Paper No.
8
USE OF THE FSM TECHNIQUE IN THE LABORATORY TO MEASURE
CORROSION INHIBITOR PERFORMANCE IN MULTIPHASE FLOW
Andrew M.Pritchxrd and Philip Webb
PIC
AEA ‘kiulOiogy
552 Harwell
Oxfordshire, U.K. OX1 10RA
HaraldHorn
COrrOceana.a.
Teglg&rden
N-7005 Trondheim, Norway
ABSTRACT
Two-phase flow in pipelines, particularly slug flow, induces high shear stresses at the walls that can interfere
with the performance of mrrosion inhibhx. Conventional eleztmchernical techniques are poorly suited to making
corrosion measurements under these conditions in the laboratory. The introduction of electrical resistance or other
corrosion probea can disturb the flow pattern. The paper describes the adaptation of m electrical resistance mapping
technique”to evaluate the performance of corrosion inhibitors in &fined two-phase flow regimes in thin-walled (1 mm)
tubes in the laboratory over periods of the order of 24 h, providing on-line irrfornrationin pipeline geometries se a
function of circumferential position. No plastic hernicylindricaljackets were designed and manufacturedwith 24 pairs
of spring loaded pins to contact the outside surface of the tubular test specimen and rneasummetal 10SSthrough changes
in the voltage between them when a currentwas passed through the specimen. Tests were carried out in slug flow with
and without corrosion inbibitorx in deoxygenated 3 w% NaCl brine under 1 bar C02 pressure using sqrecimene
nuumfacturedfrom the wall of an X-65 pipeline steel. A sensitivity of 0.1 %of wall thickness was demonstrated (1 pm
metal loea with a 1 mm wall). Good agreement was obtained between corrosion rates measured by thiS method and
weight loss and chemical analysis of corrosion products.
“ The Field Signature Method (FSM) or Electric Fingerprint, CorrOceanas., Trondheim, Norway.
Keywords:
corrosion inhibitor, inhibitor efficiency, field signature method, two-phase flow, slug flow, brine,
carbon dioxi&, sensitivity, inhibitor test method
INTRODUCTION
Fluids consisting of mixtures of different phases are ofin encountered in industry, and the different corrosion
rates of materials in contact with the different phases and at their interfaces are familiar in many stagnant situations.
Similar differences can be observed for rnixtureaof fluids in motion, but in this case tbe environment experienced by
Copyright
01998 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole must be made in writing to NACE
International, Conferences Division, P.O. BOX 218340, Houston, Texas 77218-B340. The material presented and the views expressed in this
paper are solely those of the author(s) and are not necessarily endorsed by the Association. Printed in the U.S.A.
materials depmds upon the flow pattern prevailing, which is determined by the vessel geormtriea, the physical
P-=
of ~ phMOS~ ~ OPPIW@@C
b~,
the proportion of each phase in the flow, and the auperticial
velocities (the velocities of the phases if they wem to occupy the whole cross-section of the pipeline) of each phase.
Differed fknv ccmditinnsalso affect mass transportand the fluid forces at the interface between the wall and the fluids,
which respectively influence the forrnntionand removal of protective inhibitor layers. Account has to be taken of all
these factors in modelling and mewuring corrosion in multiphase systems. It is particularly important that the corrosion
mmmring technique does not affect the flow pattern by introducing changes in local geondry, such as through the
introduction of electrodes that are not flush with the vessel surface.
One area of particularconcern is the control of corrosion in multiphaaepipelines, which are increasingly being
favoured in the oil and gas production industry for the transportof produced fluids from well heads to a gathering head
for sepamtion, to reduce the cost of building sepamte treatmmt facilities. Liquids may alsa be pmaent in gas pipelines
as the result of rnaltimctioning of sepamtors, injection of corrosion inhibitors, or condensation on the pipe wall. As in
the general case, the flow pattern adopted &penda upon the relative amounts and superficial velocities of the
COmPOO~tS,~ ~Y vw depending upon the local geometry of the pipeline, such as changes in inclination to the
horizontal, cross sectional area and other features.
