Basic Corrosion Flashcards
What is the definition of corrosion?
Deterioration of material or properties because of reaction with its environment
Which of the following is an indirect cost of corrosion?
Loss of redundancy
Which of the following is a direct cost of corrosion?
Structural collapse
Product contamination
In an electrochemical corrosion reaction, which of the following statements applies to the electrons?
They flow through the metal
Reduction occurs when which of the following happens?
Negative charge increases
Which of the following is involved in an anodic reaction?
Loss of electrons
In which of the following situations would electrochemical oxidation most likely occur?
Electrons are lost
Which of the following metals does not normally corrode in natural environments?
Gold
Which of the following relates to the Nernst Equation?
Potential of pure metals in solutions containing various concentrations of ions
Which of the following relates to the Electromotive Force (EMF) series?
Lists metals in order of their potential in solutions of standard ion concentrations
What does the term “polarization” describe?
Changes in potential due to passage of electrical current
When a metal cannot oxidize or corrode, it is said to be which of the following?
Passive
A pH greater than 7 indicates that a substance is which of the following?
A base
Which of the following applies to hot water when oxygen is present?
It is more corrosive than cold water
Hygroscopic materials absorb which of the following?
Water
Which of the following is generally true of saltwater when oxygen is present?
It is more corrosive than freshwater
A bare steel piling in saltwater experiences the highest corrosion rate in which location?
Splash zone
The submerged portion of a bridge piling over a marine waterway is an example of an item that must be able to resist corrosion from which of the following?
Salts
Which of the following pH values would result in the lowest corrosion rates for steel?
11.0
Generally, what is the effect of increasing temperature on corrosion?
Increased corrosion reactions
Which of the following descriptions applies to a cast structure?
Achieved by solidification from molten metal
Which of the following descriptions applies to wrought structures?
Altered by thermo-mechanical process
Which type of stainless steel is commonly used for scissors and surgical instruments?
Martensitic
The majority of stainless steels used worldwide are which type?
Austenitic
Which alloy is added to steel to sharply decrease oxidation at elevated temperatures?
Chromium
What are the preferred casting alloys for large pumps and valves in seawater?
Nickel aluminum bronze
Which of the following applies to aluminum in marine atmospheres?
It does not usually need to be coated
As thermoplastic polymers are heated, what generally occurs?
They soften
Silicones are generally considered less resistant to heat and chemical attack than which of the following?
Nickel alloy
What is corrosion that occurs uniformly over the surface of a metal or alloy called?
General
Which type of corrosion occurs in shielded areas where free access to the bulk environment in surrounding areas is restricted?
Crevice corrosion
Which of the following are common ways to control crevice corrosion?
Sealing lap joints where they cannot be avoided
Providing complete drainage
What is the formation of subsurface planar cavities in a metal from excessive internal hydrogen pressure?
Hydrogen blistering
Which type of corrosion occurs due to electrical contact between two dissimilar metals in an electrolyte?
Galvanic
Tensile stress and corrosion in the presence of water and H2S can cause which of the following?
Sulfide stress cracking
Which form of corrosion is characterized by the premature failure of cyclically loaded part?
Corrosion fatigue
Which of the following is an attack resulting from the combined action of corrosion and fluid flow on stationary or moving surfaces?
Erosion-corrosion
Which of the following descriptions applies to dealloying?
Selective removal of one element from an alloy by corrosion processes
What type of corrosion occurs due to repeated relative motion between two surfaces under load in the presence of a corrosion environment?
Fretting
What does the galvanic table contain?
Galvanic series
Using the galvanic table, what metals will be the least corrisive together and why?
Copper and stainless steel aloys because the closer they are in the series the more compatible.
What does the galvanic table indicate?
The need or degree of protection to be applied to reduce expected corrosion in a galvanic and salt water environment.
How can the corrosion of magnesium aloys be diminished?
By the use of the proper protective finish.
What does the formation of a tightly adhering oxide film on aluminum surfaces produce under mild corrosive conditions?
Increased conditions.
What type of corrosion indicator is usually found on steel?
Red rust.
What type of corrosion indicator is usually found on copper?
Blue, or blue green.
What type of corrosion is most commonly found on copper?
Interangular corrosion.
