Parasitic consumption of corrosion inhibitor
at the surface of emulsion droplets
in multiphase flow
Competence building project with
user participation (KMB).
Cooperation between IFE and NTNU
Organisation
• Cooperation IFE – NTNU
- IFE Materials and Corrosion Technology
• Kjell Ove Kongshaug, Research Scientist
• Egil Gulbrandsen, Research Scientist (project leader)
- NTNU Ugelstad laboratory
• Magne Knag, Dr.student
• Johan Sjøblom, Professor
Funding
- Budget: 6 MNOK
Duration: 2002-2005
- Funded by:
• Research Council of Norway (80%)
• ChevronTexaco
• Clariant Oil Services
• Conoco
• Dynea Oil Field Chemistry
• EniAgip
• Norsk Hydro
• Ondeo Nalco
• Saudi Aramco
• Statoil
• TotalFinaElf
Background
• Internal corrosion of carbon steel pipelines
- Produced water + CO2 ( + H2S)
- Worst case corrosion rates can be many mm per year
• Solutions:
•
•
•
•
corrosion inhibitors
corrosion product films
“pH stabilisation”
corrosion resistant materials
Properties of CO2 corrosion inhibitors
• Blends of different compounds
- Commonly amphiphilic molecules with nitrogencontaining polar head groups (cations)
• E.g. amines, quarternary ammonium salts, imidazolines
• In some cases anionic head groups (e.g. phosphates)
• Hydrocarbon chains C12-C20.
- Surfactants
- Inorganic salts
- Solvents
Distribution of corrosion inhibitor
•
Hydrocarbon phase
•
 Water phase
•
 Pipe wall
•
 Other
surfaces/interfaces
- Emulsions (dispersions)
- Solid particles (fines)
- Bubbles / foam
•
Chemical conversion
“Parasitic consumption” by surfaces etc.
• Potential corrosion risk by reducing inhibitor
concentration in water phase
- Corrosion failure:
• Safety and environmental issue
• Company reputation
• Replacement cost and lost production
• Excessive dose rates
• Emission of corrosion inhibitor important contributor to
“Environmental Impact Factor” in many fields
Accumulation of corrosion inhibitor at oil
water interface
•
Water phase
•
Hydrocarbon phase
Factors determining how much inhibitor
accumulates at surfaces
• Affinity for surface/interface
• Surface area available (m2/litre)
- Area per particle / droplet
- Number of particles / droplets
Formation and breakdown of emulsions
•
Formation by shear forces
- Choke valves, pumps, turbulent flow
• Shear rate, viscosity differences, interfacial tension etc.
•
Breakdown mainly by
-
Flocculation
Coalescence
- Temperature and salt content important factors
•
Sedimentation / creaming
Minimum half-life of emulsions
Fast flocculation theory – Brownian motion
Droplet
radius (um)
Volume fraction
0.1 %
1%
10%
0.1
760 ms
76 ms
7.6 ms
1
760 s
76 s
7.6 s
10
210 h
21 h
2.1 h
Emulsions can thus have substantial life-time
even if it is ”unstable”
Example calculation
• Inhibitor blend: 30 % actives, 350 g/mole
• 1 m2 surface area per litre
• 50 Å2 / molecule (typical range 20-100 Å2 / molecule)
• Depletes ca. 3 ppm of inhibitor blend
- Typical dose rates: 30-50 ppm in water phase
Thus: potential problem when surface area exceeds
1 m2 surface per litre (order of magnitude)
Volume fraction of oil in water
How much inhibitor accumulates at oil
droplets ?
1E+0
1E-1
1E-2
1E-3
30 ppm
1E-4
10 ppm
3 ppm
1E-5
1E-7
1E-6
1E-5
Oil droplet radius / m
1E-4
Objectives of the project
•
Identify the factors that control the parasitic consumption
of corrosion inhibitor at the surface of emulsion droplets
•
Generate fundamental experimental information on the
subject
•
Increase our competence on the interaction between
corrosion inhibitor and emulsions
•
Increase our competence on the effect of crude oil
components on CO2 corrosion and its inhibition
•
Contribute to long-term development of competence
(Ph.D. study)
Challenges
• Development of experimental apparatus for testing
inhibitor consumption at emulsion surfaces.
