Titanium welded tubes and fittings have high strength, good plastic toughness and corrosion resistance, and are more and more widely used in aerospace, shipbuilding and chemical industry. In order to make better use of titanium tubes, it is necessary to master its weldability. This paper mainly expounds the welding process of titanium tubes, which provides a useful reference for the welding of titanium tubes in the future.
1. Welding material
Welding wire: ERTi-2 / titanium grade 2 /UNS R50400
Wlding method: GTAW (manual argon tungsten arc welding)
Shielding gas: Use argon gas with a purity of 99.995% and a water content of not more than 50Mg%m3, and use argon gas protection for the welding pool and the areas where the temperature of the inner and outer surfaces of the welded joint is higher than 400 °C.
2. Preparation before welding
(1) Groove processing
After the titanium gr2 tube is cut, use an alumina grinder to grind out the bevel, as shown in the figure below, the processed bevel is not allowed to cause overheating and discoloration of the base metal.
(2) Groove and titanium welding wire cleaning
a. Clean the inner and outer surfaces within 50mm of the groove and both sides.
The cleaning procedure is as follows: Grinding with a sander → polishing with a sandpaper wheel → cleaning with acetone.
After cleaning, the welding operation cannot be carried out directly, and the operation can only be performed after the end face of the groove is dried. If it is placed for more than 2 hours, it must be cleaned again or the groove must be protected with self-adhesive tape and plastic cloth.
b. The welding wire should also be wiped clean with acetone-soaked sponge, and stored in a dedicated welding wire box.
c. Operators must wear clean gloves during welding.
3. Titanium Welding procedure specification
(1) Titanium Welding specification: the following table:
| Wall thickness/mm | 2~4 | 4~8 | ≥8 | |
| welding rod | 2 | 2~4 | ≥4 | |
| OD welding rod/mm | 1.6 | 2 | 3 | |
| ac/A | 50~90 | 60~120 | 100~140 | |
| vt/V | 10~11 | 11~12 | 11~12 | |
| speed/（cm/min-1） | 6~10 | 7~12 | 5~10 | |
| Ar gas flu/ (L.min-1) | gun | 12~15 | ||
| mask | 25~30 | |||
| bak | 25~36 | |||
(2) Titanium welding should be performed within the range of qualified process parameters with small input energy welding, generally controlled at 6~35KJ/cm, and low current and slow speed welding should be used.
(3) The interlayer temperature should not be higher than 200°C to prevent the grain from growing up if the high temperature time is too long.
(4) In order to protect the surface of the arc after the arc is broken, the gas supply protection should be stopped after the temperature of the welding point is below 300°C (the time is 15~60s, which can be gradually extended according to the pipe diameter from small to large).
(5) Argon filling protection: the specific measures are as follows:
a. When titanium welding pipes with DN greater than or equal to 450, the staff in the titanium pipes should wear gas masks and hold protective covers to protect the back of the welding pool.
b. For the titanium welding of titanium pipes with DN less than 450 or fixed ports, the overall protection is filled with argon, and the inner surface of the pipe is sealed with soluble paper at a distance of 150-300mm from the groove, and then a group of soluble paper is inserted to prevent the pressure in the pipe from being too high. The paper is destroyed, and then filled with argon to remove the air in the tube. The argon gas must be fully prefilled before welding, and the argon filling should be delayed after welding to fully cool the high temperature area and prevent surface oxidation.
(6) During the titanium welding process, the filler wire should always be kept under the protection of argon gas. The welding wire should not be exposed to the atmosphere immediately after the arc is extinguished, and should be taken out when the weld is out of protection. If the welding wire is polluted, oxidized and discolored, the polluted part should be cut off.
(7) It is not allowed to strike or test the arc on the surface of the weldment; the arc crater should be filled up when the arc is closed, and the interlayer joints of multi-layer welding are staggered from each other.
(8) Except for special requirements, each weld should be welded continuously at one time. If it is forced to be interrupted for some reason, inspection must be carried out when re-welding, and welding can only be continued after confirming that there are no cracks.
(9) If tungsten is caught accidentally during welding, the welding operation should be stopped, the tungsten spot should be removed with a grinder, and the end of the tungsten grade should be re-ground, and the welding operation can be resumed only after meeting the requirements.
The key points of the process mentioned above ensure the normal progress of titanium tube welding, and also meet the welding quality requirements of titanium tubes.