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Specification

AGRO INDUSTRI SURABAYA
PHONE. 031 60234888, FAX. 031 3980197, EMAIL: INDUSTRI2034@ GMAIL.COM

27 / 01 / 2012

WHAT IS IT AND HOW DOES IT WORK?

HOW DOES STEEL CORRODE IN SEAWATER?
TO UNDERSTAND CATHODIC PROTECTION ONE MUST FIRST UNDERSTAND THE CORROSION MECHANISM.

FOR CORROSION TO OCCUR, THREE CONDITIONS MUST BE PRESENT.
1. TWO DISSIMILAR METALS
2. AN ELECTROLYTE ( WATER WITH ANY TYPE OF SALT OR SALTS DISSOLVED IN IT)
3. A METAL ( CONDUCTING) PATH BETWEEN THE DISSIMILAR METALS
THE TWO DISSIMILAR METALS MAY BE TOTALLY DIFFERENT ALLOYS, SUCH AS STEEL AND ALUMINUM, BUT ARE MORE USUALLY
MICROSCOPIC OR MACROSCOPIC METALLURGICAL DIFFERENCES ON THE SURFACE OF A SINGLE PIECE OF STEEL.
IF THE ABOVE CONDITIONS EXIST, AT THE MORE ACTIVE METAL SURFACE ( IN THIS CASE WE WILL CONSIDER FREELY
CORRODING STEEL WHICH IS NON UNIFORM) , THE FOLLOWING REACTION TAKES PLACE AT THE MORE ACTIVE SITES:
2FE= > 2FE+ + + 4E- ( 2 IRON IONS PLUS 4 FREE ELECTRONS)
THE FREE ELECTRONS TRAVEL THROUGH THE METAL PATH TO THE LESS ACTIVE SITES WHERE THE FOLLOWING REACTION TAKES
PLACE:
O2 + 4E- + 2 H20 = > 4 OH-
( OXYGEN GAS CONVERTED TO OXYGEN ION - BY COMBINING WITH THE FOUR FREE ELECTRONS - WHICH
COMBINES WITH WATER TO FORM HYDROXYL IONS)
RE-COMBINATIONS OF THESE IONS AT THE ACTIVE SURFACE PRODUCE THE FOLLOWING REACTION, WHICH YIELDS THE IRON
CORROSION PRODUCT FERROUS HYDROXIDE.
2FE + O2 + 2H2O = > 2FE ( OH) 2
( IRON COMBINING WITH OXYGEN AND WATER TO FORM FERROUS HYDROXIDE)
THIS REACTION IS MORE COMMONLY EXPLAINED AS CURRENT FLOW THROUGH THE WATER FROM THE ANODE ( MORE ACTIVE
SITE) TO THE CATHODE ( LESS ACTIVE SITE) .

HOW DOES CATHODIC PROTECTION STOP CORROSION?
CATHODIC PROTECTION PREVENTS CORROSION BY CONVERTING ALL OF THE ANODIC ( ACTIVE) SITES ON THE METAL SURFACE TO
CATHODIC ( PASSIVE) SITES BY SUPPLYING ELECTRICAL CURRENT ( OR FREE ELECTRONS) FROM AN ALTERNATE SOURCE.
USUALLY THIS TAKES THE FORM OF GALVANIC ANODES WHICH ARE MORE ACTIVE THAN STEEL. THIS PRACTICE IS ALSO
REFERRED TO AS A SACRIFICIAL SYSTEM, SINCE THE GALVANIC ANODES SACRIFICE THEMSELVES TO PROTECT THE STRUCTURAL
STEEL OR PIPELINE FROM CORROSION.
IN THE CASE OF ALUMINUM ANODES, THE REACTION AT THE ALUMINUM SURFACE IS:
4AL = > 4AL+ + + + 12 E- ( 4 ALUMINUM IONS PLUS 12 FREE ELECTRONS)
AND AT THE STEEL SURFACE,
3O2 + 12E- + 6H20 = > 12OH-
( OXYGEN GAS CONVERTED TO OXYGEN IONS WHICH COMBINE WITH WATER TO FORM HYDROXYL IONS)
AS LONG AS THE CURRENT ( FREE ELECTRONS) IS ARRIVING AT THE CATHODE ( STEEL) FASTER THAN OXYGEN IS ARRIVING, NO CORROSION OCCURS.

