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Application status and process development of titanium alloy seamless pipe in oil and gas wells

The oil industry has always occupied an important position in China’s national economy, and with the development of the oil industry, the demand for oil and gas well pipes as an important material necessary for oil and gas development projects is increasing day by day. In the oil industry, every year, the wear, corrosion, fracture, cracking and other problems caused by the poor service conditions of the oil pipe, the damage caused to the country caused significant economic losses. Especially in recent years, with the continuous exploitation of oil resources, oil and gas exploration and development to the polar regions and the expansion of the sea, high pressure, high temperature wells continue to emerge, making it more and more difficult to exploit deep wells, ultra-deep wells of high temperature, high pressure environment on the strength of oil well pipe, toughness and other performance has very high requirements, in conditions beyond most low-carbon micro-alloy steel tubes and corrosion-resistant alloy tubes (such as nickel-based alloys) for long-term service. The range of capabilities.
Titanium and titanium alloys are an important metal developed in the middle of the 20th century. Their low density, high specific strength and good corrosion resistance have led to increasingly widespread applications in aerospace, biomedical, petroleum and metallurgical fields. Among them, titanium alloy oil well pipes as a supplement and alternative to existing oil well pipes, its advantages and demand are becoming more and more obvious, making the research and application of titanium alloy oil well pipes become the hottest direction for material selection and corrosion control of oil and gas wells in high temperature, high pressure and high corrosion harsh environment. With the development of science and technology in China, titanium alloy material preparation technology and product quality have been greatly improved, but there are still many problems in the production process of titanium and titanium alloy tubing, which restrict its application prospects. Now we discuss the current situation and prospect of application of titanium alloy seamless pipe in oil and gas wells at home and abroad, and provide the production process of titanium alloy pipe with new composition for oil and gas wells, in order to make up for the shortcomings of complicated manufacturing process and poor product performance of titanium alloy seamless pipe existing in the existing technology, so as to expand its application prospect.

1. Production of titanium alloy seamless tubing and its application in oil and gas wells

1.1 Current status of titanium alloy seamless pipe production

Although the high-strength titanium alloy has the advantages of better corrosion resistance, high-temperature strength and thermal stability, its thermal conductivity below 500 degrees is less than half that of steel, so it is easy to heat up and difficult to transfer heat during deformation; in addition, the specific heat capacity of titanium alloy is comparable to that of steel, so the temperature drop of titanium alloy under high-temperature conditions is faster. The high temperature deformation resistance of titanium alloys is significantly affected by the deformation temperature and phase change temperature, resulting in a narrow hot working temperature window for most titanium alloys. In addition, although the surface of titanium alloys can form a dense oxide film when processed below 450 degrees, which has excellent oxidation resistance, the oxidation products formed at higher temperatures are highly susceptible to cracks and holes, which will reduce the oxidation resistance, and the flaked oxidation products will be pressed into the substrate in the subsequent processing process, thus leading to deterioration of the surface quality. In addition, titanium alloys have poor frictional properties during high temperature deformation, high and unstable friction factor, easy to wear and corrode, and adhesion with rolling tools. Due to these property characteristics of titanium alloys, it increases the technical difficulty of manufacturing large-size high-strength titanium alloy seamless tubes, especially medium-thick-wall tubes (diameter to wall ratio 12-20) and thin-wall tubes (diameter to wall ratio 20).
The traditional hot extrusion process can manufacture titanium alloy seamless tubes with lower plasticity, but due to the limitation of extrusion ratio, it is impossible to produce tubes with larger diameter and wall. In addition, in order to obtain good surface quality of titanium alloy seamless tube, lubrication treatment such as copper cladding is required for titanium alloy tube billets, but copper and titanium will react at high temperature and generate intermetallic compounds, and interfacial compounding occurs, and it is difficult to remove the copper layer. Moreover, in hot extrusion, the surface layer of the billet and the inner layer will produce a large temperature difference, up to 200 degrees, with the result that the deformation resistance of the heart of the billet is much lower than the inner wall of the extrusion barrel and the annular area of the die hole, resulting in uneven deformation and large additional tensile stresses in the surface layer, forming a source of cracks on the surface of the pipe, making it difficult to guarantee the surface quality of the extruded pipe.
Extrusion – cold rolling (drawing) process is used to obtain the tube billet by hot extrusion method, and the tube billet is cold rolled (drawn) after surface treatment, and then annealed to eliminate process hardening in order to adjust the organizational properties. Titanium alloy cold working performance is poor, in order to ensure the wall thickness and performance of the tube, thin-walled tubes often require multiple cold rolling and annealing treatment. This process produces titanium alloy seamless tubes with high surface quality and dimensional accuracy and good performance uniformity, but its surface treatment often uses strong acid pickling, which is prone to environmental pollution, and has long processing cycle, high energy consumption and low material yield.
The slant-rolling perforation-rolling thermal processing method is currently a more popular process for producing seamless titanium alloy tubes, which makes use of existing seamless steel tube production lines and can significantly simplify the process and improve production efficiency compared to the extrusion process. However, titanium alloys are sensitive to thermal deformation parameters, which makes the tube deformation mechanism complex, and processes such as piercing, rolling and sizing (reducing) can change the organization and surface quality of titanium alloys to some extent. In addition, the organization of titanium alloys is hereditary, resulting in a diversity of tissue properties at different stages and locations of the processing process. Moreover, the longer the tube forming size, the greater the temperature difference between the head and tail, and the greater the fluctuation in tissue properties of the outer wall, inner wall and head and tail of large diameter titanium alloy seamless tubes. Therefore, there is an urgent need to develop a more mature and efficient production process for hot rolling large-diameter titanium alloy seamless tubes in short processes and to form a stable specification for the industrial preparation of low-cost titanium alloy seamless tubes.

