A Novel Strengthening Method for Damaged Pipeline under High Temperature Using Inorganic Insulation Material and Carbon Fiber Reinforced Plastic Composite Material

In this paper, a strengthening method for the damaged high-temperature steel pipeline using inorganic insulation material which was confined by carbon fiber reinforcement plastic (CFRP) composite materials was proposed. Two inorganic insulation materials were composed of magnesium phosphate cement (MPC) mixing with perlite and vermiculite powders, respectively. The influences of insulation material composites with various ratios of the perlite or vermiculite powder were discussed, in terms of compressive strength and thermal conductivity coefficients of inorganic insulation materials. The insulation materials confined by carbon fiber reinforced polymer jackets for enhancing the mechanical behavior were also investigated. From the experimental results, the main finding of the work was that the inorganic insulation materials added to the perlite powder represented greater insulation capability than added vermiculite ones under the condition of the same compressive strength. Different ratios of perlite inorganic insulation material cylinders with the dimension of ϕ 10 cm × 20 cm were confined by one layer and two layers of CFRP composite material. The compressive strength of the specimens increased by 258%–927% after using 1-layer CFRP composite material and increased by 480%–1541% after applying 2-layer CFRP composite material. A peak strength prediction model of insulation materials confined by CFRP was proposed, and it was found that the proposed model accurately predicted the peak strength of the inorganic insulation material cylinder. Finally, a verification test of the strengthening method for damaged high-temperature pipeline was performed to prove that the proposed strengthening method is feasible.