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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1. Introduction The concrete pumping pipeline is a typical abrasive pressure duct, which has two important features. First, pipe is under the Maximum pressure in concrete pumping process up to 17 MPa. Secondly, the pipe needs to resist the concrete abrasion, and the inner steel layer is easily getting thin and failure finally in the long-term service [1] . The existing concrete pipes have double-layer metal structure: the inner wear-resistant brittle steel and the outer ductile steel, and the two end flanges joined to ductile outer steel by welding. For the double-layer metal pipes, the inner steel may get cracking and shedding because of the unavoidable gap between inner and outer layer. Besides, the welding part of inner metal may fail before an expected life due to the welding thermal effect, and the lightweight and safety are hard to be promoted. Carbon fiber reinforced polymer (CFRP) can provide an excellent performances of high strength, fatigue resistance, explosion-proof, and no secondary heat input is needed. The new pipeline, made by higher wear resistant steel and strengthened by CFRP, can eliminate the gap between inner and outer layer effectively, so the pipe abrasive resistance and product stability can be improved. The hybrid structure of CFRP strengthening metal pipes can take full advantage of the light weight and high strength property of carbon fiber, and also the high wearing resistance, low cost, machinability of metal material. It has been widely researched and applied in civilian construction, transportation and mechanical industry field [2-5] . The difficulties and importance of this research on hybrid structure are the structure calculation and design of fiber-layers, and the joining structure of carbon fiber to metal. The designed filament-winded CFRP contains three layers: the inner layer for stress sharing of brittle steel tube, the middle layer for connecting ductile steel flanges and the outer layer for explosion-proof and protection. The performance analysis of inner layer and the outer layer were considered with stress sharing calculation. The connection structure between pipe flange and CFRP, the filament winding control program and process of middle layer, were determined by experiment. The lightweight and long life concrete pumping pipe was developed successfully after series of experiment and service tests. 2. Calculation and design on circumferential fiber layers The fiber layer of CFRP-steel pipe contains the stress sharing inner layer, the explosion-proof outer layer and the middle layer of connecting to steel flanges. The inner layer and outer layer are the circumferential fiber layer, and they are used to withstand circumferential loads under internal pressure. The middle layer mainly bears axial load. In this section, the design of circumferential fiber was studied by calculating and analyzing on the stress sharing relationship of hybrid structure. 2.1. Design of the stress sharing inner fiber layer The abrasion and corrosion of the CFRP-steel pipes lead to the loss of the pipe lining wall in long-term service. When the wall loss reaches a certain level, the pipe will not be able to withstand the internal high pressure, and the leakage or even burst will happen. The pipe pressure load is distributed to metal lining and carbon fiber, and the carbon fiber plays the role of sharing the stress of lining. The relationship of the circumferential stress between the lining and fibers, the thickness of carbon fibers and pipe lining wall, the prestress of fibers, the worn depth, the internal pressure and the radius of pipe can be expressed by the following formulas [6] . = ( − )[1+ ( − ) ] − +( − ) ≤ [ ] (1) = ( − )[1+ ( − ) ] + ( − ) +( − ) ≤ [ ] (2) In Eqs. (1) and (2), σ s is circumferential stress of lining; [ σ s ] is admissible stress of lining; σ f is circumferential stress of fibers; [ σ f ] is admissible stress of fibers; α E is the elastic modulus ratio of CFRP to metal ( = ) ; E f is the elastic modulus of CFRP; E s is the elastic modulus of lining; p is the internal pressure; r is the equivalent radius of hybrid