1.2 Application of titanium alloy seamless pipe in oil and gas wells

Titanium alloy seamless pipe is widely used in the oil and gas industry, especially in corrosive environment conditions with unique advantages, can serve in the humid atmosphere and seawater media, particularly strong resistance to pitting, acid corrosion and stress corrosion, and also has extremely strong corrosion resistance to CO2 + H2S + Cl-, corrosion resistance far beyond low carbon micro-alloy steel and stainless steel.
The small elastic modulus of titanium alloy seamless pipe has extremely high fatigue strength, which can prevent dynamic stress corrosion caused by wave impact and platform movement, adapt to the bending and deformation working conditions during laying, and meet the requirements of complex marine environment for oil and gas pipeline corrosion resistance and high stability requirements. For short radius wells and horizontal wells, titanium alloy drill pipe can significantly reduce the equipment load, significantly improve its service life, and is not easy to have the fatigue fracture that occurs in ordinary material drill pipes. RMI Active Metals, Inc. has successfully developed high-strength titanium alloy casing, tubing, continuous tubing and offshore drilling spacer pipes by adding rare elements to some titanium alloys to improve their corrosion resistance and adopting the hot rotation + pressure perforation tubing rolling process, and the products have been successfully applied in many oil and gas wells and drilling projects. RTI International Metals Corporation has developed extruded titanium alloy tubing and welded titanium alloy tubing, and its products have been used in sour oil and gas fields.
Compared with the development and application of titanium alloy seamless pipes abroad, titanium alloy seamless pipes in China are mainly used in aviation, aerospace and medical fields, while the development of titanium alloy seamless pipes for oil and natural gas is still in its initial stage, and the exploration of highly corrosive oil and gas fields and the development of high pressure and high temperature wells in central and western China have put forward more demanding requirements for the oil well pipes used in them. The mechanical properties of titanium alloy oil tubing are comparable to those of nickel-based corrosion resistant alloy oil tubing, which meets the development needs.

2. New process development of titanium alloy oil well pipe

2.1 Titanium alloy composition design

The addition of different alloying elements and the different amounts of addition will affect the physical, chemical and mechanical properties of the product. Targeted alloying design according to the different applications of titanium alloys is the main method to strengthen the properties of titanium alloys. Currently, the addition of alloying elements is an important means to improve the high temperature properties and corrosion resistance of titanium alloys. If the content of β-phase stabilizing elements is insufficient, it cannot play a role in strengthening and improving; adding too much will not only increase the cost and density of titanium alloy, but also easily form elemental segregation or a large number of brittle intermediate phases, thus affecting the material properties. Therefore, the selection of β-phase stabilizing elements and the precise control of the content are to be focused on.

