Corrosion Rate Modelling

Educational Material from the IOM3

Energy Transition Group

The global network for the materials cycle

Introduction

• The Institute of Materials, Minerals & Mining (IOM3) is a major UK professional engineering institution, incorporated by Royal Charter, with over 15,000 members spread across the world.

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• This slide pack is part of a series of educational material produced by the Energy Transition Group to provide the Public with information on the production of oil and gas. The IOM3 accepts no responsibility for the contents of this slide pack.

INTRODUCTION

CO2 MODELLING SOFTWARE

HOW TO USE CALCULATED CORROSION RATE

A BIT ABOUT H2S CORROSION

O2 CORROSION MODELLING

SUMMARYSECTION B

2019 – DR MUHAMMAD EJAZ 3

AGENDA

This presentation covers• Carbon steel - not Corrosion Resistant Alloys• Linear corrosion mechanism (general corrosion) – not cracking

• Objective is to:

• Provide an overview of corrosion modelling• Avoid black box approach – “Computer says…..”• Use engineering judgment with numbers• Understand limitation of modelling

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Scope and Objectives

Corrosion Modelling covers complete life cycle of a plant• Design of new facilities

- Materials Selection(C-steel vs CRA)

- Corrosion barrier requirements(Inhibition, coating,CP etc.)

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Introduction

Introduction

Corrosion Modelling covers complete life cycle of a plant• Integrity Management

- React to changes in process conditions- New facility tie-in

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Introduction II

Corrosion Modelling for Oil and Gas

• CO2 Corrosion• H2S Corrosion• O2 Corrosion

• Anodic Reaction

Fe ↔ Fe2+ + 2e-

• Cathodic Reaction(s)

CO2 + H2O ↔ H2CO3 + 2e- ↔ H2 + CO32- (CO2 Corrosion)

O2 + 4H+ + 4e- ↔ 2H2O (O2 corrosion)

H2S ↔ 2H+ + S2- (H2S Corrosion)2019 – DR MUHAMMAD EJAZ 7

Oilfield Corrosion

2019 – DR MUHAMMAD EJAZ 8Illustration courtesy of http://duoline.blogspot.com/

CO2 CorrosionGeneral Corrosion Raindrop attack - gas condensate

Mesa-type corrosion

2019 – DR MUHAMMAD EJAZ 9Illustrations courtesy of octane.nmt.edu/

Types of Predictive Models

• Mechanistic- Formulated from quantitative knowledge of reactionthermodynamic and kinetics

• Empirical- Formulated from array ofexperimental measurements

• Semi-empirical- Mix of Above

2019 – DR MUHAMMAD EJAZ 10Illustration courtesy ofNACE Corrosion Handbook

Pioneering Work

De Waard and Milliams (Carbonic Acid Corrosion of Steel,1975)

log Vcorr = 5.8 - (1710 / (273 + T)) + 0.67 log (P𝑪𝑪𝑪𝑪𝟐𝟐

)

whereVcorr is corrosion rateT is Temperature, and P𝐶𝐶𝐶𝐶2

is partial pressure of CO2

(cathode reaction: H2CO3 reduction)

2019 – DR MUHAMMAD EJAZ 11Ref: C. DE WAARD, D. E. MILLIAMS, Carbonic Acid Corrosion of Steel, CORROSION. 1975;31(5):177-181

Partial pressure of a gas

• Partial pressure quantifies gas dissolved inwater at equilibrium- Total pressure * Mole fraction in gas

For example:For 0.1% CO2 in gas at pressureof 10 bara

P𝐶𝐶𝐶𝐶2

= 10 * 0.1 = 1 bara

- Ideal gas – Henry’s law

- Fugacity correction

2019 – DR MUHAMMAD EJAZ 12Ref: Bondos et. Al: Accurate corrosion prediction through an integrated approach, SPE 111430, 2006

Effect of acid gases on pH

• pH is function of- Partial pressure of acid gases

- Temperature

- Organic acid (Acetates)

- Formation water chemistrye.g., bicarbonate ion (HCO3

-)

- Formation water >~ 4.5

- Condensed water >= 3.5

2019 – DR MUHAMMAD EJAZ 13Ref: Corros. Sci. 1987, 27 pp. 1059–1070

Temperature – scale formation

• About 60 - 70°C carbonate scale start forming oncarbon steel surface

Fe + H2O + CO2 ↔ FeCO3 (Siderite) + H2

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De Waard & Milliams Nomogram

