Expanding process of titanium tube and titanium steel composite tube plate and welding process using manual tungsten argon arc welding. The manufacturing practice of liquid ammonia cooler has proved that the titanium tube and titanium steel composite tube plate can obtain high quality weld under the premise of choosing a reasonable manufacturing process, and has accumulated certain experience for the manufacture of titanium and titanium steel composite plate heat transfer equipment.
Titanium is an active element, which can form a dense oxide film with oxygen at room temperature and maintain elevated stability and corrosion resistance. The oxide film formed above 540 "C is not dense. At elevated temperature, titanium reacts quickly with oxygen, nitrogen and hydrogen, and is prone to form brittle substances, which makes the reliability very poor. Therefore, in order to ensure the welding quality of titanium tube and titanium steel composite tube plate, we start from the aspects of material and equipment structure, through the technology test and welding process evaluation, some data are obtained.
The manufacturing technology of Titanium steel composite Tubing and Titanium Tubing bundle is expanded before welding. In order to ensure the manufacturing quality of the products, we have conducted the following technological tests.
The external cooler requires first expansion and then welding. the strength is guaranteed by expansion, welding mainly plays a sealing role. In order to ensure the strength of expansion, we carried out the process test of expansion between tube plate and tube bundle.
After the tube expansion test, we tested the expansion quality with the method of measuring the compressive force, and determined the process parameters such as the number of expansion and expansion relay to ensure that the tube expansion rate is 15. Within the range of 20°%, the design requirements are met.
Welding position selection test of titanium tube bundle and tube plate.
Through the welding test found that: when the titanium tube bundle and tube plate are welded in full position, it is necessary to use argon-filled protection trailing cover to track the hot area of the tube head, so the welding tube bundle needs two people to operate, and should be closely cooperated, Once the cooperation is not excellent, easy to make the tube head oxidation discoloration, affecting the welding quality. When welding in the horizontal position, welding the tube head in the argon filled protective cover not only has a good protection effect, but also can ensure the welding quality. And the operation is convenient. As long as one person can operate, one argon filled protection can weld more than ten tube heads, considerably speeding up the welding progress. There are pits in the factory building, and there are horizontal position welding conditions, so the titanium tube bundle of the external cooler is welded in a horizontal position.
Titanium has a strong affinity with oxygen, and can form a dense oxide film at room temperature. This layer of oxide film is a serious obstacle for welding. We welded titanium tubes with severe oxidation and found that it would cause serious cracks. The test proves that the oxide film on the weld surface must be cleaned and treated closely before welding to eliminate the source of harmful impurities.
Before threading the pipe, carefully wash the oil and dirt in the pipe hole with acetone before loading the pipe.
Before welding with tube bundle should be welded area for mechanical cleaning (with diameter of 0.1mm austenitic stainless steel wire brush to remove the surface oxidation layer to be welded), defatting (scrub with acetone), with white silk check does not alter color, qualified before welding tube bundle, welding suspension and non-welding area should be covered with white silk, it is forbidden to dust dirt into the welding area.
Cleaning the titanium tube depends on the surface quality of the titanium tube. The surface of the titanium tube is not severely oxidized. The outer surface of the tube, especially the 100mm of the tube end, is washed with acetone after threading the tube, and the tube head and hole are cleaned with acetone again before welding.
For titanium tubes with severe surface oxidation, pickling must be carried out 100mm from the front ends of the tubes. The pickling formula is as follows:
HF:HNO3: 0=5:20:75(volume ratio)
The temperature was room temperature and the pickling time was 2? 5 minutes, immediately after pickling with fresh water, no residual acid. The titanium tube end is silvery white after pickling.
On the basis of the above technology test and welding process evaluation, we essentially find out the characteristics of titanium tube bundle welding, and determine the manufacturing process of tube bundle: titanium tube bundle first expansion after welding, and the use of horizontal position welding process.
In order to control welding deformation, strengthen the cooling of titanium welds, improve the protection effect, titanium tube bundle welding, tube plug copper plug.
By adopting manual TIG welding process, selecting reasonable welding specifications, carefully cleaning the oxide film and debris of tube plate and tube end, under the condition of reliable protection (making suitable protective cover), the welding joint of titanium tube and titanium steel composite tube plate can get satisfactory quality.