PSI - Issue 22

Lunwen Guo et al. / Procedia Structural Integrity 22 (2019) 194–200 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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fiber is 1.1mm. Considering the impact protection for outer fiber, the thickness of carbon fiber layer for outer explosion-proof and protection should be at least 1.5mm.

Fig. 2. The curve of the relation between CFRP circumferential stress and thickness

3. Connection structure of CFRP-steel pipe The CFRP-steel pipe is the hybrid structure of inner metal, flanges and CFRP layer. Therefore, the strong and reliable connection is very crucial to those three parts, and the joining of CFRP and metal flanges is the most important and vital factor in the design and manufacture of CFRP-steel pipes. The maximum working pressure of pipeline is 17 MPa, thus equivalent of the pipe axial tensile load is about 21 tons. The usual connecting methods of CFRP to metal are adhesive, pin hanging or bolted together. The surface shear bond strength of CFRP-steel is ordinarily 5 to 15 MPa, so the flange length is more than 25 cm if connected by adhesive. Obviously, the bolted connections are also unrecommendable. The pin hanging connections can provide a high connection strength, reliable shock and fatigue resistance, but the reasonably designed flange structure and strictly controlled filament winding process is necessary. Considering the process feature of filament winding, a flange structure with 9 pins (fillet radius 9mm) was designed, which is shown in Figure 3(a). The scaled CFRP-steel pipes with the same diameter but shorter than standard length pipes were manufactured, and the axial load capacity tests were conducted compared with double-layer steel pipes under the same conditions. The experiment process is shown in Fig. 3(b)(c). The failure images are shown in Fig. 4. The results are shown in Table 1.

(a)

(b)

(c)

Fig. 3. Flange structure and test: (a) the flange and lining structure; (b) tensile test of scaled CFRP-steel pipes; (c) tensile test of scaled steel pipes