Note: Descriptions are shown in the official language in which they were submitted.
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Improved corrosion resistance when using chelating agents in chromium-
containing equipment
The present invention relates to a method to reduce the corrosion of chromium-
containing equipment in the oil and/or gas industry. The invention also
relates to
the use of solutions containing glutamic acid N,N-diacetic acid or a salt
thereof
(GLDA) and/or methylglycine N,N-diacetic acid or a salt thereof (MGDA) having
an
acidic pH that are contacted with chromium-containing equipment in the oil
and/or
gas industry, for example to clean or descale such equipment or downstream
equipment, but also as a chemical in such equipment, for example as a chemical
in
an oil and/or gas downstream processing plant or factory that contains
chromium-
containing tanks, boilers, tubes or other equipment. Finally, the invention
relates to
equipment made from a chromium-containing alloy containing a solution
containing
glutamic acid N,N-diacetic acid or a salt thereof (GLDA) and/or methylglycine
N,N-
diacetic acid or a salt thereof (MGDA) having an acidic pH or to a combined
system that contains equipment made from a chromium-containing alloy in
contact
with a solution containing glutamic acid N,N-diacetic acid or a salt thereof
(GLDA)
and/or methylglycine N,N-diacetic acid or a salt thereof (MGDA) having an
acidic
pH.
More in particular, the present invention relates to any of the above methods,
equipment or systems wherein compared to the state of the art the use of a
corrosion inhibitor can be greatly reduced or in some cases even omitted.
In many industrial environments, like plants, factories, but also in oil and
gas
production installations, a large part of the equipment, such as tubes, tanks,
boilers, reactor vessels, is made from chromium-containing metal alloys. Also,
a lot
of chromium is applied in oil platforms. This is because chromium-containing
alloys
have a better resistance against oxidative degradation than many other metals
and
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alloys. However, under the influence of both oxygen and carbon dioxide and a
number of other corrosive chemicals, like chloride-containing chemicals,
chromium-containing alloys also suffer negative degradation and corrosion
effects,
especially at an elevated temperature.
Hence, there has been a continued search for processes to apply, clean, and
descale equipment used in the oil and/or gas industry and for chemicals that
do not
have the above problems when contacted with chromium-containing alloys to
replace previously used chemicals.
Many documents disclose the use of alkaline solutions containing a chelating
agent
as detergent solutions, also to clean metal surfaces. It should be noted that
corrosion means gradual destruction of the metal by chemical reaction with its
environment, namely oxidation of metals in reaction with an oxidant such as
oxygen. As such, corrosion is distinctly different from fouling and descaling,
which
relate to cleaning a deposit from the metal surface and not preventing
degradation
of the metal itself or the effects thereof. For example, EP 1 067 172, JP
11158492,
WO 2004/013055, and US 2009/0298738 disclose alkaline cleaning solutions
containing a chelating agent in the sense of removing scale, grease, oil
and/or
fouling. It is said in EP 1067172 that the corrosive effect on light metals is
low, with
the light metal specified being alumina.
However, acids especially are known to cause undesired corrosion of metal
surfaces, as is seen in for example the oil industry where the use of acidic
solutions or gases like CO2 is common practice and where naturally occurring
corrosive gases like H25 and CO2 can be present.
In this respect, S. Al-Harthy et al., in "Options for High-Temperature Well
Stimulation," Oilfield Review Winter 2008/2009, 20, No. 4, Schlumberger
disclose
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that the use of N-hydroxyethyl ethylenediamine N,N',N'-triacetic acid has much
lower undesired corrosion side effects than do a number of other chemicals
playing
a role in the oil field, where the use of chromium steel is common practice.
The purpose of this invention is to provide new chemicals and solutions that
give
an even more minimized chromium corrosion side effect as well as a reduced
corrosion effect in the acidic pH range, and to provide processes to apply,
clean or
descale chromium-containing equipment as used in the oil and/or gas industry
or to
run a number of chemical processes wherein chromium corrosion is minimized,
under varying temperature and acidic pH conditions.
