Between which waters is differentiated in corrosion?
fresh water
drinking water
seawater
What are the major enviromental factors that differ in waters?
diffused gasses
minerals
organic matter
microbiological components
On what depends the pH value of waters? Between which values are waters normally?
4,5 - 8,5 pH
the pH value depends on dissolved CO2 and carbonatic species
What is understood under the carbonates equilibrium in water?
The reaction of CO2 with CaCO3 in water maintains an equilibrium of pH value
What is the Langelier index?
pHs: equilibrium pH of H2O and CaCO3
Is a water with positive or negative Langelier index more corrosive?
negative is more corrosive
What is the controlling species of corrosion in water?
Oxygen
What is the effect of Temperature on dissolved oxygen in water?
Which Chemicals are used as a oxygen scavanger in pipelines?
Hydrazine N2H4
Diethylhydroxylamine (DEHA)
Sulfite SO3 2-
What are the reactions of Hydrazine?
Why is seawater more corrosive then fresh water?
higher conductivity
chloride attack
penetrating power of chloride ions through passive layers
What is the buffering effect of seawater?
Carbon dioxid regulates the pH value.
Which kind of precipitations occur in salt water?
CaCO3
Mg(OH)2
Describe the corrosion rate of a partially in sea water submerged structure over the lenght of the structure.
How can submerged structures be protected against corrosion?
Paint and sacrificial annodes
Which materials are used for sacrificial annodes?
zink, magnesium, aluminium
Which variables have an influence on soil corrosion?
water
degree of areation
pH
redox potential
resistivity
soluble ionic species
microbiological species
Which quantitiy is used to roughly evaluate the corrosion potential of soil?
Resisitivity
What are the reasons for the creation of macrogalvanic cells?
variation in soil composition create macrogalvanic cells
variations in oxygen lead to oxygen cells
What are the major types of bacteria producing corrosion?
aerobic: lower pH value -> acid corrosion
Anaerobic: sulphate-reducing bacteria
How do Sulfate Reducing Bacteria corrode materials?
Why is Iron passivated in concrete?
A passivation layer forms at pH values larger than 11,5 concrete has an internal pH value of 13-13.5
What are the reasons concrete can lose its passivation capabillities?
chloride penetrating the concrete
carbonation process lowers pH
What stages has the lifetime of a concrete structure?
What are the effects of corrosion on concrete? What values are decreased?
reduction in crosssection of rebars
tensile strength, elongation, fatigue strength
cracking of concrete
loss of bond strength, increase in corrosion rate
hydrogen embrittlement
brittle failure of reinforcement
What is understood under concrete spalling?
Formation of rust layer and consequent chipping of concrete due to volume change
What is the parameter that controls the lifetime of a steel-concrete structure?
The diffusion coefficient of chloride
What quantity can be used to measure corrosion resistance in concrete?
Which resistivity values define a high or low corrosion?
low > 1000 ohm/m
high < 100 ohm/m
What are strategies to avoid corrosion when designing concrete structures?
improve drainages
make corrosion affected zones replaceable if possible
space out steel structures evenly
How are concrete structures tested?
drilling and inserting phenolphtalein (indicator: purple over 9,2)
What are steel-concrete protection methods?
controlling CO2 and chloride penetration
stop anodic process
hinder circulation of current
control rate of cathodic process
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