Cathodic protection compared
Galvanic vs Impressed Current
Corrosion protection — which system?
The two cathodic protection principles used in Thailand — sacrificial anode vs DC rectifier. Full spec table + decision tree + ISO 12696 / NACE / DNV standards
In short — choose by size + budget
Galvanic = small projects, no power. ICCP = large infrastructure with electricity available.
Plug-and-play
Galvanic (Sacrificial)
- No electricity — the EMF drives Zn/Al/Mg to corrode instead of the steel
- Low capex — starts from ฿500K
- Near-zero OPEX — just swap anodes every 5-10 years
- Self-limiting — no stray-current risk
- Suits seawater + wet conditions + small-to-medium structures
Best for
Jetties < 1 km, sheet piling, vessel hulls, reinforced-concrete buildings, short buried pipelines
Industrial scale
Impressed Current (ICCP)
- DC rectifier drives current at any resistivity
- Inert anode (MMO/Pt) lasts 20-50 years
- Remote monitoring 24/7 via Modbus/SCADA
- Output adjustable for seasonal change
- Suits large infrastructure
Best for
Pipelines > 10 km, bay-crossing bridges, offshore platforms, dry-soil tank farms
Decision tree — 5 questions
1How large is the area / structure?
Galvanic
Small-medium (< 1,000 m² of wet steel)
ICCP
Large (pipeline, bridge, platform)
2Soil resistivity?
Galvanic
Low (< 5,000 Ω·cm) — seawater / wet
ICCP
High (> 10,000 Ω·cm) — dry soil
3Power available 24/7?
Galvanic
No — remote location
ICCP
Yes — grid power accessible
4Budget?
Galvanic
< ฿2M
ICCP
> ฿2M + electricity ฿80K-200K/yr
5Monitoring requirement?
Galvanic
Manual quarterly OK
ICCP
Real-time remote required
12-item comparison table
| Item | Galvanic | Impressed Current |
|---|---|---|
| Principle | Sacrificial anode (Zn / Al / Mg) corrodes instead of the steel — driven by the EMF difference | DC power supply drives current from an inert anode (MMO/Pt/HSCI) into the environment |
| Power | No electricity (self-powered) | Needs a DC rectifier + AC supply 24/7 |
| Current output (mA) | Low-medium: 10-50 mA/anode | High: 100-50,000 mA per system |
| Anode lifetime | 5-25 years (sacrificial = consumed) | 20-50 years (inert anode) |
| Soil/water resistivity (Ω·cm) | Suits <5,000 (seawater, wet) | Works across the full range incl. dry soil 10,000+ |
| Initial capex (medium project) | ฿500K-฿2M | ฿2M-฿8M (rectifier + remote monitoring) |
| OPEX (per year) | Very low — anode swap every 5-10 years | Electricity + rectifier maintenance ฿80K-฿200K/yr |
| Monitoring | Manual check every 6-12 months | Real-time remote (Modbus/SCADA) |
| Risk of stray current | Low (self-limiting) | High — needs interference testing + bonding |
| Suitable for | Small-medium · short-life · simple environments | Large infrastructure · long-life · variable resistivity |
| Standards | ISO 12696, ASTM B418, NACE SP0387, DNV-RP-B401 | ISO 15589-1/2, NACE SP0169, EN 12954, DNV-RP-B101 |
| Real-world example | Jetties, sheet piling, small vessel hulls, steel-reinforced buildings | Bay-crossing bridges, pipelines 10+ km, offshore platforms |
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Related comparisons
Decide with confidence — compare from several angles
Read the related comparison tables — full specs, real prices, and a recommendation for each use.
FAQ
Common Questions
Q1.When to choose galvanic vs impressed current (ICCP)?+
By structure size + soil/water resistivity:
• Galvanic (sacrificial anode): small-medium structures, seawater, resistivity <50 Ω·m
• Impressed Current (ICCP): large structures, long pipelines, dry soil >100 Ω·m
Standards: NACE SP0169 + ISO 12696:2022.
Q2.How do initial vs maintenance costs compare?+
25-year TCO (1,000 m² structure):
• Galvanic: capex ~฿300K + maintenance ฿20K/yr × 25 ≈ ฿800K
• ICCP: capex ~฿800K + maintenance ฿50K/yr × 25 ≈ ฿2,050K
Galvanic is half the lifetime cost — but anodes need replacement every 10-15 years.
Q3.What's the anode service life?+
Depends on current demand + environment:
• Zinc anode (ASTM B418 Type II): 15-25 years in seawater
• Magnesium anode (ASTM G-97): 5-15 years in fresh water
• Aluminum anode (DNV-RP-B401): 20-30 years in seawater
• ICCP MMO anode: 20+ years (requires continuous DC power)
Q4.Which standards apply for Thai government TOR?+
EGAT / SRT / MEA / PEA + port/bridge projects commonly cite:
• ISO 12696:2022 (concrete reinforcement)
• NACE SP0169 (pipeline external corrosion)
• ASTM B418 (zinc), B843 (magnesium), B26 (alloy)
• TIS 3029-2563 (zinc anode for cathodic protection)
Q5.Does ICCP need continuous power?+
Yes — ICCP requires DC power supply 1-50 A continuously + maintenance every 6 months (rectifier check, reference electrode calibration). Galvanic needs no power — uses anode electrochemical potential. Remote / offshore / unreliable-power sites favor galvanic.
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