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Corrosion InhibitorsThe two corrosion inhibitors (designated "A" and
"B") selected for flowloop testing were evaluated at
concentrations of 100 and 250 ppm by volume.
Corrosion inhibitor "A" was a proprietary formulation
of sulfonated fatty acid alkyl amide polyamine alkylate and
isopropanol in hydrocarbon solvent. The hydrocarbon solvent
system contained the following: heavy aromatic solvent,,
ethylbenzene, naphthalene and xylene.
Physical characteristics of corrosion inhibitor "A"
include:
Form: Liquid
Color: Opaque to amber
Solubility in Water: Insoluble
Water dispersibility: Highly water dispersible
Specific Gravity: 0.93 @ 60 F. (15.60 C.)
Viscosity (ASTM D-445): 43 cst @ 75 F. (23.90 C.)
Pour Point (ASTM D-97): <-30 F. (<-34.40 C.)
PMCC Flash Point (ASTM D-93): 59 F. (150 C.)
Vapor Pressure (ASTM D-323): 61 mm Hg (1.036 psi) @ 100 F. (37.80
C.)
Corrosion Inhibitor "B" was a proprietary
"green" formulation. Green formulated production
chemicals are formulated to be more environmentally friendly.
Corrosion inhibitor "B" is an aqueous blend containing
an alkyl amino acid and ethylene glycol.
Physical characteristics of corrosion inhibitor "B"
include*:
Form: Liquid
Color: Clear, brown liquid
Odor: Geranium
Water Solubility: Water soluble
pH (@100%): 4.8 @ 20 C. (68 F.)
Boiling Point Range: 100 C. (212 F.)
Freezing/Melting Point: <-10 C. (14 F.)
Density: 1.056 gms/cm3 @ 15 C. (59 F.)
Viscosity (Cannon-Fenske): 66.30 cst @ 0 C. (32 F.)
28.40 cst @ 20 C. (68 F.)
Flash Point (PMCC): >105 C. (221 F.)
Vapor Pressure: <0.85 mm Hg (<0.0165 psi) @ 100 F. (37.8
C.)
* These are only indicative values supplied on the MSDS sheets by
the chemical supplier.Test ProceduresThe test specimens were polished to a 600 grit finish, degreased
and dimensions and weights were recorded. The degreased specimens
were mounted carefully in the flow loop test apparatus. The
deaeration of the test fluids were carried out in separate
reservoir containers. The autoclave and the flow loop were also
deaerated with ultra high purity nitroben prior to starting the
test. The test solution (synthetic seawater or brine/kerosene
mixture) was introduced into the autoclave by pumping. Once the
autoclave was 80 percent full (approximately 4 liters of fluid)
stirring in the autoclave and flowing in the loop was started.
The gassing and measurement procedures for calibration test and
for inhibitor evaluation tests are given below.The Calibration TestAt room temperature, CO2 was introduced slowly into
the autoclave and stabilized at 25 psig. The autoclave was then
heated to test temperature, 50 C. (122 F.) The pressure was
adjusted to psig at 50 C. (122 F.) The liquid flow in the loop
was adjusted to give a flow rate of 1.5 gpm which produced a wall
shear stress of 7 Pa (0.146 lbs/ft2). The corrosion
rates of 1018 steel specimens were measured in the reservoir and
laminar regions employing linear polarization resistance (LPR)
technique per ASTM G-59. The measurements were continued for a
duration of three days (65 hours). The Inhibitor Evaluation TestsThe autoclave was heated to test temperature of 150 C. (302 F.)
and the test gas was flowed into the autoclave to achieve the
test conditions: 0.075 psia (0.5 kPa) H2S; 75 psia
(0.54 MPa) CO2. The pressure and liquid flow through
the autoclave ( 30 ml/min) were maintained using a back pressure
regulator on the outlet of the autoclave and metering pumps at
the inlet. During the last three test series (100 ppm corrosion
inhibitor "A", 250 ppm and 100 ppm corrosion inhibitor
"B", the deaerated brine/kerosene mixture was saturated
with the test gas (0.1 percent H2S and the balance CO2)
before pumping into the autoclave.
