API RP 581 - 3rd Ed.2016 - Add.2-2020 - Risk-Based Inspection Methodology

5-90 API RECOMMENDED PRACTICE 581
Table 6.15—Estimated Leakage Duration from PRDs
PRD Inlet Size
(in.)
Leak Duration Discharge to Flare or
Closed System, D mild
(days)
Leak Duration Discharge to
Atmosphere, D mild
(days)
≤ 3 /4 in. 60 8
3 /4 < inlet size ≤ 1 1 /2 30 4
1 1 /2 < inlet size ≤ 3 15 2
3 < inlet size ≤ 6 7 1
Greater than 6 2 0.33
Table 6.16—Estimated Leakage Rate from PRVs
Bench Test Leak Description
Leak
Categorization
Percent of PRVs
Leaking on Bench
Percent of
All Leaks
Assumed Leakage
(Percent of Capacity)
Leaked between 70 % and 90 % of set
pressure, PRV opened at set pressure
Leakage below 70 % of set pressure,
PRV opened at set pressure
Immediate leakage or PRV leaked too
much to open
Minor 8.4 50 1
Moderate 6.6 40 10
Severe 2.4 10 25