With the rapid development of industry, a lot of methods to enhance heat transfer have been developed, among which highly efficient heat exchange (HEHE) tubes are most commonly used in engineering. A lot of research has been performed in the literature on the heat transfer performance of heat exchangers with HEHE tubes [
1,
2,
3,
4,
5]. Kareem et al. [
6] presented an extensive review of numerical and experimental studies on the heat transfer enhancement of corrugated tubes, which cover laminar and turbulent flow. In order to improve the heat and mass transfer performance of falling film and develop a new type of falling film evaporator, Huang et al. [
7] studied the heat and mass transfer characteristics of falling film evaporation and sensible heat in four different sizes of converging–diverging tubes. Rashid et al. [
8] presented a novel model of a parabolic trough-based solar thermal and natural gas hybrid power plant. Due to the intermittence of solar energy, the model can make use of natural gas combustion to supplement steam when cloud cover and solar intensity are reduced, which can improve the reliability and efficiency of solar power generation. It is worth noting that the system uses a shell and tube heat exchanger to extract more heat from the heat transfer fluid before returning to the parabolic trough. In this case, HEHE tubes are very effective in improving energy efficiency.
Due to the irregular shape and rolling from the smooth tubes, the load-carrying capability of HEHE tubes may be quite different from that of smooth tubes, of which sufficient attention should be paid in order to ensure reliable operation of heat exchangers constructed with HEHE tubes. Eyvazian et al. [
9,
10] studied the effect of crushing parameters on an aluminum corrugated tube and the compression response under transverse quasi-static loads by corrugations of different geometries through experiments and numerical simulations. The results showed that by changing the shape of the corrugations, the stress distribution pattern changed significantly. Wang et al. [
11] used the finite element method to simulate and analyze corrugated tubes in the heat exchanger. An analysis method for the stability of the corrugated tubes under internal and external pressure was proposed, and the calculation formula of single wave stiffness was obtained. Singace et al. [
12] conducted an experimental study on the energy absorption characteristics of corrugations. The experimental results show that the corrugations are an ideal controllable energy-absorbing element. Song et al. [
13] analyzed the stiffness and strength of cylindrical rods and tubes from material mechanics. It was found that when the masses of the two were the same, the cross-section stiffness of the circular tube was three times that of the cylindrical rod. Using the basic theory of elastoplasticity, the yield stress of a liquid-filled cylindrical tube was studied. Due to the incompressibility of the liquid and the strain hardening effect of the material, the yield stress of the liquid-filled tube increased and the bending strength increased. Under the dynamic load, compared to the hollow tube, the impact resistance of the liquid-filled tube was also raised due to elastic recovery. Li et al. [
14] studied the influence of heat transfer tube stiffness and tube sheet thickness on the thermal stress of tubes and tube sheets. It was found that the use of corrugations to reduce the stiffness of the tube can reduce the axial thermal stress at the tube, thus reducing the possibility of failure of the connection strength between the tube and the tube sheet. Qian et al. [
15] conducted numerical and experimental research on the axial stiffness of the corrugated tubes. Based on the analysis of axial load-displacement, the stiffness weakening factor
Kf of the corrugated tubes was proposed and formulated. Yang et al. [
16] analyzed the axial stiffness of the twisted tube by finite element and experimental methods. The results showed that the increase in the twist ratio or decrease in the lead will lead to the decrease in axial stiffness, and a formula for reducing the stiffness of the twisted tube was proposed. Shen et al. [
17] analyzed the leakage of titanium tubes in condensers of nuclear power plants, including analysis of the chemical composition of the alloy, mechanical properties, metallographic structure, and micro-morphology. The results showed that the leakage of the titanium tube is mainly caused by fatigue failure. Fatigue tests were carried out in air and steam environments, and the fatigue resistance of the titanium tube in the steam environment was significantly reduced. Vetriselvan et al. [
18] established an experimental device to simulate thermal fatigue on the inside diameter side of the tube. Based on the decoupling analysis of thermal and inelastic stresses, finite element analysis was performed to calculate the total plastic strain range of the boiler tube. Finally, the number of cycles of crack initiation was obtained through experiments, and the number of cycles of crack initiation was calculated using the modified Coffin–Manson relation. It provides a reliable basis for the fatigue failure analysis of
9Cr
1Mo steel tubes for boilers. Sajuri et al. [
19] characterized the metallurgical, mechanical, and fatigue properties of copper–phosphorus alloys and aluminum–copper bimetallic tubes by metallographic analysis and tensile, bending, and fatigue tests. The results showed that a fragile Al–Cu intermetallic compound was found in the transition layer between Al and Cu. The bending performance of the tube was affected by the volume fraction of Cu in the material. The fatigue strength of the aluminum–copper bimetal tube was reduced by nearly 55% compared to the copper alloy tube. Leber et al. [
20] studied the microstructure changes of isothermal low-cycle-fatigue samples made from industrial steel tube processing. The volume fraction of martensite determined by the optimized magnetic nondestructive test method was generally small, but it was large near the crack tip with high plastic strain, and martensite was found at the intersection of the slip zone. Hsu [
21] studied the fatigue fracture of the industrial pure titanium tube in the shell and tube heat exchanger at low temperature. As industrial titanium tubes are subjected to vibration and compressive axial loads caused by flow during use, the combined stress causes many intergranular cracks in the circumferential direction. Fracture analysis showed that the fracture was caused by high cycle fatigue.
As HEHE tubes, spirally grooved (or SG) tubes and converging–diverging (or CD) tubes are widely used in heat exchangers. However, a literature review found that with the considerable research addressing the heat exchange enhancement properties of the HEHE tubes and some on the load-carrying capability of HEHE tubes, there are few studies on the changes in their mechanical properties after rolling from smooth tubes. In this paper, the mechanical properties of the SG tubes and CD tubes are studied and compared to those of smooth tubes. The purpose is to ensure the reliable use of HEHE tubes in heat exchangers.