Application of titanium chemical equipment
1. Titanium Advantages
Titanium materials are widely used in petroleum, chemical industry, light textile (chemical fiber), hydrometallurgy, pharmacy, electric power, ocean engineering and other fields because of their excellent corrosion resistance, low density and high specific strength. The application of titanium equipment greatly reduces the dead weight of the equipment, reduces the shutdown and maintenance of the equipment, and achieves the purpose of reducing the maintenance cost. However, with the wide use of titanium equipment, accidents and exposure problems have increased correspondingly. Most of these problems are related to the unreasonable protection design. Therefore, if appropriate protective design is adopted, accidents can be effectively reduced to ensure the safe and stable operation of the equipment and avoid premature corrosion or scrap failure of expensive titanium equipment.
2. Titanium equipment used in chemical application
The application of titanium in chemical equipment mainly uses the corrosion resistance of titanium, and then considers the characteristics of high specific strength, non-magnetic, memory function and so on. The designer shall select titanium and titanium alloy materials according to the service conditions, processing degree, service life, cost, weight, product quality, environmental protection and other conditions of the equipment. Titanium cannot be simply used to replace the existing materials on the equipment. During the design of titanium equipment, different structural types shall be selected economically, reasonably and reliably according to the pressure, temperature, flow rate, equipment shape, geometric dimension, operation, etc. of the medium. Generally speaking, small vessels with low pressure and temperature can be made of all titanium. On the contrary, multi-layer structure can be used. In addition, the welding performance, thermal conductivity, stress relaxation performance, expansion performance, etc. of titanium materials shall be comprehensively considered to decide whether to select titanium materials to determine the design structure.
Table 1 below for the performance and application range of titanium materials commonly used in chemical equipment
| Item | properties | Scope of application | Max service temperature |
| gr1 | It has good corrosion resistance and low strength in oxidizing, neutral and reducing environment coexisting with corrosion inhibitor. | Can be used in applications requiring higher or cold stamping properties, as well as at low temperatures | Full titanium equipment: 315℃ Titanium clad steel equipment:350℃ |
| gr2 | The corrosion resistance is the same as that of Gr1, and the comprehensive mechanical properties are moderate | Widely used in the manufacture of shells with wall thickness <14mm, pressure components such as heads, reactors, towers, heat exchangers (mostly used as heat exchanger tubes), etc. | same as upper |
| gr3 | The corrosion resistance is the same as gr1, with higher strength and friction resistance, but poor plasticity. | Used to manufacture parts that do not require deep cold stamping, such as all-titanium tubes and fasteners for heat exchangers. | same as upper |
| gr7 | It has good corrosion resistance to oxidizing, weakly reducing and redox alternating media, and the comprehensive mechanical properties are close to gr1. In high temperature and high concentration of various chloride media, the crevice corrosion resistance of gr7 alloy is the best. | Mainly used in dilute hydrochloric acid, dilute sulfuric acid, dilute phosphoric acid environment, and also widely used in equipment parts and components prone to crevice corrosion, such as flange sealing surfaces, diamond gaskets, etc. | 350℃ |
| gr12 | It has better corrosion resistance to oxidizing and weakly reducing media, but it is inferior to gr7, the strength is the same as gr3, and it has higher medium temperature strength. | It can replace gr7 as a crevice corrosion component, and can also be used as a low PH value oxide that is not resistant to corrosion by industrial pure titanium at a higher temperature, and a pressure equipment component of dilute reducing acid solution. | 350℃ |
| gr5 | It has excellent comprehensive performance and good process performance, excellent superplasticity, suitable for various pressure processing methods for forming, and various methods for welding. | It is used for solid parts and non-welded parts, etc. which are subjected to greater stress. | 400℃ |
3. Application scope of titanium materials
3.1 Titanium can be used in the following media
3.1.1 Nitric acid, chromic acid and other oxidizing media, acetic acid, terephthalic acid and other most organic acids, urea, seawater, salt solution, chlorine ion containing bromine ion containing media, wet chlorine, dilute alkali, olefins and oil products.
3.1.2 titanium materials have corrosion in the following media, but corrosion inhibitor or corrosion-resistant titanium alloy can be used.
3.1.3 Hydrochloric acid, sulfuric acid, high temperature 65% nitric acid, phosphoric acid, high temperature high concentration citric acid, oxalic acid, gluconic acid, >10% formic acid, alkaline solution.
3.2 Titanium cannot be used in the following environments.
3.2.1 fuming nitric acid with concentration >98% or containing >6% free nitrogen dioxide shall avoid natural explosion (even if there is no burning phenomenon in the field coupon test).
3.2.2 dry chlorine gas with water content (0.1%~0.3%) in chlorine gas (such as domestic steel cylinder chlorine gas, due to the fierce reaction between titanium and dry chlorine gas, titanium tetrachloride is generated, a large amount of heat is released, and there is a risk of ignition). When it is rotating at high speed, the water content of dry chlorine gas should be increased to 1.5%.
3.2.3 liquid oxygen and some aqueous solutions with high partial pressure of oxygen, because titanium has impact sensitivity in liquid oxygen, if titanium has a fresh surface, it will spontaneously ignite at 0.35Mpa pressure and room temperature. For corrosive media containing hydrogen, in addition to considering the corrosion of media, full attention should be paid to the harm of hydrogen to titanium. Titanium equipment is required to avoid iron pollution. It is very important to avoid hydrogenation of titanium.
3.2.4 It cannot be used in the environment of hydrofluoric acid, fluoride, acetic anhydride, hydroformylation liquid, concentrated alkali, phosphoric acid, oxalic acid, non-aerated boiling formic acid, etc.; in N2O4, liquid oxygen, >30% H2O2, methanol containing halides, The H2 including <2% water at 315°C above, liquid bromine and other environments are strictly prohibited.
Life comparison of various equipment materials
| Application field | Equipment | Material and service lifetime | Titanium material and service lifetime | Increased lifetime after titanium used |
| Chlor-alkali | Wet chlorine cooler | Graphite, 3~6months | Pure titanium used for more than 10years | 20 |
| Soda ash | External cooler | Carbon steel.6~24months | Over 15 years | 7.5 |
| metallurgy | Electrolytic cathode plate | Copper, 1~3years | Pure titanium over 10years | 3.3 |
| pharmacy | evaporator | Enamel, 3years | Pure titanium over 14years | 4.7 |
| Heat exchanger | Lead pipe,2months | titanium more than 7years | 4.2 | |
| Salt making | Heating chamber | Carbon steel, 8months | Titanium, more than 10years | 15 |
| Chemical industry | Acetic acid oxidation tower | Stainless steel. 1month | Pure titanium, over 10years | 120 |
petrifaction | Acetic acid rectification tower | Mo2Ti1.5, 2years | Titanium for 15years | 7.5 |
