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Development and application of titanium alloy seamless pipe

At present, titanium pipe and titanium alloy pipes are widely used in aerospace, petrochemical, power station, biomedical and other fields. In this paper, the development and application of titanium alloy seamless pipes are summarized and analyzed in detail. The main preparation process of titanium alloy seamless pipe is introduced in detail, and the main factors affecting the quality of titanium alloy pipe and the measures to control defects are discussed. The factors restricting the wide application of titanium alloy seamless pipes are described.

development and application of titanium alloy seamless pipe - Development and application of titanium alloy seamless pipe

Since the introduction of the first titanium alloy product produced by the U.S. Titanium Metals Corporation in 1950, hundreds of titanium alloys have been developed, among which the more widely used are: Ti-6Al-4V, Ti-5Al-2.5Sn, Ti-6242, Ti-6246, Ti-1023 and other alloys. At present, the annual output of titanium processing materials in China is about 5×104t, of which the output of pipes accounts for about 20% [1]. Compared with traditional steel tubes, stainless steel tubes and copper alloy tubes, titanium tubes have many advantages, such as good corrosion resistance, especially seawater corrosion and biocorrosion; high specific strength, which can achieve the purpose of weight reduction while ensuring structural strength and stability; a wide range of alloys to meet the requirements of various fields of use; good biocompatibility, which can be stable in the biological tissue; good processing performance, easy to weld, etc.
Due to the processing difficulties of titanium tubes, high requirements for equipment, the application of titanium tubes in China is limited, mainly to replace traditional steel tubes. However, overseas, titanium alloy tubes have been widely used in various fields, especially in aviation and aerospace. This paper mainly summarizes the development technology, application status and development trend of titanium alloy seamless tube, to provide guidance for its extensive and mature application in various fields.

1. The current situation of titanium alloy seamless pipe development

At present, the international manufacturing process of titanium tubes has been basically mature. The manufacture of billets mainly includes drilling and extrusion and oblique rolling and perforation, and then the finished tubes of different specifications and uses are prepared by rolling, drawing and spinning. For low strength, low alloyed titanium (such as TA1, TA2, TA3, TA5, etc.) usually use multiple cold rolling and with vacuum annealing process to manufacture tubes, while for medium and high strength titanium (such as TC4, TC18, TA18, etc.) often use warm rolling, hot drawing, hot spinning and other deformation temperature of about 100 ℃ below the recrystallization temperature of the thermal processing process.

1.1 Extrusion of titanium alloy tubes

Extrusion technology has high efficiency, high quality, low energy consumption, less / no cutting process characteristics, so in the production of titanium alloy tubes, bars, type, wire and parts are widely used. Some common titanium alloy tube extrusion processes are shown in Table 1 [2,3,4,5,6,7]. The extrusion ratio is an important parameter in the extrusion process. Within a certain range, the larger the extrusion ratio, the more completely the original grains are broken, the finer the extruded tube grains are, and the better the mechanical properties are. The extrusion ratio of titanium alloy is relatively small (usually less than 30). The choice of billet affects the surface quality of the extruded product. Liu Shoutian [8] studied the quality of pure titanium extruded material with different billets and found that the cast billet has poor metal flow and the surface quality after extrusion is worse than that of forged billet.
Tab.1 Extrusion process parameters of titanium alloy tube

Number Extrusion method Extrusion ratio Lubrication method: inner hole copper / steel double clad, outer surface single copper clad Extrusion temperature / ℃
TA10 Forward extrusion 18 760-790
Pure titanium Forward extrusion 22 Water based lubricant (8% graphite +14%mos2+ binder and water) 400
TC2 Forward extrusion 6-20 Copper sheath 700-890
TiNiNb Forward extrusion 3.3 Graphite emulsion lubricant + glass lubricant 850-950
TA15 Forward extrusion 10.2 Copper sheath 950
TC4 Forward extrusion 3-10 Glass powder coating 980