US 2010/0078040 discloses removing rouging on stainless steel surfaces, for
example from equipment used in the pharmaceutical industry, by using aqueous
cleaning solutions that contain at least two different complexing agents in
the
neutral pH range. The complexing agents can be picked from a large group of
compounds that includes GLDA and MGDA. In the examples a cleaning solution is
made containing about 9 wt% of MGDA, but when using this solution to clean a
vessel a 50 fold dilution is made, so that the vessel is only contacted with a
solution containing less than 0.2 wt% of MGDA. Nor is a high amount of the
complexing agent used anywhere in the other examples.
The present invention relates to preventing or reducing corrosion in the oil
and/or
gas industry, where generally much more concentrated chemical solutions are
applied because in this industry using large amounts of water is not always
economically feasible, as water is often unavailable at the oil or gas
production
site, especially when the use of seawater is not an option due to the
interaction of
seawater components with the formation, equipment or other production
chemicals
resulting in more corrosion and/or unwanted precipitation. In addition, the
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application of low concentrations reduces the reaction rate considerably,
resulting
in long and costly downtimes.
It has now been found that relatively concentrated solutions of glutamic acid
N,N-
diacetic acid or a salt thereof (GLDA) and of methylglycine N,N-diacetic acid
or a
salt thereof (MGDA) having an acidic pH give a surprisingly and significantly
lower
corrosion of chromium-containing alloys than other chelating agent-containing
and/or acidic solutions, over the acidic pH and a broad temperature range.
Accordingly, the present invention provides alternative processes and systems
that
can replace state of the art processes in the oil and/or gas industry and
systems
that suffer from negative corrosion effects.
The present invention provides a process to reduce the corrosion of equipment
containing a chromium-containing alloy in the oil and/or gas industry,
comprising a
step of contacting the equipment containing a chromium-containing alloy with a
solution containing at least 1 wt% on total weight of the solution of glutamic
acid
N,N-diacetic acid or a salt thereof (GLDA) and/or methylglycine N,N-diacetic
acid
or a salt thereof (MGDA) having an acidic pH, and more specifically a process
to
reduce the corrosion of equipment containing a chromium-containing alloy in
the
treatment of a subterranean formation wherein an acidic solution is introduced
into
the formation and at least part of the acid in the acidic solution is GLDA
and/or
MGDA, preferably wherein the amount of GLDA and/or MGDA is at least 1 wt% on
the basis of the acidic solution, and the acidic solution comes into contact
with the
equipment containing a chromium-containing alloy.
The invention also relates to the use of acidic solutions containing at least
1 wt%
on total weight of the solution of glutamic acid N,N-diacetic acid or a salt
thereof
(GLDA) and/or methylglycine N,N-diacetic acid or a salt thereof (MGDA) to
prevent
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or reduce corrosion in equipment containing a chromium-containing alloy in the
oil
and/or gas industry, for example to clean or descale such equipment, but also
as a
chemical in chromium-containing equipment, for example as a chemical in a
plant
or factory in the oil and/or gas industry that contains chromium-containing
tanks,
5 boilers, tubes or other equipment, replacing other chemicals, in
treatments of
subterranean formations like in completions and stimulation by acidizing,
fracturing,
and descaling. Chemicals that can be replaced by GLDA or MGDA are chelating
agents in their acidic form but also other acids, because it is possible to
make
concentrated acidic solutions of MGDA and even more concentrated, more acidic
solutions of GLDA.
The present invention also provides a system containing a piece of equipment
applied in the oil and/or gas industry made at least partly from a chromium-
containing alloy in contact with an acidic solution containing at least 1 wt%
on total
weight of the solution of glutamic acid N,N-diacetic acid or a salt thereof
(GLDA)
and/or methylglycine N,N-diacetic acid or a salt thereof (MGDA). The system of
the
invention in embodiments contains further improved chelating agent-containing
and
acidic solutions, such as solutions used in the oil field, gas field, or oil
and/or gas
downstream processing industry in addition containing other components like a
solvent such as water, a chelating agent, a surfactant, and a corrosion
inhibitor,
wherein the amount of corrosion inhibitor can be greatly decreased or even
omitted.
