Transcript Parasitic consumption of corrosion inhibitor

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