Structural Requirements Of All-titanium Vessel

All titanium container means that the main parts, such as shell, head and receiver made of titanium, secondary parts can be made of non-titanium, for example, the flange and its connecting bolts can also be made of carbon steel.
All titanium container shell minimum thickness of 2mm, mainly to meet the welding process in the manufacture of thickness requirements and to ensure that the geometric dimensional tolerances of the requirements to meet the manufacturing, transportation and lifting process of the required stiffness requirements; as well as to save titanium, reduce costs.
Design selection principles
As titanium at a temperature greater than or equal to 200 ℃, the mechanical strength of a significant decline, and titanium's modulus of elasticity is low, therefore, all-titanium structure in the high temperature, high pressure or medium pressure and large-scale equipment applications is not appropriate.
The permissible temperature of the full titanium pressure vessel should not exceed 250 ℃, and that the pressure in 0.5MPa, the temperature is below 150 ℃ small and medium-sized container selection of full titanium structure is more economical. From the investment cost considerations calculated thickness greater than 13mm, the use of pure titanium may not be economical.

Structural requirements
Although the full titanium container in the structural design and stainless steel is somewhat similar, but because of some special properties of titanium itself, so that in the design and processing and manufacturing of its uniqueness, so in the structural design, attention must be paid to the following points:
1) In the design of the welding structure, must make the welding part easy to operate hydrogen arc welding tool, and make all in the high temperature (more than 400 ℃) of the welded joint area can be effectively protected.
Titanium, in its molten state, is capable of chemically combining with almost any element, so special protection must be taken during welding and heat processing. In order to achieve effective protection, the shape of the parts structure should be simple, and the receiver opening on the shell should be perpendicular to the axis of the shell as much as possible, so that the protection fixture is easy to make and the protection effect is better.
2) Strictly avoid the welding structure of steel, titanium mutual fusion. As iron and other metals fused to titanium weld will form a hard and brittle intermediate metal compounds, greatly reducing the weld plasticity, in addition to explosion welding and brazing, titanium and steel can not be welded.
3) Butt welded joints blunt edge clearance should be appropriate. All titanium pressure vessel butt welded joints to be smaller than the blunt edge gap of steel, this is due to the high melting point of titanium, poor thermal conductivity, heat capacity and resistance coefficient of small and welded molten pool of metal fluidity.
4) Titanium container design should ensure structural continuity and smooth transition of welded joints, try to avoid stress concentration.
5)The bending and flanging of titanium parts should adopt a larger (compared with steel) bending radius, and when expanding the pipe, a smaller expansion rate should be used.
6) Industrial pure titanium in some media prone to crevice corrosion, in the design, processing and these media contact with the container, should try to avoid the appearance of the crevice and stagnant flow area, in the crevice with crevice corrosion-resistant titanium alloy (such as titanium-palladium alloy) or coating.
7) in the design, processing and conductive corrosive media in contact with the container, such as found in titanium and other metal contact can lead to galvanic coupling corrosion, should be in the structure of the measures taken (such as the use of a third material as a transition layer) or the use of anodic protection.
8) In the design of equipment prone to corrosion, the flow rate of the corrosive medium should be lower than the critical flow rate, and try to avoid sudden changes in the flow rate or direction of flow; or in the parts prone to corrosion and abrasion to set up protective baffles.
① When the medium is corrosive or abrasive and ρv2>740kg/(m-s2) or the medium is not corrosive or abrasive, but ρv2>2355kg/(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 set up with a baffle.
② When the corrosive medium along the tangential into the equipment, or the inlet pipe is facing the wall, and the distance between them is less than 2 times the outer diameter of the pipe, should be set to protect the plate.