What is a titanium pipe?

What is a titanium pipe?

Titanium pipe is light in weight, high in strength and excellent in mechanical properties. It is widely used in heat exchange equipment, such as tubular heat exchanger, coil heat exchanger, serpentine heat exchanger, condenser, evaporator and transmission pipeline. Many nuclear power industries use titanium pipes as their unit standard pipes. According to the material, it can be divided into pure titanium pipe and alloy pipe. According to the processing technology, it can be divided into seamless pipe and welded pipe. As the raw material for the production of finished pipe, pipe blank is also used to make pipe target (pure titanium) for vacuum coating. Pure titanium pipe can be used to produce titanium coil, such as heat exchange, heating pipe, condensing pipe and pipe on heat exchanger.

• Ti Tube Standards: ASTM B338, B861, B862, DIN 17 861, AMS 4941, AMS 4942
• Tube Type: Welded Tube / Seamless Tube
• Grade Material: CP Grades 1 – 4, Alloys: Grade 5, 7, 9, 12, 24, 26, 29
• Seamless Tube Dimensions:
  • Outer Diameter Range: 0.5 – 330 mm
  • Wall Height Range: 0.4 – 10 mm
  • Length Range: < 15000 mm
• Welded Tube Dimensions:
• Outer Diameter Range: 114 – 5,000 mm
• Wall Height Range: 0.5mm – 50mm
• Length Range: < 15000 mm

Pipe Size Chart

The NPS is a commonly used titanium tube sizing standard for pipes used for high pressure and temperature applications, along with the DN standard used in Europe. We manufacture titanium pipes to both standards and also customer defined requirements.

NPS	DN	OD[in (mm)]	Wall thickness[in (mm)]
			SCH 5	SCH 10s / 10	SCH 30	SCH 40s / 40 / STD	SCH 80s / 80 / XS	SCH 120	SCH 160	XXS
⅛	6	0.405 (10.29)	0.035 (0.889)	0.049 (1.245)	0.057 (1.448)	0.068 (1.727)	0.095 (2.413)	—	—	—
¼	8	0.540 (13.72)	0.049 (1.245)	0.065 (1.651)	0.073 (1.854)	0.088 (2.235)	0.119 (3.023)	—	—	—
⅜	10	0.675 (17.15)	0.049 (1.245)	0.065 (1.651)	0.073 (1.854)	0.091 (2.311)	0.126 (3.200)	—	—	—
½	15	0.840 (21.34)	0.065 (1.651)	0.083 (2.108)	0.095 (2.413)	0.109 (2.769)	0.147 (3.734)	—	0.188 (4.775)	0.294 (7.468)
¾	20	1.050 (26.67)	0.065 (1.651)	0.083 (2.108)	0.095 (2.413)	0.113 (2.870)	0.154 (3.912)	—	0.219 (5.563)	0.308 (7.823)
1	25	1.315 (33.40)	0.065 (1.651)	0.109 (2.769)	0.114 (2.896)	0.133 (3.378)	0.179 (4.547)	—	0.250 (6.350)	0.358 (9.093)
1¼	32	1.660 (42.16)	0.065 (1.651)	0.109 (2.769)	0.117 (2.972)	0.140 (3.556)	0.191 (4.851)	—	0.250 (6.350)	0.382 (9.703)
1½	40	1.900 (48.26)	0.065 (1.651)	0.109 (2.769)	0.125 (3.175)	0.145 (3.683)	0.200 (5.080)	—	0.281 (7.137)	0.400 (10.160)
2	50	2.375 (60.33)	0.065 (1.651)	0.109 (2.769)	0.125 (3.175)	0.154 (3.912)	0.218 (5.537)	0.250 (6.350)	0.343 (8.712)	0.436 (11.074)
2½	65	2.875 (73.03)	0.083 (2.108)	0.120 (3.048)	0.188 (4.775)	0.203 (5.156)	0.276 (7.010)	0.300 (7.620)	0.375 (9.525)	0.552 (14.021)
3	80	3.500 (88.90)	0.083 (2.108)	0.120 (3.048)	0.188 (4.775)	0.216 (5.486)	0.300 (7.620)	0.350 (8.890)	0.438 (11.125)	0.600 (15.240)
3½	90	4.000 (101.60)	0.083 (2.108)	0.120 (3.048)	0.188 (4.775)	0.226 (5.740)	0.318 (8.077)	—	—	0.636 (16.154)

