Electronics; Cathodic Protection Flashcards
What is corrosion?
An electro-chemical process that involves minute current flows
What do you call the process of producing free electrons which pass within a metal to another site on the metal surface, where it is consumed by the cathodic reaction?
Anodic reaction
What are the four parts of a corrosion process?
Anode
Cathode
Electrolyte
Metallic path
Where does corrosion occur?
Anode
Where does protection occur?
Cathode
Where do ions flow (re: corrosion process)
Electrolyte
What completes the path between anode and cathode for electrons to flow? (Re: corrosion process)
Metallic path
Describe the current flow with regards to the anode
Current flows by chemical means
FROM the surface of the metal
TO the electrolyte.
Describe the current flow with regards to the cathode
Current flows by chemical means
FROM the electrolyte
TO the metal
At the anode the chemical reaction is a _________ reation
Oxidation (metal LOSING an electron and combining with another element; oxygen)
At the cathode the chemical reaction is a __________ reaction
Reduction (cathode GAINING electrons)
What kind of material is an electrolyte?
Any material in contact with both anode and cathode that will allow oxidation and reduction reactions to occur
What part of a corrosion process includes the source of elements or atoms that are required for ion transfer to and from the metal electrodes
Electrolyte
What is the purpose of catholic protection?
To create a corrosion cell in which the structure to be protected is the cathode and therefore protected from corrosion
What are the two most common types of cathoduc protection?
Sacrificial anode
Impressed current systems
What are the most common materials used for sacrificial anode systems?
Aluminum
Zinc
Magnesium
What kind of catholic protection do catholic protection rectifiers provide?
Impressed current cathodic protection
What kind of power to cathodic protection rectifiers use? What kind of power do they provide?
Use ac power. Provide dc (is a rectifier!)
What are the components of a cathodic protection rectifier?
Adjustable step down transformer Rectifier stacks Shunt to measure output current Meters to indicate output voltage and current Circuit breakers Lighting arresters Transformer tap connections
What are the two types of recifier stacks available?
Selenium plates
Silicon diodes
What type of rectifier stack should be used in high voltage or high current applications?
Silicon diode type
Which type of rectifier stack is less efficient (has a higher voltage drop)
Selenium type
Which type of rectifier stack is less affected by voltage surges?
Selenium type
Which type of rectifier stack must be protected from voltage of current spikes by metal oxide varistors?
Silicon diode type
Which type of rectifier stack ages over time?
Selenium type
On a (manual/automatic) recifier unit, the transformer tap connections normally encircle the “center tap” connections
Manual
Which connections on the transformer of a manually controlled rectifier unit provide input to the stacks? Which are the output from the stacks?
Center tap connections are the input to the stacks
Negative and positive lugs are the output from the stacks
