25 May 2005
1. Cyclohexylamine is not for use in systems having a feedwater alkalinity
more than 75 ppm.
2. These system lengths are for classification only and are not absolute. For
example, a medium-length system may have more of the characteristics of
a long system if lines are poorly insulated or because of poor design. The
characteristics of a condensate return system are best determined by a
condensate pH survey.
Morpholine. Morpholine has a low vapor-liquid distribution ratio and will
drop out of steam quickly, making it suitable for protecting condensate return systems of
short to moderate length. Morpholine is best suited for use in high-pressure systems
(103 to 6205 kilopascals [15 to 900 pounds per square inch gauge]) because of its high
boiling point. Very little morpholine is lost in deaerators from returning condensate.
DEAE. DEAE has a vapor-liquid distribution ratio between that of
morpholine and cyclohexylamine. This makes DEAE a good choice for protecting
systems of moderate length where either morpholine or cyclohexylamine, if used
separately, would not provide complete protection. The low boiling point of a mixture of
DEAE and water makes DEAE suitable for use in both low-pressure boilers and high-
Cyclohexylamine. Cyclohexylamine has a high vapor-liquid distribution
ratio and consequently is best suited for protecting extremely long systems.
Cyclohexylamine can also be used in low-pressure systems. Cyclohexylamine is not
used in systems when the feedwater alkalinity exceeds 75 ppm because of the low
solubility of cyclohexylamine bicarbonate, which can be produced and form deposits.
The likely areas for formation of these deposits are low-flow areas at the far end of the
condensate return system. This deposition problem can be avoided by reducing
feedwater alkalinity or by using DEAE. It is also necessary to treat long systems with
morpholine to protect the early part of the system where steam is first condensed.
Amine Blends. A mixture of morpholine, DEAE, or cyclohexylamine can
be used to provide full protection in medium and large systems. The optimum blend of
these amines is determined by measuring the actual pH of the condensate at various
locations in the condensate return system. If samples from far sections have a lower pH
than other samples, the cyclohexylamine in the mixture can be increased and vice
versa. Another pH survey should be done when the blending ratio is changed. An initial
blend of 1 part cyclohexylamine and 3 parts morpholine is a good starting point.
Control of Carbon Dioxide and Oxygen by Filming Amines. Carbon
dioxide corrosion can be controlled with 0.7 to 1.0 ppm of a filming amine such as
octadecylamine. This chemical will coat the condensate pipe and prevent the carbon
dioxide in the water from coming into contact with the pipe wall. Filming amines may
also be appropriate for use if there is a high degree of air leakage (oxygen) because