What is a titanium pipe
What is a titanium pipe?
Titanium pipe is a pipe made of titanium or titanium alloy. Titanium pipe has the advantages of light weight, high strength and superior mechanical properties. It is widely used in heat exchange equipment, such as tubular heat exchanger, coil heat exchanger, coil heat exchanger, condenser, evaporator and transmission pipeline. Many nuclear power industries take titanium pipes as the standard pipes for their units.
Chemical composition of titanium pipe
|Brand||Nominal chemical composition||Chemical composition (mass fraction)%|
|Main ingredients||Impurities, not greater than|
|A single||The sum of the|
|TA1-1||Pure titanium||0.20 or less||–||–||–||–||–||0.08 or less||–||0.15||0.05||0.03||0.003||0.12||–||0.10|
|TA7||Al Ti – 5-2.5 Sn||allowance||4.0-6.0||2.0-3.0||–||–||–||–||–||0.50||0.08||0.05||0.015||0.20||0.10||0.40|
|TA8||Ti – 0.05 – Pd||allowance||–||–||–||0.04-0.08||–||–||0.30||0.08||0.03||0.015||0.25||0.10||0.40|
|TA9||Ti – 0.2 – Pd||allowance||–||–||–||0.12-0.25||0.30||0.08||0.03||0.015||0.25||0.10||0.40|
|TA10||Mo Ti – 0.3-0.8 Ni||allowance||–||–||0.2-0.4||–||0.6-0.9||–||–||0.30||0.08||0.03||0.015||0.25||0.10||0.40|
|UNS||American brand||National standard||Main alloy composition (allowance: Titanium)|
|UNS R50250||Gr1||TA1||Pure titanium|
|UNS R50400||Gr2||TA2||Pure titanium|
|UNS R50550||Gr3||TA3||Pure titanium|
|UNS R50700||Gr4||TA4||Pure titanium|
|UNS R56400||Gr5||TC4||6% aluminum + 4% vanadium|
|UNS R54520||Gr6||TA7||5% aluminum + 2.5% tin|
|UNS R52400||Gr7||TA9||0.12 ~ 0.25% palladium|
|UNS R56320||Gr9||TA18||3% aluminum + 2.5% vanadium|
|UNS R52250||Gr11||TA9-1||0.12 ~ 0.25% palladium|
|UNS R53400||Gr12||TA10||0.3% + 0.8% nickel molybdenum|
|UNS R53413||Gr13||0.5% nickel + 0.05% ruthenium|
|UNS R53414||Gr14||0.5% nickel + 0.05% ruthenium|
|UNS R53415||Gr15||0.5% nickel + 0.05% ruthenium|
|UNS R52402||Gr16||0.04 ~ 0.08% palladium|
|UNS R52252||Gr17||TA8-1||0.04 ~ 0.08% palladium|
|UNS R56322||Gr18||TA25||3% Aluminum +2.5% vanadium +0.04~0.08% palladium|
|UNS R58640||Gr19||TB9||3% aluminum +8% vanadium +6% chromium +4% zirconium +4% molybdenum|
|UNS R58645||Gr20||TB9||3% Aluminum +8% vanadium +6% chromium +4% zirconium +4% Molybdenum +0.04~0.08 Palladium|
|UNS R58210||Gr21||TB8||15% Molybdenum +3% aluminum +2.7% niobium +0.25% silicon|
|UNS R56407||Gr23||TC4 ELI||Low tissue clearance of 6% Aluminum +4% vanadium ELI|
|UNS R56405||Gr24||TC22||6% Aluminum +4% vanadium +0.04~0.08 palladium|
|UNS R56403||Gr25||6% Aluminum +4% vanadium +0.04~0.08 Palladium +0.3~0.8% nickel|
|UNS R52404||Gr26||0.08 ~ 0.14% ruthenium|
|UNS R52254||Gr27||0.08 ~ 0.14% ruthenium|
|UNS R56323||Gr28||TA26||3% Aluminum +2.5% vanadium +0.08~0.14% ruthenium|
|UNS R56404||Gr29||TC23||6% aluminum +4% vanadium +0.08~0.14% ruthenium|
|UNS R53530||Gr30||Cobalt 0.3% + 0.05% palladium|
|UNS R53532||Gr31||Cobalt 0.3% + 0.05% palladium|
|UNS R55111||Gr32||5% Aluminum +1% tin +1% zirconium +1% vanadium +0.8% molybdenum|
|UNS R53442||Gr33||0.4% Nickel +0.015% Palladium +0.025% Ruthenium +0.15% chromium|
|UNS R53445||Gr34||0.4% Nickel +0.015% Palladium +0.025% Ruthenium +0.15% chromium|
|UNS R56340||Gr35||4.5% Aluminum +2% Molybdenum +1.6% vanadium +0.5% iron +0.3% silicon|
|UNS R58450||Gr36||45% niobium|
|UNS R52815||Gr37||1.5% aluminum|
|UNS R54250||Gr38||4% aluminum +2.5% vanadium +1.5% iron|
Classification of titanium pipes
Titanium pipe is divided into titanium seamless pipe and titanium welded pipe. Titanium welded pipe is made of titanium plate with the same thickness by coil welding. Titanium seamless pipe is formed by cold rolling of pipe blank through rolling mill. The pipe blank is divided into hot extruded pipes, with smooth inner surface and high cost. It is suitable for heat exchange pipes. The inner wall of the obliquely perforated pipe blank is rough, which is suitable for the production of pipes for general purposes. It can also be used to make pipe targets for vacuum coating (pure titanium).
How are titanium pipes classified? We can divide them into many kinds. It can be classified according to production method, section shape, wall thickness and use.
1. Classification by production method
(1) Titanium seamless pipe – hot rolled titanium pipe, cold rolled titanium pipe and cold drawn titanium pipe.
(2) Titanium welded pipe.
- (a) According to technology – arc welded pipe, resistance welded pipe (high frequency and low frequency), gas welded pipe and furnace welded pipe.
- (b) Divided by weld – straight welded pipe and spiral welded pipe.
