The minimum thickness of the shell of the all-titanium vessel is 2mm, which is mainly considered to meet the thickness requirements of the welding process and ensure the geometric tolerance requirements during manufacturing and meet the stiffness requirements required in the process of manufacturing, transportation and hoisting. And also save titanium material, reduce costs.

Design selection principle

Because the mechanical strength of titanium material decreases significantly when the temperature is greater than or equal to 200℃, and the elastic modulus of titanium is low, therefore, the all-titanium structure is not suitable for the application of high temperature, high pressure or medium pressure and large equipment.

The operating temperature of the all-titanium pressure vessel should not exceed 250℃, and it is considered that the all-titanium structure is more economical for the medium and small sized vessels with the pressure of 0.5MPa and the temperature below 150℃. Considering the investment cost, pure titanium may not be economical when the thickness is greater than 13mm.

Structure requirements

Although the all-titanium vessel is similar to stainless steel in structural design, it has its own uniqueness in design and manufacturing due to some special properties of titanium material itself. Therefore, the following points should be paid attention to in structural design:

1) In the design of the welding structure, the welding site must be convenient for the operation of the hydrogen arc welding tool and all the welding joint areas under high temperature (above 400℃) can be effectively protected.

Titanium can combine with almost any element in the molten state, so special protection must be taken during welding and hot working. In order to achieve the purpose of effective protection, the structure shape of the parts should be simple, and the opening of the pipe on the shell should be perpendicular to the axis of the shell as far as possible, so that the production of the protection fixture is convenient and the protection effect is better.

2) Strictly avoid the welding structure of steel and titanium melting. Because iron and other metals melt in the titanium weld will form hard and brittle intermediate metal compounds, greatly reduce the weld plasticity, except for explosion welding and brazing, titanium and steel can not be welded.

3) The gap of the blunt side of the butt welding joint should be appropriate. The gap of butt-welded joint of all titanium pressure vessel is smaller than that of steel, which is due to the high melting point of titanium, poor thermal conductivity, small heat capacity, large resistivity and large metal fluidity of welding pool.

4) The design of titanium vessels should ensure the continuity of structure and smooth transition of welded joints to avoid stress concentration as far as possible.

5) The bending and flanging of titanium parts should adopt a larger bending radius (compared with steel), and a smaller expansion rate should be adopted when expanding the tube.

6) Industrial pure titanium in some media is easy to produce crack corrosion, in the design, processing and these media contact containers, should try to avoid cracks and stagnant area, crack corrosion resistant titanium alloy (such as titanium and palladium alloy) or coating in the cracks.

7) In the design and treatment of vessels in contact with conductive corrosive media, if it is found that titanium contact with other metals can lead to galvanic corrosion, measures should be taken on the structure (such as using a third material as a transition layer) or using anode protection.

8) In the design of equipment prone to corrosion, the flow rate of corrosive media should be lower than the critical flow rate, and try to avoid sudden changes in flow rate or flow direction; Or in the parts prone to corrosion and abrasion to set up a protective baffle.

(1) when the medium is corrosive or abrasive and the ρ V2 >740kg/(m•s2) or the medium is not corrosive or abrasive, but the ρ V2 BBB>55kg /(m•s2) (ρ is the density of the medium, kg/m3, V is the linear velocity of the material flow, m/s), the material inlet should be provided with an anti-impact plate.

(2) When the corrosive medium enters the equipment along the tangential direction, or the inlet pipe is facing the wall, and the distance between it is less than 2 times the outer diameter of the pipe, the protection plate should be set.