Lubricants in extrusion mainly play the role of anti-sticky die and reduce the extrusion pressure. Commonly used lubricants for titanium alloy tubes are shown in Table 2 [9]. Finite element simulation techniques are also widely used in the extrusion process. For example, DDamodaran [10] established a glass-lubricated hot extrusion model for titanium alloy by finite element software, which can effectively predict the effect of various process parameters on the extrusion deformation process of titanium alloy. Compared with aluminum and magnesium alloys, the development of titanium alloy extrusion technology is slow, mainly due to the large deformation resistance of titanium alloy, requiring large tonnage of extrusion machine, poor thermal conductivity, uneven metal flow, and is a highly reactive metal, which is easily contaminated in the air.
Tab.2 Common lubricant for extrusion of titanium alloy tube

Lubricant type Advantage Disadvantage
Grease Easy to use, low cost, can extrude titanium material with good surface quality The length of extruded products is limited, and the end of long extruded materials is bonded
Metal cladding It can better protect titanium material from oxidation during extrusion If the temperature is too high, it is easy to form eutectic structure with titanium, the process is complex and the cost is high
Glass lubricant Low thermal conductivity, good thermal insulation, high pressure resistance and good chemical stability If the temperature is too high, it is easy to form eutectic structure with titanium, the process is complex and the cost is high

1.2 Titanium alloy tube rolling

Titanium alloy tube rolling is mainly divided into two-roller (LG type) rolling and multi-roller (LD type) rolling, two-roller rolling is mostly used to open the billet, multi-roller rolling is used for sizing and finishing. At present, the widely used tube rolling machines in China are LG-30, LG-90, LG-180, LD-90, LD-180, etc., with pipe processing sizes from 3 mm to a maximum of 250 mm [11].
In the process of rolling titanium tubes, the size of deformation is limited by the alloy properties and tube size, and the deformation allowed for cold rolling of some alloys is shown in Table 3. The ratio of relative wall reduction to relative diameter reduction (Q-value) seriously affects the weave orientation of the tube. Within a certain range, the larger the Q value, i.e., the larger the wall reduction in rolling, the more the grains will be aligned in the direction of the larger deformation, resulting in the radial weave of the tube, which in turn improves the mechanical properties of the tube. JinYX [13] investigated the effect of cold rolling process on the microstructure and weaving of TC4 tubes and found that the polar diagrams in the (0002) and (1010) directions of the tubes were clustered in the rolling direction during the rolling process, and that The large rolling deformation increased the weave strength and promoted the reorganization of the weave. In terms of rational design of roll hole type and determination of deformation parameters, Yin Yehong [14] et al. used Deform-3D software to conduct finite element analysis of the rolling process of titanium tubes, which provided a reliable basis for field tests.
Tab.3 Allowable deformation of partial alloys during cold rolling (%)

Alloy grade Pass deformation Accumulated deformation
TA1 20-60 40-75
TC4 15-65 40-70
TC16 20-35 30-45
TA18 12-48 35-60
Ti-3Zr-2Sn-3Mo-25Nb (TLM) 15-35 30-50

1.3 Other manufacturing methods of titanium alloy seamless tubes

In addition to extrusion and rolling, researchers have also explored manufacturing processes such as drawing, spinning and expanding. Yan Xiaobing [15] and others studied the influence of die parameters on dimensional accuracy, deformation on tube performance and lubrication process on surface quality during drawing of TA15 titanium alloy tubes, and developed a reasonable drawing process. Mou Shaozheng [16] et al. studied the spin forming of cast titanium alloy tube billets and found that the cast grains of the cast titanium alloy were flattened and elongated under certain spin conditions, forming obvious fibrous tissue, and the cast tissue was basically eliminated when the thinning rate exceeded 72%.
For some special specifications of titanium tubes, such as large-diameter or thin-walled tubes, the tube billets are usually first ring-rolled to thin the wall and expand the diameter, and then increased by the length of the tube through the spinning process to further thin the wall, and finally obtain large-diameter thin-walled titanium tubes [17]. In addition, LiuG [18] et al. also studied the effects of flow stress, pressure loading path and temperature on the properties of Ti-3Al-2.5V tubes during high-pressure inflation forming.

