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GRP Pipe Modeling

The FRP pipes are composite materials produced from fiber glass reinforcement filaments and thermosetting plastic resins. The mechanical behaviors of these orthotropic pipes are different from ordinary isotropic metallic ones. Their properties depend on the direction in which they are measured; accordingly, two different kinds of ultimate stresses, elasticity modulus and Poisson’s ratios are defined in axial and hoop direction. Therefore, for evaluation of calculated stresses in FRP pipes, common stress failure theorem such as maximum shear stress or energy distortion theory would be useless.


Because lack of knowledge for stress analysis of anisotropic materials, the mechanical behavior of FRP pipes and failure modes are complex and hard to be understood; hence, most of manufacturers prefer to implement a variety of extensive stress testing on their components, such as hydrostatic and cyclic pressure, uniaxial tensile and compressive, bending, and combined loading tests. In some codes and standards such as ISO 14692, BS 7159 and UKOOA, there are some methods which have been developed to calculate flexibility and stresses of a FRP process piping system along with the related testing methods and acceptance criteria.

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