BASIC CONSIDERATIONS WHEN DESIGNING SACRIFICIAL ANODE SYSTEMS
THE ELECTRICAL CURRENT, WHICH AN ANODE DISCHARGES IS CONTROLLED BY OHM’ S LAW; THAT IS:
I= E/ R
WHERE:
I= CURRENT FLOW IN AMPS
E= DIFFERENCE IN POTENTIAL BETWEEN THE ANODE AND CATHODE IN VOLTS
R= TOTAL CIRCUIT RESISTANCE IN OHMS
INITIALLY CURRENT WILL BE HIGH BECAUSE THE DIFFERENCE IN POTENTIAL BETWEEN THE ANODE AND CATHODE ARE HIGH,
BUT AS THE POTENTIAL DIFFERENCE DECREASES DUE TO THE EFFECT OF THE CURRENT FLOW ONTO THE CATHODE, CURRENT
GRADUALLY DECREASES DUE TO THE POLARIZATION OF THE CATHODE.
THE CIRCUIT RESISTANCE INCLUDES BOTH THE WATER PATH AND THE METAL PATH, INCLUDING ANY CABLE IN THE CIRCUIT.
THE DOMINANT VALUE HERE IS THE RESISTANCE OF THE ANODE TO THE SEAWATER.
FOR MOST APPLICATIONS THE METAL RESISTANCE IS SO SMALL COMPARED TO THE WATER RESISTANCE THAT IT CAN BE
IGNORED. ( NOT TRUE FOR SLEDS, OR LONG PIPELINES PROTECTED FROM BOTH ENDS) .
IN GENERAL, LONG THIN ANODES HAVE LOWER RESISTANCE THAN SHORT FAT ANODES. THEY WILL DISCHARGE MORE
CURRENT, BUT WILL NOT LAST AS LONG.
THEREFORE A CATHODIC PROTECTION DESIGNER MUST SIZE THE ANODES SO THAT THEY HAVE THE RIGHT SHAPE AND
SURFACE AREA TO DISCHARGE ENOUGH CURRENT TO PROTECT THE STRUCTURE AND ENOUGH WEIGHT TO LAST THE DESIRED
LIFETIME WHEN DISCHARGING THIS CURRENT.
AS A GENERAL RULE OF THUMB:
LENGTH OF THE ANODE DETERMINES HOW MUCH CURRENT THE ANODE CAN PRODUCE, AND CONSEQUENTLY HOW MANY
SQUARE FEET OF STEEL CAN BE PROTECTED.
CROSS SECTION ( WEIGHT) DETERMINES HOW LONG THE ANODE CAN SUSTAIN THIS LEVEL OF PROTECTION.
IMPRESSED CURRENT CATHODIC PROTECTION SYSTEMS
DUE TO THE HIGH CURRENTS INVOLVED IN MANY SEAWATER SYSTEMS IT IS NOT UNCOMMON TO USE IMPRESSED CURRENT
SYSTEMS. IMPRESSED CURRENT SYSTEMS USE ANODES OF A TYPE THAT ARE NOT EASILY DISSOLVED INTO METALLIC IONS,
BUT RATHER SUSTAIN AN ALTERNATIVE REACTION, OXIDIZATION OF THE DISSOLVED CHLORIDE IONS.
2CL- = > CL2 + 2E-
POWER IS SUPPLIED BY AN EXTERNAL DC POWER UNIT.
FIGURE 2: IMPRESSED CURRENT CATHODIC PROTECTION SYSTEM

HOW DO WE KNOW WHEN WE HAVE ENOUGH CATHODIC PROTECTION?
WE KNOW WHETHER OR NOT WE HAVE ENOUGH CURRENT BY MEASURING THE POTENTIAL OF THE STEEL AGAINST A
STANDARD REFERENCE ELECTRODE, USUALLY SILVER SILVER/ CHLORIDE ( AG/ AGCL SW.) , BUT SOMETIMES ZINC ( ZN SW.) .
CURRENT FLOW ONTO ANY METAL SHIFTS ITS NORMAL POTENTIAL IN THE NEGATIVE DIRECTION.
HISTORY HAS SHOWN THAT IF STEEL RECEIVES ENOUGH CURRENT TO SHIFT THE POTENTIAL TO ( -) 0.800 V VS. SILVER/ SILVER
CHLORIDE, THE CORROSION IS ESSENTIALLY STOPPED.
DUE TO THE NATURE OF THE FILMS FORMED, THE MINIMUM ( -0.800 V) POTENTIAL IS RARELY THE OPTIMUM POTENTIAL,
AND DESIGNERS TRY TO ACHIEVE A POTENTIAL BETWEEN ( -) 0.950 V AND ( -) 1.000 V VS. AG/ AGCL SW.
______________________

ZAP MITZUI S3, S4, S6, S8.

ZAP B TYPE, AVAILABLE UPON REQUEST.

CATHODIC PROTECTION FOR THE OIL, GAS, WATER & POWER INDUSTRIES

- ZINC & ALUMINUM ANODES
ALUMINIUM ALLOY SACRIFICIAL ANODES HAVE AN ELECTRO-CHEMICAL PROPERTY THAT MAKES THEM SUITABLE FOR USE IN CATHODIC PROTECTION SYSTEMS. AN OXIDE FILM CAN DEVELOP ON THE SURFACE OF THE ALUMINIUM THAT MAKES THE MATERIAL PASSIVE. ALUMINIUM ALLOYS HAVE BEEN DEVELOPED SO THAT ONE OR MORE OF THE ALLOYS DISRUPTS THE PROTECTIVE OXIDE LAYER AND MAKES THE ALLOY ANODIC TO PROMOTE EVEN CORROSION WHEN THE ANODE IS PLACED IN THE ELECTROLYTE.