It should be noted that WO 2008/0103551 discloses an acidic solution
containing a
chelating agent and the use thereof as a breaker fluid in the oil field. The
chelating
agent may be GLDA. However, this document only discloses the circulation of
the
solution in a wellbore and does not disclose the combination of this solution
with
any chromium-containing equipment and therefore neither discloses nor suggests
any benefits in preventing or reducing corrosion.
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The equipment containing a chromium-containing alloy may be for example a
pump, tap, tube, tank, vessel, or pipe or any other device that can hold a
solution
or through which a solution can flow. The chromium-containing alloy may be
present in the whole piece of equipment but also only in a sheet or plate or a
part
of the piece of equipment in any other form (like for example a screw or nail)
as
used in the oil industry and/or gas industry.
By the term acidic solution or solution having an acidic pH is meant a
solution
having a pH of below 7, preferably a pH below 6, and even more preferably
below
5. The pH in some embodiments is higher than -2, preferably higher than -1,
and
more preferably higher than 0.
By use or application in the oil and/or gas industry is meant any use in the
production, exploration and/or recovery of oil and/or gas from subterranean
formations, transporting the oil and/or gas to downstream processing units
such as
oil refinery and/or oil and/or gas downstream processing units, processing the
oil
and/or gas in such units, and all accompanying processes and uses such as the
cleaning, descaling, and maintenance of the equipment, removing small
particles
and removing scale to enhance oil and/or gas well performance and cleaning of
the
wellbore.
Any use according to the invention involves a step wherein the solution
containing
GLDA and/or MGDA contacts equipment containing a chromium-containing alloy.
The acidic solution containing GLDA and/or MGDA in one embodiment may
contain other components, such as primarily water, but also other solvents
like
alcohols, glycols, and further organic solvents or mutual solvents, soaps,
surfactants, dispersants, emulsifiers, pH control additives, such as further
acids or
bases, biocides/bactericides, water softeners, bleaching agents, enzymes,
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brighteners, fragrances, antifouling agents, antifoaming agents, anti-sludge
agents,
corrosion inhibitors, corrosion inhibitor intensifiers, viscosifiers, wetting
agents,
diverting agents, oxygen scavengers, carrier fluids, fluid loss additives,
friction
reducers, stabilizers, rheology modifiers, gelling agents, scale inhibitors,
breakers,
salts, brines, particulates, crosslinkers, salt substitutes, relative
permeability
modifiers, sulfide scavengers, fibres, nanoparticles.
In addition to it being found that the use of cationic surfactants, as is
common
practice in the oil and/or gas industry, can already decrease the undesired
corrosivity of fluids in the oil and gas industry, it has now been found that
GLDA
and MGDA give an even lower corrosion of chromium-containing alloys than
HEDTA, especially in the relevant acidic pH range, in the case of GLDA even
below the industry limit value of 0.05 lbs/sq.ft (for a 6-hour test period),
without the
addition of any corrosion inhibitors. Accordingly, MGDA and/or GLDA give an
unexpectedly reduced chromium corrosion side effect, and the use thereof in a
subterranean formation treatment process results in corrosion of the chromium-
containing equipment being significantly prevented and an improved process to
clean and/or descale chromium-containing equipment. Also because of the above
beneficial effect, the invention covers a method using a solution in which the
amount of corrosion inhibitor and corrosion inhibitor intensifier can be
greatly
reduced compared to the state of the art fluids and processes, while still
avoiding
corrosion problems in the equipment.
In the solutions of this invention the amount of GLDA and/or MGDA is suitably
between 2 and 50 wt% for GLDA and between 2 and 40 wt% for MGDA.
Preferably, the amount is between 2 and 30 wt%, more preferably 5 and 30 wt%,
even more preferably between 5 and 20 wt% on the basis of the total weight of
the
solution. The solutions of the invention preferably contain GLDA.
