Normally the RF type (which has strong threshold bending moments) is not recommended for cast iron or materials with very low elongation property (and #150 and below) because the bending moment at the gap between two flanges contact can be easily higher than the threshold stress of flanges. The failure on RF flange may be occured in the joints between RF (i.e. cast iron) and FF as well.

Many companies want to take the cast steel or materials with medium or high elongation (>10~15%) for RF type.

thomaseun@hanmail.net

Thank you for your reply!