2. Classification by section shape
(1) Titanium pipe with simple section – circular titanium pipe, square titanium pipe, oval titanium pipe, triangular titanium pipe, hexagonal titanium pipe, rhombic titanium pipe, octagonal titanium pipe and semicircular titanium pipe.
(2) Disordered cross-section titanium pipe – unequal hexagonal titanium pipe, five petal quincunx titanium pipe, double convex titanium pipe, double concave titanium pipe, melon seed titanium pipe, conical titanium pipe, corrugated titanium pipe and watch case titanium pipe.
3. Classification by wall thickness
Thin wall titanium pipe, thick wall titanium pipe.
4. Classification by use
Titanium pipe for pipeline, titanium pipe for thermal equipment, titanium pipe for mechanical industry, titanium pipe for petroleum and geological drilling, titanium pipe for container, titanium pipe for chemical industry and titanium pipe for special use.
Pure titanium pipe
The specific strength (strength to weight ratio) of industrial pure titanium pipe is very high in metal structural materials. Its strength is equivalent to that of steel, but its weight is only 57% of that of steel. In addition, the titanium pipe has strong heat resistance and can still maintain good strength and stability in the atmosphere of 500 ℃. Titanium pipe also has good low temperature resistance. Even at – 250 ℃ ultra-low temperature, it still has high impact strength, high pressure and vibration resistance.
Another remarkable feature of industrial pure titanium pipe is its strong corrosion resistance, which is due to its great affinity for oxygen, which can form a dense oxide film on its surface, which can protect titanium from medium corrosion. Therefore, titanium has good stability in acidic, alkaline and neutral brine solutions and oxidizing media, and has better corrosion resistance than existing stainless steel and other non-ferrous metals. Industrial pure titanium pipe has a wide range of applications. At present, industrial pure titanium pipe not only has very important applications in aerospace and aviation industry, but also has been widely used in many industrial departments such as chemical industry, petroleum, light industry, power generation and so on.
Because pure industrial titanium pipe has many excellent characteristics such as light weight, high strength, strong heat resistance and corrosion resistance, it is known as “the metal of the future” and is a new structural material with great development prospects.
Titanium alloy pipe
Titanium alloy pipe is a pipe made of titanium alloy.
Industrial pure titanium is different from chemical pure titanium. Industrial pure titanium contains oxygen, nitrogen, carbon and other elements, which improves its strength.
Grade 1, grade 2 and grade 3 refer to industrial pure titanium. The difference between them is that the larger the number, the more interstitial impurity elements increase, so the strength and hardness are higher. Grade 7 is titanium palladium alloy, grade 16 is titanium palladium alloy with high purity, and grade 12 is titanium molybdenum nickel alloy. Titanium alloy has high mechanical properties, excellent stamping properties, and can be welded in various forms. The strength of welded joint can reach 90% of the strength of base metal, and the cutting performance is good. Titanium pipe has high corrosion resistance to chloride, sulfide and ammonia. The corrosion resistance of titanium in seawater is higher than that of aluminum alloy, stainless steel and nickel base alloy.
Advantages of titanium pipe
- 1. Titanium pipe has high specific strength. The density of titanium alloy is generally about 4.5g/cm3, which is only 60% of that of steel. The strength of pure titanium is close to that of ordinary steel. Some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloy is much higher than that of other metal structural materials. See table 7-1. Parts and components with high unit strength, good rigidity and light weight can be made. At present, titanium alloy is used in aircraft engine components, skeleton, skin, fasteners and landing gear.
- 2. Titanium pipe has high thermal strength. The service temperature is several Baidu higher than that of aluminum alloy. It can still maintain the required strength at medium temperature and can work for a long time at 450 ~ 500 ℃. These two types of titanium alloys still have high specific strength in the range of 150 ℃ ~ 500 ℃, while the specific strength of aluminum alloy decreases significantly at 150 ℃. The working temperature of titanium alloy can reach 500 ℃, while that of aluminum alloy is below 200 ℃.
- 3. Titanium pipe has good corrosion resistance. Titanium alloy works in humid atmosphere and seawater, and its corrosion resistance is much better than that of stainless steel; It has strong resistance to pitting corrosion, acid corrosion and stress corrosion; It has excellent corrosion resistance to alkali, chloride, chlorine organic products, nitric acid, sulfuric acid, etc. However, titanium has poor corrosion resistance to reducing oxygen and chromium salt medium.
- 4. Titanium pipe has good low temperature performance. Titanium alloy can still maintain its mechanical properties at low and ultra-low temperatures. Titanium alloys with good low temperature properties and very low interstitial elements, such as TA7, can maintain a certain plasticity at – 253 ℃. Therefore, titanium alloy is also an important low temperature structural material.
- 5. Titanium pipe has high chemical activity. Titanium has great chemical activity and has strong chemical reaction with O, N, h, Co, CO2, water vapor and ammonia in the atmosphere. When the carbon content is greater than 0.2%, hard tic will be formed in titanium alloy; When the temperature is high, tin hard surface will also be formed by interaction with n; Above 600 ℃, titanium absorbs oxygen to form a hardened layer with high hardness; The embrittlement layer will also be formed when the hydrogen content increases. Titanium also has great chemical affinity and is easy to adhere to the friction surface.
- 6. Titanium pipe has small thermal conductivity and elastic modulus. Titanium has small thermal conductivity and elastic modulus. The elastic modulus of titanium alloy is about 1/2 of that of steel, so it has poor rigidity and is easy to deform. It is not suitable to make slender rods and thin-walled parts. During cutting, the resilience of the machined surface is very large, about 2 ~ 3 times that of stainless steel, resulting in severe friction, adhesion and bonding wear on the back surface of the tool.
What are the advantages of titanium pipe in seawater desalination equipment?
In today’s society with tense water environment, we gradually realize that seawater desalination can reduce water use. What is seawater desalination equipment? Seawater desalination equipment refers to the equipment specially used to desalinate seawater. Seawater desalination mainly uses two methods to desalinate seawater, namely distillation and reverse osmosis.
