Module 10 (uniformed or Localized Loss) Flashcards
galvanic corrosion critical factor (3)
- There must be two (or at least two) different metals
- The dissimilar metals must be electrically coupled together,.
- Both metals must be immersed or in contact with the same, continuous electrolyte
galvanic corrosion
The more noble material (_____) is protected by sacrificial corrosion of the more active material (___).
cathode / anode
galvanic corrosion
If there is a small anode-to-cathode exposed surface area ratio, the corrosion rate of the anode can be
very high.
galvanic corrosion
. If there is a large anode-to-cathode surface area ratio, the corrosion rate of the anode will be
The same metal may act as either an anode or a cathode in different situations
less affected.
galvanic corrosion
damage occurs where two different materials are joined at ____________(3)
welded, bolted, or rolled connections.
galvanic corrosion
_____ active material can suffer generalized loss in thickness or more aggressive localized loss adjacent to the point of connection, with the appearance of ___(3) ___
more /
crevice, grooving, or pitting corrosion
galvanic corrosion
a) The best method for prevention or mitigation is through
good design
galvanic corrosion
If only one can be coated, the more _______material should be the one coated
noble cathode
atmospheric corrosion
affected material
Carbon steel, low-alloy steels, and copper alloyed aluminum
atmospheric corrosion
Corrosion rates increase with temperature up to about ______ . Above _____, surfaces are usually too dry for corrosion to occur except under insulation.
250 °F / 250 °F
atmospheric corrosion
a. Marine environments can be very corrosive (about )
b. industrial environments that contain acids or sulfur compounds
c. Inland locations
d. Dry rural
a. 20 mpy
b. 5 mpy 10 mpy
c 1 to 3 mpy
d. <1mpy
atmospheric corrosion
appearance
- general or localized
atmospheric corrosion
prevention?
paint or coating
atmospheric corrosion
inspection (3)
VT / RT /UT
atmospheric corrosion
related mech?
- CUI
2. Concentration cell corrosion
CUI
affected materials?
Carbon steel, low-alloy steels, 300 series SS, 400 series SS, and duplex stainless steels.
CUI susceptible temp CS SS Duplex
a. 10 °F (−12 °C) and 350 °F (175 °C) - CS
b. 140F-280F for SS
c. 280-350F for duplex
CUI
The extent of CUI attack depends on the total amount of time the equipment remains ____from exposure to _____.
- wet
2. wet insulation.
CUI
higher operating temperature will result in a _____ corrosion rate, the total amount of attack over a long period of time may occur at a _____temperature if the metal remains wet for significantly longer periods of time at the lower temperature.
higher /
lower
CUI
CUI corrosion rates are _____to predict
difficult
CUI
appearance (2)
a. corrosion can appear to be carbuncle type pitting
b. 300S are subject to SCC is chloride are present
prevention
1. mitigation is best achieved by _________
2. ______ aluminum coatings have been used on carbon steels.
3. Thin _____foil wrapped on stainless steel piping and equipment beneath the insulation can provide an effective barrier, partly due to the galvanic effect of the aluminum in preventing Cl− SCC in stainless
steel.
4. While ____cell foam glass materials will hold less water and, studies show that an ____cell structure provides a path for water vapor to escape faster, allowing the insulation to dry quicker. Faster drying time, corresponding to less metal wetting time, should help mitigate CUI. Types of open cell insulation that limit and delay water ingress have been developed.
- coating
- Flame-sprayed
- aluminum
- closed- / open
CUI
inspection (2)
infrared thermography / neutron backscatter
Cooling Water Corrosion
appearance (2)
General or localized corrosion
Cooling Water Corrosion
Higher cooling water temperature causes ____corrosion rates
increased
Cooling Water Corrosion
If the process-side temperature is above____ , a scaling potential exists with fresh water and becomes more likely as process temperatures increase and as cooling water inlet temperatures rise.
140 °F
Cooling Water Corrosion
Brackish and salt water outlet temperatures above about ____may cause serious scaling.
115 °F
Cooling Water Corrosion
Brackish and salt water outlet temperatures above about ____may cause serious scaling.
115 °F
Cooling Water Corrosion
Increasing _____content tends to increase carbon steel corrosion rates
oxygen
Cooling Water Corrosion
suggested velocity?
