Is My Design OK? Applying API 661 Annex C to Air Cooled Heat Exchanger Designs with Viscous and High Pour Point Fluids
Winterization in accordance with API 661 Annex C may need to be considered by designers when air cooled heat exchangers are operating in climatic extremes. In order to prevent operating problems in-situ, a temperature safety margin should be added to the critical process temperature to determine the specified minimum tubewall temperature. For viscous fluids and fluids with high pour point this safety margin is 14 degrees centigrade. API 661 Sections C.3.2 and C.3.3 describe concurrent flow, and bare tube or reduced fin density as possible solutions for this type of fluids.