NPS[5]	DN [2]	OD [in (mm)]	Wall thickness [in (mm)]
			SCH 5	SCH 10s/10	SCH 20	SCH 30	SCH 40s/40 /STD	SCH 60	SCH 80s/80 /XS	SCH 100	SCH 120	SCH 140	SCH 160	XXS[5]
4	100	4.500 (114.30)	0.083 (2.108)	0.120 (3.048)	–	0.188 (4.775)	0.237 (6.020)	0.281 (7.137)	0.337 (8.560)	–	0.437 (11.100)	–	0.531 (13.487)	0.674 (17.120)
4½	115	5.000 (127.00)	–	–	–	–	0.247 (6.274)	–	0.355 (9.017)	–	–	–	–	0.710 (18.034)
5	125	5.563 (141.30)	0.109 (2.769)	0.134 (3.404)	–	–	0.258 (6.553)	–	0.375 (9.525)	–	0.500 (12.700)	–	0.625 (15.875)	0.750 (19.050)
6	150	6.625 (168.28)	0.109 (2.769)	0.134 (3.404)	–	–	0.280 (7.112)	–	0.432 (10.973)	–	0.562 (14.275)	–	0.719 (18.263)	0.864 (21.946)
7[5]	–	7.625 (193.68)	–	–	–	–	0.301 (7.645)	–	0.500 (12.700)	–	–	–	–	0.875 (22.225)
8	200	8.625 (219.08)	0.109 (2.769)	0.148 (3.759)	0.250 (6.350)	0.277 (7.036)	0.322 (8.179)	0.406 (10.312)	0.500 (12.700)	0.593 (15.062)	0.719 (18.263)	0.812 (20.625)	0.906 (23.012)	0.875 (22.225)
9[5]	–	9.625 (244.48)	–	–	–	–	0.342 (8.687)	–	0.500 (12.700)	–	–	–	–	–

NPS[5]	DN [2]	OD [in (mm)]	Wall thickness [in (mm)]
			SCH 5s	SCH 5	SCH 10s	SCH 10	SCH 20	SCH 30	SCH 40s/STD
10	250	10.75 (273.05)	0.134 (3.404)	0.134 (3.404)	0.165 (4.191)	0.165 (4.191)	0.250 (6.350)	0.307 (7.798)	0.365 (9.271)
12	300	12.75 (323.85)	0.156 (3.962)	0.165 (4.191)	0.180 (4.572)	0.180 (4.572)	0.250 (6.350)	0.330 (8.382)	0.375 (9.525)
14	350	14.00 (355.60)	0.156 (3.962)	0.156 (3.962)	0.188 (4.775)	0.250 (6.350)	0.312 (7.925)	0.375 (9.525)	0.375 (9.525)
16	400	16.00 (406.40)	0.165 (4.191)	0.165 (4.191)	0.188 (4.775)	0.250 (6.350)	0.312 (7.925)	0.375 (9.525)	0.375 (9.525)
18	450	18.00 (457.20)	0.165 (4.191)	0.165 (4.191)	0.188 (4.775)	0.250 (6.350)	0.312 (7.925)	0.437 (11.100)	0.375 (9.525)
20	500	20.00 (508.00)	0.188 (4.775)	0.188 (4.775)	0.218 (5.537)	0.250 (6.350)	0.375 (9.525)	0.500 (12.700)	0.375 (9.525)
22	550	22.00 (558.80)	0.188 (4.775)	0.188 (4.775)	0.218 (5.537)	0.250 (6.350)	0.375 (9.525)	0.500 (12.700)	0.375 (9.525)
24	600	24.00 (609.60)	0.218 (5.537)	0.218 (5.537)	0.250 (6.350)	0.250 (6.350)	0.375 (9.525)	0.562 (14.275)	0.375 (9.525)

Specifications of Titanium Pipe

Properties of seamless titanium pipe

Chemical Composition of Titanium Pipe

Titanium Grade 1-4 is pure Titanium, the other grades are alloys. Pure Titanium is used due to its high corrosion resistance, the alloys because of the extremely high strength to weight ratio.

• Grade 1. Pure Titanium, relatively low strength and high ductility.
• Grade 2. The pure titanium most used. The best combination of strength, ductility and weldability.
• Grade 3. High strength Titanium, used for Matrix-plates in shell and tube heat exchangers.
• Grade 5. The most manufactured titanium alloy. Exceedingly high strength. High heat resistance.
• Grade 7. Superior corrosion resistance in reducing and oxidizing environments.
• Grade 9. Very high strength and corrosion resistance..
• Grade 12. Better heat resistance than pure Titanium. Applications as for Grade 7 and Grade 11.
• Grade 23. Titanium-6Aluminum-4Vanadium ELI (Extra Low Interstitial) Alloy for surgical implant Applications.

