BACKGROUND OF THE INVENTION
[0001] This invention relates to corrosion control in steam condensate systems and other
aqueous systems in which the mineral content is relatively low.
[0002] More particularly, this invention relates to the use of methoxypropylamine in combination
with hydrazine to control corrosion in stream condensate systems or in other low solids
aqueous systems.
[0003] Condensate corrosion protection is becoming an increasingly important aspect of plant
operation. In these energy-concious times, an increase in the quantity and quality
of condensate will result in water and heat savings for the total boiler system.
[0004] Historically, the action of distilled gases such as oxygen and carbon dioxide have
been two of the main factors that lead to condensate corrosion. In order to understand
the role of oxygen and carbon dioxide in corrosion, one must understand the electro-chemical
nature of corrosion. Pure water has very little effect on pure iron, but this situation
is seldom encountered. Under most conditions, there is a tendency for iron to dissolve
in water, and two electrons are released for each atom that dissolves. These electrons
are transferred to hydrogen ions present in water, and the ions are reduced to elemental
gaseous hydrogen. All action ceases at this point if the hydrogen remains on the surface
of the metal since a protective coating is formed that interferes with the passage
of electrons. However, any agent which increases the number of hydrogen ions present
in the water, or which will cause the removal of the protective film, serves to increase
the rate of corrosion.
[0005] When carbon dioxide dissolves, it reacts with water to form carbonic acid, which
supplies additional active hydrogen to the system. Iron displaces the hydrogen from
this acid. When oxygen is also present in the water, a two-fold reaction takes place.
Some molecules of oxygen combine with the displaced hydrogen and thus exposes the
metal to fresh attack. Other oxygen molecules combine with iron ions to form insoluble
rust compounds.
[0006] A greater corroding influence than the mere dissolving tendency of iron is the existence
of a heterogeneous surface in commercial iron and steel due to the presence of surface
imperfections which tend to form couples with the adjacent base metal. Electrons are
released from the anodes of these couples to the hydrogen ions at the adjacent cathodic
surface, thus increasing the corroding area and accelerating the rate of corrosion.
[0007] The first product of corrosion may be converted to ferric oxide, which is only loosely
adherent and aggravates corrosion by blocking off areas to oxygen access. These areas
become anodic and iron oxide couples are set up. The iron under the oxide deposit
then dissolves, and pitting develops. Carbon dioxide attack results in thinning or
grooving of the metal.
[0008] For those systems that will permit it, filming amines will give condensate corrosion
protection against both oxygen and carbon dioxide. However, many industrial systems
cannot tolerate filming amines and must use neutralizing amines.
[0009] The ideal neutralizing amine should have the following characteristics:
1. The distribution ratio should be high enough so that a considerable amount of the
neutralizing amine fed to the boiler will end up in the condensate. This will reduce
the loss of neutralizing amine via blowdown.
2. The distribution ratio should not be too high in order to keep losses due to aeration
and venting to a minimum. The distribution ratio is the ratio of the amount of amine
in the vapor phase to that in the liquid phase.
3. The basicity value should be moderately high or very high so that the amine will
efficiently neutralize all carbon dioxide that it encounters.
4. The neutralizing amine should have sufficient hydrolytic-thermal stability so that
it will not break down to ammonia and other compounds in the boiler or in superheated
or saturated steam.
5. The neutralizing amine should be a water-soluble liquid for feeding convenience.
[0010] Neutralizing amines such as cyclohexylamine and morpholine have been used but they
have several disadvantages. For example, cyclohexylamine has a high distribution ratio
and accordingly, substantial cyclohexylamine escapes the system through the deaerator
vent. Morpholine, on the other hand, has a low basicity value which means that more
morpholine is required to attain high pH's in the condensate system and it also has
a very low distribution ratio which means that substantial amounts are lost via blowdown.
SUMMARY OF THE INVENTION
[0011] The neutralising amine of this invention overcomes the above-mentioned disadvantages
of cyclohexylamine and morpholine. Methoxypropylamine has a very desirable distribution
ratio and a fairly high basicity value.
[0012] Methoxypropylamine may be used alone or in combination with an oxygen corrosion inhibitor
such as hydrazine. In use, concentrations of 0.1 to 1000 mg/I, and preferably 1 to
100 mg/I, should be maintained in the steam condensate system. When used in combination
with hydrazine or another oxygen corrosion inhibitor, the composition should contain
on an active basis from about 1 % to about 99% methoxypropylamine and from about 0.1%
to about 50%, preferably about 1 % to about 15%, of the oxygen corrosion inhibitor.
The compositions of this invention may be fed to the steam condensate system being
treated by conventional liquid feeding means or may be fed to the boiler feedwater
or directly to the steam supply lines.
[0013] The following examples will illustrate the use of methoxypropylamine, alone and in
combination with hydrazine, as a steam condensate corrosion inhibitor in accordance
with the teachings of this invention.
