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.
As I indicated, the biggest flaw to this 24-hour test period is environmental temperature differences and how this can have a drastic impact on our testing. I then point to, how much of a drop in pressure is an “acceptable” drop. If you say “zero” and you are measuring to two (2) significant digits (which you should be) then most 24-hour testing done on outside piping in the spring and fall months will most likely fail. And in some locations/elevations, we can have issues during the summer months with this test method.
The testing that I have written about using the ASME B31 model is NOT impacted by external environmental conditions as the pressure test – test pressure is held for only 10 minutes. After a successful “pressure test” we then lower the pressure in the piping to our normal operating pressure(s) and then perform our leak testing using the soapy water/bubble method. Yes, these methods will take longer; but there are sound safety reasons why we do not want to leave our piping at pressures of 110%-150% of its design pressure for longer than 10-minutes, much less for 24-hours! And I should point out, those clients who were doing their pressure testing over a 24-hr period were NEVER meeting the test pressures as stipulated in ASME B31. We have seen process piping tested at 50 psi over a 24-hr period and accepted as “Construction and equipment is in accordance with design specifications” (1910.119(i)(2)(i) even though the piping will normally operator at pressures over 100 psi.