Page 219 - Pipeline Rules of Thumb Handbook

206 Pipeline Rules of Thumb Handbook

Table 3
Typical Anode Performance Data
Potential Approx.
Amp-hr/lb Negative Volts Current Density
Anode Type in Seawater Ag/AgCl mA/ft 2

Zinc 354 1.03 36–600
®
Galvalum III 1,150–1,204 (32–95°F) 1.10 100–1,000
in saline mud
950 (32–95°F) 1.10 100
930 (104°F) 1.08 100
600 (140°F) 1.05 100
400 (176°F) 1.04 100
400 (221°F) 1.02 100
in earth
Magnesium 400–500 1.53 36–600
Galvomag ® 500–540 1.75 36–600

Table 4 Tables 1–4 are guideline-type information suitable for
Typical Environments for Sacrificial Anodes general use. The characteristics of a specific application must
be considered and it may be necessary to contact the anode
Driving Potential
Material Volts Environment manufacturer or distributor to obtain detailed anode perfor-
mance data before finalizing a design.
Magnesium 0.9 Underground
Fresh water
200–10,000ohm-cm
Aluminum 0.25 Sea water
Brine
Saline mud
<200ohm-cm
Zinc 0.25 Sea water
Brine
Underground
<1,500ohm-cm

Comparison of other reference electrode potentials with that of copper-copper sulfate reference
electrode at 25°C

To correct readings
Structure-to-comparative between structure and
reference electrode comparative reference
reading equivalent to electrode to equivalent
-0.85 volt with respect readings with respect
Type of comparative to copper sulfate reference to copper sulfate reference
reference electrode electrode electrode

Calomel (saturated) -0.776 volt Add -0.074 volt
Silver-Silver Chloride -0.822 Add -0.028
(0.1NKCl Solution)
Silver-Silver Chloride -0.78 Add -0.07
(Silver screen with
deposited silver
chloride)
Pure Zinc +0.25* Add -1.10
(Special high grade)
* Based on zinc having an open circuit potential of -1.10 volt with respect to copper sulfate refer-
ence electrode. (From A. W. Peabody, Chapter 5, p. 59, NACE Basic Corrosion Course, Houston,
TX, 1973.)