Cathodic Protection
CATHODIC PROTECTION
P E FRANCIS
CONTENTS 1 2 3 INTRODUCTION............................................................................................................2 PRINCIPLES OF CATHODIC PROTECTION..........................................................3 METHODS OF APPLYING CATHODIC PROTECTION........................................5 3.1 3.2 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 IMPRESSED CURRENT..........................................................................................5 SACRIFICIAL ANODES..........................................................................................6 PROTECTION POTENTIALS .................................................................................8 CURRENT DENSITY...............................................................................................8 COATINGS ...............................................................................................................9 CALCAREOUS SCALES .........................................................................................9 CHOICE OF CATHODIC PROTECTION SYSTEM ..............................................9 ANODE RESISTANCE ..........................................................................................10 DANGERS TO BE AVOIDED ...............................................................................12
DESIGN ............................................................................................................................8
1
[CATHODIC PROTECTION/BM]
CATHODIC PROTECTION
P E FRANCIS
1
INTRODUCTION
The first practical use of cathodic protection is generally credited to Sir Humphrey Davy in the 1820s. Davy’s advice was sought by the Royal Navy in investigating the corrosion of copper sheeting used for cladding the hulls of naval vessels. Davy found that he could preserve copper in sea water by the attachment of small quantities of iron or zinc; the copper became, as Davy put it, “cathodically protected”. The
P E FRANCIS
CONTENTS 1 2 3 INTRODUCTION............................................................................................................2 PRINCIPLES OF CATHODIC PROTECTION..........................................................3 METHODS OF APPLYING CATHODIC PROTECTION........................................5 3.1 3.2 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 IMPRESSED CURRENT..........................................................................................5 SACRIFICIAL ANODES..........................................................................................6 PROTECTION POTENTIALS .................................................................................8 CURRENT DENSITY...............................................................................................8 COATINGS ...............................................................................................................9 CALCAREOUS SCALES .........................................................................................9 CHOICE OF CATHODIC PROTECTION SYSTEM ..............................................9 ANODE RESISTANCE ..........................................................................................10 DANGERS TO BE AVOIDED ...............................................................................12
DESIGN ............................................................................................................................8
1
[CATHODIC PROTECTION/BM]
CATHODIC PROTECTION
P E FRANCIS
1
INTRODUCTION
The first practical use of cathodic protection is generally credited to Sir Humphrey Davy in the 1820s. Davy’s advice was sought by the Royal Navy in investigating the corrosion of copper sheeting used for cladding the hulls of naval vessels. Davy found that he could preserve copper in sea water by the attachment of small quantities of iron or zinc; the copper became, as Davy put it, “cathodically protected”. The