numerical simulation of flow- induced … simulation of flow-induced corrosion damages kaushik das,...

NUMERICAL SIMULATION OF FLOW-INDUCED CORROSION DAMAGES

Kaushik Das, Debashis Basu and Todd Mintz

Center for Nuclear Waste Regulatory Analyses ®

Southwest Research Institute®

San Antonio, TX, USA

ANSYS Regional ConferenceAugust 31 - September 1, 2011 Houston, TX

OUTLINE

2

• Introduction

• Description of the Simulation Test Cases

• Results and Discussions for Test Case-1

• Results and Discussions for Test Case-2

• Summary

2011 ANSYS Regional Conference Houston, TX

INTRODUCTION

3

• Background

• Flow Assisted Corrosion Mechanism

• Species Concentration: Role of Hydrazine

• Objective


BACKGROUND

4

Ruptured Condensate Feedwater Pump Pipeline at Mihama 3 Nuclear Power

Plant (Source:” International Atomic Energy Agency, Erosion Corrosion Including FAC and EAC Issues in Nuclear Power Plants.” 2003)

• Considered a major Contributor to Pipeline Integrity

• Power Plant Components• Pipelines

• Significant Accidents in Power Plants 2005 Mihima-3; Kansai Electric Power

Company 1999 Tsuruga-2 : Japan Atomic Power

Company 1986 Surrey-2: Dominion Power

• Petrochemical Industry and Pipelines Significant Loss Due to Downtime and

Maintenance


FLOW ASSISTED CORROSION MECHANISM

5

• Flow Assisted Corrosion Diffusion of Corrosive Agent to

Metal Electrochemical Reaction on Metal

Surface Effect of Solid Particles

• Influenced by a host parameters• Temperature• Chemical Condition (pH)• Localized Species Concentration• Pipe Geometry and Material• Flow and Phase Condition Base Metal

Inner OxideLayer

Outer OxideLayer

Species Boundary Layer

Diffusion of Corrosive

SpeciesRelease of Base Metal

Fluid Shear Erosion

Erosion Due to Particle Impact

Base Metal Inner OxideLayer Reaction

Fluid Outer OxideLayer Reaction


SPECIES CONCENTRATION : ROLE OF HYDRAZINE

6


• Reduced Use in Fossil Fuel Power Plants• Used in Nuclear Power Plants• Primarily Used as Oxygen Scavenger

Stabilizes pH Acts as Alkalinizer Reduced Stress Corrosion Cracking (SCC) in Steam Generator Tubes

• Hydrogen-Hydrazine Co-injection in BWR Primary Coolant for SCC Reduction

• N2H4-O2 Reaction Important for Corrosion Condition Calculations

Affects Species Concentration Affects Electrochemical Corrosion Potential (ECP) Oxidation at Base Metal Form Protective Magnetite Layer

OBJECTIVE

7

• Part of Ongoing Research on Development of CFD Modeling Framework to Assess Erosion-Corrosion Damage Supplement System Level Corrosion Analysis

• Presented Study Computational Assessment of Existing N2H4-O2 Chemistry Models

Reaction Kinetics Inclusion of Surface Reaction

Simulate Reaction And Wall Mass Transfer in U-Bend Pipe Component

• Assess Effect of Turbulence Models in Wall Mass Transfer


DESCRIPTION OF THE SIMULATION TEST CASES

8

• Case-Study-1: Straight Pipe• Case Setup• Description of Chemical Kinetics• Assumptions and Simulation Conditions

• Case-Study-2: U-bend Pipe• Case Setup• Model Development and Assumptions• Mass Transfer Calculation Method


CASE-STUDY-1 SETUP

9


• Based on Experimental Study of Ishida et. al.• ANSYS-FLUENT® Solver Version 12.1 Used

Experimental Setup

Computational Domain

Computational Grid at a Cross Section

DESCRIPTION OF CHEMICAL KINETICS

10

• Baseline Reaction N2H4 + O2-→ N2 + 2H2O

• General Expression of Reaction Rate

• Arrhenius Rate

• Inclusion of Surface Effect

• Experimental Rate Determined Through Experimental Study of Ishida et al. Dickinson et. al

n2m

42422 OHNk

dtHNd

dtOd

RTE

expkk a0

surfacebulkeffective kr2kk


SIMULATION CONDITIONS AND ASSUMPTIONS

ASME 2011 Pressure Vessels & Piping Division Conference11

• Baseline Reaction: Kinetics of Ishida with PTFE Pipe

• Effect of Surface Based on Averaged Overall Reaction Kinetics

Ishida with CS Pipe Dickinson with CS pipe

Based on Zonal Approach PTFE Pipe Rate at bulk Metal Pipe rate near wall

Mixing Between

Zones

Near Surface Reaction= Based on Experiment

with CS/SSPipe Wall

Bulk Flow

Zone of Surface

InfluenceInlet Outlet

Bulk Flow Reaction= Based on Experiment

with PTFE

• Adiabatic Wall• Effect of Surface

Averaged Overall Reaction Kinetics: Infinite Mixing Rate

Zone Based Approach: 25% of Volume Affected by Surface

CASE-STUDY-2 SETUP

12

• U-bend Pipe Encountered Frequently in

Pipelines and Powerplants Experimentally (Chang et al.)

and Numerically Studied (Keating et. al)

