ABS Releases Guidelines for Composite Materials

ABS' release today at OTC of its guidelines for the use of composite materials on offshore structures is expected to facilitate industry consideration of alternatives to costly steel in the development of mooring systems and risers, says Ernesto Valenzuela, Offshore Technology Development Manager, ABS.

"It is no longer a question of if but when composite materials will take their first starring role in production from a deepwater hydrocarbon reservoir," said Valenzuela. "We have brought a comprehensive set of criteria to operators wanting to apply fiber reinforced plastics (FRPs) to their projects."

Valenzuela explains that the ABS Guide for Certification of FRP Hydrocarbon Production Piping Systems provides technical guidance and design procedures for using composites or FRPs on the topsides of offshore facilities.

As projects become more complex and move into deeper waters, the topsides become heavier, the steel mooring systems and risers become longer and heavier, thus presenting serious challenges to project economics, says Valenzuela.

"These challenges have spurred research into substitute materials that would do the job of steel, but at much lighter weights. Once thought of as an exotic material, composites and FRPs are gaining acceptance among operators," said Valenzuela.

ABS plans to unveil its composite guidance in three stages: first, release of criteria for FRP in topside applications; secondly, criteria for carbon-fiber composite riser piping and joint application and; thirdly, criteria for composites in cryogenic piping applications.

The move to synthetic mooring lines during the past decade has been key in making some recent deepwater projects possible and the offshore industry's first step away from steel and into alternate materials.

The use of composites, specifically carbon-fiber materials replacing steel in production and drilling risers, and in the tendons of tension-leg platforms (TLPs), is the next step.

"Anticipating this need, ABS' guide will help industry. It applies practical experience to topside design while we continue research and development to better understand the nature of composite materials in more technically demanding applications," said Valenzuela.

The ABS issued Guide for Certification of FRP Hydrocarbon Production Piping Systems is the first publication of its kind from a classification society and is expected to become the primary source of composite guidance available to the offshore industry. Along with its class criteria, ABS references criteria available from other organizations such as the American Society for Testing and Materials (ASTM) and the United States Coast Guard (USCG).

Advantages of carbon-fiber composites over the basic production material of steel includes: higher strength-to-weight ratios, superior fatigue performance and corrosion resistance and better thermal insulation. Another advantage is a high structural damping characteristic that makes composite risers (or tendons) immune to vortex-induced vibration, a cause of severe fatigue damage to steel structures.

Although weight is only one component in the complex considerations that make up an offshore production solution, weight reduction is among the most attractive benefits of composites.

"With less buoyancy expended on mooring systems or risers, loads can be increased; more riser joints can be stored on the rig and fitted through a smaller rotary table; or a rig could carry extra casing, mud or chemicals," said Valenzuela.

The ABS guide addressing the use of composites for risers is nearing completion. ABS researchers note that the vertical orientation of the piping from the seafloor to the floating structure requires detailed analysis of the longitudinal and transverse strength of the piping to verify that it can withstand the pressures.

With regard to its work with cryogenic piping, ABS sees composites having very attractive thermal properties which can make them ideal candidates for cryogenic piping. With that, ABS anticipates heightened interest for composite applications on liquefied natural gas (LNG) systems.