Hard Coating under Dynamic Oring Hard Coating under Dynamic Oring v7042800 (Mechanical) (OP) 26 Mar 14 16:23 I have a question about tungsten carbide coating on a seal sleeve. The sevice is high-pressure crude with trace H2S. My question is: which grade is better, cobalt bound or nickel bound? Thank you. RE: Hard Coating under Dynamic Oring flexibox (Mechanical) 27 Mar 14 14:57 What you should consider is what will potentially corrode the filler. If your crude contains traces of water then use Ni bound Tungsten because colbilt is likely to corrode. I have always used Ni bound and never had a problem. Also have the surface with a super finish if it is for the dynamic oring of a mechanical seal! RE: Hard Coating under Dynamic Oring v7042800 (Mechanical) (OP) 27 Mar 14 18:12 thank you, Flexibox..!