1.38 m

253.65 m

44.5 × 44.5 mm

Wall Thinning and ErosionCorrosion Damage in

Evaporating Tubes(Source:”Guidelines on Pipe

Wall Thinning” Class NK Sept 2008)


MODEL DEVELOPMENT AND ASSUMPTIONS

13

• ANSYS-FLUENT® Solver Version 12.1 Steady State Turbulent Flow Shear Stress Transport (SST) k-ω model

• Laminar Finite Rate Chemistry Model Turbulence-Chemistry Interaction Neglected Effect Retained in Species Calculations through Turbulent Schmidt Number Further Studies should include Eddy Dissipation Concept Model

• Adiabatic Walls• Experimental Reynolds Number : 5.67×104

• Compressed Liquid: Inlet Temperature 280o C and Pressure 80 MPa• Inlet Concentration of Oxygen: 700 ppb

Schmidt number 520


WALL MASS TRANSFER CALCULATION METHOD

ASME 2011 Pressure Vessels & Piping Division Conference14

• Adapted the Method of Keating et al.• Assumptions include

Mass Transfer Controlled by O2 Diffusion Formed Oxide Layer Dissolves

Instantaneously Effect of Electrochemical Reaction not

Considered• Mass Transfer Calculation Implemented as

User Defined Function (UDF)

nDρJ 2

2

omixo

Base Metal

O2 Species Boundary Layer

Diffusion of Corrosive

SpeciesRelease of Base Metal

Erosion Due to Particle Impact Removes

Oxide layer

Base Metal Fluid Interface Reaction Complete Consumption of O2

2

2

Ob2

om MW

1OJ

k

• Diffusion Flux:

• Mass Transfer Coefficient:

• Sherwood Number: D

dkSh m

RESULTS AND DISCUSSIONS FOR TEST CASE-1

15

• Baseline Simulation, PTFE Pipe Velocity and Species Concentration for Baseline Comparison of Experimental and Computed Inlet to

Outlet N2H4 Concentration Ratio• Effect of Wall Averaged Overall Reaction Kinetics

Concentration Ratio CS Pipe

Zone Based Model Concentration Ratio

VELOCITY AND SPECIES CONCENTRATION DISTRIBUTION

16

Axial Velocity Distribution along Pipe Midsection (m/s)

Comparison Of Computed Velocity Profile With

Analytical Solution at InletMolar Concentration Of N2H4

[KMol/m3] along Pipe Midsection


BASELINE N2H4 CONCENTRATION RATIO COMPARISON

17

• Baseline Simulation, PTFE Pipe• Reaction Kinetics of Ishida et al.• Deviation Due to Thermal Effects

Inlet Concentration[N2H4]inlet

Outlet Concentration[N2H4]outlet


AVERAGED OVERALL REACTION KINETICS RESULTS FOR CS PIPE

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• Effect of Surface Dominates • Less Effect of Surface Heat Transfer

Concentration Ratio for CS pipe with Average Kinetics of Dickinson et al.

Concentration Ratio for CS pipe with Average Kinetics of Ishida et al.


ZONE BASED REACTION KINETICS CALCULATION

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• Averaged Approach Provides Better Match

• Depends on Definition of Zone of Influence Estimated 25% of Total

Volume

• Stability Issues Due to Discrete Zone Dickinson CS Surface


RESULTS AND DISCUSSIONS FOR TEST CASE-2

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• Velocity Distribution

• Species Concentration Distribution

• Mass Transfer Rate Distribution Ratio of Sherwood Number with and without Reaction Along Three Lines in the Pipe


VELOCITY CONTOURS

21

• Evolving Secondary Flow• Recovery on Downstream Leg• Generated Mostly Due to Lateral Curvature

Axial Velocity Profile Along YZ Plane

Radial and Tangential Velocity Magnitude at

different Cross Sectional Locations


SPECIES CONCENTRATION CONTOURS

22

• Species Concentration BL an Order of Magnitude Smaller than Hydrodynamic BL

• Y+ = 0.1• Total Mesh points=1.5 million

Species Concentration in Mid YZ Plane

Near Wall Species Concentration

Hydrodynamic and Species

Concentration Boundary

Layer

MASS TRANSFER RATE DISTRIBUTION

23

Locations Along The U-bend Wall Used In Mass Transfer

Rate Calculations

Inlet Section

U Bend Section


SELECTION OF TURBULENCE MODELS: COMPARISON WITH EXPERIMENT


Axial Velocity (W/Wb) Radial Velocity (VR/Wb), TKE (TKE/WB2)

EFFECT OF TURBULENCE ON CORROSION RATE DISTRIBUTION


Locations Along The U-bend Wall Used In Corrosion Calculations

Inner Wall Centerline Outer Wall Centerline Top Wall Centerline

y

z

Outer Line

Inner Line

Top Line

?

SUMMARY

26

• A Two Part Study to Simulate Flow and Chemistry in NPR Secondary Coolant Pipelines

• In Part-1 Used Experimentally Obtained N2H4-O2 Reaction Kinetics in Numerical Simulations Baseline Simulation without Wall Effect Study Effect of Wall

Overall Averaged Kinetics Provide Better Results

• In Part-2 Simulated a U-Bend Pipe Mass Transfer Calculation Based on Simple Diffusion Based Model

Minimal Variation at the Inlet Section Significant Impact of Secondary Flows at the Bend

Choice of Turbulence Model Important• Affects Corrosion Rate Predictions


numerical simulation of flow- induced … simulation of flow-induced corrosion damages kaushik das,...

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