The steel we use today to manufacture pressure vessels is very different to what was used 50 years ago. Early steels often had a coarse grain structure and contained impurities that adversely affected the finish and resulted in many costly and fatal incidents.With significant advances in steel processing, modern boiler and pressure vessel grades are made of fine grain steel, with high impact resistance and are even corrosion resistant.
In this article we look at what are pressure vessels, where they’re used and why they must be manufactured with specific grade steel.
What are boilers and pressure vessels?
Boilers and pressure vessels are closed containers designed to hold liquid or gases at pressure. While theoretically they can be made into any shape, pressure vessels are typically made into spheres, cylinders or dome shapes. That said, most pressure vessels are cylindrical with 2:1 semi-elliptical heads or end caps on each end.
Smaller boilers and pressure vessels are made from pipe with end caps, while larger vessels may be constructed by welding together several rolled and possible forged sections or parts. No matter the construction method, boilers and pressure vessels are designed according to strict Australian standards and many are required to undergo regular inspections to guarantee safety.
Where are boilers and pressure vessels used?
There are many uses for boilers and pressure vessels both in industry and the private sector. Here are just a few examples:
- Diving cylinders
- Domestic hot water storage tanks
- Compressed air storage tanks
- Passenger cabin of an aircraft
- Recompression chamber
- Gas nuclear reactor
- Industrial boiler
- Road tanker
- Petrochemical storage and transport tanks
Why do boilers and pressure vessels need specific plate steel?
Many factors are considered when designing boilers and pressure vessels. These include the size and weight of the vessel and its contents, the internal and external forces, the temperatures including ambient and operational, stresses, corrosion and much more. With these specific operational requirements, it makes sense that a safe and effective design hinges the materials used.
Boiler and pressure vessel grade steel comes in a variety of grades and thicknesses, and are designed to withstand the immense internal pressure. These grades are fully killed, fine grained carbon-manganese steels produced by hot rolling and normalising. Importantly, these steel grades are designed to leak before burst.
There are many grades available, such as PT460N, PT490NR, and PT540T to name only a few. Boiler and pressure vessels steel grades are available in varying thicknesses for varying purposes. For example, there are steel grades with elevated temperature properties available.
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