CATHODIC PROTECTION DESIGN FOR BRACELET ANODE
This spreadsheet determines the anode requirements for the main line. The output represents the anode requirements to satisfy the mean and final current demand of the pipelines. Mthodology is in accordance with DNV-RP-B401 (2010). 1.0 INPUT DATA C K
Definition of Units for MATHCAD :
years 8760 8760 hr
A amp
1.1 Pipelin Pipelin e Data Pipeline Length
L p := 1600 16000 0m
Outside Diameter
D := 273.1 mm mm
Joint Length
L j := 12.2m
Corrosion Coating thickness
t c := 3.5 3.5 mm
Design Life
t f := 15 year yearss
Operating Operating Temperature
Top := 55 C
Mean Current Density (Depth (Depth > 30-100 m
i cm := 0.06 0.06 A m
and surface water temperature >20
(3LPE coating)
(Assume that the temperature for the anodes is the same as the temperature of the pipeline)
-2
(Table 10-2, DNV-RP-B401, 2010)
oC )
Final Current D ensity (Depth (Depth > 30-100 m and
-2
i cf := 0.08 0.08 A m
(Table 10-1, DNV-RP-B401, 2010)
surface water temperature >20 oC )
-2
C
-1
C) Temperature correction (>25 (>25 deg C)
Tc := 0.00 0.001 1Am
Constant in Coating Breakdown Factor (Coating Category Ca tegory III) III)
a := 0.02
(Table 10-4 DNV-RP-B401, DNV-RP-B401, 2010)
Constant in Coating Breakdown Factor (Coating Category Ca tegory III) III)
b := 0.008
(Table 10-4 DNV-RP-B401, DNV-RP-B401, 2010)
Mean Coating Breakdown Factor
f cm := a + b
Final coating brakdown factor
f cf := a + b
Design Protective Potential vs Ag/AgCl
Ec := -0.80 volt
(Section 5.4.1 DNV-RP-B401, 2010)
C) Environmental Resistivit Resistivity y (Seawater, (Seawater, 21 deg C)
ρ :=
(Figure 10-1 DNV-RP-B401 2010, The salinity is assumed 35ppt as average value)
tf ears 2 years tf years
0.225 0.225 ohm m
(Section 6.3.9 DNV-RP-B401, 2010)
f cm = 0.08 f cf = 0.14
Page 1 of 5
1.2 Half Shell Brac elet Anode Data (Al Based) Clearance Between Anode ID & coating OD
t g := 0mm
Anode Inside Diameter
IDa := D + 2 t c + 2 t g
Anode Thickness
t a := 40mm
Anode Length
La := 450mm
Half Shell Gap Anode Material Density
IDa = 280.1 mm
ga := 100mm ρa :=
-3
2700 kg m
u := 0.8
(Table 10-8, DNV-RP-B401, 2010)
Design Closed Circuit Anode Potential (Seawater)
Ea := -1.05 volt
(Table 10-6, DNV-RP-B401, 2005)
Electrochemical Capacity (Seawater )
ε a :=
Anode Usage Factor
-1
2000 A hr kg
(Table 10-6, DNV-RP-B401, 2005)
2.0 CALCUL ATIONS 2.1 Net Mass per Ano de 2
Surface Area of Anode
SAa := π ( IDa + 2 t a) - 2 ga La
SAa = 0.419 m
Cross-Sectional Area of Anode
XAa := π (IDa + t a) - 2 ga t a
XA a = 0.032 m
Volume of Anode
V a := XA a La
V a = 0.015 m
Net Mass per Anode as per calculation
mac := V a ρa
mac = 39.153 kg
Net Mass per Anode as per availability from Vendor Catalogue
ma := 38kg
ma = 38kg
Surface Area to be Protected
Acm := π D L p
Acm = 1.373 10 m
Design Steel Current Density Demand Correction for Steel Temperature (T)
i cmt := if Top < 25 C , icm , i cm + ( Top - 25 C) Tc
2
3
2.2 Mean Current Requirement
i cmt = 0.09A m
Mean Coating Breakdown Factor
4
2
-2
f cmt := if t f < 30 years , f cm , f cm + 0.002
t f - 30 years
f cmt = 0.08
Page 2 of 5
Current Demand for Specific Surface Area
Icm := Acm f cmt i cmt
Electrochemical Efficiency
ε
Total Anode Mass
M :=
:=
Icm = 98.838 A
εa
ε
Icm tf
M = 8117.07 kg
u ε
4
c a := ma ε u
Anode Current Capacity
-1
3
= 2 10 A hr kg
c a = 6 .08 10 A hr
M
Minimum Num ber of Anodes Required
nm :=
Maximum Required Anode Spacing (meter)
Lspm :=
Maximum Required Anode Spacing (number of joints)
Joints m :=
nm = 213.607
ma L p
Lspm = 74.904 m
nm Lspm L j
Jointsm = 6.14
Mean Currrent Requirements Results: RESULT mean := if( nm ca Icm t f , "The Mean Current Requirements are met" , "Not OK" ) RESULT mean = "The Mean Current Requirements are met"
2.3 Final Current Requirement End of Life Anode Mass
mf := ma ( 1 - u)
End of Life Anode Volume
V f :=
End of Life Anode CSA ( Assume Anode Length doesn't change)
mf
-3 3
V f = 2.815 10
ρa
XAf :=
mf = 7.6kg
V f La
m
-3 2
XA f = 6.255 10
m
End of Life Anode Outer Diameter Initial Aprroximation Given