Titanium pipe in seawater desalination equipment will gradually replace the original copper alloy pipe. Compared with the two, titanium pipe has the following advantages:
- 1. Under the same operating conditions, the wall thickness of titanium pipe is thinner and the amount of pipe is less. Generally, the wall thickness of copper alloy pipe is 0.9mm-1.2mm; Replace with titanium pipe. In places with low corrosivity, the wall thickness can be 0. 5mm thin wall pipe.
- 2. Titanium pipes have good thermal conductivity. The thermal conductivity of titanium is 17w/(m.K), aluminum brass is loow/(m.K), 70/30 white copper is 29w/(m.K), and the thermal conductivity of titanium is the smallest. However, using thin-walled titanium pipe, although the thermal conductivity is worse than aluminum brass, it is equivalent to 90/10 white copper and better than 70/30 white copper.
- 3. The use of titanium pipes is more cost-effective. The titanium pipe can be counterbalanced with the copper alloy pipe. Because of the low density of titanium and the simultaneous interpreting of the same thickness, the titanium pipe with the same length is only 50% of the copper alloy pipe. When the thickness of the titanium pipe is 50% of the copper alloy pipe, the titanium pipe with the same heat transfer area is only 1/4 of the copper alloy pipe. It can be seen that titanium pipes are competitive in price.
- 4. Titanium pipes have a longer service life. Because seawater is often mixed with sediment and marine organisms, they are attached in the heat transfer pipe and pipe end, which will erode the copper alloy pipe, and the copper alloy will also be corroded by Br – in seawater. However, in use, the hydrogen introduced from the external environment is called external hydrogen.
Specifically, active hydrogen atoms are generated on the metal surface through the following ways, and then enter the metal:
- (1) The medium of titanium equipment contains molecular hydrogen, such as high-temperature hydrogen atmosphere.
- (2) Hydrogen produced by overall corrosion or local corrosion of titanium is absorbed by titanium. For example, crevice corrosion of H is often accompanied by hydrogen absorption.
- (3) Hydrogen produced by galvanic corrosion or cathodic protection overprotection of titanium and negative metal.
The latter two kinds of hydrogen embrittlement caused by electrochemical corrosion cathode are more frequent, and can occur without high temperature and high pressure, which should be paid more attention.
Common uses of titanium pipes
Due to the unique density, strength and corrosion resistance of titanium, it has been used in various applications in different industries. For high-quality pipe products, titanium is much better than other competitive materials (such as superalloy and stainless steel). The density of titanium is about 60% of that of nickel based or steel based alloys, which in turn brings important weight reduction to aviation structures. Compared with ferritic or austenitic stainless steel, titanium has better tensile strength. Titanium has strong corrosion resistance, which can exceed the resistance level of stainless steel.
Application of titanium pipe
Titanium pipes are commonly used in a variety of applications because most stainless steels and other materials in different cases are inefficient. Titanium pipe is one of the most common titanium rolling mill products. It is used in countless products because of its corrosion resistance and strength weight ratio. Titanium and its alloys continue to develop to effectively meet the challenges of various industries, from which new characteristics of titanium are needed to obtain productivity and meet federal regulations. Some common uses of titanium pipes are as follows:
Titanium is used in airframe and aerospace engine parts. Titanium pipes can handle high temperatures even without creep. The pipe is recognized for its high strength density ratio because of its excellent resistance to fatigue and crack growth.
Application in power industry
Power generation – titanium pipes play an important role in high temperature water and steam environments. Grade 2 titanium has been used in different power plants to deal with problems related to boiler friction and condenser failure.
Application in chemical industry
Chemical treatment of highly corrosive environments, such as common environments in demand piping systems, chemical processing industries, heat exchangers and other systems capable of handling heavy loads. Through its excellent corrosion resistance, titanium is likely to effectively withstand high stress for a long time in extreme environments. Titanium storage tanks, valves, reactors, titanium flanges, titanium pipe fittings, etc. in the chemical industry.
Oil and gas industry
High temperature, high pressure or high pressure, high temperature applications, such as oil and gas well applications, require pipelines that can be used continuously. The oil and gas industry usually needs the high corrosion resistance of titanium, especially in the upper, seabed and downhole areas.
Titanium pipes are considered to be one of the nine most abundant elements in the earth’s crust and seven of the most abundant metals. The alloy titanium pipe and the mixture of vanadium and aluminum can improve the strength of titanium while maintaining its weight better than that of steel.
Titanium can work easily. With its stiffness, strength, toughness, ideal high-performance metal pipe and high melting point, it is likely to encourage the industry to use titanium pipe and titanium alloy pipe. It can be used in aircraft hydraulic systems, medical implants, hydraulic systems, subsea equipment, offshore drilling platform components and chemical and marine processing plants.
Pure titanium pipes can be used to produce titanium coils, such as heat exchange, heating pipes, condensing pipes and pipes on heat exchangers.
The most commonly used alloy pipes are TA10, ta9 and ta18, which have higher strength and more corrosion resistance than pure titanium. Ta18 (3al-2.5v) (good corrosion resistance and high strength) is often used to process titanium alloy bicycle frames.
Among alloy pipes, seamless pipes represented by TC4/GR5 (Ti-6Al-4V), TC11 and TC18 generally adopt drilling and hot extrusion technology due to their hard material, which are mainly used for oil logging, aerospace, deep-sea pressure equipment, etc.
Welded pipes are mostly pure titanium pipes, which are generally used in power plant water treatment devices and seawater desalination systems.
Processing technology of titanium pipe
There are four processing technologies of titanium pipe: forging, rolling, extrusion and drawing. Among the four basic methods, forging can adjust the structure, which is the first method that most titanium materials must use. Among the other three methods, rolling is the most used, that is, most pipes are processed by rolling.
Different pipe production methods are essentially the combination of different pipe billet preparation methods and different finished pipe production methods. Therefore, to evaluate the advantages and disadvantages of the production method, we should discuss the advantages and disadvantages of the production method of billet and finished pipe.
Titanium pipe billet preparation methods mainly include extrusion, cross rolling perforation, drilling and boring, powder metallurgy, plate (strip) welding.
The advantages and disadvantages of these methods are shown in Table.1.
