In the design of a shell and tube heat exchanger, the corrosion allowance

• A. need not be provided for non-pressure parts like tie rods, spacers, baffles, supports etc.
• B. for carbon steel and cast iron pressure parts is 1.5 mm (except for tubes) and for severe conditions it is 3 mm.
• C. for internal cover and tube sheet is provided on both the sides.
• D. all (a), (b) & (c).