Hi all and thanks in advance for your advice.

Last year a sloppy contractor installed a new bathroom at my place. Among the long list of regrettable mistakes, the shower supply pipe nipple is too long (photo 1) which causes the supply hub to sit approximately 3/8" out from the wall (photo 2). A generic piece of black rubber was used to try to mask the situation. The exact nipple length that I need is not a standard length, so my thought is to create a custom-length nipple using some spare half-inch copper pipe and two Copper C x MPT Adapter fittings (photo 3).

My question to you is: will a soldered custom-length nipple like the one I'm describing withstand the torque that I'll need to apply in order to connect the nipple to the female end of the pipe in the wall and to connect the water supply hub to the nipple?

 

Unscrew the pipe nipple and buy one that's 1/2" shorter. you should be able to find one somewhere.

If you want to make a custom fitting, that would probably work.

 

XSleeper's idea to buy one that 1/2" shorter is the simplest and most direct answer. Another option that you may not be aware of: Home Depot can cut threads into a pipe like that one. You'll need to measure closely for the length you need, and they'll customize a slightly shorter version of the original nipple. This may be more robust than a soldered copper pipe.

At the HD near me the pipe threader is that oily trainwreck looking thing in the plumbing aisle.

Good luck with it, let us know how it goes!
Dave

 

I'd suggest a hardware store not Home Depot. The one time I had HD custom cut a nipple it took me twenty minutes to show the plumbing associate how to do it.

 

Not all HD have the pipe fitter or threader. Do what XSPLR says.

 

Thanks for your replies! I originally did try to get the Home Depot plumbing guy to cut threads into a nipple that would've been exactly the correct length. The problem there was that the thread cutting machine has a minimum length requirement; I don't remember the exact number, but they can't cut anything shorter than 3 inches (or thereabouts). The nipple that's shown in the photo below is not the actual nipple that's being used; it was just a random pipe that we used as a placeholder.

I just measured the distance between the back of the hub and the wall with a digital caliper, and it turns out it's *exactly* 3/8". The problem that I fear with using a nipple that's 1/2" shorter than what's in there right now is not getting enough turns on the supply hub before i have to stop turning it (i.e. when the back of it is flush against the wall and the spout is pointing straight down)... I'm afraid of a leak inside my wall. Do you guys think I'm being unreasonable on that point? Is a good measure of plumbers tape or pipe dope enough to make up for a connection that's a turn or two short?

 

youll be fine 1/2"shorter.I build it up a bit with tape..Id be using brass anyway.As thats what the elbow in the wall probably is.

Dis similar metals you know.......

 

Lawrosa - would you mind educating me on the distinction that you're alluding to? The elbow is indeed brass (sharkbite to MPT)... I take it from your reply that using a nipple of any other metal would be a bad idea...?

 

It's called a galling effect. Thread galling is a common, yet seldom understood problem with threaded fasteners. Galling, often referred to as a cold-welding process. In essence two different metals will tend to meld into one. I currently have what looks like an aluminum female hose attached to a brass male fitting. I cannot get them apart. I've used two pipe wrenched with extended pipe on both and still cannot remove them. I'm going to use a saw to cut it.

 

Had to look it up to remember the name: galvanic corrosion can occur between dis-similar metals in the presence of an electrolyte. (Fresh water is a weak electrolyte.)

 

Wow. Interesting stuff! My original question was whether soldered copper can be expected to withstand torque... But maybe torque isn't the biggest concern here. Based on the most recent replies re galling, my biggest fear now is that the copper nipple and the brass fitting become inseparable...!! Does the risk of galling go away if i use a sufficient amount of tape around the thread?? I assume the answer is no...
Seems the best bet for my particular situation is what lawrosa suggested, to get a brass nipple 1/2" shorter and use a bunch of tape on both ends to address the "too few turns" issue that i previously articulated.

 

You don't have to worry about mixing copper and brass fittings at all. They are not reactive.

 

Thought I'd revive this thread for those who might be interested about dissimilar metals.

A customer brought this in the other day and asked if we could separate the nozzle from the hose. Refer to my post #9.This shows the galvanic effect of dissimilar metals.

This is a brass high pressure hose nozzle attached to a one of those ZERO-G hoses with an aluminum connection.

Brass is very reactive with aluminum, and brass screws will cause substantial corrosion of an aluminum base metal in a wet environment. As you can see from the pics the threaded portion has “welded” themselves together. The cross section with hose attached still cannot be separated.

 

brass to brass is best. Brass to steel not so good. Galvanic corrosion.

Copper to brass also OK.

But you will twist the copper if you try what you say with the copper adapters. Or a high chance of it anyway.