Table.1 Comparison of preparation methods of titanium pipe billet
|The preparation methods||Advantages||Disadvantages||Scope of application|
(1) It has a triaxial compressive stress state, which is conducive to the deformation of titanium alloy with poor plasticity;
(2) Large deformation, can break grain, can provide good plasticity, thin wall thickness of the pipe blank;
(3) Large flexibility, suitable for the characteristics of more specifications, less quantity;
(4) Under the condition of good lubrication and good mold, the dimensional accuracy is high;
(5) Facilitate the production of special-shaped pipe and composite pipe;
(6) Can produce longer pipes
(1) Large loss of metal and mold
(2) Strict lubrication requirements, such as poor lubrication, can not get good products;
(3) Complex equipment and large investment;
(4) It is difficult to guarantee the quality of the inner surface;
(5) For single variety and large batch products, the productivity is lower than cross rolling hole
|Titanium alloy pipe billet production|
|Skew rolling punch||
(1) For products with fewer specifications and large quantities, the productivity is higher;
(2) The loss of metal and mold is small;
(3) Better surface quality can be obtained;
(4) Low requirements for lubrication conditions;
(5) Simple equipment, less investment
(1) Single product with poor flexibility;
(2) The amount of deformation is limited, and thin-walled pipe billets cannot be obtained, which increases the amount of machining;
(3) The pipe blank produced is relatively short
|It is suitable for production of titanium alloy pipe billet with large quantity of specification|
(1) The inner surface quality is good;
(2) The equipment is simple and the investment is small;
(3) Not affected by material plasticity
|Big loss||Suitable for producing titanium alloy pipe billet with poor plasticity|
(1) The wall thickness is uniform and the inner surface quality is the best;
(2) High productivity and low cost;
(3) Can produce large diameter pipe, make up for the lack of extrusion machine capacity;
(4) Simple equipment, less investment
(1) Poor flexibility, should not produce more specifications and less batch products;
(2) Welds are often weak links;
(3) Weld cleaning is difficult
|It is generally used to produce titanium pipes in batches|
The main production methods of finished pipe are rolling, extrusion and drawing. Either alone or in combination, they make the pipe blank into the required pipe. The advantages and disadvantages of these methods are shown in Table.2.
Table.2 Comparison of main production methods of finished pipes
|The preparation methods||Advantages||Disadvantages|
(1) The stress state is conducive to metal plastic deformation, and can produce metal pipes with high strength and low plasticity;
(2) The amount of pass deformation and wall thickness thinning is large, reducing the intermediate auxiliary process, and the production cycle is short;
(3) The lubrication method is simpler than drawing;
(4) Accurate size, good surface quality
(1) Complex equipment and large investment;
(2) Strict requirements for tools, special equipment or special birthgear can be manufactured;
(3) Replacing tools is more complicated than drawing
(1) It has stronger triaxial stress state than rolling, and can process titanium alloy with difficult deformation and low plasticity;
(2) It can produce pipes with complex sections and has a wide range of products;
(3) Flexible production, simple process, less investment in equipment;
(4) Accurate size, good surface quality
(1) Periodic production, productivity is lower than rolling;
(2) Large waste loss, low yield;
(3) Large tool consumption, uneven product performance
(1) Accurate size, smooth surface;
(2) Flexibility, easy to replace the mold;
(3) Equipment, tools than rolling is simple, less investment, easy to manufacture;
(4) Suitable for the production of special-shaped pipe
(1) It is difficult to produce metal pipes with low plasticity and high strength;
(2) The amount of pass deformation is small, the drawing pass is many, and the production cycle is long;
(3) There are many auxiliary processes in the middle;
(4) Metal consumption is larger than rolling;
(5) The requirements of lubricants are strict
After cold plastic processing of titanium alloy pipe, its mechanical properties, physical properties and chemical properties almost changed, strength and hardness increased, and plasticity and toughness decreased, in order to make the titanium alloy pipe processed by cold plastic deformation to restore to the state before cold plastic deformation, need to heat the pipe for annealing. Intermediate annealing and finished annealing are interspersed in the plastic working procedure of titanium alloy pipe. Intermediate annealing temperature should be higher than recrystallization temperature to prevent grain growth. Through nucleation and growth, strain-free new grain structure is formed, and all kinds of property changes caused by plastic deformation disappear, and the property is restored to the original level before cold deformation, so that different passes of cold deformation can be carried out smoothly. Finished product annealing is mainly selected in the recovery temperature, namely stress annealing temperature, the purpose is to reduce its internal stress under the condition of basically maintaining the work hardening state, in order to avoid deformation or cracking and improve the corrosion resistance of the workpiece.
Long-term practice shows that the preparation methods of titanium pipe billet are mainly cross rolling perforated hot rolling method, extrusion method and titanium strip welding method, and titanium ingot drilling and boring are also used for pipes with relatively large technological difficulties. The finished titanium pipes are mainly made by cold rolling, stretching and welding. By the pipe billet making product process, although only for rolling and drawing process, but their process methods constitute the four slightly different ways, and from titanium ingot processing into 3 pipe billet process, titanium pipe processing technology according to the permutation and combination can make 12 discriminating processing craft route line art. It shows the diversity and complexity of titanium pipe processing process, almost using all kinds of plastic processing means, or various processes repeated use, or repeated use, or multiple combinations, to produce high quality titanium pipe.
The common heat treatment methods of titanium pipes are annealing, heat treatment tempering and quenching and tempering. Annealing is to better remove thermal stress, improve plastic deformation and mechanism reliability, so as to obtain good comprehensive properties. commonly α Alloy and（ α＋β） The annealing temperature of the alloy is set at（ α＋β） ─→ β 120 ~ 200 ℃ below the phase change point; Heat treatment, tempering and quenching and tempering treatment are based on rapid cooling of powder layer to obtain austenite α′ Phase and metastable β The metastable phase was dissolved by temperature control and thermal insulation in China α Phase or chemical substances and other subtle diffuse simple harmonic motion of the second phase, so as to strengthen the purpose of the alloy.
