Recently we were involved in a job where the property owner had to remove the wood siding from the side of the house in order for us to get to a clogged dry return pipe that ran behind the kitchen cabinets. And yes it was deemed easier to remove the siding on the house.
What was found, was the vertical dry return changed direction and ran horizontal for a little way before dropping vertical again. The horizontal section was pitched the wrong way. This resulted in water standing in this section of pipe which over the years started to rust the interior of the pipe, eventually rusting completely shut. When Paul cut the pipe he removed chunks of the rust build up which you can see in the picture. He then re-piped that section of the dry return.
When he sent me the picture you see here, the only apt description I could give it was 'steam turds'.
Come on I know you're laughing. Can you possibly come up with a better description? Remember when it comes to piping on a steam system, pitch of the pipe is everything!