CHEMICAL, PHYSICAL AND MECHANICAL PROPERTIES
CHEMICAL COMPOSITION	ASTM Grade
(Max. Values)	1	2	5	7	9	12	23
N, Nitrogen	0,03	0,03	0,05	0,03	0,02	0,03	0,03
C, Carbon	0,1	0,1	0,1	0,1	0,05	0,08	0,08
H, Hydrogen	0,015	0,015	0,0125	0,015	0,013	0,015	0,0125
Fe, Iron	0,2	0,3	0,4	0,3	0,25	0,3	0,25
O, Oxygen	0,18	0,25	0,20	0,25	0,12	0,25	0.13
Pd, Palladium				0,12-0,25
Al, Aluminum			5,5-6,75		2,5-3,5		5,5-6.5
Mo, Molybdenum						0,2-0,4
V, Vanadium			3,5-4,5		2,0-3,0		3,5-4,5
Ni, Nickel						0,6-0,9
Ti, Titanium	Bal.	Bal.	Bal.	Bal.	Bal.	Bal.	Bal.
MECHANICAL PROPERTIES
Tensile strength, min (Mpa)	240,00	345,00	895,00	345,00	620,00	483,00	828,00
Yield strength, 0,2% Offset, min (Mpa)	170,00	275,00	825,00	275,00	483,00	345,00	759,00
Elongation (in 4D, min, %)	24,00	20,00	10,00	20,00	15,00	18,00	10,00
Reduction of Area, min, %	30,00	30,00	25,00	30,00	25,00	25,00	15,00
Hardness * Interpolated	Rb70	Rb80	Rc36	Rb80	Rc28	Rc17*

ASTM Grade	Description
1	Unalloyed Titanium – Low Oxygen
2	Unalloyed Titanium – Standard Oxygen
3	Unalloyed Titanium – Medium Oxygen
4	Unalloyed Titanium – High Oxygen
5	Titanium – 6%Al – 4%V
6	Titanium – 5%Al – 2.5%Sn
7	Unalloyed titanium plus 0.12 % to 0.25 % Pd, standard oxygen,
9	Titanium – 3%Al – 2.5%V
10	Titanium – 11.5%Mo – 6%Zr – 4.5%Sn
11	Unalloyed titanium plus 0.12 % to 0.25 % Pd, low oxygen,
12	Titanium – 0.3%Mo – 0.8%Ni
13	Titanium – 0.5%Ni – 0.05%Ru, low oxygen
14	Titanium – 0.5%Ni – 0.05%Ru, standard oxygen
15	Titanium – 0.5%Ni – 0.05%Ru, medium oxygen
16	Unalloyed titanium plus 0.04 % to 0.08 % Pd, standard oxygen,
17	Unalloyed titanium plus 0.04 % to 0.08 % Pd, low oxygen
18	Titanium alloy – 3%Al – 2.5 %V plus 0.04 % to 0.08 % Pd
19	Titanium – 3%Al – 8%V – 6%Cr – 4%Zr – 4%Mo
20	Titanium – 3%Al – 8%V – 6%Cr – 4%Zr – 4%Mo plus 0.04% to 0.08%Pd
21	Titanium – 15%Mo – 3%Al – 2.7%Nb – 0.25%Si
23	Titanium – 6%Al – 4%V, extra low interstitial, (ELI)
24	Titanium – 6%Al – 4%V plus 0.04 % to 0.08 %Pd
25	Titanium – 6%Al – 4%V plus 0.3% to 0.8%Ni and 0.04% to 0.08 %Pd
26	Unalloyed titanium plus 0.08 to 0.14 %Ru, standard oxygen
27	Unalloyed titanium plus 0.08 to 0.14 %Ru, low oxygen
28	Titanium – 3%Al – 2.5%V plus 0.08-0.14 %Ru
29	Titanium – 6%Al – 4%V, extra low interstitial, (ELI) plus 0.08-0.14 %Ru
30	Titanium – 0.3%Co – 0.05%Pd, standard oxygen
31	Titanium – 0.3%Co – 0.05%Pd, medium oxygen
32	Titanium – 5%Al – 1%V – 1%Sn – 1%Zr – 0.8%Mo
33	Titanium – 0.4%Ni – 0.015%Pd – 0.025%Ru – 0.15%Cr, standard oxygen
34	Titanium – 0.4%Ni – 0.015%Pd – 0.025%Ru – 0.15%Cr, medium oxygen
35	Titanium – 4.5%Al – 2%Mo – 1.6%V – 0.5%Fe – 0.3%Si

What are the uses for titanium pipe?