Corrosion of pipelines is otlen controlled by the injection of inhibitom. Formation and maintenance of an
inhibitor film may be strongly influenced by the flow pattern in a pipeline, so that the selection of an inbibltor must
take account of its performanceunder all the flow conditions expected to be encountered. The range of two-phase gasliquid flow patterns in pipe flow is fairly well un&rstood, and wn be predicted from a knowledge of the properties of
the fluids at the appropriatetemperature, and their superficial velocities.
Many techniques for measuring the effici.mcy of inhibitors in single phase flow have limited applicability to
two-phase flow. Electrochemical techniques require the continuous presence of a layer of electrically conducting fluid
to reduce solution resistance and make electrical contact betweem reference, working and counter-electrodes, and are
thus unusable where the surface is covered by a non-conducting fluid, or by a thin layer of a conducting one, as in
annular flow. Fluctuations in the electrical properties of the fluid mixture associated with the flow may complicate the
interpmtatim of electrochemical measurements. Thin-layer activation techniques can provide very sensitive on-line
measurementsof material loss by a variety of mechanisms, but are usually limited to one relatively small area, require
~ial
facilities for activating the sample, and are not applicable if the products of corrosion am not removed from the
surface.
Electrical resistance probes can provide high sensitivity, but use of these or electrochemical probes to
investigate corrosion in two-phase flow quirea the provision of access fittings rather than a spool piece. Although
careful design of the probes should avoid disturbancesto the flow, there is still a risk of crevice corrosion.
This paper describes the novel application and development of a non-intmsive corrosion measuring system (the
Field Signature Method (FSM)l), which is well established in the field, to laboratory measurements of corrosion
inhibitor performance in two-phase flow in brine-carbondioxide mixtures.
CORROSIONMEASUREMENT SYSTEM
General
The non-intrusive multiple electrical resistance measurementused in this work was originally developed as an
on-line method of monitoring changes in the electrical resistances between individual pins in an array, fixed to a
structure. From the differed measurementsand a knowledge of the geometrical placement of the pins, a picture of the
changes could be built up that allowed deductions to be made about general corrosion or erosion and localised corrosion
such as pitting, and cracking of oilfield installations such as export pipelineal.
At chosen intervals a dkect current at a low voltage is passed between lwo fixed points through the pipe wall
for a short time, and the voltagea between a number of pairs of electrodes fixed to the wall between them are
measured. Changes in the voltages due to changes in resistance can then be related to deterioration pmcessea. In most
field applications the electrodes are welded directly to the outer surface of the pipe. Data are collected over long
periods and analysed to provi& measures of corrosion.
812
Development of a I&matory system
For laboratory corrosion inhibitor teats, &ta must be produced over much shorter timescales than in the field,
where the technique has demonstrated its ability to provide on-line real-time longer term metal loss trends with an
awuracy comparableto conventional nondeatnrctive testing measurements. The technique’s typical sensitivity of 0.1 %
changes in electrical ~istance is comparable to that of conventional electrical resistance probea, so that chauges in
Wall tbicknesaofo.1% Csnberneammd. It avoids the disadvantages associated with the use of a conventional probe,
such as the need form acceas fitting and possible associati crevice corrosion, as well as any disturbance to the flow.
To reduce the absolute amount of metal loss that could be detected, and thus to allow corrosion rates to be
mmsured over a shorter titie,
a tubular specimen with a wall thickness of 1 mm was designed, allowing a metal
loss of lpm to be meaured. Over a period of 24 brs this loss gives a resolution in corrosion rate of 14.4 mpy or
0.365 rmnlyr, or correspondingly less if the period of measurement is increased, as was nweasary for efficient
inhibitors. Welding the sensing pins to such a thin wall would be likely to lead to lccal changea in its metallurgical
structure, and thus its corrosion resistance. A sensing pin jacket was therefore designed and made in two semicylindrical halvea from M electrically insulating plastic that fitted around the tube. The split sleeve design allows the
user to replace the tube without having to replace the pin sensing system. There are three rows of pairs of gold-plated
1.3 mm diameter spring-loaded pins around the cinmnference of the jacket, one in the middle and one at each end.
Each row consists of eight pairs of pins equally spaced around the diameter. Eight circumferential messurernems of
wall thickness reduction could thus be made at three positions along the teat specimen. The separationbetween each pin
in a pair was 4 mm. A drawing of thejacket is shown in Figure 1.
