Module 10 (uniformed or Localized Loss) Flashcards by Wynne liu

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

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galvanic corrosion

The more noble material (_____) is protected by sacrificial corrosion of the more active material (___).

cathode / anode

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galvanic corrosion

If there is a small anode-to-cathode exposed surface area ratio, the corrosion rate of the anode can be

very high.

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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.

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galvanic corrosion

damage occurs where two different materials are joined at ____________(3)

welded, bolted, or rolled connections.

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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

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galvanic corrosion

a) The best method for prevention or mitigation is through

good design

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galvanic corrosion

If only one can be coated, the more _______material should be the one coated

noble cathode

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atmospheric corrosion

affected material

Carbon steel, low-alloy steels, and copper alloyed aluminum

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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

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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

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atmospheric corrosion

appearance

general or localized

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atmospheric corrosion

prevention?

paint or coating

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atmospheric corrosion

inspection (3)

VT / RT /UT

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atmospheric corrosion

related mech?

2. Concentration cell corrosion

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CUI

affected materials?

Carbon steel, low-alloy steels, 300 series SS, 400 series SS, and duplex stainless steels.

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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

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CUI

The extent of CUI attack depends on the total amount of time the equipment remains ____from exposure to _____.

2. wet insulation.

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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

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CUI

CUI corrosion rates are _____to predict

difficult

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CUI

appearance (2)

a. corrosion can appear to be carbuncle type pitting

b. 300S are subject to SCC is chloride are present

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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

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CUI

inspection (2)

infrared thermography / neutron backscatter

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Cooling Water Corrosion

appearance (2)

General or localized corrosion

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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?

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

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