Technical
Bulletin
Steamate* Technology
Superior Protection Against Condensate System Corrosion
Problems in Steam Distribution Systems
Condensate System Corrosion
The steam distribution system can be thought of as
the "business end" of the boiler system. The boiler
plant operator makes a substantial investment in
the "front end" of the system in terms of the capital
cost of the boiler, associated equipment, and fuel.
The steam produced is the renewable energy
source that drives the production process, whether
it involves electrical generation, heating or drying,
or a myriad of other uses. Maintaining the efficiency
and reliability of steam distribution system components is critical in controlling overall energy and
maintenance costs.
While many complex and interrelated factors are
involved with the corrosion of metal surfaces in
steam condensate systems, the two primary corrosive agents are carbon dioxide and dissolved oxygen.
Problems arising from excessive corrosion of steam
condensate system surfaces include the following:
 Loss of Capital/Increased Maintenance Costs:
Corrosion can not only result in the loss of expensive equipment, but also in greatly increased
maintenance and repair costs.
 Reduced Efficiency: The buildup of corrosion
product deposits on the surface of heat exchange equipment can dramatically reduce heat
transfer efficiency. This can lead to higher energy costs, and in severe cases, limit production
capacity. In addition, untimely outages caused
by equipment failure can be extremely expensive in terms of lost production time.
 Increased Boiler Scale Formation: Condensed
steam represents a valuable resource as a high
temperature, high purity supply of boiler feedwater. However, condensate returned to the boiler
with high levels of iron and copper corrosion
products can result in the formation of metal oxide scale on the boiler heat transfer surfaces. This
can dramatically reduce efficiency and, in severe
cases, lead to overheating and tube failure.
Carbon dioxide (CO2) is the most common cause of
condensate system corrosion. CO2 is produced in
the boiler as a result of the chemical conversion of
natural alkalinity, principally bicarbonate ions,
which enter with the feedwater. The reactions are
as follows:
2 NaHCO3 + HEAT  Na2CO3 + CO2 + H2O
Na2CO3 + H2O + HEAT  2 NaOH + CO2
The first reaction proceeds to completion in the
boiler, while the second reaction is approximately
80% complete under typical conditions. Thus, each
ppm (mg/L) of bicarbonate alkalinity (expressed as
the CaCO3 equivalent) will result in the formation of
approximately 0.4 ppm (mg/L) of carbon dioxide.
CO2 is extremely volatile and leaves the boiler with
the steam.
At points of condensation in the steam distribution
system, some fraction of the carbon dioxide present
in the steam enters the condensate, forming carbonic acid:
CO2 + H2O  H2CO3  H+ + HCO3
It takes very little carbon dioxide to create a corrosive, acidic pH, as shown in Table 1. This is because
of the high purity and low buffering capacity of the
condensate.
As shown in the equation above, the carbonic acid
hydrolyzes to produce hydrogen ions which cause
Find a contact near you by visiting www.gewater.com and clicking on “Contact Us”.
* Trademark of General Electric Company; may be registered in one or more countries.
©2014, General Electric Company. All rights reserved.
tb10en.doc 06
acidic corrosion of iron and copper alloy surfaces.
The initial corrosion reaction for iron is shown below:
2H2CO3 + Fe  Fe (HCO3)2 + H2
The ferrous bicarbonate formed is soluble and thus
has no ability to protect the metal surface against
further corrosion.
Table 1: Effect of CO2 on the pH of Pure Water
ppm (mg/L) CO2
pH
0
1
2
5
10
20
7.00
5.49
5.34
5.14
4.99
4.84
The stationary nature of pitting can result in rapid
failure of the affected component.
Condensate Treatment Technologies
The three primary methods of condensate system
treatment are neutralizing, filming, and passivating
programs. Neutralizing amines are the predominant
technology and are volatile organic bases that
readily enter the steam phase and distribute
throughout the system. Filmer treatments adsorb
onto metal surfaces and provide a physical barrier
between the corrosive environment and the metal
surfaces. Passivators work by promoting the formation of a tightly-adherent protective magnetite
layer on steel surfaces even when some oxygen is
present in the condensate.
Carbonic acid corrosion most frequently manifests
itself as generalized metal loss rather than highly
localized corrosion such as pitting. Typical corrosion
patterns include thinning or grooving of the lower
diameter of return line piping, thinning of threaded
pipe fittings, and general corrosion on the downstream side of steam traps and control valves
where abrupt pressure changes occur.
A neutralizing amine serves a dual function as a
corrosion inhibitor. First, it neutralizes the acidity
imparted to the condensate by carbon dioxide.
Dissolved oxygen is another major cause of condensate system corrosion. There are several means
by which oxygen contamination can occur, including systems under vacuum; leaking heat exchangers; inefficient or improper feedwater deaeration;
frequent start-up and shutdown cycles; and air
leakage at pump seals, receivers, and flanges.
R-NH2 + H2O  R-NH3+ + OH-
Oxygen can have two distinct effects on the corrosion rates of iron and copper alloys under condensate conditions. First, traces of dissolved oxygen
can significantly accelerate the rate of carbon dioxide corrosion. This results both from the oxidation of
the protective ferrous hydroxide (or magnetite,
Fe3O4) film to non-protective ferric hydroxide and
the tact that oxygen accelerates the rate of the
acidic corrosion reaction.
