cast iron thread repair

[Blackhawk]

I have cast iron drain pipes in my home. There is one cast iron wye fitting that goes into the concrete floor which has a cleanout. I had to remove the cleanout cap to clear a clog. It was pretty rusty and now the female threads in the wye are so damaged that the cap will not thread back in. A new cap also did not work. The thread size is 2-1/2"-8 NPT. I cannot locate a pipe tap from any rental store this size. Does anyone have any other ideas on how to repair this? I thought about grinding out the threads altogether and then having someone weld a smaller 2" fitting in place. Can you weld to these old cast iron pipes?

[HayZee518]

go to your local home depot or lowes. in their plumbing section you should be able to find a screw in plug that has a layer of lead for the threaded portion and looks to be "extremely" tapered. This should screw in place and the soft lead will form its own seal.

[Blackhawk]

Thanks. I was kind of wanting to repair the threads. In the future, I wanted to screw in another wye to the cleanout so that I could hook up a utility sink drain. Any possibilities of repairing the threads without a tap that large?

[LazyPup]

Generally Cast Iron pipe threads do not rust away, but rather the depth of the groves become loaded with rust and corrosion.

In most instances you can clean the thread groves with a stiff wire brush. If not, then retapping or running a "thread chase die" into the thread will clean it sufficiently.

The problem you are encountering here is because the code will permit a 3" pipe to have a 2-1/2" cleanout, but we are no longer permitted to use 2-1/2" pipe for DWV purposes. DWV pipe used in residential applications will be 1-1/4", 1-1/2", 2", 3" 4" and in some large multifamily dwellings we may find 6".

Galvanized Iron pipe is still listed as approved for potable water supply, distribution and DWV applications but due to the high cost of material & labor it is extremely rare to see it used outside of large commercial or industrial systems today

Understanding that 2-1/2" pipe is no longer used for DWV purposes and it is extremely unlikely to find any pipes greater than 1-1/2" in a residential potable water supply or distribution system it would then stand that you local home supply, hardware store or tool rental company will not generally keep the tools in stock therefore locating tools specific to 2-1/2" iron pipe would be extremely difficult anywhere outside of the Industrial Mill suppliers and most of those do not sell retail to the general public. Now, even if you were to locate a 2-1/2" NPT thread die, I would expect it to be rather expensive, in the order of about $30 to $50.

While there is no guarantee that it will work, you can try making a "one shot" thread chase by taking 2-1/2" pipe nipple and cutting three or four groves lengthwise to the pipe across the pipe thread(right angle to the thread groves). You then use that as a chase die by turning the nipple with a pipe wrench. This method will not cut threads into the cast iron but in most instances it will clean the rust and corrosion sufficiently to permit installing a cleanout cap back in the opening.

In regards to using this opening to create a tie in at a later time, you will not be able to do so. This 2-1/2" cleanout is for a 3" pipe and that is the code minimum diamter for the cleanout. As previously stated they no longer make 2-1/2" DWV grade pipe and fittings so the option would be to reduce it to 2" which would be too small to meet code standard for the cleanout or you could enlarge it to 3". Code also prohibits reducing the size of a line in the direction of flow and if you were to install a 3" wye it would be reduced into the 2-1/2", again prohibited by code.

Absolutely do not even attempt to make any weld joints on the DWV system. The four principal gasses found in sewer gas are Hydrogen Sulfide, Methane, Carbon Dioxide and Ammonia which are mixed with air in varying concentrations.

Hydrogen sulfide is slightly heavier than air (1.19% the weigt of air at sea level) and will normally concentrate in the house main drain, house sewer and back to the municipal main or septic tank.

Methane is lighter than air (.59% the weight of air at sea level) and will typically rise and go out the roof vent.

Both Hydrogen sulfide and Methane, when mixed with air are extremely flamable and in higher concentrations are explosive, therefore it is extremely dangerous to use any flame producing device or even smoke while working on DWV piping. Also keep in mind that while hydrogen sulfide has a very strong rotten egg smell in higher concentrations it is quickly ignored by the human olfactory system so you may not notice the danger. On the other hand, methane at moderately low concentration, but still within the flamable and explosive threshold is odorless so here again you would not notice the danger.

Attempting to weld a DWV line could cause a chain of events that would cause an explosion clear back to the municipal main or septic tank.

[Blackhawk]

Thanks for all the info. I tried cleaning out the threads with a wire brush but to no avail. Believe it or not the cheapest 2-1/2" tap that I found cost $235 bucks! I found a floor flange fitting at my plumbing supply. It is basically a flat disc with female pipe threads in the center. It then has four countersunk holes to attach it to the floor. The outside diameter of the cleanout that I have is 3-1/2", so I bougt a large enough floor flange to sit on the top of this. At my job, I have access to a lathe, so I took the flange fitting and faced it off in the lathe to be dead flat and smooth. I then drilled 4 new thru holes in the flange fitting for #10 screws. I drilled the holes on the right diameter to line up in the center of the old cast iron cleanout. I then centered the flange on the cleanout and marked the hole locations. I then drilled and tapped #10-24 threaded holes into the old cast iron. I took a large mill file and smoothed out the top face of the cleanout until it was smooth with fresh metal showing. I made myself a rubber gasket to put in between the cleanout and the flange, then bolted it down with 4 screws. The flange has a 1-1/2" female pipe thread which is smaller than 2-1/2" with respect to Lazypup's point about the required cleanout size. But the flange is easily removable by taking out the 4 screws.

Another option that I investigated was using a rubber donut that inserts into the hub and then over pvc pipe. My cast iron has a hub, so I assume that it would be possible to melt the lead and remove the old cast iron cleanout fitting, but this did not sound fun at all. If anyone is interested these rubber donuts are made by American Valve (americanvalve.com). I emailed the company from their website and I got a response to my question within 15 minutes. You don't get that type of customer service often.