The heat treatment process of titanium pipe can be combed as follows:
- (1) Aging treatment and timeliness: the purpose is to better improve its compressive strength, α Titanium pipe smooth β Strengthening heat treatment is not allowed for titanium pipes, and only annealing is carried out in production and manufacturing. α+β Titanium pipe and with small amount α Metastable phase β Titanium pipe can further strengthen the alloy according to aging treatment and aging property.
- (2) Thorough annealing: the purpose is to better obtain good ductility, improve production and processing performance, benefit reproduction and processing, and improve the reliability of specifications and mechanisms.
- (3) Remove in-situ stress annealing: the purpose is to remove or reduce the internal stress caused in the production process. Avoid organic chemical corrosion and reduce deformation in some etching natural environments.
Heat treatment process of titanium pipe
In addition, in order to better consider the special requirements of product workpieces, bi-directional annealing, isothermal process annealing β Heat treatment processing technology of metal materials such as heat treatment and deformation heat treatment.
Titanium pipes are mainly used to make aeroengine compressor parts, followed by rocket, cruise missile and high-speed aircraft. In the middle and late 1960s, titanium and alloys have been used in general industries to make electric grade of electrolysis industry, cooler of power plant, electric heater of crude oil refining and seawater desalination equipment and air pollution control equipment. Titanium and alloys have become a raw material for corrosion-resistant structures. In addition, it is also used to produce hydrogen storage raw materials and shape memory alloys.
Titanium pipe has high compressive strength, low relative density, good mechanical equipment performance, excellent ductility and corrosion resistance. In addition, the processing performance of titanium pipe is poor, drilling production and processing is difficult, and it is easy to digest and absorb residues such as hydrogen, nitrogen and carbon during heat treatment. There are also poor wear resistance and complicated production process. The industrial production of titanium was gradually in 1948. The development trend of airline industry must make the titanium industry develop at an average annual growth rate of about 8%. At this stage, the global total output of titanium pipe production and processing materials has reached more than 40000 tons, and there are nearly 30 types of titanium pipe. The most widely used titanium pipes are Ti-6Al-4V (TC4), ti-5al-2.5sn (TA7) and industrial pure titanium (TA1, TA2 and TA3).
Pickling of titanium pipe
- 1. Degreasing: after cooling and blank opening, the oil stain on the inner and outer surfaces of the pipe shall be removed with metal degreasing agent. When degreasing, pay attention to the position where the oil stain is easy to be stored in the inner hole to ensure thorough cleaning.
- 2. Pickling: the purpose of pickling is to remove the oxide scale generated after annealing inside and outside the titanium pipe. Under normal temperature, put a certain amount of purified water into the pickling tank, and then add an appropriate amount of HNO3 and HF. The normal ratio of HNO3 and HF water is (35% – 45% HNO3 + 5% – 8% HF + residual H2O), which shall be adjusted accordingly according to the actual situation. The pickling time is 10-15 minutes, which can also be determined according to the pickling situation. During the pickling process, it shall be turned and checked frequently to ensure uniform and complete pickling and prevent over pickling or under pickling.
- 3. After pickling, the titanium pipe shall be inspected visually, and the oxide skin on the inner and outer surfaces of the titanium pipe shall be removed clean and silvery white.
- 4. Scouring: after the titanium pipe passes the pickling inspection, it shall be washed in time to remove the residual acid and pickling on the inner hole and outer surface, so as to ensure the brightness of the titanium pipe.
In order to eliminate the influence of surface oxide film on hydrogen absorption process, titanium can be heated in vacuum or hydrogen. When heated to 700-850 ℃, the oxide on the surface of titanium pipe begins to diffuse into the metal. After treatment, the hydrogen absorption rate of titanium pipe increases greatly. However, in this method, the oxygen in the oxide film is not eliminated during heating treatment, but enters the metal, which will not only reduce the diffusion rate of hydrogen to the metal, but also enter the final product, thus reducing the product quality; At the same time, the particles of titanium pipe will also cause some degree of sintering and reduce its hydrogen absorption rate.
Surface treatment of titanium pipe
Titanium is a very active metal, so the surface of titanium pipe will be polluted in the processing process. How to deal with the surface of titanium pipe?
1. Surface roughening of titanium pipe
In order to reduce the surface defects and oxides of titanium pipe, it is necessary to roughen the surface of titanium and improve its bonding area. Sandblasting coarsening is often used clinically, but sandblasting will pollute the alumina on the surface of titanium. We use oxalic acid etching to obtain excellent coarsening effect. The surface roughness (RA) can reach 1.50 ± 0.30 after etching for 1H μm. The etching 2H RA is 2.99 ± 0.57 μm. Ra (1.42 ± 0.14) higher than that of sand blasting alone μ m) It has more than doubled and its bond strength has increased by 30%.
2. High temperature oxidation resistant surface treatment
In order to avoid the rapid oxidation of titanium at high temperature, titanium silicon compound and titanium aluminum compound are formed on the surface of titanium, which can avoid the oxidation of titanium at temperatures above 700 ℃. This surface treatment is very useful for the high-temperature oxidation of titanium. Perhaps the surface of titanium is coated with such compounds.
Comparison table of wall thickness of titanium pipe (DN15 – DN1200/NPS 1/2″ – 48″)
|NPS||DN||D（Outer diameter of titanium pipe)||SCH5s||SCH10s||SCH10||SCH20||SCH30||STD||SCH40||SCH40s||SCH60||XS||SCH80||SCH100||SCH120||SCH140||SCH160||XXS|
Specification comparison table of titanium flange matched with different titanium pipe sizes
Comparison of specifications and dimensions of titanium pipes matched with PN series and class series of titanium flanges. Flanges are standard parts with many specifications and dimensions. In pipeline connection, different pipe specifications should be matched with flanges of corresponding specifications. The comparison of outer diameters of titanium pipes matched with DN15-DN600 (NPS 1/2″ – NPS 24″) is as follows:
Comparison of NPS and DN:
Outer diameter of pipe corresponding to PN series titanium flange (HG/T20592-2009 Series B):
|DN||Outer diameter of pipe|
Pipe outer diameter corresponding to class series titanium flange (ANSI, ASME B16.5):
|NPS||Outer diameter of pipe|
How to weld titanium pipes
Titanium is 45 percent lighter than steel and 60 percent heavier than aluminum, more than three times stronger than any of them. Although it is much more expensive than many other metals, it has higher corrosion resistance, lower life cycle cost, longer service life, and lower maintenance and repair costs than most. Common applications of titanium include military, aerospace, Marine, chemical, power generation, oil and gas extraction and medical equipment.