2Fe(OH)2 + H2O + 1/2O2  2Fe(OH)3
Fe + 1/2 O2 + 2 H+  Fe+2 + H2O
In this case, the corrosion patterns observed are
characteristic of normal carbonic acid attack, except that the severity is significantly increased.
R-NH2  H2CO3  R-NH3+ + HCO3After it has neutralized the carbonic acid, the amine
elevates the pH of the condensate into the alkaline
range.
These reactions can help promote the stabilization
of the protective magnetite (Fe3O4) layer on steel
surfaces and minimizes the corrosion of copper alloy surfaces. In systems where oxygen may be present in the condensate, passivating and neutralizing
treatments may be combined to provide an extra
level of protection against condensate system corrosion.
The pH control range normally recommended for
softened water systems is 8.0 to 8.5, while for demineralized systems with both iron and copper alloys, a pH range of 8.8 to 9.2 is typically
recommended for maximum protection of all surfaces.
The differing ranges are a matter of economics. As
a result of the formation of a bicarbonate “buffer”
system in condensate arising from softened
makeup, a significant increase in amine feedrate
and cost is often associated with raising the pH
from 8.0-8.5 to 9.0.
Dissolved oxygen can also cause pitting, which begins at weak points in the protective magnetite film.
Page 2
Technical Bulletin
There are several important physical properties
which determine the effectiveness of a neutralizing
amine molecule. These include the (1) neutralizing
capacity, (2) basicity, (3) distribution ratio, and (4)
thermal stability. Table 2 summarizes the key
properties of the amine molecules commonly used
for steam condensate system treatment.
The neutralizing capacity measures the quantity of
amine required to neutralize a given quantity of acid, in this case carbonic acid (H2CO3). The smaller the
number, the greater the capacity of the amine to
neutralize carbonic acid. The neutralizing capacity
is a function of both the molecular weight and the
number of amine groups on the molecule. For simple reasons of economy, it is obviously desirable for
an amine to have a high neutralizing capacity. As
shown in Table 2, Diamine, by virtue of its dual
amine functionalities, has nearly double the neutralizing capacity of the other commonly used
molecules.
Table 2: Physical Properties of Neutralizing Amines
Amine
Aminomethylpropanol
Morpholine
Diamine
Methoxypropylamine
Diethylaminoethanol
Cyclohexylamine
Neutralizing
Capacity
(Note 1)
Base
Strength
(Note 2)
2.0
2.0
1.2
2.0
2.7
2.3
66
3.4
200
102
68
489
Distribution Ratio at Pressure
15 psig
50 psig
100 psig
(1.1 kg/cm2)
(3.5 kg/cm2)
(7 kg/cm2)
-0.6
0.7
--6.8
23.7
-0.8
1.3
1.6
5.9
19.2
0.5
1.0
1.7
2.5
5.3
15.9
200 psig
(14 kg/cm2)
1.0
1.2
2.0
2.4
4.5
12.3
Notes:
1. Neutralizing capacity: ppm (mg/L) amine required to neutralize 1 ppm (mg/L) of carbonic acid (expressed as CO2).
2. Base Strength at Room Temperature: Expressed as the Basicity Constant (Pkb) X 1,000,000.
The base strength, or basicity, of an amine is a
measure of its ability to elevate the pH of the condensate after all carbonic acid has been neutralized. It corresponds to the degree of dissociation of
the amine in water, and is expressed numerically as
the basicity constant, Kb. Amines with large basicity constants, such as cyclohexylamine and the
Diamine, are more effective in elevating the condensate pH per ppm (mg/L) of material fed.
As shown in Table 2, the basicity of the Diamine at
room temperature is over fifty times greater than
that of morpholine, while cyclohexylamine is over a
hundred times greater in base strength. It is important to realize that the base strength of an
amine is a function of the water temperature. The
values given in Table 1 were measured at room
temperature. The temperature/basicity profiles for
several amines are shown in Table 3. Due to its dual amine functionalities, the temperature/basicity
profile of the Diamine is more complex. However, it
retains excellent pH elevation capabilities at boiler
temperatures.
Technical Bulletin
Table 3: Amine Base Strength at Temperature
Morpholine
Cyclohexylamine
Diethylaminoethanol
72°F
(22°C)
298°F
(148°C)
338°F
(170°C)
3.4
489
68
4.9
61
11.3
3.8
32
9.2
The distribution of the neutralizing amine between
the steam and liquid phases is as important as the
neutralizing capacity and basicity in determining
the effectiveness of a particular molecule. The distribution ratio is simply a measure of the ratio of the
concentration of the amine in the steam to its concentration in the liquid when the two phases are in
contact with one another.
Distribution Ratio =
ppm (mg/L) amine in steam
ppm (mg/L) amine in water
Like the base strength and neutralizing capacity,
the distribution ratio is an intrinsic property of the
amine molecule and is a function both of the system temperature/pressure and the pH of the liquid
Page 3
phase. An amine with a low distribution ratio, like
morpholine, will tend to concentrate at the initial
condensation sites in a steam distribution system.
