PSI - Issue 22

196 Lunwen Guo et al. / Procedia Structural Integrity 22 (2019) 194–200 Author name / Structural Integrity Procedia 00 (2019) 000 – 000 3 structure ( = + + 2 ); r is the internal radius of lining; t s is wall thickness of lining; d is the wear depth; t f is the thickness of CFRP; p l is the initial strain. 2.1.1 The thickness of the stress sharing inner layer The relationship between the worn depth and the circumferential stress of the lining is shown in Fig. 1(a). When the filament winding reinforcement is absent and the lining withstands 17 MPa pressure alone, and the worn depth is about 1.5 mm, the circumferential stress of the lining is about 1100 MPa, which is larger than the limit strength of the quenched liner, and the lining or the pipeline will crack and fail. From Fig. 1(a), with the increasing of fiber thickness, the stress decreasing gradually. Typically, when the thickness of carbon fibers is 1.5mm, the wearing depth of lining is close to 2.5mm (the thickness of lining wall is 2.5mm). That denotes that the lining is worn completely without cracking failure in theory, and then with the thickness of CFRP increasing, the lining is always within the safe stress range. Considering the cost factors, the CFRP thickness of stress sharing layer should be designed to be at least 1.5 mm. 2.1.2 The prestress of the stress sharing inner layer In the conditions of winding prestress with 1 to 140 MPa, the carbon fiber thickness with 1.5 mm and internal pressure 17 MPa, the relations between the circumferential stress and the worn depth, prestress of the lining is shown in Fig. 1(b). It can be seen from the figure that the greater prestress, the greater stress sharing effect of the fiber on the lining, but the sharing effect is not obvious. Considering the characteristics of filament winding process, the solut ion of fiber prestressed 35MPa is proposed.

Fig. 1. The curves of the relation among lining circumferential stress, wearing depth and thickness (a), prestress (b) of CFRP

2.2. Design on the explosion-proof outer layer When the concrete pumping pipe is blocked and the metal lining cracks and fails, and the stress-sharing fiber layer closing to the lining is damaged immediately under extreme conditions, the outer explosion-proof and protective fiber layer is designed for the safety protection. The outer layer thickness refers to the classical pipe pressure formula: = ( 12 + 22 ) 22 − 12 ≤ [ ] (3) Here, σ f is circumferential fiber stress; [σ f ] is admissible stress; p is pressure; r 1 is internal diameter; r 2 is outer diameter. In the condition of 17 MPa, according to Eq. (3), the stress level of the fiber layer is only related to the thickness of the fiber, but not to the type of the fiber and other factors. Fiber circumferential stress changes as shown in Fig. 2. By setting the admissible safety stress of the winding CFRP material to be about 1000MPa, the design thickness of carbon