ZINC HAS BEEN USED AS A SACRIFICIAL ANODE MATERIAL IN SEAWATER SINCE 1824 BUT MODERN ZINC ANODES USED FOR CATHODIC PROTECTION ARE CAST FROM HIGH PURITY ZINC ( 99.9% ) ALLOYED WITH ALUMINIUM AND CADMIUM WITH LIMITATIONS ON THE LEVELS OF LEAD, IRON AND COPPER.

- TRANSFORMER RECTIFIERS
A VARIED RANGE OF HIGH QUALITY TRANSFORMER RECTIFIERS ARE DESIGNED AND MANUFACTURED TO MEET THE MARKET REQUIREMENT FOR ALL LAND AND MARINE STRUCTURES NECESSITATING AN IMPRESSED CURRENT CATHODIC PROTECTION ( ICCP) SYSTEM OR A MARINE GROWTH ANTI-FOULING SYSTEM.

- ANODE, CATHODE & BOND BOXES

A WIDE RANGE OF CUSTOM MADE JUNCTION BOXES FOR THE CONTROL AND MEASUREMENT REQUIRED FOR YOUR PROTECTION SYSTEM. ALL ITEMS ARE MANUFACTURED AND TESTED USING THE HIGHEST QUALITY MATERIALS. EEXD AND EEXE RATED PRODUCTS ARE ALSO AVAILABLE FOR HAZARDOUS AREA LOCATIONS.

- REFERENCE ELECTRODES / COUPONS

WE SUPPLY REFERENCE ELECTRODES FROM THE MOST RELIABLE NAMES IN THE INDUSTRY INCLUDING MC MILLER, BORIN, GMC AND EDI. WE CAN ADVISE THE CORRECT CHOICE OF PRODUCT FOR YOUR SPECIFIC APPLICATION.

- MIXED METAL OXIDE

MIXED METAL/ METAL OXIDE ( MMO) IMPRESSED CURRENT ANODES SUPPLIED BY CATHODIC PROTECTION CO LTD HAVE BEEN DESIGNED FOR THEIR USE IN SPECIFIC CATHODIC PROTECTION APPLICATIONS. THE MMO ANODE SUBSTRATE, USUALLY TITANIUM, IS ACTIVATED BY THE METAL OXIDE COATING AND IS SUITABLE FOR USE IN SOILS, CARBONACEOUS BACKFILL, FRESH AND BRACKISH WATER, SEAWATER AND CONCRETE.

SILICON IRON ANODES ARE PROBABLY THE MOST COMMONLY USED ANODES IN CATHODIC PROTECTION GROUND BED CONSTRUCTION AND THE HIGH CORROSION RESISTANCE OF SILICON IRON AND SILICON CHROMIUM IRON ALLOYS MEANS THAT CATHODIC PROTECTION SYSTEM LIFETIME IN EXCESS OF 20 YEARS MAY BE ACHIEVED.

THE ANODES CAN BE USED IN MANY DIFFERENT ENVIRONMENTS EG ONSHORE, SEAWATER AND FRESHWATER APPLICATIONS. SILICON IRON ANODES ARE FOR USE IN NEUTRAL SOILS AND FRESHWATER ENVIRONMENTS. SILICON CHROMIUM IRON ANODES ARE FOR USE IN AGGRESSIVE ACIDIC OR ALKALINE SOILS AND SEAWATER ENVIRONMENTS.

- MAGNESIUM ANODES

WE SUPPLY THE FINEST QUALITY MAGNESIUM ANODES THAT HAVE BEEN SPECIFICALLY DEVELOPED FOR THE CATHODIC PROTECTION MARKET. TYPICAL APPLICATIONS FOR MAGNESIUM ANODES INCLUDE: -
• TEMPORARY PROTECTION OF PIPELINES
• TEMPORARY PROTECTION OF TANK BOTTOMS
• PERMANENT PROTECTION OF WELL COATED PIPELINES IN LOW RESITIVITY SOIL
• PERMANENT PROTECTION OF BURIED VESSELS
• INTERNAL PROTECTION OF WATER TANKS

- CARBONACEOUS BACKFILL
METALLURGICAL AND CALCINED PETROLEUM BACKFILL FOR HORIZONTAL AND DEEP ANODE GOUNDBEDS. CHEMICAL COMPOSITIONS AND DENSITIES AVAILABLE FOR YOUR SPECIFIC APPLICATIONS. Put on Product PartnerRecommend to your friends