Prognostic and Determistic Analysis of thinning rate due to Flow Accelerated Corrosion

Presented By : Akshay Murkute Instructor : Dr. Yongming Liu

Outline Objectives Introduction Mathematical Model Validation and Verification Erosion simulation Maintenance Scheduling Future scope

Objectives Develop a mechanistic model and methodology

to predict the thinning rate of pipelines in Nuclear power plant (CANDU) due to FAC

Develop State Space model Compare the results with the experimental data Perform CFD simulations Time interval for Maintenance Scheduling

Flow Accelerated Corrosion Corrosion mechanism in which a normally

protective oxide layer on a metal surface dissolves in a fast flowing water.[1]

Rate of protective oxide layer (magnetite) dissolution is greater than the rate of protective oxide formation, when exposed to flowing water or wet steam.

Causes wall thinning and pipe rupture over time.

[1] https://en.wikipedia.org/wiki/Flow-accelerated_corrosion

Spalling / pitting

Mechanism Fe = Fe2+ + 2e–

2H2O + 2e– = 2 OH– + H2

Fe2+ + OH– = Fe(OH)+

2Fe(OH)+ + 2 H2O = 2 Fe(OH)2 + H2

Fe(OH)+ + 2 Fe(OH)2+ 3 OH– = Fe3O4 + 4 H2O

[1] “Guidelines for Controlling Flow-Accelerated Corrosion in Fossil and Combined Cycle Plants “ by EPRI

Hydrodynamics Flow Velocity (V) Reynolds Number (R) Mass transfer co-efficient (K) Turbulence intensity (TI) Surface shear stress (Ʈ)

Increases turbulence Particle hitting pitting

of oxide layer Velocity

Affects the solubility of the surface Fe3O4

Higher pH will reduce the amount of corrosion and FAC

pH

Mass transfer co-efficient Mass Transfer is the process of transporting material

(essentially magnetite) from the surface to the bulk of the flowing water or water-steam flow

The local mass transfer coefficient depends in a complex manner on fluid velocity, fluid viscosity, flow geometry, pipe/tube surface roughness and temperature

Mass transfer is usually described by the dimensionless parameters: Reynolds, Schmidt and Sherwood numbers

Temperature Affects:o pH of the water or wet

steamo Solubility of the oxide o The variables related to

mass transfer (Reynolds, Schmidt and Sherwood numbers)

FAC tends to peak at temperatures in the range of 150–180°C (300–350°FReference: Corrosion 98 – paper 721 flow accelerated corrosion, R. D port Nalco Chemical Company

Geometry Locates where FAC will occur. Certain geometries affect mass transfer due to changes in local

velocity and turbulence. Eg: elbows, tight bends, reducer tees, locations downstream of

flow control orifices and valves Geometric enhancement factors are related to the turbulence

created by the particular geometry or fitting. Larger values denote a greater propensity for flow disturbance

and which increases the mass transfer coefficients. Regression equation for FAC resistance R = 0.61 + 2.43 Cr + 1.64 Cu + 0.3 Mo , No FAC failure if R > 1

Mathematical Model FAC = K ∆C

K = Mass transfer coefficient ∆C = Solubility driving force

Reference: “Predicting and Preventing Flow Accelerated Corrosion in Nuclear Power Plant” by Bryan Poulson

𝐹𝐴𝐶= 𝑓 (T ) 𝑓 (V ) 𝑓 ( pH ) 𝑓 (𝑂 ) 𝑓 (ἀ ) 𝑓 (𝐶𝑟 ) 𝑓 (𝐺)

K - calculation

D = Diffusivity 𝛾 = Kinematic viscosity 𝑑 = diameter of pipe

ε = Roughness

Mass transfer Sherwood number (Sh) = ( / )𝐾 𝑑 𝐷Reynolds number(Re) = ( / ) 𝑉 𝑑 𝛾Schmitt number (Sc) = / .𝛾 𝐷Component enhancement factor = 16.73*(Re)-0.19

∆C (solubility driving force)

Depends on temperature, pH and water chemistry Defined within specific range ∆C = 0.0026*T2 - 1.3973*T + 195.09………(pH=9.5-11) ∆C = -5e-06*T3 + 0.006*T2 - 2.3307*T + 314.33……..(pH < 9.5)

Reference: F. H. Sweeton and C. F. Baes Jr., “The solubility of magnetite and hydrolysis of ferrous ion in aqueous solutions at elevated temperatures,”The Journal of ChemicalThermodynamics, vol. 2, no. 4, pp. 479–500, 1970

0 50 100 150 200 250 300 3500

20406080

100120140

Solubility vs temp

Temperature (C)

Solu

bilit

y pp

b

CANDU Reactor Outlet feeder Input data Temperature= 310 ˚C pH = 10.6 Velocity (V)= 8-16.5 m/s Dissolved O2 ̴ 0 ppb Diameter (d) = 2.5 in

Reference : A Mechanistic Model for Predicting Flow-assisted and General Corrosion of Carbon Steel in Reactor Primary Coolants D. H. Lister* and L. C. Lang**

Node Diagram for CANDU circuit

ComparisonDiameter (cm)

Bend Angle

Coolant Velocity (m/s)

Experimental FAC(um/a)

Calculated FAC(um/a)

6.4 42 10.5 50.2 50.436.4 73 10.4 59.0 63.56.4 73 12.3 75.6 75.96.4 73 15.6 105.9 966.4 73 16.2 110.0 99.46.4 73 17.5 123.1 1075.0 42 15.8 94.9 90.75.0 73 11.9 74.8 89.2

Comparison

10 11 12 13 14 15 16 17 180

20

40

60

80

100

120

140

FAC rate vs Velocity

Velocity (m/s)

FAC

rate

(um

/a)

Experimental

Calculated

CANDU Reactor

FAC (mm) vs Time (years)

Mass transfer vs Temp

Erosion Simulation

CFD Set up

Geometry and MeshingInflation at the interface of Wall-fluid

Convergence plot

Mass transfer co-efficient

Erosion Particle tracking

Verification

Validation with Velocity

0 2 4 6 8 10 12 14 16 180

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Thinning rate vs Velocity

Velocity

Thin

ning

rate

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.0005

0.00055

0.0006

0.00065

0.0007

0.00075

0.0008

0.00085

MTC vs Velocity

Velocity

MTC

Experimental data Calculated data

Reference: “A Mechanistic Model for Predicting Flow-assisted and General Corrosion of Carbon Steel in Reactor Primary Coolants by D. H. Lister and L. C. Lang”

25Reference: “A Mechanistic Model for Predicting Flow-assisted and General Corrosion of Carbon Steel in Reactor Primary Coolants by D. H. Lister and L. C. Lang”

Maintenance SchedulingNode Diagram of Nuclear primary circuit

26

Mathematical Model for Flow Accelerated Corrosion

FACrate = (1000*K*∆C +4.85)*10^3

I

II

III

Condition Stages

Stage 1 : >= 6.7

Stage 2 : 6.7< T <=6.4

Stage 3 : 6.4 < T <=6.1

Failure condition

27

0 1 2 3 4 5 6 7 8 9 10 115.45.55.65.75.85.9

66.16.26.36.46.56.66.76.86.9

7

Thickness vs Time

Time in years

Thick

ness

in m

m

Maintenance Scheduling IntervalAssumptions:1. 10% randomness in the variables

2. Initial Condition is 6.7 mm

3. Do nothing maintenance alternative

4. 10% failure probability

5. Both variables of line are randomized

Result:Time interval of Maintenace = 8.5 – 3 = 5.5 years

Time interval

Thank you!