• Controlled production of emulsions & characterisation
• Sampling and analytical techniques for determination of
inhibitor residuals
• Inhibitor performance testing
• Determine the parasitic consumption of inhibitor
• Order of magnitude – potential inhibition problem or not
•
Effect of x, y z ….
Scope of work - NTNU
• Ugelstad laboratory NTNU:
- Fundamental surface science of corrosion inhibitors at
oil-water and water-steel interface:
• Model inhibitor compounds (quaternary ammonium salts)
• Tensiometry
• Quarts crystal microbalance (Fe and Fe3C)
• Atomic force microscopy
- Emulsion characterisation
• Model oil
- Retention model: oil / water / o-w interface / steel
Example results – NTNU
Quarts crystal microbalance – Fe substrate
Example results – NTNU
Quarts crystal microbalance – Fe3C substrate
Scope of work - IFE
• Electrochemical studies
• Electrochemistry with inhibitor at Pt, Fe and Fe3C
• Model inhibitor compounds and commercial products
• Corrosion inhibitor performance studies in presence
of emulsions
• Emulsification technique
• Model oil and real crude oils
• Inhibitor performance test method
Inhibitor performance tests at IFE
Emulsion formation by CO2 gas driven spray
nozzle
•
Advantages:
- Simple, no rotating parts
- Prevents O2 ingress
- Ex-proof
•
Disadvantages:
- Poorly characterised
emulsion.
- Loss of solution (fog)
•
Further work:
- Membrane emulsification
technique
Example results – IFE
Test
no.
Inh
PCO2
(bar)
pH
%
NaCl
Oil
(oC)
T
%
Oil
60
0.8
4.5
1.0
Shellsol D70
10
Inh x
8
50
70
Corrosion rate (mm / y)
7
100 ppm
Tros F
6
5
microcor
4
Spray nozzle
(10 min)
LPR
3
2
1
0
0
20
40
60
80
100
Time /h
120
140
160
Example results – IFE
Test
no.
Inh
I1
10
Corrosion rate / (mm/y)
T
(oC)
60
0
PCO2
(bar)
0.8
pH
%
NaCl
1.0
4.5
Oil
%
Oil
10
Shellsol
D-70
30 ppm Inh I1 (water dispersed)
1
Spray nozzle (10 min)
Spray nozzle (10 min)
0.1
0.01
0
20
40
60
80
Time / h
100
120
140
160
Corrosion / inhibition tests with emulsions
- Impinging jet apparatus
Flowmeter
Rotameter
O2
CO2
pH
Ref.
CO2
3 mm ID
316 L pipe
Luggin capillary
Jet
Centrifugal
pump
(tor) D:/IFE/KIP/JET.DSF
Counter electrode
Jet nozzle
specimen
Corrosion rate vs. Time with
Inhibitor F (o/w emulsion)
Corrosion rate / (mm/y)
100
jet velocity 5 m/s
no oil
oil
no oil
10
1
0.1
0
5
10
15
20
25
Time / h
30
35
40
45
Corrosion rate vs. Time with
Inhibitor E (o/w emulsion)
10
Corrosion rate / (mm/y)
3 m/s
No oil
oil
no oil
1
0.1
0.01
0.001
0
20
40
60
Time / h
80
100
120
Benefits to the industry
• The information may support and simplify:
- the analysis of inhibition failure cases
- interpretation of laboratory test results
- the identification of potential inhibition problem areas
in advance
- the selection of materials (through documentation of
critical factors for inhibitor performance)
- the development of improved inhibitor products
- optimisation of inhibitor dose rates
- understanding
chemicals
material
balance
of
production