French Standard Heat-resistant Pressure Vessels Steels
French steelmaking industry is one of the most important in Europe, with a long tradition in producing high-performance steels. For the manufacture of pressure vessels, one of the most important steel types to consider are the so-called heat-resistant steels, also referred to as French standard heat-resistant pressure vessel steels. Such pressure vessels are of course subject to stringent regulations, typically in compliance with the French National Standard AFNOR NF A50202.
This type of steel proffer tremendous resistance to creep and fracture, though with a reduced resistance to corrosion. In order to ensure excellent performance, the alloy is carefully composed with alloying elements individually calibrated to guarantee optimum performance. Such elements include chromium, molybdenum and vanadium which are combined resulting in an austenitic microstructure, with a low level of ferrite and grain size in the fine range.
From the mechanical point of view, the main characterizing parameter of these steels is their yield strength, since their resistance to creep and rupture are linked mostly to this property. Yield strength of these steels range from 200MPa up to 350MPa.
In addition to its mechanical characteristics, the alloy composition composition must also be properly tailored to optimize the desired performance. This no doubt implies that accurate chemical analysis of the steels must be undertaken and fine tuned in accordance with the manufacturer’s instructions.
The most commonly used steel in France is GradeE2179/A619. Such steel is an austenitic grade with incredible weldability and excellent machining characteristics. This grade is also very resistant in terms of creep, thanks to its high molybdenum and chromium contents. Its chemical composition is as follows:
• C 0.05-0.15
• Si 0.20-0.60
• Mn 1.10-1.70
• Ni 12.0-17.0
• Cr 17.0-21.0
• Mo 5.0-9.0
• V 0.05-0.20
Another very commonly used steel are GradeE1797/A3025 and GradeE1798/A3108 which are very similar, designed to replace the obsolete Grade E2268/A327. Both grades feature excellent weldability, meaning they can be preheated up to 600C before welding. Moreover, they both contain a very high chromium content (18-20%), meaning they are highly resistant to creep. Moreover, they are pre-treated by normalising, make them suitable for high demands, such as pressure containers. Below you can find the chemical composition of GradeE1797/A3025 and GradeE1798/A3108:
• GradeE1797/A3025
• C 0.06-0.15
• Si 0.30-0.60
• Mn 1.00-1.80
• Ni 11.0-14.0
• Cr 18.0-20.0
• Mo 5.0-8.0
• GradeE1798/A3108
• C 0.06-0.15
• Si 0.30-0.60
• Mn 1.20-1.80
• Ni 9.0-12.0
• Cr 18.0-20.0
• Mo 5.0-8.0
In conclusion, special attention must be made when selecting the right steel for the manufacture of French standard heat-resistant pressure vessels. Such steels must be carefully tailored to guarantee safety, but also to optimize cost and performance. The two steels discussed above are two of the most popular grades in France, offering great weldability and machinability, together with an excellent combination of resistance to creep and rupture.
