As an important structural material in modern industry, the expansion performance of titanium welded pipes directly affects the safety and reliability of equipment systems. This article will systematically analyze the expansion characteristics of titanium welded pipes from the aspects of mechanical properties, sealing properties, material advantages, and process control.
Significant advantages in the mechanical properties of expansion
1. Excellent pull-off resistance
Experimental data show that under the same expansion pressure conditions, the pull-off force of the expansion performance of titanium welded pipes can reach 2.5~3.1 times that of conventional seamless titanium pipes, with a typical value range of 45-55MPa (depending on the specific specifications). This feature gives it a significant advantage in areas with strict requirements on structural strength, such as high-pressure vessels (such as nuclear power plant condensers) and deep-sea underwater equipment.
2. Excellent interface bonding performance
Through microstructural analysis, it was found that the interface contact area increased by about 30% after expansion, and the surface micro-deformation depth was controlled in the range of 0.05-0.15mm. This controllable plastic deformation mechanism can both ensure bonding strength and avoid excessive material damage.
Engineering guarantee of sealing performance
1. Dynamic sealing stability
In the pressure fluctuation test (0-15MPa cycle), the leakage rate of the titanium welded pipe can be controlled within <0.001mL/(m·s), and the sealing integrity can be maintained after 2000 pressure cycles. This feature is particularly suitable for occasions such as LNG pipelines and chemical reaction devices that require long-term stable sealing.
2. Adaptability to special-shaped interfaces
After finite element simulation optimization, the expansion performance of titanium welded pipes can achieve precise matching with an ellipticity tolerance of ±0.15mm, and the fit degree of special-shaped structures such as flanges and tube sheets is more than 98%, significantly improving the sealing reliability under complex working conditions.
Synergistic effect of material properties
1. Surface oxide layer protection
The naturally generated TiO₂ passivation film (thickness 2-5nm) on the surface of titanium welded pipes has unique advantages: the friction coefficient is reduced to 0.12-0.15, and the electrochemical corrosion rate is <0.003mm/a. This self-repairing oxide layer can reduce tool wear and maintain interface corrosion resistance during expansion.
2. Matching of thermal physical properties
The thermal expansion coefficient of titanium welded pipe is 8.6×10⁻⁶/℃, which is significantly lower than 17.3×10⁻⁶/℃ of 304 stainless steel. This lower thermal expansion characteristic ensures better matching with most base materials when the temperature changes. At the same time, its thermal conductivity of 21.9W/(m·K) is more advantageous than 16.2W/(m·K) of stainless steel, which is conducive to uniform heat distribution during expansion.
4. Key elements of process control
1. Key points of welding quality control
When using TIG welding, the process parameters must be strictly controlled: the purity of argon gas must be ≥99.999%, the heat input must be controlled at <1.5kJ/mm, and the weld excess height should be limited to 10-15% of the wall thickness to ensure that the mechanical properties of the weld area are consistent with those of the parent material.
2. Optimization direction of the expansion process
It is recommended to use hydraulic expansion technology. By controlling the pressure gradient (0.5MPa/s), pressure holding time (30-60s), and the chamfer radius of the transition zone (≥1.5 times the wall thickness), high-precision expansion can be achieved to avoid microcracks caused by stress concentration.
5. Industry application and development trend
Currently, the expansion performance of titanium welded pipes has been successfully applied in many fields:
Nuclear power field: the qualified rate of steam generator tube bundle expansion is ＞99.8%
Marine engineering: The service life of the deep-sea manifold system is increased to 25 years
Chemical equipment: the maintenance cycle of pickling equipment is extended by 3-5 times
Future technical development directions include:
1. Develop an intelligent expansion system with integrated strain real-time monitoring
2. Study the composite expansion process of mechanical and hydraulic synergy
3. Apply nano-surface modification technologies such as graphene-enhanced interface
Conclusion
The expansion performance of titanium welded pipes is reshaping the technical standards of modern industrial pipelines with their excellent comprehensive expansion performance. With the advancement of materials science and manufacturing technology, the efficiency of expansion joints is expected to increase by another 30-50%, providing a more reliable solution for engineering applications under extreme working conditions. It is recommended to establish an expansion joint quality prediction system based on digital twins in actual engineering to achieve full life cycle performance monitoring.
