Brass P-trap and Galvanized Steel Stub-Out

[Atulc]

Hello,
I am replacing the P-trap under a bath sink. I'd like to install a Kohler K-9000-CP brass P-trap. There is a 1-1/2" galvanized steel stub-out coming out of the wall (see the 1st picture). If I can get it out, I'd be left with a a 1-1/2" galvanized FIP hub recessed about a half inch into the tiled wall.

What's the best way to connect the brass P-trap to the steel stub-out or the FIP steel hub? I could use a brass desanco (picture 2) directly in the steel FIP hub but I believe contact between brass and steel results in galvanic corrosion. In fact, I noticed this corrosion on the steel stub-out shown in the 1st picture. The corrosion is on the underside not visible in the picture. Another problem with this approach is that I may not be able to get a grip on the nut formed into the body of the desanco as the steel hub is recessed into the wall.

I could cut the stub-out about 1" outside the wall and use a tubular coupling (e.g., Fernco Proflex 3002-150, see the 3rd picture) to connect to the P-trap outlet. The escutcheon that comes with the Kohler P-trap is not large enough to cover the tubular coupling. Do they make a chrome-finish escutcheon deep enough and wide enough to hide such a tubular coupling?

The original P-trap installed by a licensed plumber 15 years ago is shown in the 4th picture. Note this is a brass p-trap and the brass outlet was screwed on to the steel stub-out, a no-no as far as I know.

Thanks,
Atul

 

[Dj2]

I would replace the galvanized from the wall with ABS. You will need a serious plumber's wrench to remove it.

 

[Sponsor]

 

[Cacher_Chick]

We use brass pipe nipples all the time when transitioning off old galvanized pipe. A male ips desanko might leave you a little short, and a close nipple with a female desanko might leave you a little long. Either way is not wrong.

 

[Atulc]

I would replace the galvanized from the wall with ABS. You will need a serious plumber's wrench to remove it.

dj2,

Thanks for the ABS fitting suggestion. Do you mean removing the steel stub-out and installing the two fittings shown below? Do they make ABS male trap adapters/ Desanco fittings with male threads that would fit directly into the female threads in the galvanized fitting in the wall?



The following article states that "Plastic and metal expand and contract at different rates" http://www.familyhandyman.com/plumbing/repair/how-to-join-dissimilar-pipes/view-all#step6. This can possibly cause leaks. They recommend using unions because the rubber washer in the union should flex enough to keep the connection sealed. I hope this concern doesn't apply to DWV pipes. I can understand this concern for pressurized pipes.

This other article http://www.inman.com/2008/06/20/some-plumbing-materials-shouldnt-be-mixed/ recommends doing exactly what you suggested.

BTW, I do have a serious plumbers wrench and I use steel pipes as cheater bars when necessary.

 

[Atulc]

We use brass pipe nipples all the time when transitioning off old galvanized pipe. A male ips desanko might leave you a little short, and a close nipple with a female desanko might leave you a little long. Either way is not wrong.

cacher_chick,

Thanks for the suggestion. I am concerned about well documented galvanic corrosion between brass and steel. The brass p-trap outlet connected directly to the galvanized steel stub-out on the previous setup shown above caused severe corrosion on the bottom side of the stub-out in the contact region between brass and steel. Won't connecting a brass nipple to the galvanized steel fitting in the wall cause damage to the steel fitting in the long run?

 

[Reach4]

Do they make ABS male trap adapters

ABS vs PVC is largely a regional thing. Usually you would go with what is commonly used and readily available in your area. I think that is PVC in your area.

 

[Atulc]

Reach4,
You are right. The equivalent PVC fittings are readily available in my area whereas I have to special order the ABS fittings. I'll go with PVC.

 

[Cacher_Chick]

cacher_chick,

Thanks for the suggestion. I am concerned about well documented galvanic corrosion between brass and steel. ?

What do you think the valves are made of that are connected to every galvanized water supply system in the country?

Brass traps are a thing of the past, except for those sinks with exposed piping, where they are installed for cosmetic reasons.
You could always transition with PVC , but it will be harder to hide.

 

[Atulc]

cacher_chick,
You make a good point. Based on your reasoning, I researched the topic of galvanic corrosion between brass and galvanized steel further and came across this ... http://www.plbg.com/forum/read.php?1,466241. It seems that the brass used for valves on steel pipes has a different composition than brass used for nipples and fittings. Since I have witnessed the corrosion first hand, I want to stay away from direct contact between brass and galvanized steel. I've decided to use the following fittings - Schedule 80 PVC close nipple (https://www.amazon.com/gp/product/B008HQ69Q8/) and brass desanco with 1-1/2" FIP threads (https://www.amazon.com/gp/product/B00838J7QY/). The PVC will avoid direct contact between brass and steel.



I found this box escutcheon that should be deep enough to cover the close nipple and desanco - http://www.signaturehardware.com/1-1-2-od-deep-box-flange-chrome.html.



I'll post picture of the completed assembly in the next day or two.

Thanks all for your suggestions.

 

[Atulc]

I was able to remove the brass stub-out with an 18" pipe wrench with a 3-foot section of a 1-1/2" steel pipe as a cheater bar. See pictures below. First, I tried loosening the stub-out with the bare tool but the stub-out didn't budge at all. Then I sprayed some Aerokroil penetrant and gave it about 30 minutes to do its job (I came across this interesting article comparing the effectiveness of several penetrating oils -
http://honda-tech.com/attachment.php?attachmentid=166728&d=1286659461). After that, I used the pipe wrench with the cheater bar and the stub-out came out with little effort.



Here are pictures of both ends of the stub-out / galvanized steel nipple. In the picture on the left, I turned the nipple upside down to clearly illustrate the galvanic corrosion. The corroded part on the top was actually on the bottom side of the nipple. This is clear evidence that prospect of galvanic corrosion is to be taken seriously when brass and galvanized steel are in direct contact. The outlet of a brass p-trap was connected to this end of the nipple. It took about 15 years in a sink drain for the steel nipple to corrode this badly. If brass and galvanized steel were in direct contact in a fitting inside the wall (e.g., if I inserted a brass Desanco fitting directly into the steel fitting in the wall), I'd be worried that I might have to open the wall to replace the steel fitting in the future.

The picture on the right is the the other end of the galvanized steel nipple. No corrosion at this end where the steel nipple was connected to the steel fitting in the wall.



Here is a picture of the dirty threads on the fitting in the wall. The picture on the right shows clean threads. I used a 1-1/2" pipe tap (http://www.amazon.com/gp/product/B00FXKVZ1U) to clean the threads. Now it's ready for a PVC close nipple.



Pictures of the completed setup to follow in a day or two.