No pressure change at all in 24 hours? Zero leakage is certainly possible and fairly normal (most piping systems do not leak). For the pressure to not change with temperature variations id in my experience highly unlikely.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
I had a guy once that reported EXACTLY the same separator pressure month after month after month. I met him on location and opened the needle valve on the gauge and the trapped pressure was replaced by process pressure. When I see unchanging pressure I assume instrument error, not major coincidence.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The pressure did drop I'm just asking because theoretically it is a closed system loop and no drop should occur but I know that theory and application are two different things so I had to ask. Besides the leakage(pressure drop) was within limits approved by ASPE.
I'm not at all sure what "theory" you are referencing, but it isn't valid. "Pressure" is measure of one facet of total energy of a mass of fluid. The other facets are temperature, fluid composition, and volume. In your closed system, the only one of these parameters that is constant is volume. If mass leaks out then you are going to change pressure, temperature, and possibly fluid composition. On the other hand if temperature changes, then with constant fluid composition and constant volume, pressure is the only thing left to change and it does. For a system that is pure-water full (no air pockets), a change in pressure of 1[°]F corresponds to a pressure change of about 100 psi. Consequently, minuscule temperature changes (day to night in a 24 hour test) can make a pressure chart look like silhouette of the Rocky Mountains.
Temperature stratification further complicates this interaction. For example if you have a large fabrication that is partly in the sun and partly in the shade (or buried) then the part in the sun will heat rapidly and natural convection will bring cooler water into the sun and push the hot water into the shade. The local pressure change will be very high, but it is not supported by the bulk of the fluid and much of the pressure change is masked in the bulk modulus of the unaffected water.
This is one of the main reasons that 24 hour tests have fallen out of favor.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
