steel and solve the corrosion problem, Fig. 2. This procedure eliminated surface and environmental damage.

Fig. 2. Installing SCC within existing pipe in Canada.

According to ConocoPhillips, “Insertion of SCC pipe saved on damage costs, eliminated the need for a corrosion inhibition system, allowed for a larger ID because of the lack of couplings, and provided for a longer life.”

EXAMPLE 3: ALBERTA, CANADA

In June 2000, Husky faced the challenge of installing multiple production lines at the lowest possible cost. Using a large plow, SCC was installed at a rate of 13,100 ft/hr, Fig. 3. According to Montgomery McNeil, eroduction engineer with Husky, “SCC's installation costs were similar to that of HDPE flow lines, offered similar corrosion resistance, yet provided sufficient pressure containment (comparable to steel) that stand-alone HDPE flow lines could not.”

Fig. 3. Using a large plow to install two SCC flowlines simultaneously.

SUMMARY

SCC is a new technology that is being installed in areas where installation of jointed pipe would be extremely difficult. The long lengths make it a unique product that may not be ideal for all line pipe applications. However, SCC offers distinct advantages for installations in remote/ challenging areas, environmentally sensitive areas, projects that require short installation windows, low-budget areas and corrosion-plagued systems.