Currentconnections to the tubulartest piece are soft-soldered on to the enda. A reference plate is comected in
series with the specimen and used to correct for temperatureand currentfluctuations. The layout of the pins and of the
reference plate is shown in Figure 2.
The primary control unit of the system is a Direct Current Feed Module (DCF Module) that provides the
curremtto the replaceable tube. It has a programmableMenu Selection keyboard and LCD Window. The Menu Screen
is used for establishing both the type and tkequencyof readings as well as a variety of system operations and functions.
The Module automatically records the reading for each pin pair each tim a measurement current is passed through the
teat tube. It contains an internal storage capability so that readings maybe stored prior to transferto tiles in a PC.
Data display
Data is regularly transferred from the Module to a PC, where it interpreted and displayed by the system
software, which allows remote control of the DCF Module and automatic down loading of readings. A menu system
with screen selection windows allows the data to be displayed in a number of formats, reports printed, time trend
analysis provided, and historical data files stored.
System operation
Base line signature voltages AOand BOacross each electrode pair A and the reference plate B are measured at
time t= Ofor all the pin pairs, md the corresponding values At and B, at time t= t. The same current passea through the
specimen and the reference plate, so that
(1)
AO=i RMaod BO=i RM
aod since the resistances Rm between the pins and ~
tm,
of the plate are inversely proportional to the thiclcmwseatm and
(2)
BO/AO= I$JRM = tJtw
813
Since the baseplate isofthe samernaterial asthespecimem andatthe sarmternperature, changes inreaistance dueto
drills in kqwmtum or current with time am compematd for by meaaming their mtio, from which the Fingerprint
Coefficient FC for each pin pair in parts per thmsand of wall thickness is calculated
FC = 1000 [(BO/AJ.(A,/BJ - 1]
= 1000 [(tM/tJ.(tJtAJ
(3)
- 1] = 1000 [(tM/tJ - 1]
(4)
since the base plate does not corrode and its thickness therefore does not change.
Assuming that the weight loss of material WL~ betwwm a pin pair is proportional to the change in thickness,
this is calculated by the software in terms of the imtial weight Wititid from FC, as determined from the mwaured
Voltagex
Wk
=
[1 - looo/(Fc + KKlo)].w,d”d
(5)
Mean corrosion rates can be calculated from the slope of a weight loss plot over any time interval, fitted by least
squares. It is assumed that FC values are linearly proportional to pipewrdlthickness, FC = 1 repmaenting lgm of wall
thickness for a lmm pipe wall spcimen.
TWO-PHASE FLOW RIG
Design pammetem
The objective of the experiments was to measure the effectiveness of inhibitmx in horizmtal carbon
dioxide-brine two-phase slug flow at temperaturesup to 80”C. A 10 mm id. test section was chosen to reduce the fluid
inventories required and to assist in rapid tumamund of experiments. A rig was built from AISI type 316L stairdeas
steel and glass pipework, in which the required range of two-phase flow pa~rs
could be repmchced by
combination of controlled streams of liquid and gas. The flow diagramis shown in Figure 4.
Brine was drawn from one of three reservoirs, which were continuously sparged with carbon dioxide,
maintaining a small positive pressure to prevent ingress of oxygen. The brine flow was controlled manually using a
variable speed gear pump and adjusted to the required value using the reading from a calibrated magnetic flow meter
immediately downstream of the pump. It then passed through a heater before beiig combined with gas at the inlet to the
twt section. The gas flow rate was measured by a rotarneterand controlled manually by varying the speed of the
compressor.
The test section consisted of a 2000-mm flow development length of 13.5-mm o.d. x L6-mm wall stainless
steel tubing followed by two 150-mm long test specimens of the material under test insulated electrically from each
other and the rest of the rig. The test specimens were specially manufacturedto give a wall thickness of 1 mm over the
central 90 mm length, and had an internal diameter of 10.3 mm (Figure 3). The sensing pin jacket for meamring
corrosion rates fitted over the central length of one of the specimens. Downstream of the specimens there was a
pcm’px tube, in which the flow patterncould be observed.