Why are stainless steels more resistant to common rusting?
Due to passive films.
How does stainless steel interact with almost any other metal if proper techniques of sealing and protective coating are ignored?
They can cause galvanic corrosion.
What type of insulation is required between titanium and other metals?
Electrical insulation.
How are nickel and chromium used and what makes them so uniquely useful?
Used as protective platings, they form continuous oxide coatings protecting themselves and underlying metals.
Which of the following defines high-temperature corrosion?
Phenomenon that requires a specific environment and applied stress.
Formation of thick oxide or sulfide scales that cause internal swelling of the metal.
Which of the following is the most common alloy used for high-temperature exposure?
Stainless steel.
What is the primary purpose of post-weld heat treatment?
To reduce residual stresses from welding.
In design, which of the following chemical factors that can influence corrosion should be considered?
Major species
Minor species
Nature of environment
Which of the following must the design engineer take into consideration for upset temperature conditions?
Maximum operating temperature.
In designing against dissimilar metal (galvanic) corrosion, what is often more important than the position of the metals in the galvanic series?
Cathode/ anode area ratio.
Good design to minimize corrosion will ensure which of the following?
Water or corrodents cannot be trapped.
Which of the following is important in good design for inspection and maintenance?
Easy access.
If good design practices are being utilized, how can crevices at joints be avoided?
Full penetration welding instead of bolting or riveting.
Corrosion allowance is used in design for environments where the metal corrodes in which of the following ways?
Uniformly at a linear or decreasing rate with time.
During design, when must the environment be defined?
Before appropriate materials are selected.
Where safety is critical, such as in transportation of hazardous products, what is more important than cost?
Reliability.
Which of the following are important corrosion-related factors to be considered in the selection of metallic materials?
Mechanical properties of materials
Cost of materials
Which of the following are common methods for corrosion control?
Corrosion inhibitors
Materials selection
Coatings
Anodic corrosion inhibitors must cover the entire anodic area of metal surface to avoid which of the following?
Accelerated localized corrosion of anodic areas.
What is the purpose of using a biocide, such as chlorination, in a water treatment?
To control microbiological fouling.
Which of the following are common design defects that make coating application difficult?
Riveted construction
Threaded areas
Weld spatter
Which of the following is a common galvanic anode material for protection of steel?
Zinc
Which of the following are examples of impressed current anodes?
Silicon cast-iron and graphite.
In an impressed current system, the positive terminal of the power supply must always be connected to which of the following?
Anode groundbed
What is one of the simplest and least expensive non-destructive inspection methods?
Visual examination.
Which type of inspection method can non-destructive gauge the thickness of in-service equipment?
Ultrasonic.
Which inspection method can locate crack-like surface defects on a variety of non-porous materials?
Dye penetrant.
Which inspection method can detect defects voids, inclusions and pit depths but is less effective in locating cracks unless the orientation of the cracks is known?
Radiography.
What is the most commonly used method for corrosion monitoring?
Weight-loss coupons.
In galvanic corrosion monitoring, accurate measurements of current flow between dissimilar metal electrodes is achieved with which of the following instruments?
Zero-resistance ammeter.
In water chemistry monitoring, what can metal-ion concentration analysis indicate?
Changes in the corrosivity of the environment.
What is the most common method for monitoring the effectiveness of cathodic protection of a structure?
Measuring structure-to-electrolyte potential.
What is the benefit of eddy current inspection?
It can be used on electrically conductive material.
What are identifying characteristics of corrosion on silver or gold?
Silver is a brown black film, and gold is a darkening on reflective surfaces.
Where is carbon in the galvanic series?
Composites.
Why is separation of carbon/graphite metals to other metals so important?
To prevent dissimilar metal attack on the attached part.
What are the four basic standard stages of corrosion prevention and control?
Cleaning, protection, inspection, control.
What type of cleaner is used when cleaning metals in a corrosive environment and how
often should they be cleaned?
With the mildest soap possible and frequently.
What should paint surfaces be inspected for?
Itregularities, blisters, flakes, chips.
List the types of procedures used when implementing corrected treatment when corrosion is detected:
Thoroughly inspect all corroded areas, evaluate damage, remove paint/corrosion, apply chemical surface treatment, sealing, and apply paint finishes.