Galvanic Anodes

Magnesium Anodes

In cathodic protection, the most widely used sacrificial anodes are magnesium anodes. Magnesium anodes are designed for the cathodic protection of steel under fresh, brackish, and seawater conditions Magnesium anodes are also used extensively for underground structures and pipelines. Anodes can be supplied with cable connections welded to meet the customer’s requirements. For underground applications, anodes are packed in cotton bags with a gypsum / bentonite / sodium backfill to ensure immediate effect on installation and a constant environment through the anode’s working life.

Magnesium anodes are available in two standard alloys as follows;

• Standard Alloy (AZ63): -1.55V w.r.t. copper-copper sulphate reference electrode for use in average soil resistivity conditions.
• High Potential Alloy: -1.75V w.r.t. copper-copper sulphate reference electrode for use in high soil resistivity conditions.

Standard Composition

	Mg	Al	Zn	Mn	Si (max)	Cu (max)	Ni (max)	Fe (max)	Other Imp. (max)
									Each	Total
High Potential	Balance	0.01 max	-	0.50-1.30	0.05	0.02	0.001	0.03	0.05	0.30
	Balance	5.30-6.70	2.50-3.50	0.15-0.70	0.10	0.02	0.002	0.003	--	0.30
	Balance	5.30-6.70	2.50-3.50	0.15-0.70	0.30	0.05	0.003	0.003	--	0.30
	Balance	5.0-7.0	2.0-4.0	0.15-0.70	0.30	0.10	0.003	0.003	--	0.30

Electrochemical Properties

	Open-Circuit Voltage (-V respect to Cu/CuS04)	Closed-Circuit Voltage (-V respect to Cu/CuS04)	Actual Capacity (Ah/lb)	Current Efficiency (%)
High Potential	1.77~1.82	0.01 max	1.64~1.69	0.50-1.30
	Balance	5.30-6.70	2.50-3.50	0.15-0.70
	Balance	5.30-6.70	2.50-3.50	0.15-0.70

Standard Dimensions of Type ‘D’ Anode


Standard Dimensions of Type ‘D’ Anode

	Mg	Anodes				Cu (Max.)
		A(in.)	B(in.)	C(in.)	D(in.)
9D2	9	2 3/4	3	27	25 3/4	Strip
14D2	14	2 3/4	3	41 7/8	40 1/2	Strip
20D2	20	2 3/4	3	59 3/4	57 3/4	Strip
9D3	9	3 1/2	3 3/4	13 7/8	10 1/2	Wire
17D3	17	3 1/2	3 3/4	25 1/4	21 1/2	Strip
32D5	32	3 1/2	5 3/4	19 7/8	16 1/2	Strip
48D5	48	3 1/2	5 3/4	30 1/8	28 1/2	Strip

Standard Dimensions of Type ‘S’ Anode

Standard Dimensions of Type ‘S’ Anode

	Weight (lb)	Anodes
		A(in.)	B(in.)	C(in.)
3S3	3	3	3	4.5
5S3	5	3	3	7.5
9S3	9	3	3	13.5
17S4	17	4	4	17
32S5	32	5	5	21
48S5	48	5	5	31
60S4	60	4	4	60

Standard Dimensions of Tank Internal Anodes

Magnesium anodes for water storage tanks internal are available with complete hatch assembly to hang the magnesium anodes through access windows provided on the tank roof.

• 203.2mm (8”) diameter x 406mm (16”) long and 22.7Kg (50-lbs) weight
• 203.2mm (8”) diameter x 812mm (32”) long and 45.4KG (100-lbs) weight

Magnesium Ribbon Anode


Magnesium Ribbon Anode

The conventional magnesium cast anode is an economical and dependable source of current in soils and waters of comparatively low electrolytic resistivity. However, at higher resistivities, the problem becomes supplying enough current for protection without installing an excessive weight of anodes. In this case magnesium ribbon anodes offer minimum resistance to earth per unit weight of anode installed.

Chemical Composition

	Mg	Al	Mn	Zn	Ca (max)	Si (max)	Cu (max)	Ni (max)	Fe (max)	Other Imp. (max)
										Each	Total
AZ31	Balance	2.5-3.5	0.2-1.0	0.7-1.3	0.04	0.05	0.01	0.001	0.002	0.01	0.30
High Potential	Balance	0.01 max	0.5-1.3	--	--	--	--	0.001	0.03	0.05	0.30

Electrochemical Properties

	Open-Circuit Voltage (-V respect to Cu/Cuso4)	Closed-Circuit Voltage (-V respect to Cu/Cuso4)	Actual Capacity (Ah/lb)	Current Efficiency (%)
AZ31	1.57~1.67	1.47~1.57	>=501.7	>=50
High Potential	1.77~1.82	1.64~1.69	>=499.4	>=50

Dimensions

The magnesium ribbon anode is available in ¾” × ?” diameter & 1,000 ft standard length with average weight of 0.24-lb/ft.