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The solutions may be used at several temperature ranges, suitably between 0
and
200 C, preferably between 20 and 150 C, even more preferably between 20 and
100 C.
The surfactant that can be used in the present invention can be any surfactant
known in the art and can be nonionic, cationic, anionic, zwitterionic. When
the
formation to be treated is a carbonate formation, preferably, the surfactant
is
nonionic or cationic and even more preferably, the surfactant is cationic.
When the
formation is a sandstone formation, preferably, the surfactant is nonionic or
anionic, and even more preferably the surfactant is anionic.
The nonionic surfactant of the present composition is preferably selected from
the
group consisting of alkanolamides, alkoxylated alcohols, alkoxylated amines,
amine oxides, alkoxylated amides, alkoxylated fatty acids, alkoxylated fatty
amines,
alkoxylated alkyl amines (e.g., cocoalkyl amine ethoxylate), alkyl phenyl
polyethoxylates, lecithin, hydroxylated lecithin, fatty acid esters, glycerol
esters and
their ethoxylates, glycol esters and their ethoxylates, esters of propylene
glycol,
sorbitan, ethoxylated sorbitan, polyglycosides and the like, and mixtures
thereof.
Alkoxylated alcohols, preferably ethoxylated alcohols, optionally in
combination
with (alkyl) polyglycosides, are the most preferred nonionic surfactants.
The anionic (sometimes zwitterionic, as two charges are combined into one
compound) surfactants may comprise any number of different compounds,
including sulfonates, hydrolyzed keratin, sulfosuccinates, taurates, betaines,
modified betaines, alkylamidobetaines (e.g., cocoamidopropyl betaine) .
The cationic surfactants may comprise quaternary ammonium compounds (e.g.,
trimethyl tallow ammonium chloride, trimethyl cocoammonium chloride),
derivatives
thereof, and combinations thereof.
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Examples of surfactants that are also foaming agents that may be utilized to
foam
and stabilize the solutions of this invention include, but are not limited to,
betaines,
amine oxides, methyl ester sulfonates, alkylamidobetaines such as
cocoamidopropyl betaine, alpha-olefin sulfonate, trimethyl tallow ammonium
chloride, C8 to C22 alkyl ethoxylate sulfate, and trimethyl coco ammonium
chloride.
Suitable surfactants may be used in a liquid or powder form.
Where used, the surfactants may be present in the solutions in an amount
sufficient to prevent incompatibility with formation fluids, other treatment
fluids, or
lci wellbore fluids at reservoir temperature.
In an embodiment where liquid surfactants are used, the surfactants are
generally
present in an amount in the range of from about 0.01% to about 5.0% by volume
of
the solution.
In one embodiment, the liquid surfactants are present in an amount in the
range of
from about 0.1% to about 2.0% by volume of the solution, preferably from 0.1
to
1.0 volume%.
In embodiments where powdered surfactants are used, the surfactants may be
present in an amount in the range of from about 0.001 % to about 0.5% by
weight
of the solution.
Corrosion inhibitors may be selected from the group of amine and quaternary
ammonium compounds and sulfur compounds. Examples are diethyl thiourea
(DETU), which is suitable up to 185 F (about 85 C), alkyl pyridinium or
quinolinium
salt, such as dodecyl pyridinium bromide (DDPB), and sulfur compounds, such as
thiourea or ammonium thiocyanate, which are suitable for the range 203-302 F
(about 95-150 C), benzotriazole (BZT), benzimidazole (BZI), dibutyl thiourea,
a
proprietary inhibitor called TIA, and alkyl pyridines.
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In general, the most successful inhibitor formulations for organic acids and
chelating agents contain amines, reduced sulfur compounds or combinations of a
nitrogen compound (amines, quats or polyfunctional compounds) and a sulfur
compound. The amount of corrosion inhibitor is preferably less than 2.0
volume%,
5 more preferably between 0.001 and 1.0 volume% on total solution.
