API 598 Allowable Check Valve Leakage (Reference Table)

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.

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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)
2	6	0.08	3
2.5	7.5	0.11	3.75
3	9	0.13	4.5
4	12	0.17	6
5	15	0.21	7.5
6	18	0.25	9
8	24	0.34	12
10	30	0.42	15
12	36	0.5	18
14	42	0.59	21
16	48	0.67	24
18	54	0.76	27
20	60	0.84	30
24	72	1.01	36
26	78	1.09	39
28	84	1.18	42
30	90	1.26	45
32	96	1.34	48
36	108	1.51	54
40	120	1.68	60
42	126	1.76	63
48	144	2.02	72
52	156	2.184	78
56	168	2.352	84
60	180	2.52	90
64	192	2.688	96
68	204	2.856	102
72	216	3.024	108
76	228	3.192	114
80	240	3.36	120

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)
2	0	0	6	1415.85
2.5	0.3125	0.1	7.5	1769.8125
3	0.375	0.12	9	2123.775
4	0.5	0.16	12	2831.7
5	0.625	0.2	15	3539.625
6	0.75	0.24	18	4247.55
8	1	0.32	24	5663.4
10	1.25	0.4	30	7079.25
12	1.5	0.48	36	8495.1
14	1.75	0.56	42	9910.95
16	2	0.64	48	11326.8
18	2.25	0.72	54	12742.65
20	2.5	0.8	60	14158.5
24	3	0.96	72	16990.2
26	3.25	1.04	78	18406.05
28	3.5	1.12	84	19821.9
30	3.75	1.2	90	21237.75
32	4	1.28	96	22653.6
36	4.5	1.44	108	25485.3
40	5	1.6	120	28317
42	5.25	1.68	126	29732.85
48	6	1.92	144	33980.4
52	6.5	2.08	156	36812.1
56	7	2.24	168	39643.8
60	7.5	2.4	180	42475.5
64	8	2.56	192	45307.2
68	8.5	2.72	204	48138.9
72	9	2.88	216	50970.6
76	9.5	3.04	228	53802.3
80	10	3.2	240	56634

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.

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API 598 Test Duration

NPS	Shell (s)	Backseat (s)	Check Valve Closure (s)	Other Valves Closure (s)
≤2	15	15	60	15
2.5 to 6	60	60	60	60
8 to 12	120	60	120	120
≥14	600	60	120	120

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For a summary of API 598, please see the summary page.

For access to API 598 standard, please check. IHS | Techstreet |

For information on additional valve standards please see Standards Summaries.

For other quick references: Quick Reference