Alkan's composite materials offer unique alternative to metal alloys for offshore storage
Alkan's composite materials offer unique alternative to metal alloys for offshore storage
The trend of replacing more conventional metal alloys with non-metallic, composite materials of construction continues in the building of shelters and storage units.
The offshore oil and gas industry is faced with dual challenges of pursuing development opportunities in harsh production environments while at the same time decreasing both their production costs and their impact on the environment.
Offshore rigs and vessels rely on resilient and long-lasting shelters and storage containers to protect equipment, inventories and personnel from harsh environmental factors of wind, rain, ocean waves, and temperature extremes. While metal alloys have typically been the construction material of choice due to their cost, strength and availability, there are disadvantages to using them exclusively offshore.
One disadvantage is their vulnerability to the offshore elements. Metallic shelters and storage units often have a limited lifespan due to their susceptibility to corrosion in ocean environments. The relative cost savings of using metallic containers diminishes as corrosion damage leads to repairs or eventual replacement of the container.
Flexibility of storage options is another challenge when implementing metallic constructs. As more deepwater fields are brought into production and tied back to existing platforms, the offshore industry is forced to increase the flexibility of its infrastructure without having to add significant equipment or deck space. Metallic storage modules complicate these issues due to their weight and shape, as in some instances they are too heavy or large to be easily stored or stacked on the existing platform footprint.
Lightweight alternative
Composite shelter company Alkan Shelter LLC has been designing non-metallic alternatives for shelter and storage needs for the past 15 years, for various industries. The company’s alternative to metallic alloys is based on fiber-reinforced epoxy composites, comprised of a bulk matrix and a reinforcement to strengthen that matrix. In particular, they have designed a polymer-based resin matrix with fiber reinforcements to create polymer matrix composites (PMCs) that exhibit different properties from either of the starting materials.
The polymeric epoxy resin matrix has favorable mechanical properties of high electrical insulation and resistance to environmental conditions and chemical attack. The epoxy’s chemical configuration makes it a stiff material, capable of resisting water ingress and temperature extremes. As the polymer matrix sets during the curing process, there is minimal shrinkage (2% versus 8% for polyester matrices). This minimizes internal stress and improves tensile strength, stiffness and resistance to fatigue and degradation.
Embedded within the epoxy matrix, carbon fiber is often present as a reinforcement material.
Alkan reports success with carbon fibers as a reinforcement material after years of research with various fibers, pointing to their high level of specific stiffness and very high tensile and compression strength as being ideally suited for use in performance structures. In addition, carbon fibers possess high resistance to both corrosion and fatigue, and their relatively small diameter and greater fiber surface area help to spread load stresses and impart a high level of strength and stiffness. In fact, carbon fibers possess a strength-per-unit density that is two times that of aluminum and four times that of steel. In other words, one obtains a significantly lighter structural material for the same level of strength as conventional metallic materials.
While the disadvantages of using carbon fibers are few, cost may be prohibitive. In addition, carbon fiber exhibits both low thermal and electrical insulation, but these properties are offset by the more favorable insulative character of the epoxy resin.
This combination of a stiff and stress-resilient epoxy matrix with strong and lightweight carbon reinforcement fibers yields shelters that Alkan says can withstand up to a 215,000-lb vertical load on any given corner. This is achieved with a shelter that weighs only 3,000 to 4,000 lb.
Research reward
Alkan has taken their research to the field by developing a series of rugged, lightweight storage containers based on PMC technology. Their Non-Expandable ISO containers have been used by shipping companies who wanted to update their container fleet without significantly raising maintenance and transport costs. They are now looking to extend the use of these containers to offshore production platforms.
While these new containers provide 8X8X20 cu ft of well-insulated, corrosion and fatigue resistant cargo space, another attractive benefit is that they can be stacked nine-high. Alkan reports that the containers meet both ISO standards and CSC regulations for up to nine-high stacking capability.
The ability to stack containers to this height provides benefits to both vessels, which need to maximize cargo load while keeping transport costs to a minimum, and to offshore facilities, which often possess limited footprints for storage capacity.
Visit Alkan Shelter, LLC at www.alkanshelter.com for more information. •
