Pressure Testing Gas Pipe With Air.

I ran approximately 80 ' of black iron pipe with several joints and valves for natural gas. Pressured it up with air to 10 PSI. 48 hours later is is down to 8.5. Is it normal to loose some pressure due to temperature changes?

Thanks for your help!

15% loss of pressure is not normal. Check your valves as they may be causing the leak. Also, take soap solution and go over each joint to look for leaks while pipe under pressure. You will find leak easier if you pump it up to higher pressure, like 20 or 30 psi. With high pressure you will hear the air escaping from the pipe making it easier to locate.

Pressure will change when you pressurize gas pipe in hot afternoon than check your gas gauge in cold evening / night. However, overall loss should not be 15% .

Back to you. Milo