Hydrocarbon Processing - January 2021 - 69

Maintenance
and Reliability
J. A. ZURLO, SUEZ Water Technologies & Solutions,
Houston, Texas

Improving asset utilization
by closing the corrosion window
Driving profitable refinery operations
often requires owner-operators to balance production flexibility and product
optimization with asset availability and
equipment reliability. Many refineries face
periods of severe corrosion and fouling in
their crude unit distillation overhead systems. The exact cost of refinery corrosion
is unknown; various analysis reports by
NACE International and others estimate
annual profit losses due to refinery corrosion to be $2 B-$12 B. Regardless of the
exact value, it is not argued that corrosion
is expensive and there is ample room for
improvement to benefit both safety and
profits. Overhead system corrosion is an
ongoing phenomenon, but often occurs
as a series of short episodes where intense
corrosion occurs, separated by long periods when little to no corrosion occurs.
These short, intense periods are known by
some as the " corrosion window " and their
episodic nature is one reason why corrosion can be a challenging issue to tackle.
Applying a collection of new tools,
some of which have been developed in
only the last several years, enables additional visibility, faster response and more
informed decisions regarding which corrective actions to take for greatest effect.
The overarching goal is to close the elusive corrosion window and shut out corrosion altogether. Today's technology innovation has created additional on-stream
sensors to continuously monitor system
performance and treatment levels, new
methods to measure previously hidden
properties, and expanded analytics capabilities to better predict issues before they
happen. It is now possible to close the
corrosion window to an extent previously
considered impractical or uneconomi-

cal. Continuous system performance
monitoring and automated alarming allows for near instantaneous response to
changing conditions, enabling refiners to
react faster and with better direction than
previously possible. As will be illustrated,
several refiners are applying one or more
of the techniques for positive impact on
their bottom line, while achieving safer,
more reliable operations.
Corrosion causes and improvement
strategies. Overhead corrosion can

be complex to control. Three common
corrosion mechanisms account for the
majority of problems: acidic attack, saltinduced corrosion and velocity-assisted
corrosion. Multiple factors are often involved, such as chemistry, contaminant
concentration, contaminant types, operating conditions and mechanical factors.
To clarify, an example of a mechanical factor is high overhead vapor flow, which can
induce velocity-assisted corrosion.
Sometimes, one or more issues are
perceived to be related to crude quality
changes and are considered largely unavoidable, leading to overly conservative
solutions at the exclusion of more complex, but more effective, options. This
ultimately leads to increased costs and
operational risks at a refinery. Despite the
recognized high impact of corrosion, both
the measurement and control of primary
driving factors often fall short, frequently
resulting in inconsistent performance
across systems, making both the rapid
understanding of driving forces and the
consistent application of structured mitigation less effective. One possible explanation is that corrosion control programs
were designed initially to prevent acidic

attack. Advancements in chemistries and
approaches to control corrosion have
changed, but monitoring and control
practice advances have lagged, leading to
the gaps in recognizing and effectively
responding to the intense corrosion episodes occurring during episodic corrosion windows.
Using modern equipment, sensors and
techniques, it is now possible to effectively mitigate overhead corrosion while also
maintaining flexibility, production and
reliability. By taking advantage of the improved measurements, rapid testing and
sophisticated analytics available today,
much more granular and dynamic processing schemes can be effectively utilized
where they were previously not possible.
While each overhead is unique, a common approach to recognizing, responding
to, and ultimately overcoming corrosion
can be used to reduce the size of the corrosion window or completely close it. The
key elements in the approach include:
1. Reduce contaminants allowed
into the overhead system-
crude quality, desalting and
contaminants introduced from
outside the crude unit (e.g., amine
contamination/recycle)
2. Corrosion control chemistry
selection to improve performance
and operating flexibility
3. Appropriate measurement
frequency to respond to
events faster
4. Ability to control the
system within well-defined,
safe operating ranges
5. Adopt a dynamic, safe operating
window to avoid corrosion,
moving away from using a fixed
Hydrocarbon Processing | JANUARY 2021 69

Hydrocarbon Processing - January 2021

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