Originally Posted By: Ben Gromicko This post was automatically imported from our archived forum.
On a few Type B Gas vent pipes, I have seen rust. Surface rust. On the vent pipe, near the cap. What is this rust from? Water? Condensation? Hydrocarbons? Is this a normal thing. Monitoring recommended is a bad comment, since you have to climb the roof to get to the vent pipe (unlikely by most home owners).
Image of rust on a Type B Gas vent pipe.
This image is of the storm collar around the Type B gas vent pipe. The manufacturer's state that the storm collar should be sealed with a non-hardening mastic sealant. What if the sealant is cracked open or weathered, and needs to be improved? Can you get this stuff at Home Depot?
Thanks for the help.
-- Benjamin John Gromicko
Vice-President,
PEACH Inspections
NACHI & ASHI Member
Originally Posted By: ecrofutt This post was automatically imported from our archived forum.
Looks like acidic condensate from the combustion gasses that are not clearing the vent before condensing, then running down the edge coming out at the connection.
Shouldn't be happening on a B vent.
Do you see the same thing at the joints in the attic or at the furnace?
I'd recommend an HVAC guy check for proper flow of combustion gasses.
Originally Posted By: jmyers This post was automatically imported from our archived forum.
Ben,
Where have you been? It has been so long since I heard your name that I almost did not recognize it! 
That said, it is clear that Ben bought a panel van. Wears a timex. Is married, the poor woman. Ben, did you sell the old long ford pick em up?
Now about the type B....looks to me like they knew you were coming and ran up there and put a new cap on that one. The old one was probably rusty and corroded from that old oil fired heater. Since it has some rust toward the bottom I would say they did it maybe last year, two at most.
Mastic sealer is not so mastic, otherwise it would not crack, peel or chip. Otherwise you would not have to go to the big orange to replace the old stuff. 
Originally Posted By: Ben Gromicko This post was automatically imported from our archived forum.
I’ve seen worse. There have been many other Type B gas vent pipes, with alot more rust. Possibly these gas pipes are made of galvanized metal. In the photo, the cap appears newer - possibly because it is stainless steel. Shouldn’t all of the pipe sections be stainlesss steel. This house was about 7 years old. So the age of the rusting pipe shouldn’t have anything to do with the rust forming.
There's no other areas of rust or signs of drafting/combustion problems at the furnace or at other areas of the pipe (such as from the attic access).
Q: Are Type B gas pipes stainless steel, galvanized, or either? Does stainless steel rust under conditions with corrosive, acidic hydrocarbon exhausts condensing on the metal over many years? Can the Type B gas vent pipe be painted?
Thanks guys.
-- Benjamin John Gromicko
Vice-President,
PEACH Inspections
NACHI & ASHI Member
Originally Posted By: jmyers This post was automatically imported from our archived forum.
Ben,
I am certainly no metalologist or anything but the all steel rusts even stainless steel. Rusting has more to do with the composition of the steel. Both galvanized and stainless steels rust especially when you introduce water and oil because as you pointed out it produces acid. Reason would therefore dictate that is would be common to find rust of the flue that is exposed to the weather but the cap should prevent it from running down the pipe into the interior of the house. Did you find any rust on the interior pipe?
I don't really think it would hurt to paint them but you are not going to prevent it from rusting for very long unless you go up there an paint it every year. If you do decide to paint use a paint that is made for high temperatures like engine paint. Would you like chevy orange, ford blue or charcoal grill black? 
Ben, you come up with some good questions. Where exactly are you getting them from?
Originally Posted By: adufresne This post was automatically imported from our archived forum.
To All,
Looking at the pictures, the pipe is made of galvanized sheet metal.
The galvanized is a coating to protect the metal from rusting. Where the end joints are ,will be the weakest points and the galvanized usally don’t last long.
Using galvanize is cheaper than stainless steel. There is one grade of stainless steel that does rust ( 3,000 series ) True stainless steel does not rust. The cap on top looks to be Aluminum. Until I retired in Feb I have spent over thirty years as a weldor pipefitter. I don’t claim to know it all, but this type of material has made me a master in my trade. Glad to be a home inspector now. I hope this helps ya’ll. Armand QHIS
Originally Posted By: mpetner This post was automatically imported from our archived forum.
Could possibly be some form of galvanic corrosion. Basically, galvanic corrosion is when two metallic materials are in contact in the presence of a corrosive electrolyte, corrosion will increase on the least noble material (the anode) and decrease on the noblest (the cathode). The increase in corrosion is called galvanic corrosion. Erby?s previous post mentioned that acidic condensate ( the corrosive electrolyte) could be forming and Armand?s previous post states that the cap looks aluminum (dissimilar metals). Sounds like it might be a product of galvanic corrosion.
Originally Posted By: Ben Gromicko This post was automatically imported from our archived forum.
Thank you very much. What knowledge can be gained! I’ll keep looking for dissimilar metals between the vent cap and the vent pipe, and the corrosive acidic condensate, forming galvanic corrosion at the areas where the two meet.
Originally Posted By: Nick Gromicko This post was automatically imported from our archived forum.
Ben, if you change your message board name in Profile to read exactly as it appears in Featured Inspectors, the message board will automatically refer to you as a Member instead of a Non-member. You are Ben in Featured Inspectors and Benjamin on the message board. Otherwise the invisible members-only section will remain invisible to you. Once you correct your profile name and login on the message board, the invisible members-only section of the message board will appear.
I have to learn you everything. Is your whole family stupid?