NACE 2 CBT STUDY GUIDE EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED GRADED A++
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Course
NACE
Institution
NACE
NACE 2 CBT STUDY GUIDE EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED GRADED A++
Corrosion is established as a what kind of current?
Direct Current
All corrosion of iron at normal ambient conditions is ________________ ____________
an electrochemical process
Define, E=IR
E is d...
Corrosion is established as a what kind of current?
Direct Current
All corrosion of iron at normal ambient conditions is ________________
____________
an electrochemical process
Define, E=IR
E is driving voltage, I is current magnitude, R is circuit resistance.
The less noble part of a corrosion cell - negatively charged - dissolves metallic
iron then converts it to positively charged ions - generates electrons - where
oxidation occurs.
Anode
The more noble region on the electrode - where electrons are consumed -
positively charged - where reduction occurs
Cathode
The difference in potentials between the anode and the cathode create what?
Voltage difference, which is the driving force for corrosion.
Allows for electrons generated at the anode to transport to the cathode.
Return path (metallic pathway)
,Conducts ionic current - water-based - contains ions - pathway to transport ions -
carries corrosion current
Electrolyte
Negatively charged ions
Anions
Positively charged ions
Cations
Four parts to a corrosion cell
Anode, Cathode, Return Path, Electrolyte
Oxygen ____________ the rate of corrosion
Increases
Corrosion proceeds ____________ in warmer environments than in cooler ones
Faster
Chemical Salts like Sodium Chloride, act as a hygroscopic material (draws
moisture from the air), which _____________ corrosivity in non immersed areas.
Increases
The wetter the environment, the ____________ corrosion is likely to occur
more
What are the two types of corrosion?
Localized and General
Corrosion that occurs in discrete sites on the metal surface - often occurs in
areas difficult to inspect
Localized
,Corrosion that occurs relatively uniform over the entire surface
General
What type of corrosion can initiate at an open, freely exposed surface or at
imperfections in the coating?
Pitting Corrosion
The type of corrosion that occurs on a metal surface that is shielded from full
exposure to the environment because of the close proximity of another material:
(ex. common on support straps, or pipe flanges)
Crevice Corrosion
The type of corrosion that occurs through the electrochemical action of two
dissimilar metals in contact in the presence of an electrolyte and an electron
conductive path (Return Path):
Galvanic Corrosion
The less effectively the coating insulates the structure, the __________ electric
current is required to provide catholic protection.
more
Two types of Cathothic Protection Systems
Impressed; Galvanic
A device that uses power from electric utility lines to convert the alternating
current to a lower voltage direct current by means of a step down transformer
Rectifier
What is the minimum requirement for a cathodic protection potential?
-0.85V
, What occurs when potential in a cathodic protection system increases (more
negative)
Hydroxyl formation; Cathodic disbondment
Note: if the potential continues to increase(more negative) disbondment occurs through
the hydrogen process.
Formation of a protective oxide film on the surface reducing its chemical activity
and its ability to corrode
Passivation
Why perform Air Turnovers (Air Turn):
To eliminate air stratification; One to two air changes per hour is industry
recommendation
Enclosures must fit all of the following characteristics:
1.Large enough to contain the whole work area
2.Not be larger than the performance capabilities of dehumidifier
3.All weather resistant
4.Minimal leakage to maintain proper environmental conditions
Two ways to reduce RH, are:
1.Increase surface temperature 2.Dehumidification
Two methods to increase surface temperature, are:
1.Induction Heating
2.Resistance Heating
What is a common and economical dehumidification method to remove moisture
from air?
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