3fps
Cooling Water Corrosion
_____ alloys can suffer dezincification in fresh, brackish, and salt water systems.
Brass
Cooling Water Corrosion
temp____ for SS can suffer CLSCC
> 140F
Cooling Water Corrosion
temp____ for SS can suffer CLSCC
> 140F
Cooling Water Corrosion
_____carbon steel pipe or exchanger tubes may suffer severe weld and/or HAZ corrosion in fresh or brackish water.
ERW
Cooling Water Corrosion
prevention
a. Cooling water corrosion (and fouling) is best managed by proper ____3____ of cooling water systems
b. Process-side inlet temperatures of water-cooled exchangers should be maintained below____
c. With very few exceptions, cooling water should be on the ____side to minimize stagnant areas
a. design, operation, and chemical treatment
b. 140 °F (60 °C)..
c. tube
Oxygenated Process Water Corrosion
solubility of ___increases as the temperature of the water decreases, the corrosion activity due to ____-containing water tends to be higher at lower temperatures.
oxygen / oxygen
Oxygenated Process Water Corrosion
affected material? (2)
Carbon steel and low-alloy steel
Oxygenated Process Water Corrosion
critical factor? (6)
oxygen solubility and content, temperature, and velocity and turbulence/ WATER
Oxygenated Process Water Corrosion
must have?
water
Oxygenated Process Water Corrosion
only ___ppm of o2 is needed to increase CR
20 ppm
Oxygenated Process Water Corrosion
If a separate water phase is present, oxygenated water corrosion is typically found along the bottom of the _____
piping system.
Oxygenated Process Water Corrosion
______ are subject to oxygenated water corrosion because O2 enters vacuum unit systems through leaking
Vacuum units
Oxygenated Process Water Corrosion
O2 content less than _____ in non-aerated water systems is very difficult to measure
100 ppb
Oxygenated Process Water Corrosion
The use of _______ can also be considered for non-aerated systems to reduce O2.However, this is generally not recommended unless vacuum leaks cannot be eliminated.
oxygen scavenger injection
Oxygenated Process Water Corrosion
appearance? and on low velocity?
extensive general pitting on wetted surfaces. Localized pitting occurs in low-velocity areas at reduced temperatures.
Microbiologically Induced Corrosion (MIC)
resistant material?
Ti
Microbiologically Induced Corrosion (MIC)
what type of environment? Occasionally it is found in services where water is ____ present.
aqueous / intermittently
Microbiologically Induced Corrosion (MIC)
_______flow condition allow and/or promote the growth of microorganisms.
stagnant or low flow
Microbiologically Induced Corrosion (MIC)
organisms can survive and grow under a wide range of conditions including lack of oxygen, light or dark, high salinity, pH range of ______, and temperatures from _____
0 to 12/
0 °F to 235 °F
Microbiologically Induced Corrosion (MIC)
all organisms require a source of (3) for growth.
carbon, nitrogen, and phosphorous
Microbiologically Induced Corrosion (MIC)
localized pitting under deposits or tubercles that shield the organism
Microbiologically Induced Corrosion (MIC)
appearance?
localized pitting under deposits or tubercles that shield the organism
cup-shaped pits within pits (the halo effect) in carbon steel or subsurface cavities in stainless steel.
Microbiologically Induced Corrosion (MIC)
what smell indicates MIC?
foul smelling
Microbiologically Induced Corrosion (MIC)
Proper application of ______ will control, but not eliminate, microbes; therefore, continued treatment is often necessary
biocides
Microbiologically Induced Corrosion (MIC)
Empty _______ water as soon as possible. Remove moisture and prevent additional moisture intrusion
hydrotest
Microbiologically Induced Corrosion (MIC)
_____(2) ___ protecting underground structures and interiors of storage tanks have been shown to be effective mitigation methods for MIC.
Coating and cathodically
Boiler Water Condensate Corrosion
affected material
Carbon steel and low-alloy steels
Boiler Water Condensate Corrosion
o2 ppm atleast __ to ___ ppm to form a oxide layer
3 to 7 ppb
Boiler Water Condensate Corrosion
critical factors
concentration of dissolved gas (oxygen and/or carbon dioxide), pH, temperature, quality of the feedwater, and the specific feedwater treating system.
Boiler Water Condensate Corrosion
appearance? from o2 and co2?
Corrosion from oxygen is normally a pitting type damage
Carbon dioxide corrosion is normally smooth, but it can also cause grooving of the pipe wall.
CO2 Corrosion
CO2 corrosion results when CO2 dissolves in water to form ____acid
carbonic acid (H2CO3)
CO2 Corrosion critical factor (2)
a. low pH
b. water
CO2 Corrosion
appearance (2)
b. general or pitting corrosion
CO2 Corrosion affected materials (3)
a. CS / low alloys
b. SS <12% CR
CO2 Corrosion
increasing partial pressure of Co2 = ______pH = increase CR
lower
CO2 Corrosion
Corrosion usually occurs when the effluent stream drops below the dew point at approximately____F
300 °F
CO2 Corrosion
It may appear as a number of flat-bottomed pits, sometimes called _____”-type pitting.
