Black pipe, pipe dope & unions.

[paperfist]

So I know what unions are for, but is there a code that states where they are supposed to go?

What's the best pipe dope to use for gas pipe? I dunno what the previous owners used, but it was blue and it's kicking my ass even with a 20" monkey wrench on 1" pipe!

 

[NetWareHead]

Unions are typically used to provide a means of quick disconnect between the piping and appliance. You'd have a union where the gas piping meets the water heater. When you change out the water heater, disconnecting the union is simpler than disassembling joints. Unions are also advised throughout the piping system to convenience. It's easier to remove a pipe for replacement by removing a nearby union than having to figure out the best place to start unscrewing joints or cutting pipe. Same principle when replacing pipe, unions let you "splice" new pipe into existing piping without disassembling everything.

I use oatey hercules megaloc pipe dope. It's blue and seals black pipe threads. I've used it on gas and allows you to really torque down and screw the pipe tightly into the fitting.

Sometimes you have to use cheater bars on the wrenches when freeing a stubborn joint. Or bring a buddy to work the second wrench.

 

[Greenman]

Unions are typically used to provide a means of quick disconnect between the piping and appliance. You'd have a union where the gas piping meets the water heater. When you change out the water heater, disconnecting the union is simpler than disassembling joints. Unions are also advised throughout the piping system to convenience. It's easier to remove a pipe for replacement by removing a nearby union than having to figure out the best place to start unscrewing joints or cutting pipe. Same principle when replacing pipe, unions let you "splice" new pipe into existing piping without disassembling everything.

I use oatey hercules megaloc pipe dope. It's blue and seals black pipe threads. I've used it on gas and allows you to really torque down and screw the pipe tightly into the fitting.

Sometimes you have to use cheater bars on the wrenches when freeing a stubborn joint. Or bring a buddy to work the second wrench.

Incorrect. Code only recognizes the use of unions at the appliance after the shut of valve. If you use a flex connector that obviously wouldn't be necessary.
For taping into an existing line they make a reverse threaded nipple and coupling.

For dope, Rectorseal is the standard around here, though I like the stuff with PFT or PPF or whatever the heck they call it. I'm using Rectorseal Trueblu on the project I'm doing now, no verdict yet.

 

[paperfist]

Incorrect. Code only recognizes the use of unions at the appliance after the shut of valve. If you use a flex connector that obviously wouldn't be necessary.
For taping into an existing line they make a reverse threaded nipple and coupling.

For dope, Rectorseal is the standard around here, though I like the stuff with PFT or PPF or whatever the heck they call it. I'm using Rectorseal Trueblu on the project I'm doing now, no verdict yet.

After the shut off? Damn this whole house is wrong.

Reverse threaded nipple and coupling? Dang you're a genius! That will make a lot of what I need to do less brutal.

Thanks I'll hit the plumbing supply store, I didn't see that dope at the big box.

BTW, aren't the split rings supposed to be black iron too? All they had were ones that looked like chrome.

 

[NetWareHead]

Incorrect. Code only recognizes the use of unions at the appliance after the shut of valve. If you use a flex connector that obviously wouldn't be necessary.
For taping into an existing line they make a reverse threaded nipple and coupling.

Differing codes throughout the country is my guess (I'm in NH). As far as I can see, unions are permitted throughout the piping system, not just for a service disconnect at point of use. (Although it would have been cheaper to use a coupler to join the pipes than unions, but that's another point). In the examples I've seen, the unions are accessible and not buried in construction somewhere.

My fault for saying appliance when I meant things like boilers, water heaters etc... Gas dryers, ranges etc... connected with a flex hose are a different story.

BTW, aren't the split rings supposed to be black iron too? All they had were ones that looked like chrome.

You probably saw galvanized ones which I've used with black pipe. If you want black iron split rings, try supplyhouse.com