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Materials of Construction - Gas-to-Gas Heat
Exchangers
October 4, 2002
Gas-to-gas heat exchangers are constructed primarily of two different materials: carbon steel and/or stainless steel. Early exchangers were all constructed of carbon steel whether in cold or hot service. Where the exchanger saw high temperatures the inside surface of the shell was metallized and the tubes alonized to prevent high temperature scaling of the carbon steel. The use of stainless steel eliminated the need to metallized the metal surface when used in high temperature service. Also, in the cold services, stainless steel resisted corrosion from acid condensation.
The break point between using carbon steel and stainless steel is about 482°C (900 °F). Of course metallizing and alonized tubes can still be employed so carbon steel can be used as a material of construction.
An exchanger can be design and constructed of different materials to take the most advantage of the material properties. The hot end of the exchanger can be constructed of stainless steel while the cold end is constructed of carbon steel.
Item | Material | Comments |
Plate | ASTM A516 Gr. 70 | Metallize carbon steel where design temperatures exceed 371°C (700 °F) |
ASTM A240 Gr. 304H | Carbon Content: 0.040% minimum Use where operating temperatures exceed 482°C (900 °F) |
|
ASTM A240 TP304 | Carbon Content:
0.040% to 0.080% Use where operating temperatures exceed 482°C (900°F) |
|
ASTM A240 Gr. 316L | For improved corrosion resistance in Cold and Cold Reheat Exchangers and SO3 Coolers | |
Tubes | ASTM A178, ERW | Alonized where design temperatures exceed 482°C (900 °F) |
ASTM A249 TP304H, ERW | Carbon Content: 0.040% minimum Use where operating temperatures exceed 482°C (900 °F) |
|
ASTM A249 TP316L | For improved corrosion resistance in Cold and Cold Reheat Exchangers and SO3 Coolers | |
ASTM A249 TP304, ERW | Carbon Content:
0.040% to 0.080% Use where operating temperatures exceed 482°C (900°F) |