API RP 581 - 3rd Ed.2016 - Add.2-2020 - Risk-Based Inspection Methodology
Share Embed Flag
Download ePaper

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

luis.alberto.mayorga.plaza
from luis.alberto.mayorga.plaza More from this publisher
17.12.2020 Views

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-13b) If the storage pressure is less than or equal to P trans, calculated using Equation (3.5), then the release rateis calculated using Equation (3.7) This equation is based on the discharge of a gas or vapor at subsonicvelocity through an orifice; see Crowl and Louvar [1] .2 k −1kkC ⎛dMW ⋅ g ⎞c2⋅k ⎛P ⎞ ⎛atmP ⎞atmn= ⋅n⋅ s ⎜ ⎟ ⎜ ⎟ 1−⎜ ⎟C2RT ⋅s ⎝k−1⎠Ps PsW A P⎛⎞⎛ ⎞ ⎜ ⎟⎜ ⎟ ⎝ ⎠ ⎝ ⎠ ⎜ ⎝ ⎠ ⎟⎝⎠(3.7)c) In Equation (3.6) and Equation (3.7), the discharge coefficient, Cd, for fully turbulent gas or vapor flowfrom sharp-edged orifices is typically in the range of 0.85 ≤C d≤ 1.0 . A conservative value of Cd= 0.90is recommended.4.3.4 Calculation of Release Ratea) STEP 3.1—Select the appropriate release rate equation as described above using the stored fluid phasedetermined in STEP 1.2.b) STEP 3.2—For each release hole size, calculate the release hole size area, An, using Equation (3.8)based on dn.Anπ d42n= (3.8)NOTE If D< d n, then set dn= D .c) STEP 3.3—For liquid releases, for each release hole size, calculate the viscosity correction factor, K ,vn ,using Figure 4.1 or Equation (3.4), as defined in Section 4.3.2.d) STEP 3.4—For each release hole size, calculate the release rate, Wn, for each release area, An,determined in STEP 3.2 using Equations (3.3), (3.6), or (3.7).4.4 Estimate the Fluid Inventory Available for Release4.4.1 OverviewThe leaking component’s inventory is combined with inventory from other attached components that cancontribute fluid mass. Additional background on the development of the inventory group concept is provided inAnnex 3.A.4.4.2 Maximum Mass Available for Release (Available Mass)The available mass for release is estimated for each release hole size as the lesser of two quantities.a) Inventory Group Mass—The component being evaluated is part of a larger group of components that canbe expected to provide fluid inventory to the release. These equipment items together form an inventorygroup. Additional guidance for creating logical inventory groups is provided in Annex 3.A. The inventorygroup calculation is used as an upper limit on the mass of fluid available for a release and does notindicate that this amount of fluid would be released in all leak scenarios. The inventory group mass iscalculated using Equation (3.9).

3-14 API RECOMMENDED PRACTICE 581massinvN= ∑ mass(3.9)i=1comp,ib) Component Mass—It is assumed that for large leaks, operator intervention will occur within 3 minutes,thereby limiting the amount of released material (see Annex 3.A for additional background). Therefore,the amount of available mass for the release is limited to the mass of the component plus an additionalmass, mass , that is calculated based on 3 minutes of leakage from the component’s inventory group.add , nThis additional mass is calculated assuming the same flow rate from the leaking component but is limitedto a 203 mm (8 in.) release hole size. The additional mass is calculated for each release hole sizeadd , nusing Equation (3.10).[ ]mass = 180⋅ min W , W(3.10)add , n n max8In Equation (3.10), the maximum flow rate, Wmax8, to be added to the release from the surroundingcomponents, W , [limited by a 203 mm (8 in.) diameter leak] is calculated using Equations (3.3), (3.6),max8or (3.7), as applicable, with the hole area,An = 32,450 mm 2 (50.3 in. 2 ).The maximum mass available, massavail,n , for release is calculated using Equation (3.11).{ }mass = min ⎡⎣mass + mass , massavail, n comp add , n inv⎤⎦(3.11)Plant detection, isolation, and mitigation techniques, as described in Section 4.6, will limit the duration of therelease such that the actual mass released to atmosphere can be significantly less than the available mass asdetermined above.Further guidance on the basis of the above methodology for calculating the available mass and the inventorygrouping is provided in Annex 3.A.4.4.3 Calculation of Inventory Massa) STEP 4.1—Group components and equipment items into inventory groups (see Annex 3.A).b) STEP 4.2—Calculate the fluid mass, masscomp, in the component being evaluated.c) STEP 4.3—Calculate the fluid mass in each of the other components that is included in the inventorygroup, mass .comp,id) STEP 4.4—Calculate the fluid mass in the inventory group, massinv , using Equation (3.9).e) STEP 4.5—Calculate the flow rate from a 203 mm (8 in.) diameter hole, Wmax8 , using Equations (3.3),(3.6), or (3.7), as applicable, with An= A8 = 32,450 mm 2 (50.3 in. 2 ). This is the maximum flow rate that canbe added to the equipment fluid mass from the surrounding equipment in the inventory group.f) STEP 4.6—For each release hole size, calculate the added fluid mass, mass , resulting from 3add , nminutes of flow from the inventory group using Equation (3.10), where Wn is the leakage rate for therelease hole size being evaluated and Wmax8 is from STEP 4.5.

