Composite pipes design procedure

If a thermoplastic composite pipe is pressurized rmder laboratory conditions (with the pipe ends freely moving) the stress/strain in the two principal, axial (ej and hoop ( y), directions exhibit a behavior schematically illustrated in Figure 1. Three aspects of this response, namely (1) the initial stiffness of the pipe associated with the slopes and Sy (2) nonlinearity in the cr/e response and (3) the ultimate failure of the pipe corresponding to the burst pressure, are rationalized by means of micro- and macromechanical modelling. These types of modelling of the short term structural response are the initial steps in the overall design procedure. 

This chapter outlined varions applications of FRP in relation to pipes and risers, and those relevant to the petrochemical and oil and gas industries. It introduced various hybrid applications of FRP and its hybrid, such as the steel strip laminate pipe (SSLP) technology and the composite reinforced line pipe (CRLP) technology, and sandwich pipes as well as their pertinent design procedures. The issues affecting the long-term performance of these materials, as well as the issues involved in joining them, were also discussed. 

The procedure described above is straightforward in principle. However, in practice, great care must be taken in the test fixture design to assnre that applied loads cause a uniform state of stress in the test specimen. Two types of tests that have been developed for this purpose include (1) the simple tensile test for uniaxial states of stress, (2) the thin-walled tube subjected to combined torsion and internal pressure, for biaxial states of stress. Some theoretical aspects of the simple tensile test are developed in the sample problem which follows. For a more detailed discussion on experimental procedures for characterizing the material properties of composite materials, see Caisson and Pipes and Whitney et al. ... 

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