RP0193-2001
ii NACE International
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NACE International
Standard
Recommended Practice
External Cathodic Protection of On-Grade Carbon Steel
Storage Tank Bottoms
Contents
1. General ........................................................................................................................... 1
2. Definitions ...................................................................................................................... 1
3. Preliminary Evaluation and Determination of the Need for Cathodic Protection............. 2
4. Criteria for Cathodic Protection....................................................................................... 5
5. General Considerations for Cathodic Protection Design ............................................... 7
6. Design Considerations for Impressed Current Cathodic Protection .............................. 9
7. Design Considerations for Galvanic Anode Cathodic Protection ................................. 11
8. Design Considerations — Cathodic Protection for Tanks with Replacement Bottoms or
Release Prevention Barriers ....................................................................................... 12
9. Installation Considerations............................................................................................ 15
10. Energizing and Testing ............................................................................................... 17
11. Operation and Maintenance of Cathodic Protection Systems .................................... 18
12. Recordkeeping ........................................................................................................... 19
References........................................................................................................................ 19
Bibliography ...................................................................................................................... 20
Figures
Figure 1: Soil Resistivity Testing (Four-Pin Method).......................................................... 3
Figure 2: Temporary Groundbed for Current Requirement Testing .................................. 5
Figure 3: Stray Current Corrosion...................................................................................... 6
Figure 4: Vertically Drilled Anode CP System.................................................................... 9
Figure 5: Angled Anode Cathodic Protection System...................................................... 10
Figure 6: Deep Anode Groundbed................................................................................... 10
Figure 7: Horizontally Installed Anode Groundbed .......................................................... 10
Figure 8: Typical Double-Bottom Cathodic Protection Layout (Impressed or Sacrificial) 13
Figure 9: Typical Double-Bottom Galvanic Anode Design............................................... 14
Figure 10: Typical New Tank or Double-Bottom Impressed Current Anode Design ....... 14
Figure 11: Perforated Pipe Installed for Reference Electrode ......................................... 16
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