Hi @Chseeto_bim,
Hope you are well! 
Have a look at THIS POST where I provided a Screencast which goes through all of the various scenarios relating to MEP Hidden lines, visibility settings, view discipline settings and duct transparency which can affect your duct run to display as it currently does without hidden lines.
I hope this helps! 
Rudi Roux
MSc | Digital Engineering Manager
LinkedIn
Revit Mechanical & Electrical Systems 2018 Certified Professional | Revit MEP & Architecture 2015 Certified Professional
AutoCAD 2015 Certified Professional | Autodesk Building Performance Analysis (BPA) Certificate
If this post resolved your issue, kindly Accept as the Solution below. Kudos are always welcome ⇘