pwr_january-2025 - 15

FOCUS ON O&M
4. The steam drum separators shown here exhibit severe pitting damage.
Courtesy: Scott Bryan/Cortec
Small pits form on the metal surface, which can quickly grow
deeper and more severe over time.
■ Progressive Damage. These pits create weak spots in the
boiler material, which can reduce the structural integrity of
the boiler, potentially lead to leaks, decrease the overall efficiency
and lifespan of the boiler, and increase the risk of
catastrophic failure.
The severity of oxygen pitting depends on several factors
including oxygen concentration, water temperature, pH levels,
metal composition, and boiler metal surface conditions. The
consequences of uncontrolled oxygen pitting can be severe
(Figure 3), potentially leading to expensive repairs, unexpected
downtime, and in extreme cases, boiler failure. This is why
careful water treatment and oxygen control are critical in steam
boiler maintenance.
Hydrazine: Effective but Hazardous
Hydrazine (N2
H4
) has long been used in steam boilers as an
oxygen scavenger and corrosion inhibitor. Hydrazine reacts
with dissolved oxygen in boiler water, preventing oxygenrelated
corrosion of metal surfaces in the boiler system.
The chemical reaction converts dissolved oxygen to water
and nitrogen. By removing oxygen, hydrazine helps prevent
pitting corrosion, formation of rust and scale, and degradation
of boiler metal surfaces and piping. Hydrazine also
helps create a protective layer on metal surfaces, through
a process called passivation, further reducing the potential
for corrosion.
Typically, hydrazine is added to boiler water in very small,
carefully controlled concentrations to maintain water chemistry
and protect the boiler system's integrity. While hydrazine
can be part of an effective boiler water treatment
program, it is toxic, corrosive, colorless, flammable, and potentially
carcinogenic, so its use requires careful handling
and strict safety protocols. In today's modern industrial settings,
safer alternatives are available.
Total Replacement for Hydrazine Programs
For example, Cortec Corporation has developed S-15, a lower-toxicity
alternative that can completely replace hydrazine
programs. S-15 combines volatile neutralizing amines with
an oxygen scavenger/metal passivator. This formula works in
three main ways. First, it neutralizes acidic species and increases
pH, creating an alkaline environment that reduces the
January 2025 | POWER
www.powermag.com
15
risk of acidic corrosion. Second, this alkaline environment allows
the oxygen scavenger/passivator to act more quickly to
reduce oxygen in the water. Third, S-15 passivates areas that
have already started to rust by converting hematite (soft red
rust) to magnetite (hard black rust). S-15 also works in the
vapor-phase as the boiler water evaporates into steam, carrying
S-15 to protect surfaces above the water level, as well as
those in direct contact with it.
S-15 is easy to feed into the deaerator, feedwater tank, or
steam drum (Figure 4). It can also serve as a building block
for custom water treatment formulations. S-15 is thermally
stable and highly efficient at inhibiting corrosion from oxygen
and carbon dioxide. It can be recycled with condensate
water and is typically effective at a very economical continuous
dose of 2 parts per million (ppm) to 5 ppm. S-15 does
not leave solid residue in boiler systems or compromise
steam quality.
Regardless of local hydrazine policies, the availability of
a safer option demands attention. By choosing S-15 as a
building block for your next water treatment formulation or
as a main part of your boiler maintenance strategy, you can
stay one step ahead of both oxygen pitting and hydrazine
concerns. ■
-Cortec Corporation contributed this article.
Funnies
http://www.powermag.com
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