The author developed two new composition titanium alloy based on the existing TC4 titanium alloy composition, respectively, TC4-based titanium alloy chemical composition is shown in Table 1. from Table 1 can be seen: one is TC4 alloy added Ru and Bi, etc.; the other is TC4-NiNb alloy, adding trace amounts of β-phase stabilizing elements Ni and Nb, can improve the oxidation resistance and solid solution strengthening of titanium alloy, improve the strength, high temperature The metallographic organization of TC4-NiNb alloy billets and hot-rolled tubes is shown in Fig. 1. 1 shows.

The chemical composition of grade 5 Ti-6Al-4V alloy.

Element Content (%)
Titanium, Ti 87.6 – 91
Aluminum, Al 5.5 – 6.75
Vanadium, V 3.5 – 4.5
Iron, Fe ≤ 0.40
Oxygen, O ≤ 0.20
Carbon, C ≤ 0.080
Nitrogen, N ≤ 0.050
Hydrogen, H ≤ 0.015

The physical properties of grade 5 Ti-6Al-4V alloy.

Properties Metric Imperial
Density 4.43 g/cm3 0.160 lb/in3
Melting point 1674 °C 3045 °F

The mechanical properties of grade 5 Ti-6Al-4V alloy.

Properties Metric Imperial
Tensile strength ≥ 895 MPa ≥ 130000 psi
Yield strength ≥ 828 MPa ≥ 120000 psi
Poisson’s ratio 0.31 0.31
Elastic modulus 105-120 GPa 15200-17400 ksi
Shear modulus 41-45 GPa 5950-6530 ksi
Elongation at break ≥ 10 % ≥ 10 %

The thermal properties of grade 5 Ti-6Al-4V alloy.

Properties Metric Imperial
Thermal expansion co-efficient (@0.000-100°C/32-212°F) 9 µm/m°C 5 µin/in°F
Thermal conductivity 6.60W/mK 45.8 BTU in/hr.ft².°F

Equivalent materials to grade 5 Ti-6Al-4V alloy.

AMS 4928 AMS 4965 AMS 4967 MIL T-81915 MIL T-9046
AMS 4920 AMS 4954 ASTM B265 MIL T-81556 MIL T-9047
AMS 4911 AMS 4935 ASTM B348 MIL F-83142 SPS M618
AMS 4906 AMS 4934 ASTM B381 GE C50TF12 DMS 1570
AMS 4905 AMS 4930 DIN 3.7164    

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Fig.1 metallographic structure of TC4 NiNb alloy pipe blank and hot rolled pipe

2.2 New process of titanium alloy seamless pipe

Traditional seamless steel pipe production line adopts a set of ring heating furnace or inclined-bottom heating furnace for heating billet, and its heated billet will lead to the existence of surface oxygenation layer due to the long time of uniform heat in the furnace, and when this process is used to produce titanium alloy seamless pipe, it will make the internal and external surface quality of titanium alloy seamless pipe poor and defective, and only a single variety of steel pipe or titanium alloy pipe can be rolled at the same time, so the production switching has high energy consumption, long cycle time, low equipment utilization rate, and cannot realize short time of rolling. In addition, the utilization rate of the equipment is low, and it cannot realize short process production.

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  • 1. Loading table
  • 2. Ring heating furnace
  • 3. Discharge table
  • 4. Titanium billet heating furnace
  • 5. Perforating machine
  • 6. Barren tube moving device
  • 7. Pipe rolling machine
  • 8. Intermediate cooling bed
  • 9. Reheating furnace
  • 10. Induction heating furnace
  • 11. Fixed ( reduction ) diameter unit

