In the Energy Industry, there are two distinct manufacturing processes of composite pipe; Filament Wound and Rotary Casting. Similarities are fiberglass strands or other material that can be wrapped around or in a mold to create strong tubulars and engineered with characteristics that overcome weaknesses in metals. These strands are then encased in a resin or epoxy solution that binds the strengthening material into a unified, fit for purpose tubular.
A LOT OF GRE GOES A LONG WAY
GRE pipe has a lot of uses in the Energy industry including miles of pipeline
Filament Wound and Rotary Casting are the two manufacturing processes of today's GRE pipe
The Energy Industry has adopted composite pipe into applications where metals corrode or where lightweight is required. These composite tubulars are well known and referred to as Glass Reinforced Epoxy (GRE).
The differences in manufacturing methods are critical to the strength profile the composite pipe will have. Inclusions of trapped air are the weak link to consider when strength is required.
MAKING COMPOSITE PIPE: FILAMENT WINDING METHOD
Filament winding is the process of passing fiber strands through a resin bath and then winding them under tension onto a rotating mandrel. Once the material is wound it is heated in the oven to cure it. This process is the most common method of producing composite pipe. The process can be used to create composite pipe out of different materials.
The benefits of filament winding are:
1. It's a fast method and therefore economical
2. Resin content can be controlled by metering the resin onto each fiber tow through nips or dies
3. Cost of fiber is minimized as there is no need for a secondary process to convert fiber into fabric prior to use
4. It produces a material composed of straight fibers which can be laid in a complex pattern to match applied loads
5. Filament wound composite pipes are also corrosion resistant, chemical resistant, abrasion resistant, and have a low weight to strength ratio
6. The method allows reinforcement to be placed in areas that will incur the most stress such as collars which are generally a weak point
7. The dual helical winding process can produce more durable pipes.
Disadvantages of this method of producing composite pipe are:
1. The process can only produce convex shaped components
2. It's not easy to lay the fiber exactly along the length of a component
3. Mandrel costs can be high
4. The external surface is not cosmetically attractive
5. Mechanical and health and safety properties are reduced as low viscosity resins usually need to be used with their attendant
6. Air and moisture inclusions can amount to a large portion of the total volume of the resin component of the pipe, this degrades the strength and penetration resistance of the pipe.
Overall this method is fairly low cost and allows for extra strength to be placed in areas that require it, however the main drawback is that the end product will never be as strong as it can be and will degrade with time due to the angle of the fibers with the pipe and because of the inclusion of air bubbles in the resin.
MAKING COMPOSITE PIPE: ROTARY CASTING METHOD
The rotary casting method, rotational molding or rotocast, is a process for producing items which are hollow, like composite pipes. The basic method involves filling a mold with a polymer, heating the tool in order to melt the material, cooling and removing the article.
Advantages of this method for creating composite pipe include:
1. The fibres can be orientated is any combination of directions
2. Molds are inexpensive
3. Manufacturing lead time is relatively short
4. All humidity and air voids can be eliminated
5. Overall it produces pipes with good mechanical and aesthetic properties.
Drawbacks of this method include:
1. Long manufacturing times
2. Material costs can be high
3. Machines are complex and relatively expensive
Overall rotational casting produces strong material that is aesthetically pleasing. The Energy Industry optimistically looks to this method for breakthroughs in increased tensile strength and tensile moduli.
AKIET'S USE OF ROTATIONAL CASTING
Akiet is a company who produce composite tubulars via the rotational casting process. They have refined the process to enable them to have greater control of the manufacturing process. They produce pipes with a constant inner and outer diameter, with maximum drift diameter and extra wear resistance. Akiet manufacture a product called HSCT (High Strength Composite Tubulars). This material is made from fiberglass and epoxy, which was recently used to break the world record depth in the deepest composite casing application. The use of Akiet HSCT will extend the reach of horizontal drilling. HSCT piping is near buoyant in drilling mud, enabling the string to float out to very long horizontal sections. HSCT is 80% lighter than steel assisting drillers with much lighter hook loads and the ability to use smaller rigs. The geothermal energy industry will benefit from its use as well in the battle against corrosion.