Titanium is an active metal, easy to interact with oxygen, easy to oxidize and pollute, and difficult to weld. However, careful preparation, steady handling and plenty of practice can lead to a successful weld.
This paper focuses on gas tungsten arc welding (GTAW, also known as TIG welding or tungsten inert gas welding) using ASTM Gr5, domestic TC4 (Ti6Al4V) as reference for titanium pipe, titanium alloy pipe and pipeline.
Cleanliness is crucial
Welding titanium pipes requires extreme cleanliness – the base metal, filler metal and welding conditions must be immaculately perfect. Oil stains, workshop dust, paint, dirt, cutting fluids and lubricants during shaping and drawing can all lead to embrittlement and welding failure if the welder uses hand cream and other body creams.
First clean the working area and remove all kinds of debris, and make sure to choose the place with the smallest air flow, as far as possible to ensure the environment without wind, so as not to disturb the protective gas during the welding process. Next clean the filler rod and base metal of oil: wear nitrile gloves specially designed for this purpose to prevent the operator’s hand cream or other hand oil from rubbing the titanium pipe to be welded. Methyl ethyl ketone (MEK) is then applied to a clean flunt-free cloth and wiped with titanium to remove any remaining surface contaminants. Place the filler rod in an airtight container to prevent further contamination.
Prior to welding, the surface of the pipe is removed from the oxide coating formed when titanium reacts with oxygen. The oxide layer provides significant corrosion resistance to titanium. However, it must be removed before welding because it melts at a higher temperature than titanium and can enter the molten pool to produce inclusions that weaken the interlayer.
Either a die grinder with a carbide deburring tool or a carbide file dedicated to titanium alloys will best remove the oxide layer from the welded joint. Steel velvet and abrasives are not recommended as they cause pollution. Remember to use low grinding speeds to prevent overheating. After the oxide layer is worn off, wipe the joint again with a cloth soaked in MEK or acetone. Because some solvents have low flash points, etc., it is necessary to wait until the solvent completely evaporates before hitting the arc.
A perfect fit
For titanium pipes, assembly is probably more important than for any other metal pipe, as it is crucial to prevent oxygen from entering the weld. Joints should be square (no V-notch) to help reduce the amount of heat and welding metal needed to fill joints; This, in turn, reduces the likelihood of burn through and contamination.
Clamp the parts on a positioner or workstation to ensure that the ends are as tightly and accurately connected as possible.
Most thin-walled titanium pipes and pipes do not require preheating. However, if you plan to weld titanium pipes that are more than 1/3 inch thick, consult your welding equipment supplier, as some preheating and post-heating may be beneficial.
Importance of shielding gas coverage
Pure argon is recommended for titanium welding because of its high purity and low moisture content. A 75/25 argon/helium mixture can be used to improve stability and increase permeability only when specified.
The American Welding Society (AWS) recommends measuring welding gas purity to ensure it meets standards for each application. The protection gas is at least 99.995% pure, does not exceed 20 parts per million (PPM) of oxygen, and has a dew point greater than -76 degrees Fahrenheit. Other applications require 99.999% pure argon flow.
It is vital to equip the torch with the tail shield – otherwise there is an increased risk of oxygen contamination and, with it, the possibility of cracking. Some welders make their own trailing shields, although there are many styles available for purchase. The trailing guard fits the shape of the pipe and cuts the torch along the GTAW of the pipe. The shield provides additional argon protection on the weld after the torch and argon flow. Setting the torch and trailing guard airflow to 20 CFH provides the best protection coverage.
Always use a clean, non-porous plastic hose to deliver protective gas to the torch, tail guard and purge.
Selection of filler metal
Weld titanium pipes larger than 0.010 “in thickness using a filler metal (see Figure 1). In general, you should match the filling metal to the grade of titanium being welded – theoretically it should be a perfect match. Exceptions are allowed for some applications, such as fill metals with lower yield strength than the base metal to improve ductility. However, any changes should be carefully tested and investigated to ensure compliance with process requirements and specifications.
|Titanium filled metal alloys are recommended|
|Based on filling||AWS A5.16 ERTi – 2||AWS A5.16 ERTi – 2||AWS A5.16 ERTi – 3||AWS A5.16 ERTi – 5||AWS A5.16 ERTI-9 and ERTI-9ELI||
Gr1 (CP – 1)
[Industrial pure titanium]
|Gr2 (CP – 2)||X||X|
(Ti3A12. 5 v)
Pick the right flame and consumables
GTAW gives the welder better control over the heat input and pool than any other welding process. The GTAW inverter with high frequency arc start, remote current control features, rear flow timer and at least 250 amp output will weld titanium well.
Always set the polarity of the machine to dc electrode Negative (DCEN). The DCEN has deeper penetration than the dc positive electrode (DCEP).
Match inverter with air or water cooling torch. If your welding temperature is less than 150 amps and it costs less than a water cooled torch, the air cooled torch can provide good performance. The water-cooled torch, on the other hand, is smaller, easier to operate, and allows welds to be made at higher amperes for longer periods of time, although most welds on titanium are short and occur at output levels below 150 amperes.
Ground using a 2% metal tungsten electrode, matched to the welding current, as shown below:
Up to 90 amps:
- 1/16 of an inch or less.
- 90-200 amps: 3/32 inch.
- Over 200 amperes: 1/8 of an inch.
A gas lens is used to protect the gas evenly and to form a smooth flow over the weld pool.
Strike an arc and start working
First, cut off the end of the feeding rod to expose a clean, pollution-free spot and begin welding. Start the argon gas flow for a few seconds and then strike the arc to ensure that the welding area is completely covered.
Use high frequency arc starting function of frequency converter to strike arc. Cutting torch Angle similar to welding stainless steel, cutting torch speed and filling wire Angle provide the best conditions for welding titanium pipe.