Titanium pipe is being used in an increasing number of applications because there are so many cases in which stainless steel and other materials are simply insufficient. Tubing is one of the common titanium mill products, and it is used in a range of products because of its superior strength-to-weight ratio and corrosion resistance. Let’s take a deeper look at titanium pipe and what it is commonly used for.

Application of seamless titanium pipe

1. Military seamless titanium pipe
For typhoon class nuclear submarines, seamless titanium tubes are widely used in military industry. Nuclear powered submarines, hydrofoil boats, mortar tubes, anti tank missiles, missile launchers, tank shields and bulletproof vests use a large number of titanium tubes. It is understood that the use of titanium tubes is as high as 9000 tons, which shows that the military industry has a huge demand for titanium tubes.
2. Application of seamless titanium pipe in aerospace
The number of titanium tubes used in civil aircraft accounts for about 20-25% of the weight of the frame. In addition, a large number of titanium tubes are also used in strategic rocket engines, spacecraft (such as Shenzhou 5 and Shenzhou 6) and satellite antennas. Titanium tubes are widely used in aviation industry.
3. Application of seamless titanium pipe in marine industry
Seamless titanium pipe has corrosion resistance, which can not be compared with other metal materials. Especially in seawater, it can withstand high-speed corrosion. At present, the United States, Japan, France and other countries have developed various advanced titanium controlled deep submersibles, submarines and submarine laboratory equipment for marine research. In addition, titanium control equipment and devices have been widely used in coastal power stations, offshore oil production equipment, seawater desalination, marine chemical product production and marine aquaculture.
4. Application in chemical industry
The types of equipment have developed from small and single to large and diverse. According to the prediction of the chemical industry department, the application of seamless titanium pipe equipment has expanded from the original soda and caustic soda industry to the whole chemical industry. The number of titanium tubes used in the chemical industry will exceed 1500 tons per year. State owned vacuum salt enterprises gradually began to use titanium tube metal materials to manufacture equipment, and the corrosion of equipment has been greatly improved.
5. Application in oil refining
Sulfide, chloride and other corrosive substances in petroleum processing products and cooling water. In the process of petroleum refining, the condensing equipment of atmospheric tower and vacuum tower in refinery, especially low-temperature light oil, is highly corrosive. One of the outstanding issues. In recent years, the United States, Japan and other countries have introduced seamless titanium control equipment for these high corrosion links, and achieved good results.
6. Application in automobile industry
Titanium tubes have been used in racing cars for many years. The lightweight and high strength characteristics of titanium tubes have always been the focus of automobile manufacturers. At present, almost all titanium tubes are used for racing. The number of titanium tubes for automobiles in Japan has exceeded 600 tons. With the development of the global automobile industry, titanium tubes for automobiles are still growing rapidly.
7. Application in medicine
With the progress of medical technology, metal implantation into the human body is a very rare surgical operation. Due to the weak rejection between seamless titanium tube and human tissue, it is widely used in human bone implants, such as artificial bone, artificial joint and artificial tooth. In addition, the application of titanium tubes in pharmaceutical machinery and medical equipment has been further recognized, and the future demand should not be underestimated.
8. Demand of titanium and titanium alloy tubes in shipbuilding industry