2. The main factors affecting the quality of titanium alloy seamless tubes and pipes

There are many different types of titanium alloys, different tube processing techniques and methods, and many factors that affect the quality of tubes. Table 4 lists the main influencing factors and their control measures [19]. Starting from the melting and preparation of titanium alloys, the content of impurity elements (e.g. O, C, N) has an influence on the organization and properties of the finished titanium alloy tubes [20], and generally a high content of interstitial elements increases the strength and decreases the plasticity of the tubes. The choice of preparation method also greatly affects the tube properties. For example, extruded billets have fine grain size and good overall performance, while diagonally rolled and perforated billets have coarse, uneven grain size and often high temperature deformation, making the former easier to process for subsequent tubes. The preparation method also influences the residual stress state of the pipe [21], which increases the fatigue limit and stress corrosion resistance when the pipe has residual compressive stress.
Tab.4 The influence factors and control measures of titanium tube quality

Influence factor Problem description Control measures
Alloy quality The formation of high-density inclusions, segregation or brittle hard phases leads to uneven pipe forming and cracks or even cracking during pipe preparation.
1. adopt multiple vacuum consumable smelting;
2. reduce the melting current and slow down the melting speed;
3. use advanced electron beam cooling bed furnace for smelting.
Tube blank quality The extruded tube billet has fine microstructure and good plasticity, but the equipment is complex and the investment is large; The cross rolled perforated tube blank has coarse structure, poor plasticity and good surface quality.
1. the extrusion process is applicable to the production of titanium tube blanks with low strength and high dimensional accuracy;
2. the cross rolling piercing process is applicable to the production of titanium tube blanks with high strength, fixed specifications and large batch.
Heat treatment system Too high temperature will lead to coarse structure, too low temperature will lead to underannealing, residual stress and work hardening cannot be eliminated, affecting subsequent processing and finished product performance.
1. accurately determine the alloy transformation point for each batch of materials;
2. formulate reasonable heat treatment process in combination with pipe processing path and alloy mechanical properties;
3. strictly control the heat treatment atmosphere.
Deformation Excessive deformation will lead to poor surface quality, cracks, cracks, etc; If the deformation is small, the coarse original grains cannot be broken. The mechanical properties of the pipes are low and the production efficiency is low.
1. arrange the processing passes reasonably according to the allowable pass deformation and the maximum cumulative deformation of the alloy;
2. pay attention to the matching of Q value and deformation, so as to produce favorable texture orientation.
Lubrication process High efficiency lubricant can reduce the plastic forming resistance, ensure the surface quality of pipes, prevent local overheating and reduce the loss of tools and dies.
1. considering the forming process, select the appropriate lubricant according to the alloy characteristics;
2. analyze the anatomical processing process and accurately design the combined lubricant.

The amount of deformation in the process of tube processing significantly affects the performance of the tube. A large amount of deformation can not only improve the productivity but also break up the coarse as-cast tissue better and make the tube grains finer and more uniform, but too much deformation can increase the tube forming resistance, and the heat of deformation can lead to local temperature rise, uneven deformation and abnormal grain growth. A reasonable amount of deformation can improve the performance by forming a weave in the radial, axial and circumferential directions of the tube. Yang Yingli [22] et al. found that in the rolling process of pure titanium tubes, when the Q value was 1.2-2.3, a strong radial weave was formed and the tube properties were improved. Meanwhile, reasonable annealing process, straightening process and efficient oil removal method are the keys to ensure the quality of titanium tubes.

3. Titanium alloy seamless pipe application status

3.1 The wide application of titanium alloy seamless pipe

Titanium alloy tubes are used in the transportation of offshore oilfield platforms, mainly to reduce the weight of the platform, reduce costs and increase service life [23]. Baoti developed and produced the diameter of Ф90 – Ф120mm oil and gas open using TC4S alloy high-performance extruded pipe fully meet the performance index of P110 steel in API5CT, has been successfully delivered and used [24]. Titanium alloy also has outstanding seawater resistance and chloride corrosion resistance, which makes it in the geothermal industry applications not only increases the reliability of equipment, but also reduces operating costs. Further applications are expected in the prevention of aquifer depletion, steam generation from dry heat rock, etc. [25].
As an advanced lightweight structural material with excellent mechanical properties and high specific strength, titanium alloys are widely used in the aerospace field, especially in piping systems such as pilot gas lines, hydraulic lines, and fuel lines. Among them, TA18 titanium alloy has been the best choice for aerospace tubes because of its good room temperature and high temperature mechanical properties (tensile strength ≥ 620 MPa at 700°C), excellent cold and hot working plasticity and weldability [26]. In addition, the good biocompatibility of titanium alloy makes it widely used in the fields of biomedical and orthopedic implants, and the typical Paragon stent is a balloon-expandable martensitic stent made by laser engraving of nickel-titanium superelastic alloy capillary tubes [27]. The properties and applications of some commercially available titanium alloy tubes are shown in Table 5 [28,29,30,31,32].