~t
The fluids leaving the test section were separated by passing them through a length of 30 mm id. glass
pipeline feediig into a 2-litre pot. The gas was recompressed, passed through a cooler and a knock-out pot to remove
condcnd water droplets, and then through the rotarneterand a heater before being returned to the test section. The
brine was returnedthrough a manifold into one of the three reservoirs.
A bypass line installed between the inlet to the test section and the reservoir manifold minimised air ingress
into the main part of the rig during spcirnen changeover. The oxygen level in the brine was measured by a commercial
814
monitor specially modified for use with carbonated brines. The outputs from temperature, pressure and flow semwrs
were continuously monitored by a PC.
The two-phase flow pattern in the teat section was setup to the required gas and liquid superficial velocities,
using the flow patterndiagram of Maodhane et al.z (Pigum 5).
operation
The rig was lined with a 3 wt per cent solution of analytical grade NaCl in distilled water, whose temperature
was adjusted to the required value in the heat exchanger. The oxygen concentration in the rig was reduced to less than
10 ppb by purging first with high purity nitmgeo, and themwith C02, while the brine was recirculated through the
bypass.
The teat apecirmmbore was abradedwith 240 grit emery paper to a uniform surface finish. The wirea to carry
the current through it were soldered to the thick ends of the specimen with low temperaturesolder, and the sensing pin
jackel fitted around the central section. Car&d setting up allowed good contact between the spring-loaded pins in the
two halvea of the jacket and the specimen to be achieved without breaking them. The jacketed specimen was installed
horizontally in the teat section so that the pin pairs were at O“(top dead c.entre),and 45”, 90°, 135”, 180”, 225°, 270”
and 315° tlom the vertical. The flow was then diverted back fiwm the bypass into the test section. This caused a
temporaryincrease in the oxygen concentration up to a maximum of 400 ppb, atler which it fell to <10 ppb within 90
min.
When tbe oxygen concentration had fallen below 7 ppb, nmsurements were started. In each case the
uninhibited cmroaion rates were measuredbefore introduction of any inhibitor. Direct injections of inhibitor were made
by a syringe into the return brine flowline from the separator through an airtight septum. In some casea the specimen
was removed from the rig and the inhibitor bmahed on to the prepared specimen, which was then allowed to drain
before it was insmted into the rig.
At the ead of the experiment the specimen was removed from the rig aod the rig cleaned using the washing
sequenm 4N HC1, Wlonised water, acetone, xylene, acetone, deionised water, dktilled water. ‘Ilk was found to be
very effective in removing corrosion deposits and traceaof the inhibitor from the glass.
Uninhibited and inhibited corrosion rate measurements were made within the range of superficial gas and
liquid velocities of 1-10 M/see and 0.4-3 rnbc respectively corresponding to horizontal slug flow.
RESULTS
Validation of the system
Although good agreement between this and other methods has previously been demonstrated in larger
systemsl, two validation experiments were carried out in view of the developments of the technique that had taken
place in the intervening period, and the different size of the laboratoryunit. The aim of these experiments was to make
direct comparisons between the decrease in wall thickness of a carbon steel specimen as measured by the technique,
and the amount of iron released either as a weight loss or by chemical analysis of the cording solution.
In the first experiment a chemical polishing solution was slowly circulated by a peristaltic pump through a test
specimen surrounded by the sensing pin jacket for 120 min. The specimen was weighed before and after the
experiment, and samples of the solution taken at intervals and analysed for iron.
The solution used was Marshall’s solution3, which contains 0.2 moles of oxalic acid, 0.38 moles of hydrogen
peroxide and 0.001 moles of sulphuric acid per Iitre. The solution has been shown to work by promoting periodic
growth and dissolution of an oxide film on the steel surface, which causes the corrosion potential to alternate betweem
active and passive valuea3, Very reproducible material rernovsl rates and smooth surface finishes csn be obtained with
this solution, provided that the recirculation rate is not too high.
