# Experimental Analysis of a Novel GFRP Stiffened Pipe
## 2 Materials and Methods
### Fabrication of Test Specimens  
To investigate the effect of the proposed GFRP pipes on the PS, comparison tests were conducted with the plain GFRP pipes and two groups of GRFP pipe specimens were tested, each including proposed and plain pipes. One group had diameters of 400 mm, and the other group had diameters of 500 mm. The proposed GFRP pipe and the plain pipe in the same group used almost equal weight of materials to ensure cost consistency. The pipes had different nominal diameters and different winding methods, i.e., DN = 400 mm (continuous arrangement winding), DN = 400 mm (spacing arrangement winding), DN = 500 mm (continuous arrangement winding), and DN = 500 mm (spacing arrangement winding), where DN refers to nominal diameter. The fabrication details of each part of the tested pipe specimens are listed in Table 2 and the corresponding geometric properties are presented in Table 3. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Material** & **Density (g/cm\({}^{3}\))** & **Tensile Modulus (GPa)** & **Ultimate Tensile Strength (MPa)** & **Tensile Strain at Break (\%)** & **Viscosity Cst** & **Gelation Time** \\ \hline E-Glass Fiber \({}^{1}\) & 2.54 & 72.5 & 3430 & 1.4 & / & / \\ Unsaturated & 1.18 & 3.6 & 70 & 3.0 & 0.45 & 10–12 \\ polyester resin & 2 & 0.906 & / & / & / & 10–12 \\ \hline \end{tabular} \({}^{1}\) The code of E-Glass Fiber is SE2307, \({}^{2}\) Polyester resin and its curing agent (slow hardener) with mixture ratio 100:1 by mass at a constant temperature of 25 \({}^{\circ}\)C.  
\end{table} 
Table 1: Mechanical properties of E-Glass Fiber and unsaturated polyester resin. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
\begin{tabular}{c} Spacing arrangement \\ (2 shares from the 1 st \\ to the 5 th comb teeth \\ + 0 shares from the 6 th to the 10 th comb \\ teeth) \(\times\) 4 (shown in Figure 2b) \\ \end{tabular} & SE2307, 2000 tex & Web-stiffened inside \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Fabrication details of each part of the tested pipe specimens. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Specimen Type** & \begin{tabular}{c} **Internal** \\ **Diameter (mm)** \\ \end{tabular} & \begin{tabular}{c} **No. of** \\ **Layers** \\ \end{tabular} & \begin{tabular}{c} **Average** \\ **Thickness (mm)** \\ \end{tabular} & \begin{tabular}{c} **Total** \\ **Weight (Kg)** \\ \end{tabular} & \begin{tabular}{c} **Resin Mass** \\ **Fraction (\%)** \\ \end{tabular} \\ \hline DN400 & \begin{tabular}{c} P1 \({}^{1}\) \\ P2 \\ P3 \\ P3 \\ P3 \\ P3 \\ P3 \\ P3 \\ P3 \\ \end{tabular} & \(384\) & \(16\) & \(8.44\) & \(5.49\) & \(26.60\) \\ \hline DN400 & \
\begin{tabular}{c} P1 \({}^{1}\) \\ OS1 \({}^{2}\) \\ OS2 \\ OS3 \\ \end{tabular} & \(384\) & \(16\) & \(8.44\) & \(5.50\) & \(26.51\) \\ \hline DN400 &
\begin{tabular}{c} P1 \({}^{1}\) \\ OS2 \\ OS3 \\ \end{tabular} & \(384\) & \(16\) & \(11.25\) & \(5.41\) & \(25.54\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: GFRP pipe geometric properties. Two types of spiral winding were used in this research, as illustrated in Figure 2. The manufacturing process and test specimens of the proposed GFRP pipe are shown in Figures 2-4. The manufacturing details were as follows:  
(a) For outer stiffened GRFP pipes:  
(1) On the pipe mandrel of the continuous winding system, the glass fiber continuous yarn was dipped in resin, and then wound through the mandrel device to form the inner structural layer using the continuous arrangement winding method as presented in Figure 2a. The thickness of the inner structural layer can be designed according to the pressure grade of the pipeline, and the thickness range is 1-50 mm;  
(2) On the inner structure layer, the web core was formed by cross winding of glass fiber continuous yarn with a discontinuous arrangement, as presented in Figure 2b. The warp orientation relative to the pipe axial axis was \(\theta\) = \(\pm\)55\({}^{\circ}\) (Figure 2a).