I was recently reminded of how so many in process safety struggle to see their process(s) thru different lenses based on the piping’s life cycles. Using ASME B31.3 and 31.5, we see that these codes (e.g. RAGAGEPs) are design and build piping standards. Looking at API 570 series we see these are codes (RAGAGEPs) for the inspection of “in-Service” piping. Yes, both have pressure testing requirements for certain types of piping, but this pressure testing has its place based on the piping’s life cycle.
NEW piping for a PSM/RMP cover process has to be designed and built to a baseline RAGAGEP and in the USA our baseline RAGAGEP is the ASME B31 series, most notable being B31.3 for ordinary process piping and B31.5 for refrigeration processes. Both of these standards have their basic requirements, which includes welding requirements, inspection requirements and testing requirements that must be executed BEFORE the piping is put into service.
EXISTING piping (e.g. in-service) that is part of a PSM/RMP cover process has to be inspected per a chosen RAGAGEP and in the USA our piping baseline RAGAGEP is API 570 series. Some piping, most notably buried/underground piping has a requirement that it be “pressure tested” as part of its “in-service” inspection. And this pressure test is much different than the one we did we be erected the piping!
In B31 series our pressure test is only a 10-minute test, whereas the API 570 pressure test is an 8-hour test period. You may have the same immediate question as most… Why is ASME B31 test only 10-minutes and the API 570 test 8-hours? Two main drivers at play:
1) The ASME B31 test in intended to test ONLY the welds/flanges on NEWLY erected above ground pipe and thus the test period for this new piping is ONLY 10-minutes. Now keep in mind that after our pressure test, comes the “leak test” and in reality, this leak test can take hours and sometimes even days to complete. Basically, we will know of any structural issues in 10-minutes and we will be able to visual observe these failures as the piping is UNCOVERED (e.g. no coatings or insulation) and ABOVE ground; couple this with the fact that each and every weld and/or flange has to then be leak tested at the pipings operating limit.
2) The API 570 pressure test is 8-hours because this test applies to underground pipe which we can not see. This means no external NDE/NDT can be performed on this buried pipe so we have ONLY one means to verify the integrity and that is via the pressure test. PLEASE NOTE that “pressure testing” is considered an alternative and/or supplemental to “pigging” and excavating the piping so that it can be externally inspected. But when the pressure test is used, the pressure must be maintained for 8-hours. The pressure drop can be up to 5% for the pipe to pass (with re-pressurizing allowed after 4-hours); so really the actual test is a 4-hour period within the 8-hour window.
So again, B31 series is all about design and installation and API 570 is all about inspection of in-service piping. In fact, B31 series assumes the piping is “empty” and API 570 assumes the piping is still in-service. Of course, during their actual testing B31 has contents (e.g. water or compressed gas) and API piping will be removed from service, purged and cleaned before it is pressure tested. But these two standards play key roles in the life cycle of our piping, but at different stages.