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Vent Corrosion

Alan (California Radiant) Forbes
Alan (California Radiant) Forbes Member Posts: 4,074
edited September 2022 in THE MAIN WALL
I see this so often on plumbing vents, always in the kitchen. The deterioration is from the inside, out and the pipe is filled with the sloughed off material.

Does anyone know why this happens? Electrolysis?

8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

Two btu per sq ft for degree difference for a slab


  • Jamie Hall
    Jamie Hall Member Posts: 23,523
    This is a bit of a WAG, but I'd think it was because the inside of that vent is always wet or perhaps better said damp, with just enough air flow for a continuous supply of oxygen, and likely with some interesting acids in the "air" as well. Not a friendly environment.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Alan (California Radiant) Forbes
  • BenDplumber
    BenDplumber Member Posts: 49
    Hi Alan, see the same problems in my area and from my experiences is more prevalent in grease carrying lines i.e restaurant dedicated grease lines, residential kitchen sink DWV and Laundry drains. More specifically ferrous/iron piping. Talking with our drain rodder, the newer detergents used in liquid soaps and especially dishwasher and Laundry tablets where the discharge from the K/S is into the food waste disposal are highly acidic to dissolve proteins so you don't have to pre rinse or pre clean before adding dishes or laundry into the appliance. The acidic fumes rise through the vent due to the drainline being choked by grease. Considering most newer homes after the 70's are piped with PVC the detergent manufacturers only test with newer drainage materials thinking unfortunately that anything before that should've been replaced by now. Replaced several badger1 and badger5 disposals with the dishwasher branch connection from the same conditions. Disposals with SS grind chambers hold up fine. Made sense to me, been working with this drain rodder for 30 years and has no reason to BS me. Hope this helps sir.
    Alan (California Radiant) Forbes