• 1) Submarine. Russia is an international leader in the research and manufacturing skills of creating titanium alloy submarines. It is also the first country to create pressure resistant shells with titanium alloy titanium tubes. At its peak, the annual output of titanium alloy thick plates and pipes for submarines reached 10000 tons, accounting for 30-50% of the annual output of titanium alloy processing. Since the 1960s, Russia has developed four generations of submarines. Russia created the first “Alfa” class submarine in 1970. In the 1970s-1980s, six submarines were built successively, each with about 3000t titanium. The typical application of titanium on ships, such as the Russian typhoon submarine, has a shell made of titanium alloy. Due to military needs, the double shell layout is selected. Its double shell shares 9000t of titanium, making it non-magnetic, deep diving, fast speed, low noise and less repair times.
• (2) Titanium alloy ship. Japan Tsai has good practical experience in making titanium ships. In the 1990s, DONGBANG titanium company, Nisheng industry company, Tengxin shipyard and Jiangteng shipyard all created all titanium fishing boats or speedboats. The advantages of titanium alloy ship are light weight, fast speed, small engine, low fuel cost, low carbon dioxide emission, no need for external coating, easy sorting of attachments, etc. the defects are high data cost, difficult processing and manufacturing skills and strict maintenance requirements. The results of the ship test show that the functions of ship speed, stability and noise are very good.
• (3) Atomic powered ship. Russia uses titanium alloy instead of stainless steel to make ship steam engine, heat exchanger and cooler, which overcomes corrosion damage. Titanium steam engines are widely used in the power plants of existing atomic powered icebreakers in Russia. The use of titanium alloy can extend the service life of the engine by more than 10 times.
• (4) Related parts of deep submersibles and rescue boats. The United States, Japan and France have successively created deep submersibles. The pressure shell is made of titanium and titanium alloy. Meanwhile, there are American aivin, sea cliff submersible, French sm97, Japanese deep-sea “2000”, and American Navy deep-sea rescue boat.
• (5) Sonar shroud. Titanium alloy sonar deflector has superior function and is used in the sonar system of Russian aircraft carriers “Kursk”, “titanium plate Minsk” and “Kiev”. According to the different requirements of underwater and surface applications, at present, there are basically two kinds of shell plate sound transmission data for the sonar fairing of ships in service in China, one is stainless steel and the other is fiber-reinforced FRP.
• (6) Propeller. The propeller has high data demand intensity, good fatigue function in seawater medium, erosion resistance and cavitation corrosion resistance. Titanium alloy can meet the above summarized functional requirements. American sailors first used 1500mm diameter four blade detachable supercavitation titanium alloy propeller on hydrofoil boats. China developed hydrofoil speedboat propeller in 1972, and has produced various titanium alloy propellers with a diameter of 450-1100mm. Long term application shows that the service life of titanium alloy propeller exceeds that of copper alloy propeller by more than 5 times.
• (7) Ship pumps, valves and piping. Because the working conditions of pumps, valves and pipes on ships are very poor, the service life of pipes made of copper and stainless steel is only 2-5 years. After replacing titanium alloy, it has excellent effect and is suitable for moving seawater pipeline with high flow rate. The life rule of Russian ship pipeline has three life requirements. That is, the time limit for the first docking repair is 8-9 years; The service life shall not be less than 15 years. Full life requires that all classes of ships should operate reliably within 25-30 years.

What is the right grade to use?

Production process of titanium pipe

The production process of industrial pure titanium pipe is as follows:

Pickling process

• 2Ti + 6HF = 2TiF3 + 3H2

• 3Ti + 4HNO3 + 4H2O = 3H4TiO4+ 4NO
• 3Ti + 4HNO3 + H2O = 3H2TiO3 + 4NO

• (35 %～40 %) HNO3  +  (5 %～7 %) HF + Remaining H2O 

Development of rolling process

• φ76mm x 7mm → φ51mm x 3mm → φ48mm x 2mm → φ45mm x 1. 2mm

Heat treatment process

Table 1 Relationship between thickness of oxide layer and annealing temperature

Annealing temperature / ℃	Color of oxide layer	Thickness of oxide layer / mm
<200	Silvery white	Extremely thin
-300	Canary yellow	Extremely thin
-400	Golden	Extremely thin
-500	Blue	Extremely thin
-600	Violet	0.005
-700—800	Red gray	0.0067~0.025
-900	Grey	0.03~0.050

The heat treatment of titanium tube usually adopts the chamber furnace cover to pass argon, but the furnace temperature of the chamber annealing furnace is very uneven, and the sealing performance of the cover is poor. Although argon is used for protection, the surface oxidation of titanium tube often occurs. In serious cases, the surface color of titanium tube is red gray or gray, which can be seen from table 1 as relatively thick oxide layer. This has brought some difficulties to pickling. Improper operation will lead to under pickling or over pickling, and the loss of titanium tube matrix will be large; moreover, the consumption of fuel and argon will also be large, resulting in high production cost. Therefore, in order to improve the heat treatment effect of titanium tube and reduce the production cost, the continuous roller hearth furnace is used instead of the chamber furnace heat treatment.

