|
|
 |
|
| |
Impressed current cathodic protection supplies
the needed protection current from outside and makes the protected
metal cathode. Special materials are used for the auxiliary
anode.
The impressed current cathodic protection system consists of
the following components: ¢Łdirect-current power supply, ¢Śauxiliary
anode and ¢Ūreference electrode. In order to make the protection
current evenly to avoid overprotection near the anode, screening
painting is applied around the anode when needed. Earthing has
to be made for protection of shaft and propeller of ships.
Direct-current power supply
In the impressed current cathodic protection system, a steady
direct-current power supply is needed. Two power sources, rectifier
and potentiostat, were widely used. When the condition (e.g.
immersed area, water quality, etc.) of the protected object
is stable, manually controlled rectifier can be used. When the
condition is not stable, potentiostat has to be used to keep
the potential of the object at request value.
Three kinds of potentiostat were commonly used, silicon-controlled,
magnetic saturation and transistor. The silicon-controlled potentiostat
has bigger power, smaller size, but lower overloading capacity.
The magnetic saturation potentiostat is tough and durable with
high overloading capacity, yet the size is comparatively bigger
and the manufacture is also more complex. The transistor potentiostat
is steady, noise free, high control accuracy, yet the circuit
is complex.
Auxiliary anode
The function of auxiliary anodes is to deliver the direct current
from the power source to the protected metal structure through
the media. A lot of materials can be used for the auxiliary
anode, e.g. steel or iron scraps, graphite, lead-silver alloy,
high-silicon cast iron, platinum plated titanium, platinum plated
niobium and mixed metal oxide, etc. These materials have their
own characteristics and are applicable to different situation.
QRIMC has done a lot of work on the research and development
of auxiliary anode materials. The product of platinum plated
niobium anode is little in size but is great in current discharge
and has a long working age. They have been widely used to protection
of ships, steel piles, water circulating pump, condenser and
seawater pipelines.
Reference electrode
The reference electrode has two functions: first, monitor the
potential of protected structure; second, provide the control
signal for the potentiostat to regulate the current output and
to keep the structure in a good protection condition. The commonly
used reference electrode is copper/saturated copper sulphate,
silver / silver halide and zinc electrode. These reference anodes
have different features and are applicable to different situations.
The long lifespan copper/copper sulphate reference electrode,
developed by QRIMC especially for the cathodic protection of
underground pipelines, has been widely used for its reliability.
Ag/AgCl and high purity zinc composite reference electrode was
developed for seawater by QRIMC to guarantee the control and
monitor of the impressed current protection system.
|
| |
|
| |
|
Ordinary
auxiliary anode materials and the performance
|
|
Material
|
Application environment
|
Maximum working current density A/m2
|
Consuming rate Kg/A”¤a
|
|
High silicon casting iron
|
SeawaterÖŠ |
50 |
0.3”×1.0 |
|
Freshewater and soil
|
10 |
0.05”×0.2 |
|
Graphite
|
Seawater
|
10 |
0.16 |
|
Freshewater
|
2.5 |
0.04 |
|
Pled silver alloy Plumbous silver
little platinum
|
Seawater
|
30”×300 |
0.03 |
|
Platinum titanium plated
|
Seawaterand freshewater |
1000 |
6”Į10-6 |
|
Platinum niobium
|
Seawaterand freshewater |
>1000 |
6”Į10-6 |
|
Titanium base/mixed metal oxide
|
Seawater
|
600 |
(3”×6)”Į10-6 |
|
Freshewater and sea mud
|
50”×150 |
|
|
Specification
and type of auxiliary anode commonly used in seawater system
|
Type |
Rated Current A
|
Life span Y
|
Applicable condition |
HFPF-4 |
4A |
6 |
Seawater pip[e
|
HFPF-6 |
6A |
6 |
Vertical slanting pump
|
HFLF-1 |
1A |
4 |
Seawater pipe below ¦µ377
|
HFLF-2 |
2A |
4 |
¦µ377”צµ630 seawater pipe
|
HFLF-3 |
3A |
4 |
Pipe over ¦µ630
|
|
| Remark: HFPF is platinum plated niobium wire series;
HFLF is titanium based mixed metal oxide series. Pedestal is
provided with each kind of auxiliary anode for the convenience
of installation. |
|
Type and
specification of common high silicon cast iron anode
|
Type |
Specification£¬mm |
Weight£¬Kg |
Anode cable
|
|
Section, mm2
|
Length£¬mm |
HFZT-1 |
¦µ50x1500 |
22 |
25 |
2000 |
HFZT-2 |
¦µ75x1200 |
40 |
25 |
2000 |
HFZT-3 |
¦µ75x1500 |
50 |
25 |
2000 |
HFZT-4 |
¦µ100x1500 |
90 |
25 |
2000 |
|
| Remark: High silicon cast iron anode is mostly used
in the impressed current protection of soil environment. It
is also used in the sea water environment, such as steel pile
protection in the wharf, etc. In order to prolong the protection
life, Cr containing high silicon cast iron anode is recommend
for high Cl- content environment. |
|
Type and
specification of ordinary permanent electric potential appearance
|
|
Type
|
Input pressure
|
Output current/output pressure
|
SF-200 |
220V/50Hz380V/50Hz
|
0”×50A/0”×12V£¬0”×16V£¬0”×24V |
0”×100A/0”×12V£¬0”×16V£¬0”×24V£¬0”×36V |
|
|
Type and specification of ordinary
reference electrode
|
|
Material
|
Type
|
Specification diameter”Įlength£¬mm
|
Life span£ØY£©
|
Applicable condition
|
|
Copper/saturated copper sulphate
|
RET-¢ń |
¦µ25”Į160 |
Can be continuously used after supplement
of copper sulphate
|
Portable type, applicable to spot
measurement in water and soil
|
RET-¢ņ |
¦µ100”Į250 |
10 |
Buryed long life electrode
|
|
Silver/Chlorine ization silver
|
REY-¢ń |
¦µ24”Į150 |
3 |
Powder pressure type, applicable to
medium of seawater
|
REY-¢ņ |
¦µ30”Į150 |
6 |
Hot immersing and
spreading, network, applicable to medium of seawater
|
|
Zinc electrode
|
REX-¢ń |
¦µ20”Į150 |
£¾6 |
High purity zince£¬applicable to Seawater
and freshewater
|
REX-¢ņ |
¦µ20”Į150 |
£¾6 |
Zinc alloy£¬applicable to
Seawater and freshewater
|
|
Complex electrode
|
HFYX-1 |
Upon requirement |
4 |
Seawater and freshewater
|
HFYX-2 |
Upon requirement |
4 |
Seawater and freshewater
|
|
| |
|
|
