Zinc Anode / Cathodic Protection — Prices and Contractors in Thailand 2026: A Procurement Guide for Engineers

Corrosion is a silent threat that continuously eats away at steel and concrete structures, especially in humid environments, in contact with seawater, in waterlogged soil, or in industrial atmospheres with high Chloride content. Cathodic Protection (CP) using a Sacrificial Anode is the method proven over more than 200 years to be the most effective and cost-efficient way to protect steel and steel alloys from corrosion.

This article compiles market prices, how to select an Anode to suit the environment, the relevant standards, and the procurement steps for engineers and project buyers in Thailand for 2026.

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How Sacrificial-Anode Cathodic Protection Works

Cathodic Protection works on the principle of a Galvanic Cell — when two dissimilar metals are immersed in the same electrolyte solution, the metal with the lower Electrode Potential (Anodic) corrodes first, while the metal with the higher potential (Cathodic) is protected.

The principle: install an Anode made of an Anodic metal (Zinc, Magnesium, Aluminum) connected to the steel structure to be protected → the Anode corrodes instead of the steel → the steel does not rust → once the Anode is fully consumed, replace it.

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Types of Sacrificial Anode and Their Suitable Environments

1. Zinc Anode

Composition: Zn ≥ 95%, Al 0.1–0.5%, Cd 0.025–0.07% (ASTM B418 Type II)

Suitable environments:

• Seawater — works best; low Resistivity (15–30 Ω·cm) allows good current flow
• Brackish Water with Cl⁻ > 1,000 ppm
• Submerged steel structures: Offshore pipelines, ships, jetties, bridges, sea-crossing bridges

Limitations: does not work in soil with high Resistivity (> 1,500 Ω·cm) or in freshwater with very high Resistivity — delivers too little current.

2. Magnesium Anode

Composition: Mg ≥ 90%, Al 5.3–6.7%, Zn 2.5–3.5% (ASTM B843)

Suitable environments:

• Soil / Earth with Resistivity 1,000–10,000 Ω·cm
• Buried pipelines, underground water/oil storage tanks (UST)
• Reinforced concrete structures in moist soil
• Freshwater with high Resistivity

Advantage: high Driving Voltage (~0.75 V compared with Zinc ~0.25 V), so it delivers sufficient current even in high-Resistivity environments.

Limitations: shorter service life than Zinc in the same environment due to lower Efficiency; higher unit price.

3. Aluminum Anode

Composition: Al ≥ 97%, In 0.015–0.04%, Zn 2.0–6.0% (ASTM B843)

Suitable environments:

• Seawater and brackish water at high temperatures
• Offshore structures requiring light Anode weight
• Work requiring higher Current Capacity than Zinc per unit weight

Advantage: delivers Electrochemical Capacity ~3 times higher than Zinc (2,000–2,800 A·h/kg vs Zinc ~780 A·h/kg), so less weight is needed to protect the same area.

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Comparison Table of the 3 Sacrificial Anode Types

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🧮 Before the price, you need the quantity. A price per kilo means nothing until you know the total mass your structure actually needs — work that out in the Anode Sizing Calculator, then multiply against the table below.

Sacrificial Anode Prices in the Thai Market, 2026

Zinc Anode Reference Prices

Magnesium Anode Reference Prices

Aluminum Anode Reference Prices

Note: prices may change according to global metal market prices — contact the sales department for prices and minimum order quantities.

⚠️ The most common anode procurement mistake: comparing price per piece

Two anodes that look identical can differ three- to fourfold in what you are actually buying. Price per piece tells you nothing until you know three things:

1. Net weight (kg) — anodes are priced on metal mass, not per lump. A 3 kg zinc bar and a 10 kg zinc bar differ threefold by definition. Always ask for net weight before comparing.

2. Alloy → delivered capacity — from the table above, aluminium delivers 2,000–2,800 A·h/kg while zinc delivers ~780 A·h/kg. One kilogram of aluminium does the work of roughly three kilograms of zinc. An aluminium anode that costs more per piece can therefore cost less per unit of actual protection.

3. Standard and alloy composition — ASTM B418 Type II zinc requires Al and Cd as activators. Low-grade zinc without activators passivates and stops delivering current while the metal is still visibly intact — you paid for protection that quietly ended in year one.

The correct basis — baht per A·h:

baht per A·h = price per piece ÷ (net weight kg × capacity A·h/kg × current efficiency)

Example: an 11.6 kg aluminium anode at ฿3,100 → 11.6 × 2,000 × 0.90 ≈ 20,880 A·h → ฿0.148 per A·h Versus a 10 kg zinc anode at ฿1,300 → 10 × 780 × 0.92 ≈ 7,176 A·h → ฿0.181 per A·h

In this example the piece that is "2.4× more expensive per unit" is in fact 18% cheaper per unit of delivered protection — and needs fewer pieces, which further reduces installation labour and connection points.

Ask every supplier for net weight, standard (ASTM/TIS) and current efficiency, then compare in the same unit. If a supplier cannot give you those three numbers, that is itself the answer.