It is fairly easy to make a welding pool out of titanium, but it may not be easy to move. Best results are usually obtained by pushing the weld pool with the arc and the filler rod, but the filler rod must be kept inside the protective gas housing during welding. It is also important to reduce heat input because too much heat can break the weld. Dab technique using filler metal (at a steady speed).
After soldering, allow a follow-up flow of 20 to 25 seconds to protect the joint as it cools to a threshold below 800 degrees Fahrenheit. So that oxygen doesn’t react with titanium anymore. Some welds may require temperatures below 500 degrees Fahrenheit.
Once the welding is done, the titanium can show its true color. The final color of the welded joint indicates the extent to which the shielding gas protects the weld from contamination and oxide thickness. In addition to visual inspection, dye penetration inspection, hardness testing, X-ray, ultrasonic inspection and destructive testing can also determine the quality of titanium welds.
|Color acceptance criteria|
|Welding color||Quality indicators|
|Purple||Unacceptable B, C|
|Deep blue||Unacceptable B, C|
|Light blue||Unacceptable B, C|
|Green||Unacceptable B, C|
|Note: Discoloration comes in a variety of shades.|
|Discoloration must be removed before further welding.|
|In the weld and HAZ, the maximum outside the weld is 0.03 inches.|
|If additional welding is required, violet, blue and green discoloration will result. The finished welds accept blue and green discoloration but must be removed prior to subsequent processing.|
Factors affecting welding quality of titanium
There are many welding methods. The appropriate welding method should be selected according to the design structure and specific application conditions of titanium equipment or components.
The principle of selecting welding method is to ensure the quality of welded joint, high production efficiency, simple operation and low cost. Among them, ensuring weld quality should be put in the first place. Only by fully recognizing all factors affecting welding quality can we achieve the purpose of ensuring the quality of welded joints.
Effect of gas impurities on properties of weld metal
Titanium has high chemical activity and high affinity with oxygen and nitrogen in the air. At a lower temperature, titanium interacts with oxygen to form a dense oxide film. With the increase of temperature, the thickness of the oxide film thickens. After exceeding 600 ℃, titanium begins to absorb oxygen and dissolve oxygen into titanium. When the temperature rises again, the activity of titanium increases sharply and reacts violently with oxygen to form titanium oxide. Titanium begins to absorb hydrogen above 300 °C and nitrogen above 700 °C. The result of oxygen and nitrogen pollution on titanium is that the strength and hardness of titanium are increased and the plasticity is reduced. Oxygen has a greater influence than nitrogen.
When the mass fraction of hydrogen in titanium is 0.01% ~ 0.05%, the impact toughness of weld metal decreases sharply, but the plasticity decreases less. This indicates that it is hydride induced brittleness (hydrogen brittleness). Hydrogen is also the root cause of weld porosity.
In the process of fusion welding, the molten pool is like a small metallurgical furnace, and the molten metal is exposed to the atmosphere. If no corresponding protective measures are taken to isolate the molten metal from the air, gas elements such as oxygen, nitrogen and hydrogen will integrate into titanium to form brittle oxides or nitrides, which will reduce the plasticity of weld metal and improve the tensile strength. In serious cases, brittle fracture will occur, and the plasticity is equal to 0.
Effect of other impurities on weld metal properties
Other impurities refer to impurities that may melt into the molten pool except for gas impurities. The source may be that the welding operation environment is not clean, the welder wears dirty gloves to touch the weldment, leaving oil stain, scrubbing the joint with cotton yarn before welding may leave cotton wadding, rust, moisture and other organic matter that may be produced by the mixing of welding production environment and steel welding. These pollutants decompose into oxygen, hydrogen, nitrogen, carbon and other elements under the action of arc high temperature, and then dissolve in the dissolved titanium. When the amount of these elements exceeds the solubility in titanium, corresponding compounds are formed, such as titanium dioxide, titanium hydride, titanium nitride, titanium carbide, etc. These compounds enter the crystal lattice of titanium with the crystallization of molten pool, resulting in distorted outer region, which changes the mechanical properties of titanium.
Some trace elements are incorporated into titanium in small amounts. If the amount does not exceed the allowable range, it is still possible, and sometimes people want it. However, the excessive content of impurity elements is not allowed, especially organic impurities, which are harmful but not beneficial. This is because these impurity elements make the mechanical properties of titanium welds worse and reduce the corrosion resistance, which is also the root cause of pores in the cold wind.
Microstructure changes of weld metal and joint heat affected zone
Titanium is a metal with allotropic transformation. The solid-state transformation of the structure begins at 886 °C. The crystal structure below 886 °C is close packed hexagonal structure, which becomes α Titanium; Above 886 °C α The structure of titanium is transformed into body centered cubic structure β Titanium. This transformation process is completed at the moment when the molten pool changes from liquid to solid. The difference of instantaneous length has an effect on the crystal form of molten pool. The longer the instantaneous length is, the more conducive to the growth of columnar crystal. Because titanium has the characteristics of high melting point (1668 °C), large heat capacity and poor thermal conductivity, the weld receives the influence of welding line energy and weld forced cooling during welding, and the moment when the cold wind stays at high temperature is different. The short instantaneous length provides conditions for the growth of columnar crystal in molten pool and the widening of joint heat affected zone. This is also one of the main reasons for the decrease of plasticity of welded joints. The tensile strength end of the joint often occurs in the weld heat affected zone. In order to reduce this adverse effect, a softer welding specification should be used as far as possible, that is, a smaller welding line energy and a faster cooling rate.
Porosity is a common and unavoidable defect in titanium weld
Porosity is a common process defect in titanium welding. The mechanism of pore formation is that the gas mixed with liquid metal in the welding process forms bubbles through the processes of diffusion, desolvation, nucleation and growth. Because the solidification and crystallization speed of the molten pool is very fast, when the growing bubbles have no time to escape from the liquid metal, they remain in the solid metal in the form of pores. Hydrogen, carbon monoxide and other gases forming pores are mainly produced by the thermal action of organic pollutants. Sometimes the weldments and welding materials are fully cleaned, cleaned and protected with varnish before welding, but there are still pores in the cold wind. This shows that the important pollution sources have not been completely removed. Practice has proved that an important air source is often ignored, that is, moisture in the air. A comparative experiment proves this. Welding in two environments without air humidity: one is welding in cloudy and rainy weather with relative humidity above 90%, and the other is welding in sunny weather with humidity less than 40%. Other pre welding cleaning, cleaning and welding operations are exactly the same. When the air humidity is high in cloudy and rainy days, there are many and large pores in titanium welds, but there are no pores in welds with low air humidity. This also fully shows that there is an important correlation between the generation of pores and the size of air humidity.