Preferably, the chromium-containing alloy contains a stainless steel or
another
metal alloy in which chromium is present, which is often to improve the
corrosion
properties thereof. In a preferred embodiment the chromium-containing alloy
10 contains between 1 and 40 wt% of chromium on total metal content, more
preferably it contains between 5 and 30 wt% of chromium, even more preferably
between 10 and 25 wt% of chromium. Preferably, the chromium-containing alloy
contains stainless steel.
Examples of chromium-containing stainless steels are (i) austenitic steels,
which
contain a maximum of 0.15% carbon, a minimum of 16% chromium, and sufficient
nickel and/or manganese to retain an austenitic structure at all temperatures
from
the cryogenic region to the melting point of the alloy, wherein a typical
composition
of 18% chromium and 10% nickel is often used in flatware; (ii) superaustenitic
stainless steels, which exhibit great resistance to chloride pitting and
crevice
corrosion due to a high molybdenum content (>6%) and nitrogen additions, and
which by a higher nickel content ensure better resistance to stress-corrosion
cracking versus the 300 series; (iii) ferritic stainless steels, which
generally have
better engineering properties than austenitic grades but reduced corrosion
resistance due to the lower chromium and nickel content, which contain between
10.5% and 27% chromium and very little nickel, if any, although some types can
contain lead, and wherein many compositions include molybdenum and some
include aluminium or titanium, (iv) martensitic stainless steels, which are
not as
corrosion-resistant as the other two classes but are extremely strong and
tough, as
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well as highly machinable, and which can be hardened by heat treatment, which
steels contain chromium (12-14%), molybdenum (0.2-1%), nickel (less than 2%),
and carbon (about 0.1-1%) (giving the material more hardness but also making
it a
bit more brittle); (v) precipitation-hardening martensitic stainless steels,
which have
a corrosion resistance comparable to austenitic varieties but can be
precipitation-
hardened to even higher strengths than the other martensitic grades; (vi)
Duplex
stainless steels, which have a mixed microstructure of austenite and ferrite,
the aim
usually being to produce a 50/50 mix, although in commercial alloys the ratio
may
be 40/60, which steels have roughly twice the strength compared to austenitic
stainless steels and also improved resistance to localized corrosion,
particularly
pitting, crevice corrosion, and stress corrosion cracking and are
characterized by
high chromium (19-32%) and molybdenum (up to 5%) and lower nickel contents
than austenitic stainless steels
Experimental
Example 1
A beaker glass was filled with 400 ml of a solution of a chelating agent as
indicated
in Table 1 below, i.e. about 20 wt% of the sodium salt of about pH 3.6. This
beaker
was placed in a Burton Corblin 1-liter autoclave.
The space between the beaker and the autoclave was filled with sand. Two clean
steel coupons of Cr-13 (UNS S41000 steel) were attached to the autoclave lid
with
a PTFE cord. The coupons were cleaned with isopropyl alcohol and weighted
before the test. The autoclave was purged three times with a small amount of
N2.
Subsequently the heating was started or in the case of high pressure
experiments
the pressure was first set to c. 1,000 psi with N2. The 6-hour timer was
started
directly after reaching a temperature of 149 C. After 6 hours at 149 C the
autoclave was cooled quickly with cold tap water in c. 10 minutes to <60 C.
After
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cooling to <60 C the autoclave was depressurized and the steel coupons were
removed from the chelate solution. The coupons were gently cleaned with a non-
metallic brush and flushed with a small amount of water and isopropyl alcohol.
The
coupons were weighted again and the chelate solution was retained.
Table 1: Acid/Chelate solutions:
Chelate Active ingredient and pH as
Content such
GLDA 20.4 wt% GLDA-NaH3 3.51
HEDTA 22.1 wt% HEDTA-NaH2 3.67
MGDA 20.5 wt% MGDA-NaH2 3.80
Results
In the scheme of Table 2 the results of the corrosion study of Cr-13 steel
coupons
(UNS S41000) are shown for the different solutions.
