Gr1 titanium alloy plates for nitric acid and phosphoric acid equipment: Detailed analysis of engineering practice in corrosion-resistant material selection
In environments where strong acids are present, Titanium Alloys have become a key material due to their excellent corrosion resistance. In chemical production, did the lining plate of the 50% nitric acid reactor get corroded and perforated within three months? Do the welds on the phosphoric acid concentrator frequently crack? For the selection of materials for use in highly corrosive environments, it is necessary to go beyond macro concepts and focus on the microcosmic corrosion resistance boundary of materials.
1. Why have titanium alloys become a 'must-have' material for nitric and phosphoric acid equipment?
Corrosion resistance mechanism and supporting data
Nitric acid environment: Gr1 titanium alloy (purity ≥ 99.5%) forms a dense Ti₅O₅ oxide film on the surface in a 20–70% nitric acid solution at temperatures below 200°C, with a corrosion rate of <0.01 mm/a. Key detail: When the temperature exceeds 200°C or the concentration exceeds 80%, 0.1–0.3% silicon-containing corrosion inhibitors (such as sodium silicate) must be added to prevent intergranular corrosion.
Phosphoric acid environment: Under working conditions of 30% industrial phosphoric acid at 60°C, the annual corrosion rate of Gr1 Titanium Plate is only 0.05 mm, which is ten times better than that of stainless steel. However, it is necessary to strictly control fluoride ions at ≤50 ppm (fluoride catalyses the phosphoric acid corrosion reaction).
'Ceiling' parameters of material performance:
Core indicators of Gr1 titanium alloy (ASTM B265 standard):
Yield strength: ≥240 MPa
Elongation: ≥24%
Oxygen content: ≤0.18% (to control the risk of hydrogen embrittlement)
Hot working forbidden zone: The annealing temperature must be precisely controlled within the range of 650–760 °C (above 800 °C will cause grain coarsening, resulting in a significant decrease in corrosion resistance).
2. 'Fatal details' in engineering applications and solutions
The success or failure of the welding process depends on the following:
Automatic gas tungsten arc welding (GTAW) is used and the back must be protected by 99.999% pure argon to prevent oxidation and discolouration of the weld (the darker the colour, the worse the corrosion resistance).
After welding, pickling and passivation are required, involving treatment with a mixed solution of nitric acid (20%) and hydrofluoric acid (2%) to restore the integrity of the oxide film.
Guidelines for avoiding pitfalls in equipment design
Case study: phosphoric acid concentrator:
Mistake: Direct bolt connection between a titanium plate and a 316L flange → galvanic corrosion perforation (potential difference >0.5 V).
Correct solution: Use a PTFE insulating gasket and titanium alloy bolts.
Case study: nitric acid storage tank
The area where the liquid level fluctuates has been thickened to 8 mm (the standard plate thickness is 4–6 mm) to avoid erosion corrosion at the gas–liquid interface.
3. Cost optimisation: Net profit is increased.
Using clad plates instead of solid plates: The phosphoric acid reaction tank uses 3 mm Gr1 titanium and a 20 mm Q345R steel base with explosive cladding, reducing material costs by 40%. Titanium Alloy Plates:
Surface treatment efficiency: Sandblasting treatment (Ra = 3.2 μm) improves adhesion of the oxide film and extends the pickling cycle to once every two years.
When the service life of your phosphoric acid pump impeller is less than one year due to corrosion or the nitric acid condenser leaks frequently, a selection parameter table of Gr1 titanium alloy plates can transform the maintenance cycle of the entire production line. Contact us for more information about titanium alloy plates and to find out how you can stop corrosion-resistant design being a 'trial and error' process.