The results showed a uniform rate of wall loss as measured by tbe unit, and a uniform rate of increase of the
815
curve between 75and%mins. was due toternpomry fiilureof
disanlvd iron concentration (Figure 6:thekinkinthe
the peristaltic pump used to circdate the solution). The mean thickness of metal removed from the 1 nun thick waif
during the teat, rnruwwd by the technique, was 39 * 2 ~m. The weight 10SStlom the specimen during the same period
was 1.93 g (initiaf weight 265. 10g), corresponding to a loss of 52 pm mean wall thickness. This compared with a total
loss of 2.10 g iron ddermid by chemicaf analysis of the solution, equivalent to a loss of 57 pm waif thickness. A
small amount of nwtal was observed to have been removed from the ead facea of the specimen, which probably
accounted for the higher valuea obtained by weight loss md chemicaf analysis.
In the second experiment two similar specimens in series, separatedby an insulator, were loaded into the test
section train of b two-phase flow corrosion rig. The sensing pin jacket was fixed round one of these, and the other
was used for weight loss 333eamm3ner3ts.
The rig was setup to provide slug flow conditions in &aerated carbonated 3
wt% NaCl brine, and the average metaf loss was measured over a 47 hour period. For the specimen surroundedby the
jacket a 13.4pm reduction in wall thickness was found, cmrwponding to a corrosion rate of 2.50 rmnlyr. The second
specimen lost 0.56 g during the same period, which corresponded to a 14.6 ~m reduction in WSIIthickness assuming a
mnteriafdensity of 7700 kg m-3.
The good agreement between these two value-swas considered to provi& firm vsfidation of the technique and
system for measming corrosion rates in the rig.
Corrosion measurementsin two-phase flow conditions
The average corrosion rateaand their standarddeviations for an X-65 pipeline steel in 3 % NaCl brine at 80”C
for the pin pairs at each circumferential position for a range of chosen slug flow conditions, and for four different
specimens, are presented in Table 1. Each specimen was separately prepsred before use by abrading to a 240 grit
surface finish. For each specimen flow rates were changed directly as indicated without changing any of the other
operating parametersor removing the specimen. Corrosion rates measured under one set of flow conditions may thus
have been affected by corrosion md corrosion product film formation under the previous flow conditions.
The results show that the standard deviation of the measurements for any one pin pair, assuming a constant
corrosion rate, decreases as the time over which rneaaurernentsare msde increases, and is in the approximate region of
6-10% for a corrosion rate of 6 mrnlyr, measured over a 24-hour period. Values of + 25% can be achieved in 4 hours,
allowing meaaure-ts of inhibitor persistency to be made on-line.
It is also clear that for the liquid and gas superticiaf velocities used in these experiments the differences in
corrosion rate with circumferential position were not statistically significant. The differences in mean corrosion rates
between two different specimens experiencing the same liquid and gas superficial velocities were not significant at the
1%level.
The measured corrosion rates are in general somewhat less than the value of 8.8 rnrnlyrpredicted from the
correlation of de Wbardand Milliams4’5, W
on laboratory measurements in 0.1 % solutions of NaCl at various
partiafpresaurw of C02:
Ioglo(corrosion rate) = 7.% - 2320/T - 0.00555(T-273) + 0.67 loglOP
(6)
where the corrosion rate is in nmdyr, T is in K, and P is the COZpressure in bar.
The corrosion rates increased with gas supeficiaf velocity, with no significant effect of the liquid superficial
velocity.
Corrosion inhibition un&r two-phase flow conditions
Some typicaf results of tests under two-phase horizmtal slug flow conditions are shown in Table 2. The data
were taken at 80°C with a corrosion inhibitor described as a water-soluble and oildispersible blend of an imidasoline
salt am-fa quaternarynitrogen compound. The same spechmn was used for all the tests in Table 2. The corrosion rates
were initially rnemumd for the ss-installed specinmr without any inhibitor present, and the concentration of inhibitor
816
wasthar increasedin two stages,to 10 ppmandthento 20 ppm. The efficiency of the inhibitor E is defined as
E = 100 (RO- RJ/RO
(7)
where ROand Ri am respectively the mean corrosion rates without and with inhibitor over the indicated period.
The results indicate that, under the chosen conditions, the efficiency of the inhibitor drops with time at the
10 ppm level, but on increasing the concentration to 20 ppm, it is much more stable. Reducing the liquid superficial
velocity at this level doea not, however, produce a significant change in efficiency. There is no significant difference in
corrosion rates around the circumference of the specimen. This was confirmed by subsequent destmctive analysis,
which showed shallow depremions typical of “mean-type corrosion.