Table 2: Different chelate or acid solutions
Test Chelate pH Temp. Pressure Assay after 6 Hrs
no. C (PSI) corrosion test corrosion
LBS/sq.ft
#01 GLDA 3.5 160 - 18.4wt% as
0.0013
GLDA-NaH3
#02 GLDA 3.5 149 - 20.1wt% as
0.0008
GLDA-NaH3
#03 HEDTA 3.7 149 - 24.4 wr/o as
0.3228
HEDTA-NaH2
#04 GLDA 3.5 149 >1000 20.1wt% as
0.0009
GLDA-NaH3
#05 HEDTA 3.7 149 >1000 16.0wt% as
0.5124
HEDTA-NaH2
#06 MGDA 3.6 149 >1000 22.7wt% as
0.0878
MGDA-NaH2
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The corrosion rates of HEDTA (pH 3.7) at 149 C and pressure of 1,000 psi are
significantly higher than for MGDA (pH 3.8) and much higher compared to GLDA
(pH 3.5). The corrosion rates of both HEDTA (pH 3.7) and MGDA (pH 3.8) at
149 C and pressure of 1,000 psi are higher than the generally accepted limit
value
in the oil and gas industry for chromium based alloys of 0.03 LBS/sq.ft (6
hours test
period), which means that they will need a corrosion inhibitor for use in this
industry. As MGDA is significantly better than HEDTA, it will require a much
decreased amount of corrosion inhibitor for acceptable use in the above
applications when used in line with the conditions of this Example. The 6-hour
corrosion of GLDA for Cr-13 steel (stainless steel S410, UNS S41000) at 149 C
(300 F) is well below the generally accepted limit value in the oil and gas
industry
of 0.03 LBS/sq.ft. It can thus be concluded that it is possible to use GLDA in
this
field without the need to add a corrosion inhibitor.
Example 2
In Figure 1 the corrosion rate of 20wr/o GLDA at 150 C was compared with other
frequently used acids in the oil and gas industry for Cr-13 steel. The
corrosion tests
were performed according to the procedure described in Example 1. Without any
addition of corrosion inhibitor the corrosion caused by 10 wt% acetic acid, 15
wt%
acetic acid, 20 wt% HEDTA at pH=3.8, and 10 wt% formic acid is above the
generally accepted limit for chromium-containing alloys of 0.03 LBS/sq.ft
during a 6
hr test. The corrosion caused by 20 wt% GLDA at pH=3.8 is far below this
limit, i.e.
0.008 LBS/sq.ft.
Figure 2 shows the ICP-ES element analysis of the corrosion fluids after the 6
hr
corrosion test at 150 C. The analysis shows that 20 wt% HEDTA at pH=3.8 and 10
wt% formic acid attack the iron and chromium ions in the stainless steel to
the
same extent, resulting in high concentrations of these elements. It was even
observed that the colour of the HEDTA fluid turned from pale yellow before the
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corrosion test to dark purple after the test. The colour of Cr-HEDTA is
purple. The
acetic acids cause a smaller increase in iron and chromium ions in line with
the
lower corrosion rate. The 20 wt% GLDA solution at pH=3.8 caused a negligible
increase in iron and chromium in the solution, indicating that GLDA does not
cause
any corrosion on Cr-13 steel under these conditions.
Example 3
Corrosion tests with anionic surfactants and/or corrosion inhibitors were
performed
with Cr-13 steel according to the method described in Example I. The
surfactant,
Witconate NAS-8, was selected from the group of anionic water-wetting
surfactants. Witconate NAS-8 consists of 36% 1-octanesulfonic acid, sodium
salt,
60% water, and 4% sodium sulfate. Armohib 31 represents a group of widely used
corrosion inhibitors for the oil and gas industry and consists of alkoxylated
fatty
amine salts, alkoxylated organic acid, and N,N'-dibutyl thiourea, with 100%
active
ingredients. The corrosion inhibitor and anionic surfactant are available from
AkzoNobel Surface Chemistry.
