Estimation of Flow Accelerated Corrosion (FAC) in Process Piping Using CFD Software and Low Temperature Experimental Determination of FAC.

Principal parameters on which FAC depends are temperature, pH, oxygen content, and water velocity.

This phenomena was identified as a result of research in France, Germany, and the United Kingdom over the past twenty years.

In the EC the oxide film is mechanically removed from a metallic substrate.

In the FAC process, the protective oxide film is not mechanically removed. Rather, the oxide is dissolved or prevented from forming, allowing corrosion of the unprotected surface.

Single-phase FAC caseTwo-phase FAC case

Parameter Detail Feeder titleG-06Line numberPH-478Operating temperature at FP567 0FMass flow rate27.41 lb/secVelocity of fluid8.3 m/secDensity of fluid784.4 Kg/m3Nominal thickness 5.54 mmThinning rate0.1084 mm/EFPY

Grid Cells = 450,000Time for solution = 1.25 hrsGrid Cells = 550,000Time for solution = 1.75 hrs

Here

B=495 (for 2.75mm diameter particles)V=7.64 m/sec

So Maximum Erosion Rate isERmax=1.1 mm/year

Water tankPipe lines and FittingsPump

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Sr No.ParameterCondition1Coupon materialM.S.2Coupon area51.0 cm23Temperature90 oC4Total running time12 hrs5Working pressure1 atm6Flow rate0.2947 lit/sec7Fluid velocity1.338 m/sec

Sr No.ParameterRange1LiOH0.01 g/lit2pH9 103Conductivity20 30 s4Chlorides 1ppm5DO 10 ppb6Hydrazine20 - 30 ppb

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CouponNoInitial weight(g)Final weight(g)Change in weight(g)Corrosion rate(g/cm2 year)1110.7041110.60670.09741.39412107.783107.6690.1141.63173108.8162108.72310.09311.33264110.8500110.76660.08341.1937

Sr No.Time(hrs)pHConductivity(s)109.3228.8229.2944.6349.2651.9469.2655.2589.2559.96109.2463.27129.2467.8

CFD analysis of give the maximum wall thinning rate of 1.1 mm per year, while in the plant the data maximum thinning rate of feeder is given 0.1084 mm per EFPY.

A great difference in thinning rate is due to neglecting the welding points in feeder geometry development, Ignoring chemical addition effect in primary stream etc.

From experiment maximum corrosion rate found in coupon no 2 because of maximum eddies formation due to flow pattern.

No evidence of FAC observed on coupons (orange peel appearance) surface and not remarkable wall thinning measured.

At 90oC no FAC occurred so there is no need to do experiment below this temperature.