Scaling of results to pipehnea
The details of how the results can be scaled to pipelioes of different sizea is beyond the detailed scope of this
paper. In single phase flow, calculations indicated that neither the &livery of corrosive reactants by bulk flow, nor
mass transferratea, were limiting the corrosion rate, which was therefore being detemined by corrosion reaction at the
pipe wall. In larger pipelines both the ratio of flow area to wall surface area and the mass transfer coefficient will
increase, and hence the corrosion rate will be independent of flow, and thus of the wall shear stress, provided that an
increase in shear stmaadoes not affect inhibitive processes such as corrosion scale formation.
Some mrroaion measurementsmade in the presence of inhibitors indicated that the wall shear stress played a
significant role in &temrining the efficiency of the inhibitor, suggesting that flow force-s were. m.moving inhibitive
layers from the surface. This indicates that in order to prdct corrosion rates for a given system, knowledge of the wall
shear stress is required, so that it can be compared with valuea measured in the rig by hot film anemometry
will depend upon the flow patternand the model used, e.g. for slug flow.
~~qW@.
l’he dcuIated vdw
CONCLUSIONS
A commercial non-intmaive multiple electrical resistance measurementtechnique has beemadapted to provide
real-time nonintmaive mmaures of metal 10SSdue to corrosion in pipe geometries suitable for laboratory inveatigationa.
Its use has been &monatrated, using a 10 mm id. x 1 mm wall thickness tubular teat section to measure corrosion
inhibitor performance in single-phase and mukipbase flow. corrosion rates were measumd with a reanlution of
14.4 mpy or 0.365 mndyr in 24 h, or correspondingly less over longer tirnescale-s.
Direct meaaurmof inhibitor efficiency can be made in real time, bawd on metal loss measurements, avoiding
the uncertainties of electrochemical measurements and the introduction of probes or electrodes that may produce or
experience unrepresentativeflow conditions.
ACKNOWLEDGEMENTS
The work reportedabove formed part of a joint industrial project on Corrosion Inhibition in MultiphaaeFlow,
~pported by Amoco UK Exploration r-%-y,
BP InternationalLimited, the Health and Safety Executive of the UK
government, Kerr-McGee Od (UK) PLC, Mobil North Sea Limited, Phillips Petroleum Company UK Limited, Suo Oil
Britain LimitMI,and Toti Oil Marine PLC.
REFERENCES
R.D. Stmmmen, H.Horn and K.R. Weld, “FSM - a unique method for monitoring corrosion, pitting, erosion
1.
and cracking”, COltROSION/92, paper no.7.
2.
J.M. Mandhane, G.A. Gregory and K.Aziz, InternationalJournalof Multiphase Flow 1 (1974): pp.537-553.
817
3.
W.A. MIusIudl,J.Electmdep.Tech.Soc. 28 (1952): p.27.
C.de Ward, U.Lotz znd A.Dugstzd, “The influence of flow velocity on C02 mrmsiom a semi-empirical
4.
model”, CORROSION/95, paper no. 128.
5.
European Federation of Cormsioo, A Working P~ Report on Predicting C02 Corrosion in the Oil and Gas
Industry,Publication number 13. The Institute of Materials, London 1994.
6.
A. H.Govan, G.F.Hewitt, D.G.Owen and G.Bumelt, Intemationzl Journal of Multiphzse Flow 15 (1989):
pp.307-325.