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Standards Used in Thailand

ASTM B418 — Zinc Anode Standard

ASTM B418 specifies the chemical composition of Zinc Anodes, divided into 2 Types:

• Type I: for freshwater — lower Al and Cd content
• Type II: for seawater — the primary standard used in Thai projects

ISO 12696:2022 — Cathodic Protection in Concrete

ISO 12696 specifies requirements for Cathodic Protection systems in reinforced concrete structures such as bridges, coastal buildings, and jetties, covering:

• Protection Criterion: generally requires Steel Potential ≥ -770 mV (vs Ag/AgCl/0.5M KCl)
• Monitoring methods throughout the project life

DNV-RP-B401:2021 — Offshore Cathodic Protection

DNV (Det Norske Veritas) specifies the design standard for CP systems for Offshore structures, including:

• Current Demand calculation based on surface area, environment type, and temperature
• Anode Material selection and total weight calculation
• Design Life and Monitoring Requirements

ACI 222R-19 — Protection of Metals in Concrete

ACI 222R-19 is a Guide from the American Concrete Institute that covers all strategies for protecting against corrosion in concrete, including Sacrificial Anode and Impressed Current Cathodic Protection (ICCP).

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Procurement and Project Execution Steps for CP

Step 1: Submit Structural Drawings and Environmental Data

The engineer must specify:

• Structure type (buried pipeline, bridge, ship, jetty, etc.)
• Structural material to be protected (steel, Cast Iron, etc.)
• Environment (seawater, brackish water, soil, etc.) together with Resistivity if measurable
• Approximate total surface area (m²)
• Required Design Life

Step 2: Engineer Estimates the Number of Anodes

Using the basic formula:

Number of Anodes = (Total Current Demand) / (Output Current per Anode)

Where Current Demand is calculated from:

• Surface area to be protected × required Current Density (A/m²)
• Current Density depends on the environment, e.g. seawater = 0.02–0.10 A/m²

Step 3: Select the Anode Form and Design the Installation

• Ship work: Flush-Mount or Weld-On Hull Anode
• Buried pipeline work: Packaged Magnesium Anode with Backfill
• Bridge/concrete work: Embedded Zinc Anode or ICCP system
• Offshore work: Bracelet Anode or Stand-off Anode

Step 4: Procure + Install + Test

After installation, test by measuring the Steel-to-Electrolyte Potential with a Reference Electrode (e.g. Ag/AgCl, Cu/CuSO₄) to confirm that the structure is protected to the standard criterion.

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Case Study: Jetty and Bridge Projects in Thailand

Coastal Jetty in the Gulf of Thailand

Steel structures in the Gulf of Thailand seawater have a high Chloride Concentration (~19,000 ppm); the corrosion rate without protection is as high as 0.1–0.3 mm/year.

Approach: install Weld-On Zinc Anode Type II (ASTM B418) on the submerged steel structure, designed per DNV-RP-B401 for a Design Life of 20 years.

Result: reduced the corrosion rate from 0.2 mm/year to < 0.01 mm/year; payback within 3–5 years from reduced repair costs.

Buried Steel Water-Supply Pipeline

A steel pipeline buried in waterlogged clay soil (Resistivity ~500–2,000 Ω·cm) suffered repeated leaks from Pitting corrosion.

Approach: install Packaged Magnesium Anode (ASTM B843) every 15–30 meters along the pipeline, with Test Points for annual measurement.

Result: reduced Maintenance Cost by 60–70% and extended the pipeline life from 8–10 years to 25–30 years.

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Full Service: Supply + Install + Engineer

Sahawatthanakit (1988) Co., Ltd. does not merely sell Anodes but provides a complete service:

1. Corrosion Survey — inspect the structural condition and measure Soil/Water Resistivity
2. CP Design — design the system with experienced engineers, including Anode quantity calculation to standard
3. Supply Anode — supply Zinc, Magnesium, Aluminum Anodes to specification, with ASTM Test Certificate
4. Installation — install by a skilled technician team
5. Commissioning & Testing — test the system after installation and issue a report
6. Annual Monitoring — annual measurement and recommendation to replace worn Anodes

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Frequently Asked Questions about Cathodic Protection

Q: How often must Anodes be replaced? It depends on the Anode size used and the structure's Current Demand. Generally, Zinc Anodes in seawater are designed for a life of 5–15 years per set. Annual inspection will reveal how degraded the Anode is.

Q: Can Cathodic Protection be used together with painting? Yes, and they should be used together. Coating reduces the CP System's Current Demand by 80–95%, allowing far fewer Anodes to be used and saving cost.

Q: Can CP be retrofitted onto an existing building? Yes. For concrete bridges and coastal buildings, there is an Embedded Zinc Anode system installed in concrete repairs (Repair Mortar) per ISO 12696, which protects against rust at the repair joints and surrounding areas.

Q: How does CP differ from anti-rust painting? Anti-rust painting is Barrier Protection — it creates a barrier layer between the steel and the environment, but once the paint peels or is penetrated, rust forms immediately. CP is Active Protection — it continuously supplies electron current to the steel, so even where the paint peels at some spots, it is still protected. The two methods therefore complement each other rather than replace one another.

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Ordering and Price Inquiries

Sahawatthanakit (1988) Co., Ltd. supplies and contracts Cathodic Protection systems nationwide, with tax invoices and ASTM Certificate documentation.

• Tel: 02-096-2118 / 061-541-6939 (Khun Chin)
• Email: info@sahawatthanakit1988.com
• LINE: @sahawatt1988
• Web: sahawatthanakit1988.com
• Monday–Saturday 08:00–17:00
• Nationwide delivery | Express delivery to Bangkok / Nonthaburi / Pathum Thani

Send your structural drawings or project details via LINE or email to receive an assessment and quotation from our engineers within 48 hours.