WELCOME: SHIP CATHODIC PROTECTION DESIGN

Transcription

1 What this Excel Sheet does WELCOME: SHIP CATHODIC PROTECTION DESIGN This excel sheet helps the user estimate the number of anodes required for corrosion protection of a ship, depending on the properties of the anode supplied and the surface area needed to be protected Calculates the Initial, Mean and Final currents required for cathodic protection Calculates the current output of the anode based on properties supplied by the user Calculates the total number of anodes required based on Anode Weight/Current required Very useful in determining the quantity of anodes needed for Cathodic Protection of the vessel, and also in selecting the right anode type for the ship Based on DNV-RP-B-401 CATHODIC PROTECTION DESIGN Directions for Use 1. All the cells which require input are in the Worksheet 'Inputs' and have blue background. Please fill only input cells, i.e., ones with blue background. Leave the other cells untouched, as they are output cells 2. Fill in the inputs in the Worksheet 'Inputs'. Please don't fill anything in the worksheets named 'Outputs - " 3. Once the 'Inputs' sheet is completed, the calculations will be carried out to provide the number of anodes required to protect the desired area Assumptions and Limitations 1. Resistivity for Temp < 5 degrees is same as that for 5 degrees, 2. Resistivity for Temp > 25 degrees is same as that for 25 degrees 3. It doesn't cover cathodic protection of concrete reinforcing steel or other concrete embedded steel structures (Sec DNV-RP-B401) References 1. DNV Recommended Practice DNV-RP-B401 CATHODIC PROTECTION DESIGN, October

2 Doc. No:Date:Revision No:Prepared By:Page 2 of 9 - ENVIRONMENT INPUTS Environment parameters Category Name Temperature Range Tropical > 20 o C Particular Value Default Value Units Sub-Tropical o C Depth of Water d w 10 m Temperate 7-11 o C Temperature T 22 degrees C Arctic < 7 o C Environment type (Seawater, Sediments) Seawater Salinity (Please enter between 30 and 40) % Area to be protected Particular Value Units Coating category (See Table 2) Design Protective Potential* *Note: The design protective potential as per DNV-RP-B-401 is fixed at -0.8 V E c o Category II V Table 1: Temperature Category Table 2 Coating Categories

3 Doc. No:Date:Revision No:Prepared By:Page 3 of 9 - Surface Area Surface Area to be protected Name Value Units Area m 2 Area 2 0 m 2 Area 3 0 m 2 Area 4 0 m 2 Area 5 0 m 2 Area 6 0 m 2 Area 7 0 m 2 Area 8 0 m 2 Area 9 0 m 2 Area 10 0 m 2 Area 11 0 m 2 Area 12 0 m 2 Area 13 0 m 2 Area 14 0 m 2 Area 15 0 m 2 Area 16 0 m 2 Area 17 0 m 2 Area 18 0 m 2 Area 19 0 m 2 Area 20 0 m 2

4 Doc. No:Date:Revision No:Prepared By:Page 4 of 9 - ANODES Anode parameters Particular Symbol Value Default Value Units Anode Material (Aluminium/Zinc) Zinc Anode Type (See options) Flush Mounted Design Life t 7 Years Anode Electrochemical Capacity (See Table 10-6 DNV RP-B-401) ε A-Hr/kg Anode Geometry Particular Value Units Anode Length L 200 mm Anode Width w 100 mm Anode Thickness t 30 mm Mean of Anode Length and Width S mm Total surface area of anode A mm 2 Anode Surface Area in contact with protected surface* A f mm 2 Design Closed Circuit Potential (See Table 10-6 DNV RP-B-401) o E a -1-1 V Net initial mass of one anode m ai 3.6 kg Density of anode material d a 7140 kg/m 3 *The default value for the surface area in contact is assumed to be Length x Width for Flush-mounted anodes, and half of total surface area for other types (e.g, bracelet) Slender Stand Off Type Flush Mounted Type Bracelet Type (Other)