CRscale = CRfree x SF → Use a ruler to estimate corrosion rate

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Development of Predictive Model Software

Main inputs

• pH

• Scale

• Steel composition

• Glycol %

• Inhibition

• Wettability

• Organic acids (ppm)

2019 – DR MUHAMMAD EJAZ 16Ref: Joint industry projects at IFE 1998 – 2008 (EFC report in 2007/8)

NORSOK M-506 (2005)

• Input

• Limitations

• Output

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Comparison of Predictive models

ƒ Temperature ƒ pH

ƒ Pressure

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Illustration Ref: https://www.gateinc.com/gatekeeper/gat2004-gkp-2014-03

Using Predictive model out put

Corrosion allowance (mm)• Calculated corrosion rate x design life

If corrosion allowance is more than 10 mm for carbon steel –consider using corrosion resistant alloys (NORSOK M-001)

• Complete life cycle costanalysis with carbon steel+ inhibition

• Be aware of differentcorrosion rates (outputs)from different models

Carbon steel + inhibitor

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Example: Corrosion Allowance Calculation

p Corrosion Inhibitor 95% Pipe OD 219.1 mm 196.5 mm IDDesign Life 15 years WT 11.3 mm8" Production NDC ECE

Year Temperature PressureAverage Mol% CO2

Mol% H2S

Oil Flowrate

Water Flowrate

Gas Flowrate

pH Uninhibited Inhibited Inhibited

°C bara m3opd m3wpd sm3/d mm/yr mm/yr mm/yrPHACT BP93 DW93 BP95 DW95

1 1 67 73 6.50 0 2584 79 113267 4.4 0.8 1.2 0.9 1.0 20 1.1 0.11 11 67 73 0.89 0 2584 79 113267 5.3 0.2 0.3 0.2 0.2 2.7 0.2 0.012 1 67 73 6.50 0 3483 228 339802 4.4 0.8 1.2 1.2 1.4 23 1.2 0.32 11 67 73 0.89 0 3483 228 339802 5.3 0.2 0.3 0.3 0.3 3 0.2 0.13 1 67 73 6.50 0 1048 1984 339802 4.4 0.8 1.2 1.2 1.3 22 1.2 1.83 11 67 73 0.89 0 1048 1984 339802 5.3 0.2 0.3 0.3 0.3 3 0.2 0.44 1 67 73 6.50 0 911 2411 339802 4.4 0.8 1.2 1.2 1.3 23 1.2 1.84 11 67 73 0.89 0 911 2411 339803 5.3 0.2 0.3 0.3 0.3 3 0.2 0.45 1 67 73 6.50 0 804 2443 339802 4.4 0.8 1.2 1.2 1.3 23 1.2 1.85 11 67 73 0.89 0 804 2443 339803 5.3 0.2 0.3 0.3 0.3 3 0.2 0.46 1 67 73 6.50 0 578 2926 311485 4.4 0.8 1.2 1.2 1.3 23 1.2 1.86 11 67 73 0.89 0 578 2926 311486 5.3 0.2 0.3 0.3 0.3 3 0.2 0.47 1 67 73 6.50 0 470 3070 311485 4.4 0.8 1.2 1.2 1.3 23 1.2 1.87 11 67 73 0.89 0 470 3070 311486 5.3 0.2 0.3 0.3 0.3 3 0.2 0.48 1 67 73 6.50 0 340 3186 283169 4.4 0.8 1.2 1.2 1.3 22 1.2 1.78 11 67 73 0.89 0 340 3186 283170 5.3 0.2 0.3 0.3 0.3 3 0.2 0.39 1 67 73 6.50 0 291 3236 254852 4.4 0.8 1.2 1.1 1.2 22 1.2 1.79 11 67 73 0.89 0 291 3236 254853 5.3 0.2 0.3 0.3 0.3 3 0.2 0.3