The process is as follows:

Quality assurance of titanium pipe

Problems and solutions in titanium tube processing

Defect name	Causes	Ways to prevent or eliminate
Transverse scratch on external surface	1. hole opening is insufficient. 2. the location of the Ma Tai plate is incorrect. 3. the hole opening is not smooth or the flange is too sharp.	1. increase the opening degree of groove. 2., adjust the location of the market. 3. repair opening flange.
Longitudinal scratches on external surfaces	1. the roll of multi roll mill is not flexible. 2. roll and pass asymmetry. 3. the outlet is not smooth.	1. adjust rolling mill, repair copper tile, adjust balance spring; 2. adjust the pass; 3. repair outlet.
Pipe end cracking	1. the plasticity of the metal is poor. 2. pass through hole. 3. excessive air reduction; 4. there are serious defects in both ends of the billet. 5. the clearance of the roll is too large.	1. reduce the amount of deformation; 2. reduce hole opening. 3. reduce the null value. 4. remove the defects of the tube billets to ensure that the ends are neat. 5. replace roller bearings and adjust clearance.
The external ellipticity is too large.	1. pipes do not rotate. 2. the finishing section of the pass or slipway is too short. 3. roll and pass asymmetry. 4. roll and pass wear seriously. 5. the diameter of the roll bottom groove is different. 6. the height of several slideways is inconsistent, or the position of adjusting the diagonal iron is different.	1. adjust the feeding mechanism; 2. increase the length of finishing section. 3. replace or adjust the pass; 4. replace the roll and choose the same roll with the same diameter. 5. replace the slideway and adjust the position of the diagonal iron, so that the positions of the skew iron of each block are the same.
The outer surface is rough and not smooth.	1. lubricants are not suitable or lubricants are not clean. 2. the clearance is too large. 3. pass and roll sticky metal; 4. pass and roll surface rough. 5. excessive delivery.	1. replace lubricants and keep lubricants clean. 2. adjust the rolling mill and reduce the clearance. 3. repair or replace pass and roll; 4. reduce delivery.
Internal surface abrasion	1. the surface of cores is sticky or defective. 2. the inner surface of pipes is poorly lubricated. 3. the adjustment of rolling mill is unreasonable.	1. repair or replace the core; 2. strengthen inner surface lubrication; 3. adjusting rolling mill.
Inner surface pit	1. the inner surface of the billet is not clean. 2. the location of the Ma Tai disk is incorrect, causing a string movement. 3. lubricants are not clean. 4. slipway or pass curve is not appropriate, causing local deformation too large and the bonding core.	1. clean the inner surface of the billet. 2. strengthen inner surface lubrication; 3., adjust the location of the market. 4. improvement of slideway or pass curve design.
Ring indentation	1. the opening of the roll pass is not proper. 2. core position is too close.	1. repair hole opening; 2. adjust the position of the core.
Uneven wall thickness on the same cross section	1. the deviation of tube wall thickness is too large. 2. the rotation angle of the pipe is not suitable. 3. the pre finishing section of the pass or slipway is too short. 4. the rolling center line is not correct. 5. core or guide rod bending; 6. the height of the slideway is different, or the diameter of the roll neck is different.	1. improve the quality of billet. 2. adjust the rotation angle; 3. increase the length of pre finishing section; 4. adjust the rolling center line; 5. replace the core or guide bar. 6. replace slideway or roll (multi roll mill)
Dimension overshoot	1. the size of the core is incorrect or the position is not accurate. 2. the clearance is too large or the pass wear is serious. 3. tool manufacturing error.	1. adjust clearance. 2. replace Tools.
Surface crack	1. the quality of billets is not good. 2. excessive variation. 3. inadequate annealing or uneven annealing temperature.	1. repair and inspect the tube billet seriously and improve the quality of the billet. 2. reduce deformation. 3. re annealing.
Metal or non-metal pressing in	1. the end of the tube blank has a puncture. 2. there is metal on the pass, roll and core. 3. lubricants are not clean. 4. inner and outer surfaces of tube billets are not clean.	1. remove pipe burrs; 2. regular inspection and repair tools; 3. replace lubricants; 4. scrub the inner and outer surfaces of pipes.
Wave	1. excessive delivery. 2. the length of the back cone is too short or the taper is too small. 3. the hole finishing section is worn to cone type. 4. variant size is too large and finishing section is too short.	1. reduce delivery; 2. increase the length or taper of the inverted cone after slideway. 3. replace the pass; 4. improving the pass design.
Flex press in	1. the opening of the pass is too small. 2. part of the pass wear is serious. 3. excessive delivery or uneven delivery. 4. gap is not suitable. 5. pipes do not turn.	1. enlarging hole opening. 2. replace the pass; 3. adjust the sending organization; 4. adjust clearance. 5. adjusting slewing mechanism.