Aluminum anodes have long been used in the fight against corrosion offshore. Applications for aluminum anodes are used primarily in seawater applications include ship hulls, tank interiors, offshore structures, submerged pipelines, piers, pilings, etc.

Aluminum anodes are designed for optimum performance under a variety of environmental conditions and temperature ranges. Cast in a variety of alloys, sizes and weights, anodes provide maximum performance in seawater and brackish environments. Custom shapes and sizes can be made.

Aluminum Anode

Aluminum anodes are not used in fresh water, except as impressed current anodes. They are not used underground. An alloy of aluminum-zinc and indium is used as a sacrificial anode on reinforced concrete structures. Aluminum anodes are commonly used in process vessels containing brine. At temperatures above 120°F (49°C), however, the current output may be reduced.

Aluminum anodes are commercially available in three standard alloys as follows:

• Galvalum I™* - contains zinc and mercury for use in seawater
• Galvalum II™*- contains zinc and mercury for use in saline mud
• Galvalum III™ - contains zinc and indium for use in seawater, brackish water, and saline mud
* Seldom used due to mercury content.

To get more information about aluminum anodes and their dimension, kindly contact AFIC sales department.

Zinc Anodes

Zinc anodes are the most traditional anodes and were first used more than 160 years ago by Sir. Humphery Davy for protection of warships. In modern times, zinc anodes are widely used and are designed for the cathodic protection of steel in salt water, brackish water, fresh water & saline mud environments and for underground structures and pipelines. Zinc anodes can be supplied with cable connections welded to requirements. For underground applications, anodes are packed in cotton bags with a gypsum/bentonite mixture to ensure immediate effect on installation and a constant environment through the anode’s working life.

Zinc anodes are commercially available in two standard alloys as follows;

• ASTM B418 Type I – for salt water and brackish water
• ASTM B418 Type II – high purity for underground and fresh water

AFIC supply Zinc anodes in different shapes according to customer’s request. There are hull, condenser, tank anodes and bracelet shape anodes. The anodes also can be made in strings.

To get more information about Zinc anode and their dimensions, kindly contact AFIC sales department.

Zinc Ribbon Anodes

Zinc Ribbon Anodes

Zinc ribbon anodes are used in a variety of applications. They are used for cathodic protection on buried pipelines, for A.C. mitigation on pipelines, for sacrificial cathodic protection of secondary bottoms on above-ground storage tanks, for A.C. mitigation grounding mats and for other corrosion protection applications.

Dimensions

The zinc ribbon anodes are available in following dimensions;

• Super: 25.4mm x 31.75mm (1” x -1/4”) diameter, 30.5m (100 ft) standard length and average weight of 3.570Kg/m (2.4-lb/ft)
• Plus: 15.88mm x 22.22mm (5/8” x 7/8”) diameter, 61m (200 ft) standard length and average weight of 1.785Kg/m (1.2-lb/ft)
• Standard: 12.7mm x 14.28mm (1/2" x 9/16”) diameter, 152m (500 ft) standard length and average weight of 0.8925Kg/m (0.6-lb/ft)
• Small: 8.73mm x 10.32mm (11/32" x 13/32”) diameter, 305m (1,000 ft) standard length and average weight of 0.372Kg/m (0.25-lb/ft)

High Temperature Zinc Anodes

Composition

Element		Analysis (by weight)
Alloying Elements	Al	0.10-0.25 %
	Mg	0.05-0.15 %
	Zn	Balance
Other Elements	Fe	max. 0.002 %
	Cu	max. 0.001 %
	Pb	max. 0.006 %
	Cd	max. 0.001 %
Others	Total	max. 0.10 %

High temperature zinc anode is a special zinc alloy developed to meet the demand for a sacrificial anode for use at elevated temperatures. AFIC supplied high temperature zinc anodes are practically cadmium free and are recommended for environmental reasons.

Anode Performance Data (ambient sea water)

Element
Capacity	781 Ah/kg (354 Ah/lb)
Consumption rate	11.2 kg/Ayr (24.7 lbs/Ayr)
Closed circuit potential	-1.03 volts (Ag/AgCl)
Specific Gravity	7.13 kg/dm³ (0.258 lbs/cu.in)