Brown McFarlane



Pressure Vessel Steels – Grade P355

Thermax Boiler

A pressure vessel is a sealed container designed to hold liquids or gases at a certain pressure that is significantly different from the ambient pressure. High chemical process efficiency is vital for manufacturers of pressure vessels for cost reasons. Large equipment operating at high pressure and/or high temperature is usually required to improve efficiency. To build high temperature pressure vessels you must employ materials that can withstand higher stresses and temperatures with concurrently unchanged wall thicknesses.

One of the biggest challenges for pressure vessel manufacturers relates to the storage of hydrogen sulphide-containing gases. The release of hydrogen atoms from these gases can cause hazardous corrosive damage to the materials used to create the vessel. To tackle this obstacle manufacturers have created sour gas-resistant steels that can resist this corrosion.

Sour Gas Resistant Steels

When an electro-chemical corrosion reaction happens between the sour gas-containing environment and the surface of the metal, hydrogen induced cracking (HIC) can occur. HIC starts with hydrogen atoms diffusing in to the material. As temperature rises, hydrogen becomes increasing soluble and therefore disperses into the material more easily.

When these atoms meet and combine in tiny metal voids to create molecules of hydrogen, they produce pressure. When elevated, this pressure can cause the metal to lose its ductility and tensile strength; until it reaches the point of cracking. To avoid HIC we use a special sour gas-resistant steel specification with a high degree of purity and low vulnerability to segregation.

P355 Pressure Vessels Steel

EN10028-2 P355NL1 is one of the most popular fine grained steels used to make pressure vessels, specified by EN10028-2 and EN10028-3. Some plate grades are categorised by high weldability and/or fine grain make-up; whilst others have enhanced properties ensuring they are suitable for elevated temperatures. Plates are usually obtainable in thicknesses of 6mm to 250mm but there are also usually thicker plates available on request.



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