3.2 Factors limiting the widespread use of titanium alloy seamless tubing

At present, the international manufacturing process of titanium tubes has been basically mature, but the application of titanium tubes has been constrained by the cost, especially for thin-walled tubes, ultra-high strength tubes, ultra-long tubes and other special requirements of tubes, the production of titanium seamless tubes is difficult, complex equipment, long cycle time and low yield rate. Therefore, the titanium welded pipe came into being. In developed countries, titanium seamless tubes have been gradually replaced by titanium welded tubes for condensers in coastal power stations and nuclear power stations [33]. The annual production of titanium welded pipes in China has exceeded 12,000t [34]. It can be expected that titanium welded tubes will partially replace titanium seamless tubes in the future due to the cost advantage.
Tab.5 Properties and applications of commercial titanium alloy seamless tubes

Number Nominal component Tensile strength /MPa Elongation(%) Us
TA1

TA2

Pure titanium 440-620 18-30 Aircraft pneumatic system, power plant condenser, ship pipeline
TA18 Ti-3Al-2.5V 800-950 16-24 Aerospace piping systems
TA16 Ti-2Al-2.5Zr 700-800 13-15 Hydraulic system, fire protection, fuel pipeline
TC4 Ti-6Al-4V 900-1000 10-19 Oil pipeline, deep sea oil and gas transmission
Ti-Ni Ti-50Ni 600-800 25-40 Medical interventional catheter, hydraulic pipe connector and connecting piece

Titanium tubes do not have zero corrosion in the service environment; HMShalaby et al. found that pure titanium condenser tubes had severe corrosion perforations and edge ruptures on both internal and external surfaces after 15 years of service [35]. In addition, bending, welding, and end machining of the tubes are often required in the assembly application of titanium tubes. Due to the high yield-to-elasticity ratio of titanium tubes, the rebound during bending is significant and excessive rebound makes it difficult to control the tube geometry and accuracy [36]. li et al [37] used finite element simulation to analyze and predict the rebound phenomenon of Ti-3Al-2.5V tubes in cold bending process, but the process is very complex and the forming is difficult to control. Titanium tubes due to strong chemical activity, high melting point, poor thermal conductivity and other physicochemical properties, in the welding prone to porosity, cracking and other defects, high requirements for welding equipment and protection devices [38]. These are the factors that limit the widespread use of titanium alloy seamless pipe material.

4. Conclusion

Titanium alloy seamless tubes and pipes have high specific strength, high corrosion resistance, good heat resistance, good low temperature performance, low modulus of elasticity and thermal conductivity, high chemical activity, and good biocompatibility, which make them popular in various fields. However, the application of seamless titanium tubes is limited by the complex equipment, long cycle time, low yield rate and high cost of production. In addition, China has excess production capacity of low-end titanium tubes, but there is a lack of research and production of high-performance titanium tubes for important chemical devices, aerospace hydraulic lines, rocket engine fuel tubes, biomedical and other fields.

At present, the development of titanium seamless pipe material continues to develop towards high performance, low cost and functionalization. On the one hand, a large number of applications of finite element software simulation of the forming process to achieve the optimization of existing equipment and processes to improve the quality and yield will become the trend. On the other hand, we should continue to explore innovative titanium tube preparation methods, simplify the process, reduce costs, and actively promote the application of seamless titanium tubes. All these require the joint efforts of relevant researchers.

Authors: Yu zhiyuan, Yu Zhentao, Liu hanyuan, Eddie, Li siying

SourceChina Titanium Pipe Manufacturer: www.titaniuminfogroup.com

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