818
Table 1
CORROSION RATES AS A FUNCTION OF ANGULAR POSITION IN HORIZONTAL
SLUG FLOW, NO INHIBITOR, 80”C, mrrr/yr
A
A
B
m/6
3.0
3.0
0.9
B
3.0
c
0.9
D
0.9
m/s
2.0
8.2
2.0
2.0
8.2
2.0
Specimen
‘L ‘
‘G ‘
Start,
h*
End,
he
Angle,
9.5
15
31.5
11
47
69.5
36
68.5
0
0
25
4
deg.
o
5.71*0.24
8.51*0.19
6.59*0.58
7.06*0.73
10.85
45
5.64*0.02
5.75*0.18
8.44*0.12
8.48*0.22
6.52*0.56
6.51*0.76
7.41*0.04
7.31*0.32
10.76*0.12
11.06*0.27
90
*O.11
4.33*0.26
5.97*0.75
4.79*0.14
135
5.59*0.41
8.51*0.34
6.54KI.50
7.33*0.39
11.03*0.40
3.91*1.70
180
5.60*0.10
5.89*0.11
8.70*0.15
8.68*0.10
6.87*0.83
6.62*0.74
7.48*0.13
7.17*0.11
10.72*0.14
10.66*0.46
5.19*1.12
4.Sl*O.65
225
270
5.94*0.22
8.41*0.23
6.84*0.65
7.36*0.63
11.00*0.27
5.05*0.68
315
6.39*0.40
8.57*0.01
5.98*0.15
7.70*0.18
10.72*0.37
4.52*1.99
5.80*0.33
8.54*0.22
6.58*0.68
7.34*0.44
10.84*O.34
4.82*1.24
Mean
**
“ start and ead times refer to the times from the introduction of the specimen into the loop between which
measurementswere taken
‘theaemthemeans
andthestandarddeviations fromthemeansof theaetsofvahrea for allpinpairs,takeo together
Table 2
CORROSIONRATES AT80”CININHIBITED
‘L ‘ mf a
VG,
m/s
3.0
3.0
3.0
3.0
3.0
0.9
2.0
2.0
2.0
2.0
2.0
2.0
o
10
o
22.5
Inhibitor
PPm
Start,
~ ●
End, h
Angle,
deg.
o
45
90
135
180
225
270
315
7.06*0.73
7.41*o.04
7.31*0.32
7.33*0.39
7.48*0.13
7.17*0.11
7.36*0.63
7.70*0.18
Mean* *
7.34*0.44
Efficiency
HORIZONTALSLUG FLOW
10
20
0
13
0
13
26
7.5
20
7.5
20
22
22.5
29.5
1.61*0.48
3.95*0.48
1.48*0.75
1.75*0.80
1.34*0.37
1.42+0.48
3.81*0.09
1.49*0.50
2.14*0.36
1.08*0.34
1.86*0.58
4.25*0.04
1.96*0.18
2.08*0.04
1.50*0.35
1.42*0.36
2.11+0.49
4,01*0.18
1.67+0.17
1.76*0.08
1.58*0.48
1.41*0.14
1.1O*1.14
4.43*0.26
3.64k0.91
1.32*0.20
1.87*0.29
1.64*1.37
0.99*0.20
3.41*0.77
3.74*0.07
1.60*0.58
1.36+0.87
0.93
1.41+0.46
1.61*0.64
1.63+1.30
2.12*1.14
1.31*0.65
1.23
1.54*0.83
3.91*0.57
1.54*0.57
1.73*0.71
1.42*0.46
79%
47%
79%
76%
81%
“startandendtirnes refertothetimes duringwhichFSM measurementsweretalmw the first start time refersto the
introductionoftheapecirneninto the loop; srrbsequentstsrttimesrefer tochangesininbibitorconcentration
““thesesrethemeans andthestandarddeviations fromthemeansof thesetsofvalues meaauredforsllpin pairs,tskerr
together
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FIGURE 4- Flow diagram for two-phase rig
FIGURE 1- Sensing pin jacket
20
Pinangda
position
Disperseh
10
I
Flow
I
I
I
0
1
90
:
.
E
m
3—
180
01
270
001
0002
FIGURE 2- Layout of pins and reference plate
r ----
LOW VOI,KW
.,,,,.”1
,“PW
---
?
I,
1
ug5[ P1/sec
01
10
100200
I
FIGURE 5- Horizontal two-phaseflow pattern mapz
~ .... . . ..-
!,,
,,
uzzzzzz-+)?///L9
jj A%
PTFE
,aCk.!
j j
Pt”mr
: Elec,rlc,l
okc~
0
20
40
60
Exposure
CO””K+O”$
80
time
100
120
140
in m,n”tes
FIGURE 6- Controlled corrosion test
FIGURE 3- Electrical connections
8110
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