Manual welding technology of titanium pipe

Titanium alloy has the characteristics of low density, high strength and corrosion resistance. As a new material, titanium alloy pipe is widely used in the field of aerospace, and the proportion of titanium pipe in Aeroengine pipeline is increasing. In addition, titanium alloy is a very active metal. It has great affinity for oxygen, hydrogen, nitrogen and other gases at high temperature, and has strong ability to absorb and dissolve gases. Especially in the welding process, this ability is particularly strong with the increase of welding temperature. During welding, it is necessary to control the absorption and dissolution of oxygen, hydrogen, nitrogen and other gases to avoid product scrapping, This brings great difficulties to the welding of titanium alloy pipe.

Manual argon arc welding of titanium pipe

Weldability of titanium pipe

(1) Embrittlement of welded joints
At room temperature, titanium reacts with oxygen to form a dense oxide film, which makes it have good chemical stability and corrosion resistance. At high temperature, especially in the welding process, the reaction speed of titanium alloy with oxygen, hydrogen and nitrogen is very fast. When harmful gases such as oxygen, hydrogen and nitrogen are invaded into the molten pool, the plasticity, toughness and surface color of the welded joint change obviously. Especially above 882 ℃, the grain growth tendency of the joint is serious, and martensite structure is formed during cooling, resulting in the strength, hardness The plasticity and toughness decrease, the overheating tendency is serious, and the joint is seriously embrittled. Therefore, during titanium alloy welding, comprehensive and reliable gas protection should be carried out for the molten pool, droplets and high-temperature area, whether on the front or back.
(2) Stomata
Porosity is the most common defect in titanium and titanium alloy welding, which mainly occurs near the fusion line. Hydrogen is the main reason for the formation of pores. During welding, titanium has a strong ability to absorb hydrogen (stronger at high temperature), but the solubility decreases significantly with the decrease of temperature. Therefore, the hydrogen dissolved in liquid metal often accumulates near the fusion line before it can escape to form pores.
(3) Delayed crack near crack
Titanium alloy is prone to crack (delayed crack) in the near seam area for a period of time after welding. The reason is that hydrogen diffuses from the high-temperature molten pool to the low-temperature heat affected zone. With the increase of hydrogen content, the amount of TiH2 precipitated increases, which increases the brittleness of the heat affected zone. In addition, the microstructure stress generated by the volume expansion of precipitated hydride finally leads to cracks.

Welding requirements and precautions of titanium pipe

• (1) A special welding workshop shall be set as far as possible. Smoking is strictly prohibited in the room. The environment shall be kept clean and dry, and the convection of air shall be strictly controlled.
• (2) Welders shall wear clean work clothes and degreasing gloves during welding. It is strictly prohibited to touch parts with bare hands.
• (3) The welding area and welding wire surface shall be degreased with acetone.
• (4) High purity argon shall be used for protection, and the purity shall not be less than 99.99%. The air supply flow during welding shall protect the front and back of the weld bead according to the value specified in the process specification.
• (5) During the welding process, the argon flow in the pipe and the argon flow in the welding tool nozzle shall be kept constant to prevent the convex concave phenomenon of weld pool forming in the pipe.
• (6) Short arc welding shall be adopted as far as possible and small welding line energy shall be adopted.
• (7) When spot welding the nozzle, the gap shall be less than 30% of the wall thickness. Each weld shall be welded at one time as far as possible.
• (8) During welding, the welding tool shall not swing left and right, and the melting end of the welding wire shall not move out of the gas protection zone. During arc striking, air shall be supplied for 10-15s in advance. During arc stopping, the welding gun cannot be lifted immediately. Air supply shall be delayed for 15-30s until the temperature drops below 250 ℃.