10 1 67 73 6.50 0 240 3313 169901 4.4 0.8 1.2 1.0 1.1 21 1.1 1.610 11 67 73 0.89 0 240 3313 169902 5.3 0.2 0.3 0.2 0.3 2.9 0.2 0.311 1 67 73 6.50 0 196 3294 198218 4.4 0.8 1.2 1.1 1.2 22 1.2 1.611 11 67 73 0.89 0 196 3294 198219 5.3 0.2 0.3 0.2 0.3 2.9 0.2 0.312 1 67 73 6.50 0 164 3382 198218 4.4 0.8 1.2 1.1 1.2 22 1.2 1.612 11 67 73 0.89 0 164 3382 198219 5.3 0.2 0.3 0.3 0.3 2.9 0.2 0.313 1 67 73 6.50 0 154 3404 198218 4.4 0.8 1.2 1.1 1.2 22 1.2 1.613 11 67 73 0.89 0 154 3404 198219 5.3 0.2 0.3 0.3 0.3 2.9 0.2 0.314 1 67 73 6.50 0 135 3442 198218 4.4 0.8 1.2 1.1 1.2 22 1.2 1.614 11 67 73 0.89 0 135 3442 198219 5.3 0.2 0.3 0.3 0.3 2.9 0.2 0.315 1 67 73 6.50 0 121 3472 198218 4.4 0.8 1.2 1.1 1.2 22 1.2 1.615 11 67 73 0.89 0 121 3473 198219 5.3 0.2 0.3 0.3 0.3 2.9 0.2 0.3

4.3 6.2 5.0 5.3 4.8 5.9Required corrosion allowance

M-506

Cassandra Norsok

Inhibited Rate mm/yr

Basic Flow-sensitive

4.3 6.2 5.0 5.3 4.8 5.9Required corrosion allowance

Flow regimes in horizontal pipe

Example of steady-state flow regime map for a horizontal pipe.Superficial liquid velocity VL vs superficial gas velocity VG.

2019 – DR MUHAMMAD EJAZ 21Illustration Ref: http://www.drbratland.com/PipeFlow2/chapter1.html

Flow regimes play a critical role where inhibition is required or condensation may occur

Exploiting Output – Inhibition categorisation

B. Hedges, D. Paisley and R. Woollam, “The corrosion inhibitor availability model,” in Corrosion 2000. 2019 – DR MUHAMMAD EJAZ 22

H2S corrosion

H2S RegimeSour

pCO2 / pH2S = 20

pCO2 / pH2S = 500CO2 + H2S RegimeMixed

CO2 RegimeSweet

pCO2

pH2S

Losses typically localised corrosion.

Localised corrosion generally lower than rate predicted by CO2model.

CO2 model applies.

Carbon and low alloy steels

2019 – DR MUHAMMAD EJAZ 23Ref: NACE Corrosion Conference 02235, 06122 and 09564

Fe2S passive layer

CO2 only Corrosion rate

Fe2CO3 is protective scale above ~60C.

Fe2S is semi-protective layer and does not provide corrosion inhibition. This leads to localised corrosion.

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NACE Logigram

Metallurgy and Corrosion Control in Oil and Gas Production by Robert Heidersbach, 2011

Corrosion Modelling for Oil and Gas - II

• O2 Corrosion• Corrosion Product:

Geothite – FeO(OH)Hematite – Fe2O3

Magnetite – Fe3O4

Ferous Hydroxide – Fe(OH)2

• Anodic Reaction

Fe ↔ Fe2+ + 2e-

• Cathodic Reaction(s)

O2 + 4H+ + 4e- ↔ 2H2O (O2 corrosion)2019 – DR MUHAMMAD EJAZ 26

O2 Corrosion

Where:Co is the oxygen concentration in ppb,Uo is the fluid velocity in m/s,Re is the Reynolds number,Pr is the Prandtl number

(temperature dependant), andCr is Corrosion rate in mm/y.

Where:VCORR is the oxygen corrosion rate in mm/y,U is the fluid velocity in m/s [assumed U=1 if U<1],CO2 is the oxygen equivalent in ppm, andT is temperature in °C [assumed T=30 if T<30].

2019 – DR MUHAMMAD EJAZ 27OST and Salama Fischer O2 corrosion model. Graph Ref: Corrosion 960593 K.P. Fischer et al.

Summary

Various Corrosion prediction models are available

• Use corrosion prediction model with care andengineering judgment should always be applied.

• Always challenge and sense check the out put - Don’talways believe what “Computer says………..”.

• Understand the limitation of predictive models andcompare results from at least two models.

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