Insulating Steam and Condensate Lines Together

It sounds like an atypical installation to me.

The only other thing I would consider is the pressure on the condensate return line. For saturated steam systems temperature and pressure go hand-in-hand, so if the pressure on the return line is ~15 psi that would correspond to saturated steam at 250F (i.e. its normal and should be expected).

The pressure is 8 psi

Saturation temperature for 8psig would be about 235F. So it appears the "condensate return" line is absorbing some heat from the steam line to the point it is no longer a condensate return but a super-heated steam return!

I'd venture a guess it probably makes alot of noise.

No, it won't be superheated, as there is still condensate present.

I'm sure there is condensate present (hence my comment about there being alot of noise).

However, the bulk temperature is ~250F with a pressure of 8psig. The steam table I'm looking at says that's superheated steam. Liquid water exists in that condition only transiently until it absorbs the heat to vaporize.

RE Post #7 boiling violently in the hotwell ... it's likely the 8psig steam expanding and collapsing in the hotwell.

Karamat is right. This happens because the pipeline installer spaced the steam and condensate line so close that that the insulation space of minimum 5" (if each line has a 2" thickness insulation) was not there.As a result, both the lines were insulated together.Nevertheless, the steam line is radiating off its heat to the condensate line.

And would this be sufficient to creat steam in the condensate line and cause the small hotwell tank to boil violently?

No, because if the hotwell is vented then irrespective the temperature will be 99.9C.

The boil violently is the Flash steam. You need to study this. Or check with USL Detectors, 35% of steam traps may be passing steam.