Consideration of The Minimum Bending Radius of Fiberglass TCP Pipe
Thermoplastic composite pipe(CFTCP/RTP) structure comes up with inner and outer thermoplastic layers, flexible bonded structure with fiberglass or carbon fiber as reinforcement material. In order to let clients better know the TCP better, this article will concentrate on minimum bending radius and brief suggestions for TCP coiler design.
Since we already shared the article regarding the TCP structure, which is bonded structure of the inner layer, reinforcement layer, and outer layer. Since TCP is fully bonded type of composite pipe, which means it is not a flexible enough pipe, in other words, it is a strong reinforcement pipe. When deformation situation happens, the TCP bears the axis direction strain of the pipe rather than the strain in the fibre direction. It is because the fiberglass tapes were wrapped on the liner pipe, the bending is the axial bending other than direct bending( to be simple of this, it is Twisted Bending). It means the strain of fibre direction is different, which depends on the direction of the fibre – reinforcement layer direction. Therefore it is not hard to think that the design of the thermoplastic composite pipe can impact the minimum bending radius. If the composite pipe bending radius lower than the MBR limit, there will be damage to the fiberglass reinforcement layer.
The fibre usually layup with the TCP axial direction, and combined with the hoop direction of the fibre. In order to meet the pressure balance of the fibre orientation. The fiber orientation alternates with the axial direction at +55 and -55 degrees angle. The bending stiffness of the matrix material affects thermoplastic composite pipe (TCP) bending stiffness, for example, the stiffness of fiberglass tape is based on the tape other than each single fibre wire. The thermoplastic polymers lead to the lower bending stiffness of CFTCP/RTP.
The delamination of the TCP pipe layers caused, since large bending strains’ tensile stress. As research, the minimum bending radius is at least 14 times the TCP outer diameter, which means it shall be higher than 14 times.
For the raisers, the axial direction is directed. Since the raiser is usually used for oil transfer, therefore, the pulling load is quite great, which leads to larger strains in the fibre direction. Therefore, fibre failure is one of the most important parts that need to consider while designing thermoplastic composite pipe (TCP). As our research, the tensile strength of the fibre is about twice the compressive strength, so, the failure of the fiber in compression becomes the key failure mechanism in bending.
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