Study of internal pressure strength of the titanium-steel composite tube based on yield and shear failure mechanisms

Abstract

Combining the high mechanical strength of carbon steel with the excellent corrosion resistance of titanium, titanium-steel composite tubing, which consists of an inner tube made of titanium (Ti) and an outer tube made of carbon steel, is not only an ideal material for the oil and gas pipelines system, but also has huge application prospects in the oil and gas industry [1,2]. However, the yield and shear failure of the titanium-steel composite tube occurs easily under internal pressure due to its own structural features, especially concerning shear failure. Hence, based on the elastic-plastic theory, a mechanical model capable of calculating internal pressure strength of the Ti-steel composite tube prepared by metallurgical bonding has been established by combining the yield failure mechanism and the shear failure mechanism. The corresponding design methods of internal pressure strength have been proposed respectively, for users and manufacturers. The effects of the inner pipe wall thickness, the radius-thickness ratio of the outer pipe, the elastic modulus, and the bonding strength and bonding rate of the Ti-steel composite tube on internal pressure strength have been analysed. According to the national standard, design drawings for selecting Ti-steel composite tubes under different internal pressures have been presented for users. The accuracy and reliability of this model are verified by comparing the results with the API/ISO standard. These research results can provide an important reference for manufacturing, strength design and specification optimization of Ti-steel composite tubing.