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Sulphuric Acid on the WebTM Technical Manual DKL Engineering, Inc.

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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)