Most, if not all threaded automotive fasteners have specified torque, which is ensured by using torque wrenches. But how about threaded pipe, galvanized steel for water or black pipe for gas, especially the latter? Should it be torqued to spec using something like a torque version of a pipe wrench, to ensure a proper joint?
Plumbing – Should threaded pipe be torqued to spec
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As a general rule, fittings with tapered pipe threads (NPT) should not be assembled to a specific torque because the torque required for a reliable joint varies with thread quality, port and fitting materials, sealant used, and other factors. (Source: Parker Hannifin Catalog 4300 Port End Assembly, page T7)
Leakage path through NPT threads occurs between the very peaks of one thread and the very valley of the opposing thread. No matter how tight you make NPT threads, a leakage path still exists. It is the function of the sealant to block the path between the male and female thread.
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Most screwed piping is tightened until it feels "right" and the fitting is pointing in the desired direction. What the experienced mechanic is often "feeling" is how the fitting is getting tight. Screw it into until it starts to seat. Then up the force a little by yanking. If each yank gives less movement, you probably have a sound joint. If the movement stops suddenly, you have probably bottomed out. The experienced plumber knows when to stop before he damages the fitting or boss. Caution is advised, tapered pipe fittings into an aluminum boss as excessive torque can crack the boss. This is especially true when using Teflon tape because the low friction of Teflon makes it easy to over-tighten.
You use a fitting called a union.
It allows you to thread a nipple into the elbow, and a nipple into the tee. Then you use the union to connect the two nipples.
photo courtesy of Wikipedia
They are available in many sizes and materials.
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Best Answer
No. Automotive parts (generally anything you'd find a torque spec on) and fasteners are engineered to a degree that residential galvanized and gas piping simply isn't.
None of these are issues with water and gas lines (except with soft metals like copper). The proper amount of torque is somewhere between "it doesn't leak anymore" and "I can't move it with a wrench anymore" (assuming, of course, that the former comes before the latter).