Precautions for titanium pipe in maintenance, storage, installation and transportation.
Maintenance and storage of titanium pipe and titanium alloy pipe
- Titanium alloy pipes and titanium elbows shall be inspected regularly to keep the surface clean and remove dirt. They shall be stored in an indoor ventilated place. They shall not be stacked or stored in the open air.
- When the ball valve, stop valve and gate valve of titanium alloy pipe elbow are used, they are only fully open or fully closed, and are not allowed to be used for regulating flow, so as to prevent the sealing surface from erosion and accelerated wear.
- The gate valve and upper thread stop valve are equipped with reverse sealing equipment. The hand wheel is screwed to the top head surface to ensure that it will not rust and degenerate. Keep the environment for storing titanium alloy pipes, titanium elbows, titanium big and small ends, titanium tees and other titanium pipe fittings dry and ventilated, keep the surface of pipes and pipe fittings clean and neat, and store them accurately according to the requirements.
Precautions for installation and transportation of titanium pipe and titanium pipe fittings
- 1. Installation of titanium and titanium alloy pipes during transportation and storage of titanium and titanium alloy pipes, the titanium pipe manufacturer shall pay attention not to contact and collide with ferrous materials.
- 2. Titanium and titanium alloy pipes shall be cut by mechanical method, and the cutting speed shall be low; Special grinding wheel shall be used when cutting or grinding titanium pipe with grinding wheel; Flame cutting shall not be used. The groove should be machined by mechanical method.
- 3. Inert gas shielded welding or vacuum welding shall be adopted for the welding of titanium alloy welded pipe, oxygen acetylene welding or carbon dioxide gas shielded welding shall not be adopted, and ordinary manual arc welding shall not be adopted.
- 4. When installing titanium and titanium alloy pipes, iron tools and materials shall not be used for knocking and extrusion; Rubber plate or soft plastic plate shall be padded between carbon steel supports and hangers and titanium and titanium alloy pipes to prevent them from direct contact with titanium and titanium alloy pipes; When titanium and titanium alloy pipes pass through the wall and floor, they shall be equipped with sleeves, the gap shall not be less than 10mm, and filled with insulating materials, which shall not contain iron impurities.
- 5. Titanium and titanium alloy pipes should not be directly welded with other metal pipes. When connection is required, looper flange connection can be used. The non-metallic gasket used is generally rubber gasket or plastic gasket, and the chloride ion content shall not exceed 25ppm.
Inspection and test of titanium pipe
Ultrasonic flaw detection, eddy current flaw detection, tensile test, flattening test, flaring test, visual surface inspection, chemical element analysis, and testing in strict accordance with the standard provisions or the testing requirements specified by the customer.
How to identify the authenticity of titanium pipe
The accurate identification of titanium pipes usually needs the help of professional Rockwell hardness tester. Our daily identification of titanium alloys mainly includes the following methods:
- 1. Specific gravity: the specific gravity of titanium alloy is about 4.51, which is 57% of that of stainless steel, so it is easy to distinguish from the hand feeling.
- 2. Color: the metal color of titanium alloy is gray white, and its color and texture are different from stainless steel and aluminum alloy. Because titanium alloy is difficult to polish and color, the surface of titanium alloy products is usually mechanically polished or frosted. Only a few high-grade titanium alloy products are partially polished, while the surface color of mechanically polished and frosted is the unique gray or dark gray of titanium alloy.
- 3. Strength: the strength of titanium alloy is higher than that of general stainless steel and aluminum alloy, which can reach twice that of stainless steel.
TA2 is pure titanium and TC4 is titanium alloy. It is difficult for non professional users to find a real TC4 in the market, because TA2 and TC4 are basically indistinguishable from the surface. Although the density of TC4 is a little heavier, it can not be used as a standard, but the processing technology of pure titanium pipe and TC4 pipe is different. Pure titanium is threaded, TC4 can not be threaded, and can only be machined. The simple visual identification method can refer to the inner wall of titanium pipe. If the machining is not smooth, it is more likely to be TC4 or other titanium alloy, while the smooth is pure titanium, but this method is not necessarily accurate.
Now the pipe industry is developed, and the process and quality of impermeable 304 seamless steel are actually very good. For example, 304 seamless steel pipe with outer 32 and inner 26 (wall thickness 3mm) or outer 35 and inner 28 (wall thickness 3.5mm) (theoretically, the smaller the outer diameter is, the more it can withstand high pressure) as long as there is no obvious deformation or damage inside and outside, the critical point can withstand about 20 MPa air pressure, but this is the critical point, It could explode at any time（ MPA: the normal air pressure is 1 standard atmospheric pressure ≈ 0.1MPa, that is, 1MPa ≈ 10 standard atmospheric pressure, that is, when 1 cubic 1MPa is released to the standard atmospheric pressure, 10 cubic meters of space can be filled, and so on. For example, when the pressure of your titanium pipe is 20MPa, the released air can fill the titanium pipe in your hand for about 200 times, compressing about 200 times the pressure. It can be imagined that carelessness is not allowed).
The specific gravity of stainless steel 304 is about 7.93, so it is easy to distinguish according to the formula. The calculation formula is as follows:
- 4.51 (specific gravity of titanium alloy) × 3.1416 (PI) × (Outer diameter – wall thickness) × Wall thickness ÷ 1000 × Length = kg/piece
For example: outer 32, inner 26, 50cm length: 4.51 × three point one four one six ×（32-3) × 3÷1000 × 0.5 = 0.616kg/piece.
Source: Network Arrangement – China Titanium Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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