Flow+Accelerated+Corrosion (1)

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

Temperature Experimental Determination of FAC.

This presentation includes idea about Flow Accelerated Corrosion (FAC),

FLUENT analysis of KANUPP feeder in order to find FAC in them and

experimental work regarding to study FAC at low temperature.

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.

Flow Accelerated Corrosion (FAC) is a process in which a normally

protective oxide coating dissolves into a rapidly moving water, or a

water/steam mixture.

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.

FAC and Erosion Corrosion (EC) are normally considered same which is

wrong. The differences involves the mechanism by which the protective

film is removed from the metal surface.

There is a cleared difference b/w single and double phase FAC. Single-

phase FAC produces a scalloped appearance, similar to an orange peel

while Two-phase FAC produces a “tiger striped” or streaked appearance.

Single-phase FAC case Two-phase FAC case

FAC rate is peaked in 130-150 oC and is due to fact that at higher

temperature magnetite layer becomes denser and solubility of Fe3O4

reduces in water.

FAC rate increases with increase in pH of working fluid however

temperature contribution should must keep in mind as it considered a

sort of pH control agent.

FAC: transfer of Fe(OH)+ and Fe(OH)2 is accelerated by not only average

velocity but also turbulence factor which can described on shape factor

bases, higher the Kc higher will be the FAC.

FAC rate also depend on material used, in carbon steel FAC is maximum

while it suddenly decreases according to Cr(+Mo) contents thus FAC in

carbon steel can mitigated with high Cr contents.

FAC rate decreases with increasing Dissolved Oxygen (DO) and it is due

to the hematite formation which prevent FAC more than magnetite layer

that form in common.

Process piping isometric drawing and detail description is used to make

its geometry, meshing, CFD analysis etc.

Parameter Detail

Feeder title G-06

Line number PH-478

Operating

temperature at FP

567 0F

Mass flow rate 27.41 lb/sec

Velocity of fluid 8.3 m/sec

Density of fluid 784.4 Kg/m3

Nominal thickness 5.54 mm

Thinning rate 0.1084 mm/EFPY

Geometry is developed by using Pro/Engineer and then is saved in IGS

format.

GAMBIT is used for meshing. Hex core mesh is used in order to lower cell

counts and improve the quality, this type is generally used for flow

volumes with complexity near the walls.

Meshed file that has generated is solved in segregated solver, 3D space,

implicit formulation, cell based gradient option and absolute velocity

formulation at steady state condition is set for analysis.

In order to check grid independency (GIT) two grids with different counts

are made and solved to get velocity contours when these give very less

remarkable difference grid independency proved.

Grid Cells = 450,000

Time for solution = 1.25 hrsGrid Cells = 550,000

Time for solution = 1.75 hrs

Velocity contours and velocity vector are determined.

Contours of wall sheer stress and absolute pressure also give an idea to

predict the location of high corrosion attack.

Discrete phase model enhancement feature can be used to calculate

erosion rate at walls result shows in unit less quantity which in actual

heaving units of length/time.

Further description of model provide more deep analysis of Erosion Rate,

from velocity contours corresponding to maximum velocity erosion rate

of 1.1 mm per year calculated

Here

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

So Maximum Erosion Rate is

ERmax = 1.1 mm/year

Layout of experimental setup for determination of Flow Accelerated

Corrosion is shown. Open system design is selected in order to examine

phenomena at low temperature.

Centrifugal Pump, water storage tank, pipeline and fitting that used in

setup are shown. Pipe lines of UPVC are used in order to retain integrity

above 90oC.

Water tank

Pipe lines and FittingsPump

Specimens Holder different views and coupon used in experiment are

shown, specimens holder is also made of thermal resistance plastic

material.

Assembled setup in operating and non operating condition is shown

while proceeding experimental clip provide better visual aid of completed

experiment.

video.mp4

Main objective of experiment is to determine FAC at low temp which may

further explained as determination of threshold temperature for FAC,

Experimental working conditions are given in table.

Sr

No.

Parameter Condition

1 Coupon

material

M.S.

2 Coupon area 51.0 cm2

3 Temperature 90 oC

4 Total running

time

12 hrs

5 Working

pressure

1 atm

6 Flow rate 0.2947 lit/sec

7 Fluid velocity 1.338 m/sec

During experiment water chemistry is maintained as of chemistry of

secondary side of KANUPP or as chemistry of water used in CIAL

experimental rig.

Sr No. Parameter Range

1 LiOH 0.01 g/lit

2 pH 9 – 10

3 Conductivity 20 – 30 µs

4 Chlorides ≤ 1ppm

5 DO ≤ 10 ppb

6 Hydrazine 20 - 30 ppb

Observations and calculations at end of experiment give the idea of

corrosion rate in coupons maintained at specific conditions, in coupon 2

maximum corrosion rate is observed

Coupon

No

Initial weight

(g)

Final weight

(g)

Change in weight

(g)

Corrosion rate

(g/cm2 year)

1 110.7041 110.6067 0.0974 1.3941

2 107.783 107.669 0.114 1.6317

3 108.8162 108.7231 0.0931 1.3326

4 110.8500 110.7666 0.0834 1.1937

1

2

3

4

pH and conductivity trend of working fluid during experiment w.r.t time

shows almost constant pH and increasing trend of conductivity; increase

in conductivity is due to addition of crud from old pump.

Sr

No.

Tim

e

(hrs)

pH Conducti

vity

(µs)

1 0 9.32 28.8

2 2 9.29 44.6

3 4 9.26 51.9

4 6 9.26 55.2

5 8 9.25 59.9

6 10 9.24 63.2

7 12 9.24 67.8

RESULTS AND DISCUSSION

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.

RESULTS AND DISCUSSION (Contd....)

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.