You can use gravity pipe networks to represent your pressue pipe networks.
Go to a 3d view. Explode the pressue pipes and fittings twice.
Export to FBX format.
Open in 3ds Max Design and export in .3ds format.
Attach the 3ds file as 3d model in InfraWorks.
It's not an ideal workflow, but it works.
OK - cool, I'll try that. What I was trying to do though, was to get the Alignment from C3D and import that into AIM. Then use AIM to generate their piping from that, or vice-versa, where I draft a pipe in AIM and then export to C3D. It does not seem that there is a Profile View available for the pipes in AIM...hmmm. Future addon?