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-13

b) If the storage pressure is less than or equal to P trans

, calculated using Equation (3.5), then the release rate

is calculated using Equation (3.7) This equation is based on the discharge of a gas or vapor at subsonic

velocity through an orifice; see Crowl and Louvar [1] .

2 k −1

k

k

C ⎛

d

MW ⋅ g ⎞

c

2⋅

k ⎛P ⎞ ⎛

atm

P ⎞

atm

n

= ⋅

n⋅ s ⎜ ⎟ ⎜ ⎟ 1−⎜ ⎟

C2

RT ⋅

s ⎝k−1⎠

Ps Ps

W A P

⎛

⎞

⎛ ⎞ ⎜ ⎟

⎜ ⎟ ⎝ ⎠ ⎝ ⎠ ⎜ ⎝ ⎠ ⎟

⎝

⎠

(3.7)

c) In Equation (3.6) and Equation (3.7), the discharge coefficient, C

d

, for fully turbulent gas or vapor flow

from sharp-edged orifices is typically in the range of 0.85 ≤C d

≤ 1.0 . A conservative value of C

d

= 0.90

is recommended.

4.3.4 Calculation of Release Rate

a) STEP 3.1—Select the appropriate release rate equation as described above using the stored fluid phase

determined in STEP 1.2.

b) STEP 3.2—For each release hole size, calculate the release hole size area, A

n

, using Equation (3.8)

based on d

n

.

A

n

π d

4

2

n

= (3.8)

NOTE If D< d n

, then set dn

= D .

c) STEP 3.3—For liquid releases, for each release hole size, calculate the viscosity correction factor, K ,

vn ,

using Figure 4.1 or Equation (3.4), as defined in Section 4.3.2.

d) STEP 3.4—For each release hole size, calculate the release rate, W

n

, for each release area, A

n

,

determined in STEP 3.2 using Equations (3.3), (3.6), or (3.7).

4.4 Estimate the Fluid Inventory Available for Release

4.4.1 Overview

The leaking component’s inventory is combined with inventory from other attached components that can

contribute fluid mass. Additional background on the development of the inventory group concept is provided in

Annex 3.A.

4.4.2 Maximum Mass Available for Release (Available Mass)

The available mass for release is estimated for each release hole size as the lesser of two quantities.

a) Inventory Group Mass—The component being evaluated is part of a larger group of components that can

be expected to provide fluid inventory to the release. These equipment items together form an inventory

group. Additional guidance for creating logical inventory groups is provided in Annex 3.A. The inventory

group calculation is used as an upper limit on the mass of fluid available for a release and does not

indicate that this amount of fluid would be released in all leak scenarios. The inventory group mass is

calculated using Equation (3.9).

logo

products

Resources

Company

Terms of service
Privacy policy
Cookie policy
Cookie settings
Imprint
Change language
Made with love in Switzerland
© 2024 Yumpu.com all rights reserved

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!