Materials with higher volatility, such as cyclohexylamine and diethylaminoethanol (DEAE), tend to
concentrate in the steam and will effectively
“chase” carbon dioxide, which has a very high distribution ratio, to the far ends of long distribution
lines or units receiving flash or cascaded steam
from higher pressure sources.
In practice, the best protection is provided by a
blended product which contains the proper ratios of
component amines covering a broad range of distribution ratios. This is particularly true in complex
and/or extensive distribution systems where the
steam is used for a variety of process and heating
applications. It is very important that the proper
blend is selected to provide effective pH elevation at
all points in the condensate return system.
Another important property of a neutralizing amine
is its thermal stability. Not only is the temperature/pressure profile for thermal decomposition of
amines a key consideration, what the molecule
breaks down to is equally important. The amines
selected for Steamate* provide excellent thermal
stability over a wide range of pressure and temperatures.
As an example, molecules which decompose to
produce significant levels of ammonia would be
unacceptable in a system with extensive copper
alloy surfaces, where formation of the soluble ammonia copper complex can increase corrosion
rates.
In designing a Steamate treatment program, the
loss of amine to blowdown must be considered. Although amine blowdown losses are often overstated, it is a significant concern in lower pressure,
lower cycle systems. The quantity of amine lost to
the blowdown is a function of two variables: the
distribution ratio of the amine (which depends on
pressure/temperature), and the boiler cycles of
concentration.
Table 4 compares the blowdown losses for several
amines at a pressure of 100 psig (7 kg/cm2). Note
that the blowdown loss is expressed as a percentage of the amount of amine fed to the boiler. Some
loss of amine (usually minor) also occurs in the deaerator. Fortunately, because of its extremely high
volatility, a much larger fraction of carbon dioxide is
Page 4
removed with the vent dearator steam than neutralizing amine.
Table 4:
% Blowdown Loss of Amine Versus Feedwater
Cycles at 100 psig (7 kg/cm2)
Amine
Morpholine
Diamine
DEAE
Cyclohexylamine
10
Cycles
25
Cycles
50
Cycles
10.0
6.1
2.1
0.7
4.0
2.4
0.8
0.3
2.0
1.2
0.4
0.1
Steamate Series
GE Water and Process Technologies offers a complete line of condensate treatment programs
through our Steamate series products:
 Steamate NA Series- Blends of volatile neutralizing amines primarily designed to combat carbonic acid and low pH corrosion.
 Steamate PAS Series- Product combinations
which include both neutralizing amines and passivating chemicals to provide protection against
both carbonic acid and oxygen corrosion.
 Steamate FM Series- Filmer treatments which
can protect against both carbonic acid and oxygen corrosion.
 Steamate NF Series- Combination filmer and
neutralizer treatment blends which protect
against carbonic acid and oxygen corrosion.
GE Water & Process Technologies Research and
Development has worked intensively for years to
develop an advanced, real world, computer-based
Condensate Modeling System* (CMS) that realistically reproduces the complex behavior and interactions of neutralizing amines and carbon dioxide in
even the most sophisticated boiler systems. This
capability, combined with GE’s vast practical experience developed over decades of treating thousands of steam distribution systems, has
culminated in the development of the Steamate
series of products. Some of the key benefits to our
customers include:
 The Steamate products represent the most
technically-advanced, cost-effective condensate
treatment programs available in the industry.
Our customers benefit from superior protection
of critical heat transfer equipment, reduced
maintenance costs, and increased system reliability and availability.
Technical Bulletin
 Our BoilerCalc computer program allows us to
choose the most effective and economical
Steamate blend for each specific application.
Steamate products offer superior pH elevation due
to the high basicity of the component amines and
excellent thermal stability for maximum effectiveness, even in high pressure systems.
Steamate condensate treatment programs assist in
maintaining cleaner, more efficient boiler internal
surfaces by minimizing the return of corrosion
product with the condensate. The value of the condensate as a renewable energy source is maximized.
Steamate products are concentrated for maximum
cost effectiveness. By delivering less water, we save
our customers money and reduce chemical inventory and container disposal concerns.
Automated, drum-free delivery, and "hands off"
chemical feed systems are available in a wide
range of tank volumes and configurations, customdesigned to meet the needs of your system. Only
GE offers this range of technology and delivery system flexibility.
Technical Bulletin
Key to Chemical Symbols
NaHCO3
Na2CO3
CO2
NaOH
H2CO3
HCO3Fe
Fe(HCO3)2
H2
Fe(OH)2
O2
Fe(OH)3
H+
Fe+2
R-NH2
R-NH3+
OH–
Sodium bicarbonate
Sodium carbonate
Carbon dioxide
Sodium hydroxide
Carbonic acid
Bicarbonate ion
Iron metal
Ferrous bicarbonate
Molecular hydrogen (dissolved gas)
Ferrous hydroxide
Molecular oxygen (dissolved gas)
Ferric hydroxide
Hydrogen ion
Ferrous ion
Primary amine (general)
Primary ammonium ion
Hydroxide ion
Page 5