Venting pipe question

[ronqc]

Hi all -

Would it be possible to get some opinions on the following problem please? Any thoughts would be greatly appreciated.

Context: In my attic, there are 2 venting pipes that emerge from the house. They are labelled "A" and "B" in the images below. Pipe "C" is the exit venting pipe to the roof.
Problem: A pipe "D" is connected to pipe A. Pipe "D" runs perpendicular to the axis of the house. This pipe is now cracked in one location, and water is dripping from it. My theory is that vapour (from pipe A, which connects to D) condenses when tempteratues fall below freezing, and builds ice inside pipe "D". Pipe "D" shows signs of freying along the axis (in one spot). When the temperature climbs above freezing, I can feel water drip at the freying location.
The question: I do not understand the need for pipe "D". Pipe "D" exits to the the roof soffit. It does not even point upwards at the exit. Nor does any other pipe from the house connects to it.
Does anyone see a reason why pipe D should exist?
Does anyone see any issue if pipe D were removed completely (and capped at the point of exit from pipe A).

Thank you again

 

[MicEd69]

I'm confused about your description of "D". All vent piping must be sloped toward the drain in which they are venting at least at 1/4" per foot. There should be NO pockets where any moisture can accumulate. Do you have a picture of the "freying"? Is that a crack? Is it a place that has been rubbed by the movement of the pipe?

Are you in the USA?

 

[ronqc]

Thank you for the response. Good questions.

Fraying image attached. It may not be obvious to see, but hairline cracks run parallel to the tube long axis. It's as if the inside was under pressure, and made the cylinder expand outward radially.

Pipe "D" is the long horizontal pipe that you can see going all the way to pipe "A". One of the images shows were D and A connect. Pipe D does continue horizonally through the elbow and ultimately another (approx. 10 feet) to the soffit. No picture captures this.

The little vertical pipe extending down from D, that you point to with a question mark, is just a stand. It's not an actual venting pipe. That is, it LOOKS like it's coming up from the ceiling into the attic, but it is only about 6 inches high from the attic floor with a cap at the bottom. It sits on the floor of the attic to hold up pipe D. That's all it does. It's just a supporting column for D.

This is why I find all this so bizarre. Pipes A and B connect to C, which exits to the root. Is it possible that pipe C gets obstructed somehow, and pipe D is acting as some backup relief vent?? Hence why I'm asking the "collective" if they have ever encountered something like this previously. SOMEONE went to the trouble of adding an almost 25' pipe (including elbow) that is open at the end. Why would someone do this? My concern is that if I just remove "D", there is SOMETHING will happen with A, B, and C that I am seeing, at the moment.

I am in Canada.

Thank you again