This is a common question we get regarding pressure testing and leak testing of process piping. I have written quite a few posts regarding the ASME B31.3 and 31.5 requirements for pressure and leak testing over the years, but this question about holding pressure for 24-hours is one that just will not die. I am not here to say this practice is wrong, I’m just saying it is not one that is mentioned in either B31.3 or 31.5 so anyone using this method most likely would be challenged by a regulatory agency. But beyond the compliance aspect, there are a lot of factors that could cause a pressure drop in the piping being tested over a 24-hr period.
Hint: it snowed here in Cincinnati on 4/21/21, I am reminded that it was 68ºF yesterday afternoon at 5:00 pm and this morning we woke up to 3″ of snow and 30ºF temps.