Figure 3 clearly shows the difference in corrosion behaviour between GLDA and
HEDTA. Without additives GLDA shows no corrosion, whereas the corrosion rate
of HEDTA is 0.2787 lbs/sq. ft, which is far above the generally accepted limit
of
0.05 lbs/sq ft. Upon addition of the corrosion inhibitor the corrosion rates
of HEDTA
and GLDA are similar. Addition of an anionic surfactant leads to an increase
in the
corrosion rate to unacceptable rates of 0.7490 lbs/sq.ft for GLDA and 0.9592
lbs/sq.ft for HEDTA, indicating the corrosive character of this anionic
surfactant
itself. When both 0.5 vol% corrosion inhibitor and 6 vol% anionic surfactant
are
combined with HEDTA, the corrosion rate is reduced to 0.2207 lbs/sq. ft, which
is
still far too much. In contrast, the corrosion rate of GLDA decreases to
acceptable
rates under identical conditions, indicating the surprisingly gentle character
of
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GLDA for this metallurgy. Even when the amount of corrosion inhibitor is
increased
to 1.5 vol%, the corrosion rate of HEDTA is still 3 times more than the
acceptable
rate. For GLDA the corrosion rate increases when the amount of corrosion
inhibitor
is increased to 1.5 vol%, indicating that the optimum corrosion inhibitor
5 concentration under these conditions is around 0.5 vol%, which is
significantly
lower than the amount required for HEDTA.
Example 4
10 To study the effect of the combination of a corrosion inhibitor,
cationic surfactant,
and GLDA on the corrosion of Cr-13 steel (UNS S41000), a series of corrosion
tests were performed using the method described in Example 1. The results
expressed as the 6-hour metal loss at 163 C are shown in Figure 4. The
cationic
surfactant, Arquad C-35, consists of 35% cocotrimethyl ammonium chloride and
15 water. Armohib 31 represents a group of widely used corrosion inhibitors
for the oil
and gas industry and consists of alkoxylated fatty amine salts, alkoxylated
organic
acid, and N, N'-dibutyl thiourea. The corrosion inhibitor and cationic
surfactant are
available from AkzoNobel Surface Chemistry.
The results show that the corrosion rate of GLDA is significantly less than
for
HEDTA under all studied conditions. In combination with 0.01 vol% of corrosion
inhibitor and/or 6 vol% of cationic surfactant the corrosion rate of GLDA
remains
well below the acceptable limit of 0.05 lbs/sq.ft. Even in the absence of
corrosion
inhibitor acceptable results were obtained for this type of metallurgy, but
for inferior
quality metal types a minor amount of corrosion inhibitor is expected to be
needed.
For HEDTA 1.0 vol% corrosion inhibitor is not yet sufficient to reduce the
corrosion
rate below this limit. The results show that, in contrast to HEDTA, GLDA is
surprisingly gentle to Cr-13 metal and that combining GLDA with corrosion
inhibitor
or cationic surfactant or not does not influence the corrosion rate.
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Example 5
Corrosion tests were executed according to the method described in Example 1
with various types of chromium containing alloys. The composition of the
metals is
given in Table 3. Under conditions that are typical for the North Sea area,
i.e.
120 C and in the presence of 10 mol% H25/5 mol% CO2/balance N2, a 20 wt%
GLDA solution at pH=3.8 required only a minimum quantity of 0.05 v% corrosion
inhibitor (Armohib 5150, available from AkzoNobel) to stay below the industry
limit
of 0.03 lbs/sq.ft for these types of alloys, which is far below the normal
corrosion
inhibitor loadings used under these conditions during acid treatments.
Table 3: Composition of the steel coupons
Element Cr-13 Duplex 2205 SA2832
(S41000) (S31803) (N08028)
C 0.13 0.017 0.008
Mn 0.39 1.43 1.5
Si 0.4 0.36 0.3
Cu 0.1 0.31 1.21
Ni 0.3 3.71 30.65
Cr 12.2 22.42 26.75
Mo 0.03 3.18 3.46
Fe balance Balance balance
