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

5-68 API RECOMMENDED PRACTICE 581
F = 1.
0 for all other cases
r
Cost of Lost Inventory
The cost of lost fluid inventory, Cost inv , can be calculated using Equation (5.120) or Equation (5.121). Note
that when determining the consequence of leakage, the fluid costs, Cost flu , in Equation (5.120) should be
based on the fluid that exists in the protected equipment where the PRD is physically located.
mild
inv r flu mild mild
Cost = 24⋅F ⋅Cost ⋅D ⋅ lrate
(5.120)
so
inv r flu so so
Cost = 24⋅F ⋅Cost ⋅D ⋅ lrate
(5.121)
Environmental Costs
The environmental costs, Cost env , are added when leakage through a PRD either to atmosphere or to a flare
system could possibly result in cleanup costs or regulatory fines.
Costs of Shutdown to Repair PRD
The cost associated with repair and maintenance is added to calculate a PRD, Cost sd , if a leaking device
cannot be tolerated. The following values can be used to calculate repair and maintenance cost:
Cost sd =
$1000 for PRDs < NPS 6 inlet size
Cost sd
= $2000 for PRDs ≥ NPS 6 inlet size
However, API recommends using actual owner–user work order costs associated with the maintenance,
testing, inspection, and repair of the PRD.
Cost of Lost Production
The cost of lost production to repair a leaking PRD, Cost prod , can be calculated using Equation (5.122) or
Equation (5.123). Where spare PRDs are installed in parallel or in cases where isolation valves underneath
the PRD offer flexibility to repair without shutting down, production losses need not be considered. For the
stuck open case, it is assumed that prolonged operation cannot be tolerated, in which case Equation (5.124)
should be used.
mild
prod
Cost = 0.
0 if a leaking PRD can be tolerated or if the PRD can
be isolated and repaired without requiring a shutdown
(5.122)
mild
prod prod sd
Cost = Unit ⋅ D if a leaking PRD cannot be tolerated
(5.123)
so
prod prod sd
Cost = Unit ⋅ D for a stuck open PRD
(5.124)
Calculation of Leakage Consequence
The consequence of leakage is calculated for two leaks cases.
a) Minor or Moderate Leakage