Hydrocarbon Processing - June 2022 - GP-33

INSPECTION & MAINTENANCE
Case study: The science behind amine process
column corrosion and remedial solutions
D. SNIJDERS, IGS, Al Khobar, Saudi Arabia
This case study examines how and
why corrosion takes place within amine
vessels, the corrosion mitigation strategies
available, and a comparison of highvelocity
thermal spray (HVTS) with a
low-velocity alternative.
In 2015, a gas plant in the Middle East
identified internal corrosion in two of its
amine process columns and contracted
the author's company to apply HVTS
alloy cladding to protect the base metal.
The HVTS cladding was applied, and in
2016, the plant went out to public tender
for the completion of a similar work
scope on six more columns. The plant
decided to use a local thermal spray contractor
on a cost basis, which involved using
a conventional low-velocity thermal
spray process technology.
Amine vessel corrosion mechanisms.
To understand the solution to the problem,
it is important to first understand
the science behind the problem of corrosion-in
this case, the amine vessel corrosion
mechanisms. In the amine system,
most of the corrosion is related to acid
gas breakout and the subsequent attack
on the metal surface, usually at elevated
temperatures. Since corrosion is a chemical
reaction, high temperatures always accelerate
corrosion activity because reactions
occur faster and more aggressively
at higher temperatures.
Often, several factors contribute to failure
by corrosion. Statistics show that almost
50% of corrosion incidents occur in
the hottest part of the plant: the reboiler
and the bottom of the amine regenerator.
In amine plants, most corrosion is related
to hydrogen sulfide (H2
ide (CO2
S) or carbon diox)
breakout and the subsequent
attack on the metal surfaces, usually in areas
of elevated temperature or high pressure
drop (leading to condensation).
More potential corrosion mechanisms
exist in amine columns. In the lower
section of a regenerator, for example,
carbon steel surfaces not wetted by the
amine solution may be attacked by water
vapor and the formation of carbonic
acid. Acid gas ratio, choice of amine
(DEA, MEA, MDEA, DGA, AGR, etc.),
contaminants, two-phase flow, flashing,
high velocities, vessel design and insulation
are all contributing factors. Pitting,
crevice corrosion, flow-enhanced corrosion
and general corrosion loss are frequent
problems.
In this case, the plant in the Middle
East conducted a planned inspection and
noticed pitting in its amine process columns
that would eventually lead to failure
if left untreated and potentially cost
the plant millions of dollars to replace
the columns.
Several solutions are available to treat
the issue of corrosion; while the damage
cannot be reversed, if repaired using the
correct technique and application, the
lifespan and performance of the equipment
can be significantly increased.
Corrosion mitigation strategies in
amine treatment. Many amine towers
have the top dome and upper area of
the vessel clad with 316 stainless steel as
part of the original design. Process control
and changes to the feed typically
mean that the amine column will experience
corrosion in other areas of the vessel,
often directly below the clad section.
The nature and form of the corrosion
mechanism often manifest themselves as
a localized pitting attack with high corrosion
rates. That can quickly remove
the corrosion allowance and damage the
integrity of the unit, requiring intervention
and mechanical repair to rebuild the
pressure boundary.
Aside from operational considerations,
several mitigation or repair strategies
have historically been employed
when internal shell loss occurs. Some
mechanical options include the installation
of temporary clamps and plugs, vessel
section replacement, and the application
of an internal weld overlay. The time
required for these, as well as the postweld
heat treatment (PWHT) required
to remove heat affected zones (HAZs)
and structural support considerations,
often demand extended turnaround
or shutdown schedules and associated
production losses. Temperature and
chemical compatibility limitations have
prevented the effective use of organic
coatings. Due to the nature of the sour
feed, loss of containment poses major
safety and environmental risks.
The gas plant in the Middle East
chose to use an alloy cladding solution
to fix the issue of corrosion in its amine
process columns. This solution provides
the same benefits as a high-nobility weld
overlay corrosion barrier, with several additional
advantages-including a rapid
application speed-without requiring
an HAZ or PWHT, or distortion of base
FIG. 1. The 2021 inspection of HVTS in 2015
(applied by the author's company) shows the
cladding in excellent condition.
Gas Processing & LNG | MAY/JUNE 2022 33
Hydrocarbon Processing - June 2022

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