1 Products Description
Under certain corrosion conditions, titanium has better corrosion resistance than stainless steel and aluminum copper. Although the cost is higher than that of stainless steel equipment, under certain conditions, titanium equipment has high reliability and long service life, so titanium has been widely used. China has used titanium materials to manufacture chemical equipment for more than 40 years. However, titanium chemical equipment, especially titanium - steel composite plate chemical equipment, is more technically difficult than steel chemical equipment and has much less accumulated experience. Therefore, the design and manufacture of titanium - steel composite plate chemical equipment has attracted much attention. In the chemical equipment made of titanium-steel composite plate, the largest amount is used for vessels, and also for pressure vessels. In general, when the operating pressure and temperature (above 200 ℃) are high, the head and all shell sections of the pressure vessel are made of titanium-steel composite plate, which is commonly known as GR12 titanium clad steel plate for vessels.
2 Grade of titanium steel composite plate for pressure vessel
Titanium-steel explosive composite plates for pressure vessels are divided into Level 1, Level 2 and Level 3. three point two.
Grade 1 composite plate, with a non-bonding rate of 0%, is used for transition joints, flanges and other high bonding strength, and the non-bonding zone is not allowed; Grade 2 composite plate, with unbound rate ≤ 2%, is a composite plate that uses titanium as strength design material or special purpose, such as tube plate; Grade 3 composite plate, with unbound rate ≤ 5%, is a composite plate that uses titanium as a corrosion resistant design without considering its strength.
3Main technical regulations for titanium-steel composite plate materials for pressure vessels
The clad material shall be in annealing state before composite. The technical requirements of the base material (such as delivery status, mechanical property inspection rate, ultrasonic testing, etc.) shall also comply with the provisions of GB150 or JB4732. When the forging is used as the base material, the grade III or IV forgings shall be used. The titanium-steel composite plate for pressure vessel shall be delivered after heat treatment (stress relief annealing), leveling, shearing (or cutting) and oxide scale removal treatment on the surface of the clad material. The titanium-steel composite plates for pressure vessels shall be ultrasonically tested one by one, and the scanning method shall be 100% scanning. The binding state shall comply with the corresponding level regulations.
4 Bonding shear strength of composite interface of composite plate
The standard NB/T47002-2009 stipulates that the combined shear strength of the composite interface of the GR12 Titanium Clad Steel Plate for vessels for pressure vessels should not be less than 140MPa, and the combined shear strength of the composite interface of the stainless steel-steel composite plate should not be less than 210MPa. Compared with the lower limit of the standard shear strength, the former is 70 MPa less than the latter, mainly due to the results of the annealing treatment of the titanium-steel composite plate at 650 ℃. There is internal stress in the composite plate after explosion. When the internal stress is large, titanium and steel will be separated during transportation or cold correction, so the internal stress should be removed by annealing.
5 Rolling of titanium steel composite plate cylinder for pressure vessel
In the process of rolling steel plate into cylinder, in the direction of steel plate thickness, the outer layer of the neutral line of steel plate thickness is stretched and the inner layer is compressed. The closer the outer layer is, the greater the tensile deformation is, and the closer the inner side is, the greater the compression deformation is. There is a sliding trend in the microscopic layers, that is, there is shear stress. Although some of the stress caused by explosion is eliminated by annealing, there is still some stress at the interface, and then the shear stress generated by coiling is superimposed, which makes the interface of titanium - steel composite plate with low bonding shear strength face huge peeling risk. These factors determine the special requirements for the rolling of Ti-steel composite plate cylinder.
6 Welding of titanium-steel composite plate joints for pressure vessels
Because the fusion of titanium and steel will produce intermetallic compounds TiFe2 and Te, which will reduce the comprehensive mechanical properties of weld metal and reduce the corrosion resistance of titanium, the welding of titanium and steel composite plate joints is actually titanium welding and base steel welding. Typical butt joints of common titanium-steel composite plates are shown in Figure 1, and the welding sequence is as follows: base material welding - base material welds pass NDT - one drilling inspection hole - laying titanium backing plate - assembling and welding titanium cover plate.
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