Welding of zirconium tube

Zirconium tube is generally used in conveying the medium with strong corrosion, such as acetic acid used in the petrochemical engineering construction is relatively small, but it has its particularity compared with other metal material welding, we passed the test of the welding and welding procedure qualification for zirconium tube method, this article introduces the welding process and the matters needing attention, for your reference.

1 Preparation
1.1 Material
(1) The construction site shall be equipped with a fixed welding material library or a mobile welding material library that meets the requirements.
(2) The welding wire used must have quality certificate or material certificate. (3) before using the welding wire, acetone or alcohol must be used to remove the grease and other sundries on the surface, and the use of carbon tetrachloride chloride as a degreasing solvent is strictly prohibited. It must be used up within 30 minutes after cleaning, otherwise it should be cleaned up again before use.

1.2 Protect argon
It is particularly important to ensure that the argon gas used is at least 99.999% pure.

1.3 Machine
The welding machine is a special argon arc welding machine with high frequency arc starting device, and with remote control current device and water cooler.

Welding wire cylinder, planer hammer (surfacing stainless steel layer), stainless steel wire brush, file and other tools must be complete and special, and regularly degreased cleaning. It should also be equipped with small hand phone, endoscope, split-port detector, contact thermometer and air cooler (if the site has conditions, air cooling device can be used).

1.4 Operating conditions
Welders must have ASME 1X certificate. Weld as far as possible in the indoor prefabricated plant. If installed on site, no matter what the environment is, a wind shelter must be installed. If the ambient temperature is below 15℃, it must be preheated to above 15℃ before welding. The welding machine shall not be more than 5m away from the welding parts.

2 Welding Process
2.1 Beveling requirements
Bevels shall be machined by mechanical means.

2.2 Group requirements
The inner wall of the tube is flush, and the wrong mouth quantity is not more than 0.5mm. Before group pair, use acetone or alcohol to clean up oil stains and other debris in the groove and the range of 75 mm on both sides, and use stainless steel wire brush to clean the groove and the base material within the range of 25 mm on both sides.

2.3 Welding Method
All joints are made of full argon arc welding and full penetration welding. All parts in contact with the base metal shall be zirconium or austenitic stainless steel. Specific methods are as follows:

(1) The spot welding mode is bridge welding, the process and welding material are the same as the formal welding process, and the number of welding spots is 3~4.

(2) arc starting using back welding method, and high frequency arc starting, do not allow friction arc starting. Welding should be conducted with a small current and a slight swing.

(3) When the back is protected by argon, both ends of the pipe can be sealed with sponge, and the welding joint is sealed with high-temperature adhesive paper (medical tape is not allowed), and the length of the opening is the length of the primary welding seam. If the pipe section to be welded is short, argon should be used as a whole; For longer periods, argon is filled locally. Argon filling time for welding stainless steel 5~10 times.

(4) During the welding process, pay attention to the end of the welding wire do not leave the argon protection area. If the welding wire leaves the argon protection, cut off at least 25 mm of the end of the welding wire when continuing the welding.

(5) Try to avoid using grinding wheel machine for grinding, and use metal grinding head for grinding. If grinding machine is used for repairing and grinding, watering and cooling shall be required at the same time, and the grinding temperature shall not exceed 315 ℃ to avoid strong oxidation.

(6) The temperature between layers should be strictly controlled, and the temperature between layers should not be higher than 107 ℃.

(7) After the welding, cool to room temperature before removing the tail cover, and then mark the welder's steel mark, pipeline number and welding joint number 50 mm away from the weld with a marker.

3 Precautions
(1) The argon bag must be kept dry to ensure the purity of argon.

(2) The purity of argon gas must be checked after each replacement of the argon cylinder or air bag.

(3) When welding, the tail protection device is used, so that the whole area of the weld is well protected in solid state and melting state, until room temperature. The radius of curvature of the protective device should be adapted to the outside diameter of the staggered pipe to protect the weld and the heat affected zone.

(4) After welding, hammering is not allowed.

4 Color Check
After welding, light yellow, dark yellow and light blue indicate that the weld has been oxidized and need to be cleaned with a stainless steel wire brush. Silver-white indicates that the weld is well protected. Dark blue, blue-gray, gray and white indicate that the weld is strongly oxidized and need to be polished and repaired.

5 Conclusion
Zirconium tube (ZirR60702) has been successfully welded with the welding qualification rate above 98%. Practice has proved that argon gas with purity up to the requirements for welding protection and tail protection is the key to welding wrong pipe. At present, there is no specification for staggered pipe welding in petrochemical and chemical industries in China. Therefore, relevant departments should consider formulating relevant specifications as soon as possible, so that construction units can have "law" to follow.