EXAMPLE 1
[0014] Distribution ratios of a number of neutralizing amines were calculated by preparing
solutions of each amine having a concentration of 100 mg/I and adding 500 ml of this
solution to a brine pot which is slowly and uniformly heated so that 100 ml of distillate
is produced every 40 minutes. Additional solution is manually introduced to the brine
pot every 5 to 10 minutes to maintain the brine pot solution at the 500 ml mark. Each
100 ml aliquot of distillate is collected and pH determined until constant pH is attained
for three successive aliquots. This is taken to represent the establishment of equilibrium
conditions. At equilibrium, the brine and the final 100 mls are analyzed by gas chromatography
to determine the amount of amine in each and the Distribution Ratio (D.R.) calculated
by the following formula:
![](https://data.epo.org/publication-server/image?imagePath=1981/17/DOC/EPNWB1/EP78400209NWB1/imgb0001)
[0015] Similarly, the basicity value (K
b) or measure of the amine's ability to react with carbon dioxide is calculated in
accordance with the formula:
![](https://data.epo.org/publication-server/image?imagePath=1981/17/DOC/EPNWB1/EP78400209NWB1/imgb0002)
wherein [BH
+], [OH
-] and [B°] are defined as:
[BH+] = concentration of dissociated amine
[OH-] = hydroxide concentration
[B°] = concentration of free, undissociated amine
[0016] The results of these tests and calculations are set forth in Table 1.
![](https://data.epo.org/publication-server/image?imagePath=1981/17/DOC/EPNWB1/EP78400209NWB1/imgb0003)
EXAMPLE 2
[0017] The hydrolytic-thermal stability of various neutralizing amines is measured by a
test in which the neutralizing amine at a concentration of 1000 mg/I is autoclaved
for 24 hours at 41 bar (600 psi) at 254°C (489°F) and the final concentration of ammonia
measured. The results of this test are set forth in Table II.
![](https://data.epo.org/publication-server/image?imagePath=1981/17/DOC/EPNWB1/EP78400209NWB1/imgb0004)
EXAMPLE 3
[0018] A condensate test system is used to evaluate neutralizing amines. This system comprises
a boiler capable of producing 45 kilograms/hour of a steam at pressure of 13,7 bar
(200 psi), pumps and metering devices to control the composition of the make-up water
to the boiler, and cooling coils with temperature control means to condense the steam.
The condensate is recirculated through a test loop where metal coupons and corrosometer
probes evaluate the corrosion rate. The test water is distilled water containing <1
mg/l S0
4, < 1 mg/I CI, <1 mg/l Si0
2 and 10 mg/I CO
2. Table III sets forth the results of corrosion tests in this system.
![](https://data.epo.org/publication-server/image?imagePath=1981/17/DOC/EPNWB1/EP78400209NWB1/imgb0005)
EXAMPLE 4
[0019] The condensate test system of EXAMPLE 3 was used to demonstrate the effect of the
addition of hydrazine to methoxypropylamine in the inhibition of corrosion.
![](https://data.epo.org/publication-server/image?imagePath=1981/17/DOC/EPNWB1/EP78400209NWB1/imgb0006)
1. A steam condensate corrosion inhibiting composition consisting essentially of methoxypropylamine
and hydrazine.
2. A steam condensate corrosion inhibiting composition of Claim 1 which contains from
1 to 15% by weight hydrazine.
3. A method of inhibiting corrosion in steam condensate systems which comprises maintaining
an effective amount of a composition consisting essentially of methoxypropylamine
and hydrazine.
4. A method of inhibiting corrosion in steam condensate systems as in Claim 3 wherein
a concentration of at least 1.0 mg/I of said composition is maintained.
5. A method of inhibiting corrosion in steam condensate systems as in Claim 3 wherein
the composition contains from 1 to 15% by weight hydrazine.
1. Korrosionsschutzmittel für Wasserdampfkondensatsysteme, bestehend im wesentlichen
aus Methoxypropylamin und Hydrazin.
2. Korrosionsschutzmittel für Wasserdampfkondensatsysteme nach Anspruch 1, welches
1-15 Gewichtsprozent Hydrazin enthält.
3. Verfahren zur Korrosionsinhibierung in Wasserdampfkondensatsystemen, dadurch gekennzeichnet,
dass man eine wirksame Menge einer Zusammensetzung, bestehend im wesentlichen aus
Methoxypropylamin und Hydrazin, aufrechterhält.
4. Verfahren zur Korrosionsinhibierung in Wasserdampfkondensatsystemen nach Anspruch
3, dadurch gekennzeichnet, dass eine Konzentration von wenigstens 1,0 mg/I an dieser
Zusammensetzung aufrechterhalten wird.
5. Verfahren zur Korrosionsinhibierung in Wasserdampfkondensatsystemen nach Anspruch
3,. dadurch gekennzeichnet, dass die Zusammensetzung 1-15 Gewichtsprozent Hydrazin
enthält.
1. Composition inhibitrice de corrosion par condensat de vapeur, caractérisée en ce
qu'elle consiste essentiellement en méthoxypropylamine et en hydrazine.
2. Composition inhibitrice de corrosion par condensat de vapeur selon la revendication
1 ; caractérisée en ce qu'elle contient de 1 à 15% en poids d'hydrazine.
3. Procédé d'inhibition de la corrosion dans des systèmes à condensat de vapeur, caractérisé
en ce qu'on maintient la présence d'un quantité efficace d'une composition consistant
essentiellement en méthoxypropylamine et en hydrazine.
4. Procédé d'inhibition de la corrosion dans des systèmes à condensat de vapeur selon
la revendication 3, caractérisé en ce qu'on maintient une concentration d'au moins
1,0 mg/1 de ladite composition.
5. Procédé d'inhibition de la corrosion dans des systèmes à condensat de vapeur selon
la revendication 3, caractérisé en ce que la composition contient de 1 à 15% en poids
d'hydrazine.