Fig. 2 Schematic diagram of seamless pipe processing flow

In view of this, the author proposed a short process for the production of titanium tubes, that is, the traditional seamless steel pipe production line to increase the titanium billet heating furnace, ring heating furnace heating billet, titanium billet heating furnace heating flaw qualified titanium billet, so that both can use the same production line, high fault tolerance, improve equipment utilization, but also to reduce the titanium billet heating process of oxygen absorption, hydrogen absorption. In the plan to roll the same titanium tube and steel pipe specifications, from the steel pipe rolling can be directly switched to titanium tube rolling. When switching, the perforator guide, top head and rolling movement bar or top head do lubrication treatment, so that the perforation process is more smooth, as far as possible to reduce the wall defects and tangential shear stress during the deformation of the pipe billet, to avoid the cross-forging effect, so as to get uniform quality of the barren pipe. Lubrication of the inner wall of the burr tube in the finishing rolling effectively reduces the friction factor between the roll and the titanium tube, reduces the rolling force, avoids the friction between the roll and the titanium tube due to the friction of the titanium tube rolled into impurities, and effectively improves the surface quality and internal properties of the rolled parts. Subsequently, according to the degree of temperature drop of the gross tube after rolling, the high quality titanium alloy seamless tube is produced by selecting sizing (reducing) diameter or direct sizing (reducing) diameter rolling after electric induction supplementary heat, followed by warm straightening, cooling, polishing or centerless turning. This process can realize the common line production of products with different heating process and different rolling temperature through the change of billet heating process, and realize the mixed rolling of steel pipe and titanium tube, which can be used for the short process processing of high-strength titanium alloy or pure titanium tube with high equipment utilization rate and solve the problem of time-consuming exchange and low production efficiency.

Based on the process of perforation + rolling + heat treatment, a high-efficiency, short-process processing process with a common production line for seamless tube steel and titanium has been developed to avoid the cooling and heating operation of the ring furnace during the switching of titanium seamless tube and steel seamless tube production, which can realize timely arrangement of production schedule; in addition, online solution treatment can be realized to better regulate the organization and mechanical properties of titanium alloy seamless tubes. to realize the production of high strength and high toughness titanium alloy oil well pipes. The TC4-NiNb alloy seamless pipe was produced using this process on a trial basis. Firstly, based on the chemical composition of TC4-based titanium alloy, the high-strength and high toughness titanium alloy pipe material TC4-NiNb was developed by proper alloying of Ni and Nb, then the titanium alloy pipe billet was heated after forging the billet melted in vacuum electric arc furnace, perforated to obtain the gross pipe and obtain the two-phase organization, further continuous rolling or oblique rolling in the temperature range of the two-phase zone of titanium alloy, i.e., plastic deformation at the temperature of the two-phase zone to Then, the tube is heated to the solid solution temperature and held for a certain period of time, i.e., online solid solution treatment, and some of the lamellar tissues are transformed to spheroidized tissues through dynamic polygonization and recrystallization of the two-phase zone deformation, and then the finished Φ139.7mm titanium alloy seamless tube is finally spheroidized and mixed microstructure through subsequent sizing and aging processes. The impact fracture of Φ139.7mm titanium alloy seamless tube consists of small toughness nests, which is typical of ductile fracture, and this organization has not only better strength and plasticity but also higher high temperature performance and fatigue fracture resistance than the simple lamellar, net basket and bimodal organizations. The strength at room temperature can be increased by more than 100MPa compared with conventional TC4 titanium alloy, and the product performance can reach the performance standard requirement of P110 or Q125 steel grade oil well pipe. This high-efficiency, full-process thermal processing and online heat treatment process can effectively replace the traditional hot extrusion process and offline heat treatment process, which is of great importance for the key process of producing high-strength and high-toughness titanium alloy oil well pipes and their applications.

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Fig. 3 SEM photo of TC4 NiNb titanium alloy on-line heat treatment pipe

3. Conclusion

  • (1) Economical titanium and titanium alloy seamless tubing has become the ideal choice for the development of high-pressure, high-temperature and ultra-high-pressure hot sour oil and gas wells, and both domestic and foreign countries are actively developing titanium alloy tubing for oil and gas wells, which has a broad application prospect.
  • (2) For high-strength and high-toughness titanium alloy seamless pipes for oil and gas wells with extra-long dimensions, the hot rolling process with optimized design of the whole process can be used for production, which can effectively improve the stability of the forming process, significantly improve the organizational properties and internal and external surface quality of the finished pipes, and effectively reduce the tooling loss and improve the rolled material rate.

Source China Titanium Alloy Seamless Pipe Manufacurer:



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