Corrosion Inhibitors and Corrosion Inhibitor Selection.ppt · 2020. 6. 3. · Corrosion Inhibitors and Corrosion Inhibitor Selection Aberdeen, 15 th March 2011. Classification of

Corrosion Inhibitors and Corrosion Inhibitor SelectionCorrosion Inhibitor Selection

Aberdeen, 15th March 2011

Classification of Corrosion Inhibitors

� Scavengers - remove O2 and H2S

� Biocides - remove microbes

� Organic Film Forming - prevents corrosive substance interacting with metal

� Anodic - passivating, inhibits oxidation reactions

� Cathodic - inhibits reduction reactions

Integrity & Hydrocarbons Group, Oil & Mining Services, Application Development (Copyright Clariant. All rights reserved.)

� Vapour Phase - volatile inhibitors

Organic Film Formers

� Generally contain nitrogen, phosphorus, oxygen or sulphur polar groups

� Examples are amines, phosphate esters, imidazolines, betaines

� Polar group attaches to metal surface


� Hydrophobic end dispels water

� Changes wettability of metal surface

� This provides a barrier between the corrosive water phase and the metal surface

Colloidal Aspects

� Corrosion Inhibitors are SURFACTANTS

� They can form colloidal dispersions (MICELLES)

� Increased dose rate does NOT always equal increased corrosion inhibition

– the formation of micelles means less inhibitor at the metal surface


– the formation of micelles means less inhibitor at the metal surface

Two-phase System

Oil Phase

Interface

OILSOLUBLE

MOLECULESOIL

DISPERSED

MOLECULES


METAL SURFACE

Water Phase

Interface

WATERDISPERSEDMOLECULES

ADSORBEDFILM

OIL

FILM

WATERSOLUBLE

MOLECULES

Partitioning

� We want the inhibitor to partition into the water phase

� The partitioning co-efficient of the inhibitor can be derived experimentally

� This helps determine the suggested dose rate


� A change in water cut will require a change in dose rate

Water Cut (%) 90 20 10 5 2

Total Fluids Dose Rate to Give 30 ppm in Water Phase (ppm) 31.0 11.2 7.5 5.7 4.6

Formulating- Composition of a Corrosion Inhibitor

� Corrosion Inhibitor bases

– Can be combinations to achieve synergistic effects, or to protect against more

than one type of corrosion.

� Salting agents – MEA, GAA

– To make bases more water soluble

Solvents – Water, Glycols, Aromatics


� Solvents – Water, Glycols, Aromatics

– To improve viscosity, improve thermostability, alter dose rate, reduce cost

� Synergists – generally sulphur based

– To improve performance

� Other bases – anti-foams, demulsifiers, scale inhibitors, hydrate inhibitors

Project design

Field Modelling

Laboratory Test

Design

Field Trial

Deployment


Final Confirmation

by Laboratory /

Specialist TestingThird Party

Confirmation /

Specialist

Testing

Field Testing

Field TrialCorrosion Test

Techniques

Project design

� A full system review should be performed and a questionnaire completed

� Relevant system information includes:

– water chemistry (including organic acids)

– CO2 and H2S partial pressure = (mol% / 100) * total pressure

– system temperatures


– system temperatures

– production rates, pipeline diameters, flow regime

– materials used in the system

– sand production

– weld corrosion (galvanic corrosion risks)

Project design

� Other information required:

– are there any compatibility issues with other system chemicals?

– are there any environmental restrictions?

– is there a restriction on dose rate?

– are there any cost constraints?


– is a sample of the incumbent available?

– is oil in water or foaming a major concern?

– is an oil sample available?

Target corrosion rates

� mm/year, or mmpy (millimetre per year)

� mils/year, or mpy (milli-inches per year)

� 1 mm/year = 39.4 mils/year


� A combination of electrochemical techniques and coupon weight loss measurements

used to measure corrosion rate

� A low corrosion rate is considered as below 0.1 mm/year (4 mils/year)

Performance Requirements

� General (CO2) corrosion

� Pitting corrosion

� Sour (H2S)

� High temperature

� High pressure


� Under deposit

� Weld

� High shear

� Scale, antimicrobial, scavenger etc. in combined products

Standard techniques – wheel test

� Wheel Test

– 10 spaces available

– Ambient to 90 oC (194 oF)

– Weight loss coupons

– Microscope evaluation


– Ambient pressure

� Can be used to test:

– Inhibitor screening

– Partitioning

– Batch treatment

– Persistency

Linear Polarisation Resistance

� 2 or 3 electrode probe inserted into process system

� Electrodes are electrically isolated from each other

� A small potential is applied (up to 20mV) between the electrodes


� Resultant current is measured

� Polarisation resistance is the ratio of the applied potential and resulting current level

� Measured resistance is inversely related to the corrosion rate

Standard techniques – LPR bubble cell test

� Bubble Test


– Linear Polarization Resistance

– Electrochemical Impedance

– Galvanic corrosion



– Inhibitor screening

– Partitioning

– Persistency

LPR bubble cell test graph

4

5

6

Co

rro

sio

n R

ate

(m

m/y

r)

Crude Oil Added

Corrosion Inhibitor Added


0

1

2

3

0 2 4 6 8 10 12 14 16 18 20 22 24

Time (hours)

