Theoretical Study on Thermal Hydraulic Expansion Process of Stainless Steel Lined Clad Pipe

The stainless steel lined clad pipe (SSLCP) can be widely used in different fields. Industrial SSLCP are generally manufactured by the cold hydraulic expansion (CHE) method which requires high hydraulic pressure and good sealing property. The interlayer bonding force is difficult to obtain by the CHE when there is little difference between the yield strengths of inner and outer pipes. Furthermore, the hydraulic expansion process nearly cannot be achieved when the yield strength of inner pipe is higher than that of outer pipe. The thermal hydraulic expansion (THE) method can overcome these difficulties. In this paper, the graph method was adopted to analyze the THE principles for “inner strong and outer weak (ISOW)” and “outer strong and inner weak (OSIW)” pipes. The effective hydraulic expansion criterion conditions of SSLCPs were proposed and can be used as basis of clad pipe material matching and forming process selection. Through the stress and strain analysis of inner and outer pipes during THE process, the deformation coordination conditions of elastic deformation and thermal deformation of the inner and outer pipe were established. The correlation between the residual contact pressure p*_c, the hydraulic expansion pressure p_i, and the effective temperature difference ΔT_e were derived. The calculation formula of the maximum expansion pressure p_imax and the minimum expansion pressure p_imin was obtained. The maximum heating temperature of outer pipe was also derived. Furthermore, the finite element analysis (FEA) method was adopted and simulated results verify the feasibility and applicability of the theory study.