Corrosion Inhibitors and Corrosion Inhibitor Selection.ppt · 2020. 6. 3. · Corrosion Inhibitors and Corrosion Inhibitor Selection Aberdeen, 15 th March 2011. Classification of
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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
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� 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
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� 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
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– the formation of micelles means less inhibitor at the metal surface
Two-phase System
Oil Phase
Interface
OILSOLUBLE
MOLECULESOIL
DISPERSED
MOLECULES
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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
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� 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
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� 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
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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
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– 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?
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– 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
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� 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
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� 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
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– 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
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� 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
– Ambient to 90 oC (194 oF)
– Linear Polarization Resistance
– Electrochemical Impedance
– Galvanic corrosion
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� Can be used to test:
– 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
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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)
– Ambient to 90 oC (194 oF)
– Linear Polarization Resistance
– Electrochemical Impedance
– Shear stress up to 80 Pa
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� Can be used to test:
– Shear conditions (
Dynamic RCE test graph
4
5
6
7
Co
rro
sio
n R
ate
(m
m/y
r)
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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
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� Can be used to test:
– 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
– Ambient to 90 oC (194 oF)
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� Can be used to test:
– 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
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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
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-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
– Ambient to 90 oC (194 oF)
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� Can be used to test:
– Inhibitor performance with solids
– Galvanic currents
Test matrix
Wheel TestBubble
TestRCE Test Weld Test
Under
DepositAutoclave
Product Screening � �
Partitioning � � � � �
Persistency � � �
CO / H S � � � � �
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CO2 / H2S � � � � �
High Shear �
Weld �
Solids �
High Temperature �
High Pressure �
Third party laboratories
Autoclave Flow LoopJet
Impinge
Microbial
Testing
H2S
ScavengerJIP
� �
� �
� � �
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� � �
�
� �
�
�
Criteria
� Performance
� Cost
� Environmental
� Material compatibility
– Brine, oil, other chemicals, elastomers, metals
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� 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
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– 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
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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
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� 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
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� 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
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