Nace CP 1, Руководство по эксплуатации

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RP0176-2003
NACE International
41
(b) Check whether for this anode, the left-hand side of
Equation (E1) is equal to the right-hand side.
(c) If there is no match, two options exist. First the
anode can be modified and steps 6a and 6b repeated
to optimize the anode to meet the design criteria. (Al-
though an infinite number of anodes that will satisfy
Equation (E1) can be designed, there is a smaller sub-
set that is practical to manufacture and install.) Alter-
natively, the selected anode may be accepted, and
Equation (E1) may be rearranged, as shown in Equa-
tion (E2), to determine the actual design life that will
result.
kS i
w R
T
m
a
=
(E2)
7. Once the anode has been sized, Equation (E3) can be
used to calculate the surface area that each anode will
protect, A1:
a
1
R
S
A
=
(E3)
where:
8. Determine the total surface area for the structure or
zone to be protected, A
total
, and divide by the area protected
by each anode to determine the number of anodes needed,
as shown in Equation (E4).
1
total
A
A
N
=
(E4)
where:
N = total number of anodes
9. Determine whether the design slope based on final
conditions (90% anode consumption) is acceptable but
using the value of R
a
for an expended anode. R
a
of an ex-
pended anode can be calculated using the same procedure
described to determine the current output of an expended
anode in Equations D5 and D6. The long-term potential of
the anode might be different from the value exhibited during
the polarization process, so that the design line may shift up
or down on the polarization graph.
If a large number of designs will be done for structures in
similar conditions, steps 1 through 7 and 9 of this procedure
may need to be followed only once. A standard anode that
will protect a certain cathode area, A1, on each structure, is
thereby defined.
If a design requires that different sizes and shapes of
anodes be used because of complex structure geometry,
then each anode type should be independently determined
to satisfy the design equation in step 6 above. The area
protected by each anode type is different.
A
1
= area protected per anode in m
2