Welding technology 

1. Cleaning before welding.
The occurrence of welding defects is closely related to the surface cleanliness of weldments and welding wires. Before welding, the oil stain, water, oxide film and other dirt within 15 ~ 20mm of the edge of the pipe joint and the surface of the welding wire shall be cleaned. The cleaning method can be chemical (pickling) or mechanical (stainless steel brushing) to remove the surface oxide scale. Before welding, it shall also be scrubbed with acetone or alcohol. The cleaned weldment must be welded within 24h, otherwise it needs to be cleaned again. The welding wire shall be subject to vacuum dehydrogenation treatment after pickling, and degreased with acetone before welding.
Gas protection. When welding titanium pipe joints, in order to prevent the welded joints from being polluted by harmful gases and elements at high temperature, necessary argon protection must be provided for the welds, and the purity shall not be less than 99.99%. Argon flow is shown in table 2-1.
2. Selection of welding process parameters.

• (1) Selection of welding wire. The grade of filler wire shall be selected according to the base metal. Generally, the principle of homogeneity with the base metal is adopted. Sometimes, in order to improve the plasticity of the joint, the welding wire with a slightly lower alloying degree than the base metal can also be selected. The diameter of welding wire shall be selected according to the thickness of base metal, as shown in table 2-1.
• (2) Selection of power supply and polarity. Titanium and titanium alloy welding generally adopts DC manual tungsten argon arc power supply, and its polarity connection method adopts DC positive connection.
• (3) Selection of tungsten electrode. The diameter of tungsten electrode shall be selected according to the wall thickness of titanium alloy pipe, generally between 1.0-3.0mm, and the tungsten electrode shall be ground into a cone of 25 ° ~ 45 °.

Installation of titanium pipe

After the arrival of titanium pipes, the owner, construction director, constructors, quality inspectors and welding technicians shall be arranged to inspect the material, standard, quantity, quality and quality certificates of pipe valves. It is necessary to have the factory certificate and quality certificate of the manufacturer. Moreover, the outer diameter and wall thickness shall be measured one by one, and its outer diameter, wall thickness and ovality must meet the specification requirements. The internal and external surfaces shall be lubricated and clean without pinholes, cracks, folds, excessive corrosion and other defects.
Titanium pipes shall be placed equally during transportation. Nylon or synthetic fiber sling should be selected during hoisting. If steel wire rope and shackle are selected, they shall not be in direct contact with the pipeline, and rubber or asbestos products shall be selected for isolation.
For the titanium pipe with good material, if the diameter is small, it is best to get on the bed and make the groove. The speed of the lathe should be slow and pay attention to cooling. For larger diameter (above DN100), a grinder should be used to grind the groove. The operation speed should be slow, complete in several times, and pay attention to cooling. When approaching the requirements, remove the contaminated layer with a fine tooth file until the groove requirements are met. The groove surface shall be flat without crack and double skin, and the burr, slag and oxide shall be completely removed. The groove angle shall meet the welding process requirements. After the groove is processed, pickling and finishing shall be carried out within 50mm on both sides of the groove. Then seal it with plastic cloth and mark it. When grinding and cutting is selected, the operation shall be carried out in other places that meet the requirements. After the groove processing meets the requirements, it shall be moved to the special place for prefabrication.
In the construction of titanium pipe, some small holes such as condensate drainage, drainage and external source taking parts are often encountered, which is difficult to open with conventional methods. Before welding the titanium pipe, draw the size of the hole and the specific and accurate position of the hole on the corresponding titanium pipe. Use a lathe to drill many small holes along the marginal center line of the hole. The denser the better. After all the holes are drilled, tap the central arc plate of the hole with a copper hammer to separate it, and then process the hole to meet the requirements with special tools such as fine tooth round file.
Impurities such as oil stain and oxide film on the surface of titanium pipe will pose a hazard to welding. It is necessary to sort them out before welding. All welding surfaces and the surface of base metal on each side of weldment shall be cleaned with non induced steel wire brush within at least 50nrn. The surface of titanium pipe with oxide layer shall be cleaned of oxide film, and then the base metal shall be cleaned with acetone. It is also necessary to arrange the welding wires in the same way. The processed weldments and welding wires shall be assembled and welded immediately. If the storage time exceeds 2h, the above process must be repeated. It is necessary for the operators to wear clean gloves during the welding process. The welding environment should be clean and the wind direction and wind force should be appropriate to reduce the dust in the air, so as to protect the cleaning of both sides of the groove and the welding wire.
Matters needing attention:

• 1. 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.
• 2. Inert gas shielded welding or vacuum welding shall be adopted for the welding of titanium alloy pipe, oxygen acetylene welding or carbon dioxide gas shielded welding shall not be adopted, and ordinary manual arc welding shall not be adopted.
• 3. 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.
• 4. 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.