ODf := IDa XAf = ( π OD f - 2 ga) ( ODf - IDa) ODf := Find( ODf )
OD f = 0.289 m
End of Life Anode Surface Area
SAaf := ( π ODf - 2 ga) La
SAaf = 0.318 m
End of Life Anode Resistance
R af :=
End of Life Anode Current Output
Iaf :=
0.315 ρ SAaf Ec - Ea R af
2
R af = 0.126 ohm
Iaf = 1.991 A
Page 3 of 5
The Design Final Current Density for Steel, Corrected for Temperature
i cft := if Top < 25 C , i cf , i cf + ( Top - 25 C) Tc i cft = 0.11A m
-2 4
Steel Surface Area to be Protected
Acf := π D L p
Final Coating Breakdown Factor
f cft := if t f < 20 years , f cf , f cf + 0.004
2
Acf = 1.373 10 m
tf - 20 years
f cft = 0.14
End of Life Current Demand for Surface Area to be Protected
Icf := Acf f cft icft
Minimum Num ber of Anodes Required
nf :=
Maximum Required Anode Spacing (meter)
Lspf :=
Maximum Required Anode Spacing (number of Joints)
Jointsf :=
Icf = 211.404 A
Icf
nf = 106.2
Iaf L p
Lspf = 150.659 m
nf Lspf
L j
Jointsf = 12.349
Final Current Requirements Results RESULT final := if( nf Iaf Icf , "The Final Current Requirements are met" , "Not OK" ) RESULT final = "The Final Current Requirements are met"
2.4 Required Anode Spacing and Number of Anodes Required Anode Spacing (number of Joints) Jointsrequired := min( Jointsm, Jointsf ) Joints rounded := floor(Jointsrequired )
Required Number of Anodes
N required :=
Jointsrequired = 6.14 Jointsrounded = 6
L p Joints rounded L j
N rounded := ceil( N required )
N required = 218.579
N rounded = 219
Page 4 of 5
2.5 Check Final Anode Thic kness 2
Steel Surface Area Protectable per Anode
Acmc := π D ( Jointsrounded L j)
Acmc = 62.803 m
Current Demand for Surface Area to be Protected per Anode
Icmc := Acmc f cmt i cmt
Icmc = 0.452 A
Mass of Anode Used to Protect the Surface Area
mused :=
Icmc t f
mused = 29.708 kg
ε
Remaining Mass per Anode (Final Anode Mass)
mfinal := ma - mused
Final Anode Volume
Vol final := t af :=
Final Anode Thickness requirement
t af_req :=
-3 3
Vol final = 3 .0 71 1 0
ρa
Volfinal
Final Anode Thickness
Check Final Anode Thickness
mfinal
mfinal = 8.292 kg
m
t af = 9.643 mm
SAaf
(ODf - D - 2 tc) 2
t af_req = 4.419 mm
Check_taf := if( t af t af_req , "OK" , "Not OK" ) Check_taf = "OK"
Page 5 of 5
23 - 41 Willowdale Place, Aberdeen, AB24 5AQ
AF ‘Defender’ Rigid Pipe Aluminium Bracelet Anodes B1 Examples Anode Code (A =Al Bracelet Wt x 10 )
Anode ID (mm) (NB pipe) D double, SSingle band
Anode OD (mm)
O/all Length (mm)
Anode Weight (Nett kg/ Gross kg)
AFA B 200
(4”) 118 D
198
416
20/25
AFA B 126
(6”) 170 S
250
235
12.6/16
AFA B 186
(6”) 170 S
250
368
18.6/16
AFA B 235
(8”) 225 D
315
410
23.5 / 28.4
AFA B 333
(8”) 223.5
303.5
475
33.3/37.7
(10”) 280 S
360
325
28 /35
(10”) 280 D
360
450
38/35
(12”) 328 S
408
290
29.2 / 34
(12”) 328 S
408
425
42 / 46
AFA B1200
(16”) 410 D
492
800
120/ 135
AFA B350
(16”) 435 D
515
280
35/47.5
AFA B610
(20”) 512 D
592
450
61/85
AFA B520
(20”) 520 D
610
315
55/69
AFA B550
(20”) 550 D
640
300
55 / 70
AFA B570
(22”) 570 D
660
295
55/71
(10”) 286 Rubber lined, 40mm to363 D Hinged
453
680
75/90
AFA B 280 AFA B 380 AFA B 292 AFA B 400
AFA B790
Design Examples
Rigid pipes
…….Fully Bolt on gusseted bands (Single, S or Double, D) Tapered ends Continuity straps; Epoxy coat inside neoprene liner optional
Example: High temp pipe anode heavy rubber lined to order
* All weights and dimensions are nominal Material Specification: AF Defender G3 AF Al-Zn-In-Si anode alloy Fe Si Cu Zn In Others Al 0.12 max. 0.08-0.21 0.006 max. 2.8 – 6.5 0.01 – 0.02 0.02 max remainder Potential –1.09* Volts Ag/AgCl Capacity (Amp Hrs) 2540* per Kg min Density 2750Kg/m3 * AFDefender G3 alloy performance Data for long term test by DNV Certificate No S-5615 to DNV RP B401 Appendix B
Aluminium and Zinc Castings • Aluminium Offshore Anodes • Zinc & Al Marine Hull Anodes •Tank Anodes • Pipeline Anodes • Down-hole Centralisers and Clamps • Ballast Weights AFA Bracelet Anodes Sheet B 1 Rigid Pipes taper NEW sept 09 to Ab internet (2).doc
