Ch 5 Related Science Flashcards
Define the term corrosion.
Corrosion is the deterioration and destruction of a substance, usually a metal, or its properties because
of a reaction with its environment.
What are the three basic kinds of corrosion.
- Chemical
- Physical
- Electrochemical
Corrosion created by ____ causes is sometimes referred at as ____.
physical, corrosion-erosion
High velocities of liquids can affect the corrosion rate of a pipeline. Explain.
Where a high velocity condition continues to cause removal of the corrosion coating as it is formed,
the metal becomes progressively thinner until finally it is completely eaten through.
A chemical reaction involving oxidation, reduction and transfer of electrons is defined as
____ corrosion.
electrochemical
The term ____ is used to describe that portion of the metal surface which is corroded, and it is
the location where current leaves the metal to enter the solution (electrolyte).
anode
The term ____ is used to describe the metal surface from which current leaves the solution
(electrolyte) and returns to the metal.
cathode
The most common type of localized corrosion is ____.
pitting
Reddish-brown iron rust on uncoated cast iron pipe is a form of ____.
oxidation
T or F
Local action cells may be responsible for corrosion of buried pipelines that contain a
solution which can conduct electricity.
What are the three main types of corrosion cells that take part in the electrochemical corrosion
reaction?
- Different temperature cells
- Concentration cells
- Dissimilar electrode cells
Define the term “galvanic” cell.
A galvanic cell is two electrodes and an electrolyte capable of producing electricity by chemical
action. It consists of two dissimilar metals in contact with an electrolyte, or two similar metals in
contact with dissimilar electrodes. A galvanic cell converts energy liberated by a chemical action
directly into electrical energy.
The galvanic series rate the ____ activity of metals.
relative
Electrochemical corrosion will take place if ____ is present to conduct an electric current.
water
Corrosion may result because of the ____ of soils.
variation
The formation of a ____ cell is possible where two different soils are in contact with a
single piece of metal.
concentration
Water is a piping system with a pH below 7 would be considered ____.
corrosive
Usually the rate at which a material corrodes ____ as the temperature increases.
increases
What are six kinds of corrosion resistant materials commonly used in the pipe trades?
- Cast iron 7. Glass
- Brass 8. Terracotta
- Copper 9. Bituminous fiber
- Aluminum 10. Plastic
- Stainless steel 11. Cement
- Non-metallic or synthetic 12. Copper alloys
How is electric current produced by galvanic corrosion in a dry cell battery?
Electric current produced by galvanic corrosion in a dry cell is created by wasting away of two
dissimilar metals in electrical contact when exposed to an electrolyte. The current obtained from a dry
cell is generated by the chemical action of the chemicals used to form the electrolyte. The flow and
amount of electrical current produced results in corrosion of the anode.
How can cathodic protection be used to control corrosion of buried or immersed metallic waterlines
and tanks?
Cathodic protection prevents corrosion of metallic structures buried or immersed in a continuous
electrolyte by making them the cathode and applying direct current to the electrolyte from an anode
source. By making waterlines or tanks the cathode, all anode areas from local corrosion cells are
eliminated and direct current is prevented from leaving the tanks or pipes thereby stopping further
corrosion.
What are the two proven methods of applying cathodic protection to a buried pipeline?
The two proven methods of applying cathodic protection to a buried pipeline are with galvanic anodes
(usually magnesium or zinc) and impressed current systems.
Cathodic protection prevents corrosion of metallic structures buried or immersed in a continuous
electrolyte by making them the ____ and applying direct current to the electrolyte from an
____ source.
cathode, anode
List four methods of corrosion control that can be used on piping systems.
- Cathodic protection
- Coatings
- Dielectric insulation
- Test stations
Stray electric current ___corrosion__ can be caused by the effects of direct current source from a
cathodic protection rectifier.
corrosion
How can piping systems be protected against stray electrical currents?
- Bonding the pipe system to the source
- Cathodic protection
- Insulating coupling in the pipe lines
- Coatings
Instantaneous hot water heaters should be provided with the necessary connections for
____ to remove sediment.
backwashing
Instantaneous hot water heaters should be provided with the necessary connections for
____ to remove sediment.
backwashing
A ____ is a substance which can be added to an environment to decrease the rate
of attack on a metal.
corrosion inhibitor
Bituminous coatings containing ____ are used on underground pipelines.
asphaltum
A common problem associated with coatings on pipelines is ____to the coating after it has
been applied.
damage
List three materials that are commonly used as sacrificial anodes in piping systems.
- Magnesium
- Aluminum
- Zinc
T or F: Zinc offers the same type of cathodic protection as aluminum.
T
T or F: Corrosion of metals themselves can form a protective coating to prevent further corrosion.
T
T or F: The impressed current system of cathodic protection is externally powered usually by an
AC-DC rectifier.
T
T or F: Test stations are the most practical method which can be used for cathodic protection
of pipelines.
F
T or F: The solution forming an electrolyte is called the corrodent.
T
T or F: Oxygen can be removed from piping systems by heating or neutralizing.
T
T or F: Ground joint unions with brass seats should be used in galvanized piping systems.
F
