API 598 differentiates check valve from all other valves when it comes to allowable leakage rate. This is because check valve inherently relies on passive pressure force to seal, which causes it to be more difficult to seal depending on the force applied on the disc. If the flow of the test bench cannot generate adequate flow to achieve proper sealing, the valve may even fail to seal during the test. The following table is for the allowable closure leak value testing with water at 1.1 times rated pressure and gas at low pressure (about 80 psig) or high pressure if specified by customer.
This table is only for check valve, for all other valves, please see API 598 allowable leakage.
For resilient seated valves, such as check valve with ptfe seating surfaces, there are no allowable visible leakage through the seating surface. It’s important to note the values for m3/h and ft3/h is not a direct conversion as published and thus is not equal value.
API 598 Check Valve Allowable Leakage Rates
|Size (NPS)||Liquid Test (ml/min)||Gas Test (m3/h)||Gas Test (ft3/h)|
For help with conversion between NPS vs DN, please check this table.
For reduced bore valves the valve shall be tested according to 12 NPS values unless otherwise agreed. This is normally not applicable to check valve.
Finally, if direct visual identification is not possible, a tube with an ID of 2 to 4 mm can be connected to the proper area of the valve and submerge 3 to 6 mm into water for observation for bubble count.
Compare check valve leakage rate to standard API 598 leakage rate
So how much differences are there between allowable leakage between check valve and other valves? To start, we can see that check valves in all sizes are allowed to leak during test. The differences however becomes dramatically evident the larger the valve becomes. The below table have been converted so that all units are in ml/min. We can see that the allowable leakage rate for a check valve in large sizes, especially with pneumatic testing, is worlds apart from other valves.
API 598 Allowable Leakage Rates
|Size (NPS)||Liquid (ml/min)||Gas (ml/min)||Check Liquid Test (ml/min)||Check Gas Test(ml/min)|
Looking at graph below, one can’t even see the normal gas test leakage line when compared to check valve allowable leakage line. Thus, think twice before specifying leakage rate on check valves, rather, it’s smarter to design a system that can deal with these type of leakage rates.
API 598 Test Duration
|NPS||Shell (s)||Backseat (s)||Check Valve Closure (s)||Other Valves Closure (s)|
|2.5 to 6||60||60||60||60|
|8 to 12||120||60||120||120|
For a summary of API 598, please see the summary page.
For information on additional valve standards please see Standards Summaries.
For other quick references: Quick Reference