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

5-88 API RECOMMENDED PRACTICE 581
Table 6.11—DF Classes for Protected Equipment
DF Class DF Description
None 1 New vessel or inspection shows little if any damage.
Minimal 20
Minor 200
Moderate 750
Severe 2000
Equipment has been in service for a reasonable amount of time and inspection
shows evidence of minor damage. Damage mechanisms have been identified and
inspection data are available.
One or more damage mechanisms have been identified, limited inspection data
available, and fairly minor evidence of damage.
Single damage mechanism identified, recent inspection indicates minor evidence of
damage.
Moderate damage found during recent inspection.
Low susceptibility to one or more damage mechanisms, and limited inspection
exists.
One or more active damage mechanisms present without any recent inspection
history.
Limited inspection indicating high damage susceptibility.
Table 6.12—Categories of PRD Service Severity (LEAK Case Only)
PRD
Service
Severity
Typical
Temperature
Expected Stream Characterization
Examples of Service
Mild
Low
temperature,
always
<< 500 °F
Many heavy liquid streams such as crude
oil tend not to leak through a PRD and are
considered mild service severity
— Cooling water and amine services are
examples of corrosive/fouling fluids that do
not leak
— Clean fluids such as LPG, air, and nitrogen
are MILD leakage services
Moderate
Up to
500 °F
(may exist)
Most of the intermediate and product
hydrocarbon streams and most
hydrocarbon vapors
— Lube, seal and cycle oils, and process
water (NOT cooling water, condensate, or
BFW)
Severe >500 °F High-temperature services
BFW/condensate, steam, and corrosive liquids
such as caustic and acids
NOTE
Refer to Table 5.4 for the categories for the FAIL case.