Co

rro

sio

n R

ate

(m

m/y

r)

50ppm CI 100ppm CI 75ppm CI

Standard techniques – dynamic RCE test

� Rotating Cylindrical Electrode (RCE)


– Linear Polarization Resistance

– Electrochemical Impedance

– Shear stress up to 80 Pa



– Shear conditions (

Dynamic RCE test graph

4

5

6

7

Co

rro

sio

n R

ate

(m

m/y

r)


0

1

2

3

0 5 10 15 20 25

Time (hours)

Co

rro

sio

n R

ate

(m

m/y

r)

Standard techniques – HP/HT Autoclave

� Autoclaves

– Maximum Temperature 350 oC (660 oF)

– Maximum Pressure 200 kgf/cm2 (2845 psi)

– Weight loss coupons or electrochemical



– High temperatures

– High pressure CO2/H2S

– Partitioning

– Localised corrosion (sour)

Specialised techniques – weld test

� Segmented Weld Testing

– Customised electrode fabricated specifically for individual projects

– Parents materials, weld consumables and welding technique specified




– LPR corrosion rate

– Galvanic current

– Partitioning

Weld test LPR corrosion rate graph

4

5

6

Co

rro

sio

n R

ate

(m

m/y

r)

Addition of 30 ppm MULTITREAT 9347


0

1

2

3

0 2 4 6 8 10 12 14 16 18 20

Time (hours)

Co

rro

sio

n R

ate

(m

m/y

r)

Weld HAZ Parent 1 Parent 2

Weld test galvanic current density graph

0.05

0.1

0.15

0.2

Cu

rren

t D

en

sit

y (

mA

/cm

2)

Addition of 30 ppm MULTITREAT 9347


-0.2

-0.15

-0.1

-0.05

0

0 2 4 6 8 10 12 14 16 18 20

Time (hours)

Cu

rren

t D

en

sit

y (

mA

/cm

2)

Weld HAZ Parent 1 Parent 2

Specialised techniques – under-deposit test

� Under Deposit Testing

– Developed in IFE JIP

– Deposit specific i.e. sand, FeS, scale




– Inhibitor performance with solids

– Galvanic currents

Test matrix

Wheel TestBubble

TestRCE Test Weld Test

Under

DepositAutoclave

Product Screening � �

Partitioning � � � � �

Persistency � � �

CO / H S � � � � �


CO2 / H2S � � � � �

High Shear �

Weld �

Solids �

High Temperature �

High Pressure �

Third party laboratories

Autoclave Flow LoopJet

Impinge

Microbial

Testing

H2S

ScavengerJIP

� �

� �

� � �


� � �

�

� �

�

�

Criteria

� Performance

� Cost

� Environmental

� Material compatibility

– Brine, oil, other chemicals, elastomers, metals


� System compatibility

– Foaming, emulsion, water quality

� Physical properties

– Viscosity, flash point, gunking

� Stability

– High temperature, low temperature

Secondary performance

� Includes:

– Emulsion tendency

– Foaming tendency

– Brine compatibility

– Chemical compatibility


– Thermal stability

– Elastomer compatibility

– Viscosity

– Flash point

– Residual analysis

A typical study

Product Stability

(Ambient)

Performance

< 0.1 mm/yr

Compatible

with incumbent

Foaming Stability

(low temp)

Viscosity Elastomer

Compatibilit

y

Cost

A PASS PASS PASS PASS PASS FAIL N/A N/A

B PASS PASS FAIL N/A N/A N/A N/A N/A

C PASS PASS PASS PASS PASS PASS FAIL PASS

D PASS PASS PASS PASS PASS FAIL PASS N/A


D PASS PASS PASS PASS PASS FAIL PASS N/A

E FAIL N/A N/A N/A N/A N/A N/A N/A

F PASS PASS FAIL PASS PASS PASS N/A N/A

G FAIL N/A N/A N/A N/A N/A N/A N/A

H PASS PASS PASS PASS PASS PASS PASS PASS

I PASS FAIL N/A PASS PASS PASS PASS PASS

J PASS PASS FAIL PASS PASS PASS N/A N/A

K PASS PASS PASS PASS PASS FAIL PASS N/A

L PASS PASS PASS PASS PASS PASS PASS FAIL

Summary

� Corrosion inhibitors are surfactants and partition between oil and water phases

� They inhibit corrosion by

– Removing factors that cause corrosion (O2, H2S, microbes, acidity)

– Forming films on the metal surface


� Formulating is required

� Products need to be tailored to suit specific applications

� Increased dose rate does NOT always equal increased corrosion inhibition

Summary Part II

� A full system review is essential to understand the corrosion risk and system

requirements

� A number of routine and specialised techniques are available

Third party evaluations may be necessary depending on the system conditions


� Third party evaluations may be necessary depending on the system conditions

� The correct choice of tests are essential and these are based on the system

conditions and requirements

� Secondary performance influences selection of inhibitor

Integrity & Hydrocarbons Group

Oil & Mining Services

Application Development

19.10.2010

Thank You!

Documents

Corrosion Inhibitors and Corrosion Inhibitor Selection.ppt · 2020. 6. 3. · Corrosion Inhibitors and Corrosion Inhibitor Selection Aberdeen, 15 th March 2011. Classification of