Insulate them and enclose them for better performance and less noise.

that's what I'm trying to avoid - these risers are the only sources of heat for the apartment. They aren't beautiful, but necessary. So, if I don't enclose them, how can I 'pretty them up'?

You forgot to tell us you don't have any radiators in your apartment. What do the pipes serve on the floor above?

the risers run up the entire building thru all the apartments in the same line at the same location. My risers are in the kitchen and bathroom. On the top floor, above me, the riser has a valve that lets out the steam (as I understand it). And, yes - no other radiators are in the apartment. I don't know whether to call these steam pipes, heat risers or both.

A steam riser is any vertical pipe that carries steam up to a heating unit. If there are no heating units the riser could be called the heating unit but it is configured for poor heat transfer (radiant and convection). You can chemically strip it and paint it with a rust and heat resistant spray paint but avoid aluminum paint if you want good heat transfer.

I have the same issue. My contractor doing our renovation came up with an encasement that allows the pipe to breath but it is not attractive to me. Any suggestions?

Could they do something similar to a rad enclosure with a grill on the front and perhaps line it with a reflective material to help the heat come into the room?

Oops, didn't notice this was an old post...