Page 218 - Pipeline Rules of Thumb Handbook

Corrosion/Coatings 205

or: for a special size mold. Also, the mold size will be a factor in
determining anode spacing.
Pipe OD ¥ lb/amp.-yr ¥ 1.1781 = lb of anode material/ These calculations assume a utilization factor of 100% and
1,000 linear ft of pipeline the designer should select the appropriate utilization factor
for the specific application. For estimating, you may wish to
Example. How many lb of zinc will be required for a use 85%. Temperatures used in the examples are assumed to
30-in. OD line installed in seawater and operating at 80°F? be the anode operating temperature.
Pounds of zinc per ampere-year = 24.8 (seawater). Generally, zinc anodes should not be used if the pipeline
will be operated at temperatures above 90°F. See ASTM
B418-80 and NACE Paper No. 311 by Elwood G. Haney pre-
#
30 ¥ 24 8 1 1781 877 1 000 linear ft of pipeline
.
¥
=
.
,
sented at CORROSION/85.
See Table 3 for typical anode performance data. All per-
®
How many lb of Galvalum III will be required for a 30-
formance data shown here are suitable for estimating. For
in. OD line installed in seawater and operating at 80°F? final design purposes, the anode manufacturer or distributor
®
Pounds of Galvalum III per ampere-year in seawater = 7.62
should be consulted for actual anode performance data
(32–95°F).
required for a specific application.
¥
.
¥
,
=
.
30 7 62 1 1781 269 1 000 linear ft of pipeline Galvalum III is a registered trademark of Oronzio De Nora S. A.,
#
®
®
Lugano (Switzerland). Galvomag is a registered trademark of Dow
®
How many lb of Galvalum III will be required for a 30- Chemical Company.
in. OD line installed in saline mud and operating at 80°F?
®
Pounds of Galvalum III per ampere-year in saline mud = Typical Anode Specifications
9.22 (32–95°F). Table 1
Zinc Anodes
,
.
.
#
30 ¥ 9 22 1 1781 326 1 000 linear ft of pipeline
=
¥
Mil. Spec.
Material MIL-A-1800 1H ASTM Type I ASTM Type II
®
How many lb of Galvalum III will be required for a 30-
in. OD line installed in saline mud and operated at a tem- Lead 0.006 max — —
®
perature of 160°F? Pounds of Galvalum III per ampere-year Iron 0.005 max 0.005 max 0.0014 max
in saline mud = 21.9 (140–170°F). Cadmium 0.025–0.15 0.03–0.1 0.003 max
Range
.
=
¥
30 ¥ 21 9 1 1781 774 1 000 linear ft of pipeline Copper 0.005 max — —
.
#
,
Aluminum 0.10–0.50 max 0.1–0.4 0.005 max
Silicon 0.125 max — —
It is always a good idea to check with the bracelet vendor
Zinc Remainder Remainder Remainder
to determine the nearest size mold available to avoid the need
Table 2*
Cast Magnesium Anodes
H-1 H-1 H-1
Grade A Grade B Grade C
Material Type III Type II Type I Galvomag ®
AI 5.3–6.7 6.3–6.7 5.0–7.0 0.010 max
Zn 2.5–3.5 2.5–3.5 2.0–4.0 0.05 max
Mn 0.15 min 0.15 min 0.10 min 0.5–1.3
Fe 0.003 max 0.003 max 0.003 max 0.03 max
Ni 0.002 max 0.003 max 0.003 max 0.001 max
Cu 0.02 max 0.05 max 0.10 max 0.02 max
Si 0.10 max 0.30 max 0.30 max 0.05 max
Others 0.30 max 0.30 max 0.30 max 0.05 max, each
0.30 max, total
* Reprinted courtesy of Dow Chemical U.S.A.