“mesa
CO2 Corrosion
It may appear as a number of _____ pits, sometimes called _____”-type pitting.
flat-bottomed / mesa
CO2 Corrosion
_____inhibitors can reduce CO2 corrosion in steam condensate system
Corrosion
CO2 Corrosion
_____inhibitors can reduce CO2 corrosion in steam condensate system
Corrosion
CO2 Corrosion
inspection?
Monitor _______to determine changes in operating conditions
water analyses (pH, Fe, O2, etc.)
Flue Gas Dew Point Corrosion At temperatures\_\_\_\_\_\_(2) these gases and the water vapor in the flue gas will condense to form acid
at or below the dew point,
Flue Gas Dew Point Corrosion
The dew point of sulfuric acid depends on the concentration of sulfur trioxide in the flue gas but is typically about______
280 °F (140 °C).
Flue Gas Dew Point Corrosion
Dew points for sulfurous, hydrochloric, nitric, and carbonic acids depend on the concentrations of SO2, HCl, NO2, and CO2 and on the water content of the flue gas, but they occur typically at temperatures lower than the water dew point,___________
212 °F (100 °C)
Flue Gas Dew Point Corrosion
The metallic surfaces at the back end of the boilers and fired heaters and stacks should be kept at least ________ above the dew point temperature of sulfuric acid
10 °F (6 °C)
Flue Gas Dew Point Corrosion
inspection
UT
Soil Corrosion
affected material
Carbon steel, cast iron, and ductile iron
Soil Corrosion
Soil ______is related to the soil moisture content and dissolved electrolytes
resistivity
Soil Corrosion
Soils having high moisture content, high dissolved salt concentrations, and high acidity are usually the ____corrosive.
most
Soil Corrosion
_____ areas are often much more susceptible to corrosion than the rest of the structure because of moisture and oxygen availability.
Soil-to-air interface
Soil Corrosion
appearance
Soil corrosion appears as ________with a roughened surface and localized deeper attack or pitting.
external thinning
Soil Corrosion
appearance
Soil corrosion appears as ________with a roughened surface and localized deeper attack or pitting.
external thinning
Soil Corrosion
minimized through the use of appropriate ___(2) __ along with special backfill to prevent rock damage to the coating
coatings and cathodic protection
Soil Corrosion
A _______survey on a cathodically protected line may be used to verify that the buried piping has a protective potential throughout its length.
close-interval potential
Brine Corrosion
appearance
Widespread or localized pitting
Brine Corrosion
________are generally more resistant to pitting in brine solutions than stainless steel and carbon steel
Copper alloys
Brine Corrosion
_____) piping is immune to this damage mechanism
Fiber reinforced plastic (FRP
Brine Corrosion
what affect the CR? presence of what?
type of salt / H2S
Brine Corrosion
appearance for CS /SS
Carbon Steel - Heavy scaling and possible tubercles
Stainless Steel – Sharp, deep, isolated pits
Brine Corrosion
prevention?
a. Sources of ______ should be identified and eliminated. B. A ______water source should be used for desalter wash water make-up.
a. dissolved oxygen
b. deaerated
Concentrated Cell Corrosion
Concentration cell corrosion occurs in ______environments.
aqueous
Concentrated Cell Corrosion
potentially ____aqueous environment must exist
corrosive
Concentrated Cell Corrosion
appearance for CS /SS
CS - Pitting
SS- sharp, narrow, deep pits.
Concentrated Cell Corrosion
inspection (2)
Vt/ UT
Concentrated Cell Corrosion (not a single damage mech but related mechs are )
under-deposit corrosion, crevice corrosion, contact point corrosion (also called touch point corrosion), soil/air interface corrosion (see 3.57), and CUI (see 3.22).
Concentrated Cell Corrosion (not a single damage mech but related mechs are )
under-deposit corrosion, crevice corrosion, contact point corrosion (also called touch point corrosion), soil/air interface corrosion (see 3.57), and CUI (see 3.22).
Co2
Corrosion may occur along the bottom surface of a pipe if there is a separate ______or along the top surface of a pipe if condensation in wet gas systems occurs.
water phase
Co2
Corrosion may occur along the bottom surface of a pipe if there is a separate ______or along the top surface of a pipe if condensation in wet gas systems occurs.
water phase
Flue Gas Dew Point Corrosion
critical factors? (2)
contaminants / operating temperature
galvanic corrosion
Heat exchangers are susceptible if the tube material is different from the tubesheet and/or baffles
CUI
most server at ___ F
212
Boiler water
Copper/zinc alloys can suffer ___in fresh, brackish and salt water systems.
dezincification
CO2 affect equipment?
Boiler feedwater and condensate systems in all units are affected.
CO2 affect equipment?
Boiler feedwater and condensate systems in all units are affected.
CO2
resistant material?
300 SS
Fuel Gas
All fired process heaters and boilers that burn fuels containing sulfur have the potential for sulfuric acid dewpoint corrosion in the economizer sections