5 Doc. No:Date:Revision No:Prepared By:Page 5 of 9 - OUTPUTS Environment properties 0.4 Temperature Resistivity Salinity 30 Salinity 35 Salinity 40 Particular Symbol Formula Value Units Depth of Water 10 m Temperature 22 degrees C Temperature Category Tropical 0.3 Salinity Environment type (Seawater, Sediments) Seawater Salinity Salinity 35 % 0.25 Salinity40 Factor for Resistivity in Sediment (See Sec DNVf res See DNV RP B RP-B401 on right) Seawater Resistivity (See Graph on the right) ρ See DNV RP B Anode Properties 0.15 Particular Symbol Formula Value Units Anode Type (See Table 10-7 on right) Short Flush Mounted Initial Anode Resistance (See Table 10-7 on right) R ai ohm Anode Utilization Factor (See Table 10-8 on right) u 0.8 Final anode mass (See sec DNV RP-B-401) m af m af = m ai * (1-u) 0.72 kg Final Anode Surface Area (See Sec DNV RP-B- 401 for Short Fluch Mounted/Other Anode types) A f mm 2 Final Anode Resistance (See Table 10-7 on Right) R af ohm Design Protective Potential of Anode (See Sec of DNV RP-B-401) ΔE o o o E c - E a 0.2 V Initial Anode Current Output (See Sec of DNV RP-B-401) I ai ΔE o /R ai ma Final Anode Current Output (See Sec of DNV RP-B-401) I af ΔE o /R af ma

6 Doc. No:Date:Revision No:Prepared By:Page 6 of 9 - OUTPUTS General Particulars Particular Symbol Formula Value Units Water Depth d w 10 m Temperature Category Tropical Design Current Densities Initial Current Density i ci See Table ma/m 2 Final Current Density i cf See Table ma/m 2 Mean Current Density i cm See Table ma/m 2 Coating Breakdown Particular Value Units Coating breakdown factor 'a' (See Sec 6.4 DNV RP-B- 401) a See Table Coating breakdown factor 'b' (See Sec 6.4 DNV RP-B- 401) b See Table Design Life t See Anode Inputs Table 7 Years Initial Coating Breakdown factor f ci 0.05 Final Coating Breakdown factor f cf Mean Coating Breakdown factor f cm

7 Doc. No:Date:Revision No:Prepared By:Page 7 of 9 - Anodes Weight Required Current Densities Coating Breakdown Anode Properties Initial Current Density, i ci (ma) 150 Initial, f ci 0.05 Design Life, t (Yrs) 7 Mean Current Density, i cm (ma) 70 Mean, f cm Anode Capacity, ε (A-Hr/Kg) 780 Final Current Density, i cf (ma) 100 Final f cf Utilization Factor, u 0.8 Estimation of Anodes Needed Area Name Surface Area A c Current Demand I c = Current Density (i c ) x Surface Area (A c ) x Coating Breakdown (f c ) Anode Weight Required, M a Initial I ci = i ci x A c x f ci Mean I cm = i cm x A c x f cm Final I cf = i cf x A c x f cf I cm x t (yrs) x 8760 /(u x ε) m 2 (Amp) (Amp) (Amp) kg Area Area Area Area Area Area Area Area Area Area Area Area Area Area Area Area Area Area Area Area

8 Doc. No:Date:Revision No:Prepared By:Page 8 of 9 - NUMBER OF ANODES Particular Symbol Formula Value Units Weight Required Total Weight of Anodes needed M a kg Net Weight of one Anode m a 3.6 kg Current Required Initial Total Current Demand I ci 3.73 Amp Final Total Current Demand I cf Amp Anode Initial Current Output I ai 0.78 Amp Anode Final Current Output I af 0.46 Amp Number of Anodes Particular Value Units No. of Anodes to meet Required Weight N1 M a /m a 131 No. of Anodes to meet Initial current demand N2 I ci /I ai 5 No. of Anodes to meet Final current demand N3 I cf /I af 25 Required Number of Anodes N Max of N1, N2, N3 131

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