flow accelerated corrosion (fac)

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FlowFlow--Accelerated Accelerated Corrosion SolutionsCorrosion SolutionsCorrosion SolutionsCorrosion Solutions

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FlowFlow--AcceleratedAccelerated Corrosion?Corrosion?• Flow-Accelerated Corrosion (FAC) is a chemical corrosion

process that causes wall loss in piping

FlowFlow Accelerated Accelerated Corrosion?Corrosion?

process that causes wall loss in piping.

• FAC is caused by the dissolution of the oxide layer on the inside surface of piping in flowing water or wetthe inside surface of piping in flowing water or wet steam.

• This affects carbon or low allow steel. The pipe wall p pthickness can progressively be reduced to the point of rupture.

FAC i ll l t d t t b l i ll• FAC is normally related to turbulence especially near fittings, e.g., elbows, orifices, valves

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MihamaMihama UnitUnit 33 ---- 20042004Mihama Mihama Unit Unit 3 3 20042004

• A 22 inch condensate line downstream of an orifice ruptured catastrophicallycatastrophically

• Five fatalities and several injuries

l dresulted• Failure was

downstream of andownstream of an orifice

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MillstoneMillstone 33 –– 19901990Millstone Millstone 3 3 19901990• Simultaneous failure of

t 6 i h d i litwo 6-inch drain lines downstream of the moisture separator pdrain tank

• Failures were downstream of leveldownstream of level control valves

• Two parallel trains pfailed.

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FortFort CalhounCalhoun ---- 19971997Fort Fort Calhoun Calhoun 19971997• Failure in a

hi hhigh pressure extraction line.

• FailureFailure occurred in bend.

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Pleasant Prairie Power Pleasant Prairie Power Plant Plant ----19951995

• Failure in a f d t t tfeedwater system to a fossil fueled boiler.

• Failure occurred downstream of a teetee.

• Two workers killed.

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Single and Two Phase SystemsSingle and Two Phase SystemsSingle and Two Phase SystemsSingle and Two Phase Systems

• FAC occurs in both single and two phase systems.g p y• These systems include:

‣ Feedwaterd‣ Condensate

‣ Extraction/Bleed Steam‣ Heater Drains and Vents‣ Boiler Blowdown‣ Others

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What Factors Influence What Factors Influence FACFAC??

• Material Chemistry Chromium Copper Molybdenum

• Water ChemistryWater Chemistry −pH−O2 ConcentrationO2 Concentration−Temperature

• Geometry and Steam Quality88

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• Geometry and Steam Quality

Material Chemistry Material Chemistry yy

• Affects Carbon Steel and Low Alloy Steel

• As Chromium increases, FAC rate ,decreases. This is the primary element that affects FAC

• As Copper increases, FAC rate decreases.decreases.

• As Molybdenum increases, FAC rate increases

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increases.

FAC Wear Rates FAC Wear Rates Decreases as Decreases as Chromium Content IncreasesChromium Content Increases

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Water Chemistry Water Chemistry yy• pH

• pH influences the solubility of the oxide film.H l i f h b d i i lif• pH control is one of the best ways to extend piping systems life

• pH should be as high as possible to provide the best FAC protection.

O C t ti• O2 Concentration• Oxygen affects the composition of the surface oxide layer• Higher oxygen levels increase the stability of the surface oxide

hi h d th t f FACwhich reduces the rate of FAC.• Temperature

• Temperature affects the formation and solubility of the oxide layer.

• At moderate temperatures (> 250F - 400 F) the magnetite layer is porous and irregular. FAC rate is the highest.

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FAC Wear Rates as pH IncreasesFAC Wear Rates as pH Increases

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FAC Wear Rates as Oxygen Level FAC Wear Rates as Oxygen Level IncreasesIncreasesIncreasesIncreases

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FAC Wear Rates FAC Wear Rates as Temperature as Temperature IncreasesIncreasesIncreasesIncreases

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Geometry and Steam QualityGeometry and Steam Qualityy Q yy Q y

• Higher velocity gives higher FAC rates• Transitions in geometry, like at elbows,

orifices, tees, valves, and other changes , , , gin flow direction creates turbulence and increases FAC susceptibility.p y

• Both single phase and two phase flows can cause FAC.can cause FAC.

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FAC Wear Rates as Velocity FAC Wear Rates as Velocity IIIncreasesIncreases

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FAC ThinningFAC ThinningFAC ThinningFAC Thinning

• Single phase FAC damage looks like small scallops or g p g phas an “orange peel” appearance.

• The edges of the scallops are usually fairly smooth.• Two phase flow damage may have a “tiger striped”

appearance. There may be plateaus on the pipe surface over a fairly wide area.surface over a fairly wide area.

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FAC DamageFAC DamageFAC DamageFAC Damage

• Single phase• Single phase FAC damage looks like small scallops.

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FAC DamageFAC DamageFAC DamageFAC Damage

• Tiger Striping• Tiger Striping.

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An Effective FAC ProgramAn Effective FAC Programgg

• System Susceptibility Screeningy p y g• Input on Operations, Maintenance, Water Chemistry• Computer Modeling (EPRI Codes commonly used)• Selection of Inspection Locations• Inspections

l l f• Structural Evaluation of Inspection Data• Component Life Determination• Mitigating Actions to Slow the FAC rate if necessary• Mitigating Actions to Slow the FAC rate, if necessary

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Methods to Mitigate FAC DamageMethods to Mitigate FAC DamageMethods to Mitigate FAC DamageMethods to Mitigate FAC Damage

• Improve Water ChemistryImprove Water Chemistry• Use Improved Materials• System Design Changes• System Design Changes

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