I recently had a reader ask these questions:
- How bad is it to use regular galvanized pipe instead of black?
- How tight should 1/2″ pipe be?
- I was taught to use sealant dope but to skip the first thread.
- Should a pressure test always be done?
- How much pressure and doesn’t that damage the valves or gas meter in the system?
First and foremost, it is always best to check what local code requirements are. Some areas will not allow galvanized pipe. Different pressure test procedures may be required in different areas.
In general: In the International Fuel Gas Code (IFGC-2012) under Section 403.4.2 for steel and wrought-iron pipe it states: “Steel pipe must be Schedule 40 or heavier, must comply with one of the listed standards and can be black iron or galvanized. Contrary to popular belief, natural gas does not adversely react with the zinc coating on galvanized pipe”
What you need to remember is galvanized is usually more expensive so, if the local code does not require it, why use it? Also, if going from galvanized pipe to copper , you do need to use dielectric fittings to avoid galvanic reactions causing leaks in the copper piping.
How tight — tight enough so it does not leak :>). Kidding aside, I have seen guys tighten 1/2 pipe with 18 inch wrenches and crack the elbow. I have seen guys tighten 1 inch pipe with 10 inch wrenches and never have a leak. I do not know if there is a specific torque spec for tightening pipe. (If someone knows of one, let me know and I will pass it on in a posting).
The practice of not putting sealant on the first thread came about because mechanics would put too much on and then when it was tightened, the sealant would come off in the fitting. If you don’t over-do-it, you can put sealant on all the treads. Keep in mind, most manufacturers today require “drip legs” right before the appliance to keep this debris out of the equipment/valves.
Should a pressure test ALWAYS be done? ABSOLUTELY — Any new gas line should be properly tested. Again, your local utility or municipality will tell you what their code requirement is. When I was running pipe, we still used mercury manometers and the pipe had to hold 8 to 10 inches for 15 minutes. Today, 15 psi for 15 minutes is used in some areas. Some require 20 minutes. Rule of thumb — 1.5 times the maximum working pressure but not less than 3 PSI (remember 28 inches water column equals 1 psi) and if system is in a single family dwelling, 10 minutes. There should be NO pressure drop. Any drop means a leak and needs to be found and fixed.
Hope this helps. Any comments, suggestions, additions or corrections are always welcomed. Unfortunately, for some of the questions, there is no “pat” answer. Always refer to manufacturer specs, local utility and local municipal codes for your area so you do it correctly.