ASTM A213 T22

It is practically not economical to use a single material for large capacity SA213 T22 Boiler Tube with high superheat temperature of the order of 540°C and above. The reason for this is due to the fact that the steam from boiler drum enters the superheater around 350°C and leaves around 540°C. At each unit length of T22 boiler tube the steam travels from the drum take-off pipes to the roof tubes to the low temperature tubes and high temperature superheater outlet, it picks up temperature. This process changes the temperature of ASME SA213 T22 Tube at each unit length of it.

As the temperature of ASTM A213 T22 Tube increases there is a drop in the hoop strength of it. This makes the requirement tougher to the manufacturers by forcing them to increase the thickness required to withstand the internal pressure in the tubes. However, beyond a certain range the thickness of the tubes cannot be increased and this makes it obligatory to reform the element of A213 T22 Tubing to accept the increase in temperature. Manufacturer uses materials beginning from carbon steel, to low alloy steel, to high alloy steel, and then to stainless steel to fulfill the demands of the increase in SA213 T22 Tubing as the steam picks up temperature in super heaters. The location where such material transformation demanded is fixed by the manufacturer is based on the margin between the allowable temperature for the SA213 T22 material and the calculated metal temperature at the A213 Gr T22 seamless tube length. To avoid failures in the super heaters it is very critical to select this point correctly. The point at which the difference between the acceptable temperature and the forecasted temperature can differ due to other reasons like low steam flow through the section of superheater due to high de-superheating water quantity, over loading of the unit, the upset in the radiation heat in the area, excess area for heat transfer provided, etc. For improving the transformation point in any heat transfer surface like reheater & superheater, will only be possible with a large volume of in-situ welding a long shutdown.