Gas line pressure testing, is there an acceptable limit for losses?
You have a leak, and given that it's gas piping, you need to fix it.
For an air compressor, you might live with that sort of leak, but you don't have to.
For gas, it's unacceptable.
&quot;Nothing is going to stay pressurized forever without maintenance&quot; - for adequate values of forever, sure, the pipe will rust away. My &quot;properly assembled&quot; portable air tank, with a gauge and a quick-disconnect and a hose left on the quick disconnect with another quick-disconnect and a tire chuck holds pressure for (at least) months. If your gas piping won't hold pressure for a week, that's going to be a problem.
Small variations (which can go up as well as down) may be seen due to changes in temperature. I very much doubt that's the case for your pipe. Add more pressure, get out the soapy water (plus glycerine if you can find some, or buy &quot;leak detector fluid&quot; if you like - or just bubble solution for blowing bubbles) and start checking every joint. At least one is bubbling and needs to be remade properly.