Once the environment was established, the flow rate in the loop
was adjusted to produce a wall shear stress value that
corresponded to 10 ft/sec (3.05 m/sec) liquid flow in the 14.25
inch (36.2 cm) pipe in the field based on flow modelling
performed (see Table 3). The corrosion
rates in the uninhibited environment were measured on specimens
(X-65 and 0.5 percent Cr enhanced X-65) in the reservoir and
laminar flow regimes and on X-65 in the impingement regime using
the LPR technique.
Once the corrosion rates were stable, the inhibitor was pumped
into the autoclave to give a concentration of (1) Test 1 - 250
ppm, (2) Test 2 - 100 ppm (Corrosion Inhibitor "A"),
(3) Test 3 - 100 ppm and (4) Test 4 - 250 ppm (Corrosion
Inhibitor "B") based on total liquid volume. The
pumping rate of the inhibitor was then adjusted to maintain a
constant inhibitor concentration during the test. The corrosion
rates for the inhibited environment were measured at the above
mentioned locations at five different flow rates in the flow
loop.
The flow rates were selected to simulate 40, 60, 80, 100 and 120
percent of wall shear stress. Higher wall shear stresses were
measured later on during the study. At each flow rate corrosion
rates were monitored until stable values were reached. After
completing the initial sequence of measurements, the flow rate
was brought down to represent 100 percent of wall shear stress
value and corrosion monitoring was continued for a total of 2.8
days.
During the initial inhibitor evaluation test (Test 1 - 250 ppm
corrosion inhibitor "A"), the baseline corrosion rates
were monitored for 20 hours. However, it was noticed that
there was a tendency for iron carbonate filming and electrode
passivation after prolonged exposure to the non-inhibiting test
environment which interfered subsequently with the measurement of
inhibitor efficiency.
This effect was also noted in the earlier HP-HT Flowing Autoclave
Test work. Therefore,
the procedure was changed for the second flowloop test to monitor
the corrosivity of the non-inhibited environment for a shorter
duration (one hour) and proceed with the LPR measurements in the
inhibited environment (Test 2 - 100 ppm corrosion inhibitor
"A", Test 3 - 100 ppm corrosion inhibitor "B"
and Test 4 - 250 ppm corrosion inhibitor "B".)
Corrosion rate measurements were taken at flow rates which
corresponded to 40, 60, 100 and 120 percent of wall shear stress
value (velocity = 10 ft/sec for 100 percent t). The flow rate was then adjusted to
represent 100 percent of wall shear stress value and the
corrosion monitoring was continued for 40 hours. The corrosion
rate measurements were continued further at higher flow rates
which corresponded to 1-- - 865 percent of wall shear stress
value. The test was terminated after 2.8 days.
The test specimens were visually examined, cleaned with non
abrasive pads and weights were recorded. Input Data - Field
RHO
[kg/cu.m.] | I.D.
[cm] | Velocity
[m/s] | MU
[poise] | Reynolds No Re | Roughness
e/D | Friction factor
[f] | Tau
Pa | Tau
Lbs/sq ft | 691.04 | 36.2 | 3.05 | 0.001626 | 4692357 | 0.00014 | 0.013 | 41.78 | 0.872 |
Percent
TAU | TAU
Pa | TAU
Lbs/sq/ft | RHO
[Kg/cu.m.] | I.D.
[cm] | Velocity
[m/s] | MU
[poise] | Reynolds No.
Re | Friction
factor [f] | Velocity
[ft/sec] | Flow Rate
[gpm] | 100 | 41.78 | 0.872 | 967.61 | 1.27 | 2.13 | 0.002825 | 92738 | 0.019 | 6.99 | 4.28 | 40 | 16.71 | 0.349 | 967.61 | 1.27 | 1.28 | 0.002825 | 55790 | 0.021 | 4.21 | 2.58 | 60 | 25.07 | 0.523 | 967.71 | 1.27 | 1.61 | 0.002825 | 70016 | 0.02 | 5.28 | 3.23 | 80 | 33.42 | 0.698 | 967.71 | 1.27 | 1.91 | 0.002825 | 82947 | 0.019 | 6.26 | 3.83 | 120 | 50.14 | 1.047 | 967.71 | 1.27 | 2.4 | 0.002825 | 104373 | 0.018 | 7.87 | 4.82 |
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