Chemical Engineering January 2023 - 43

Dates
Volts
Amps
TABLE 1. CP OPERATION DATA, RECTIFIER OUTPUT: 2012-2019
October 4, 2012-June 3, 2014 June 4, 2014-June 23, 2019
5.0-5.7
5.0-5.7
20.5-30.3
Tank-floor current
density, mA/ft²
1.7-2.5
metal, oxygen and an electrolyte or
other corrosives.
The Cushing terminal tank project
presented an excellent opportunity
to evaluate the effectiveness of CorroLogic
VpCI. In 2014, the tank operator
contracted MESA Products
to apply CorroLogic powder. The
powder was mixed with water, and
the resulting 1,500 gal (5,678 L) of
slurry were applied through the floor
via eleven 0.75-in. (19-mm) temporary
injection ports in the floor plates
(136 gal injected at each port). A
corrosion-monitoring system comprising
five electrical-resistance (ER)
probes was also installed below the
tank bottom. The same CP system
used since 2012 was turned
on again. Rectifier output data are
shown in Table 1.
The results of MFL scanning from
the June 2019 API 653 inspection five
years after the injection of CorroLogic
VpCI were significant. This time, 92%
of the tank bottom was scanned. The
remaining thickness threshold was
0.21 in. (5 mm). Previous corrosion
indications from the 2014 MFL scan
were no longer in play due to repair
or patching. It is therefore noteworthy
that the 2019 inspection revealed
only 11 corrosion indications, substantially
fewer than the 115 total
corrosion indications detected in
2014 inspection indications, 3 years
after construction
Remaining
thickness
0.200
0.195
0.190
0.185
0.180
0.175
0.160
0.150
Totals
115
Total number
of corrosion
indications
67
11
26
3
5
1
1
1
Average metal
loss over 3-yr
period, mpy
16.7
18.3
20.0
21.7
23.3
25.0
30.0
33.3
20.0-33.0
1.6-2.7
2014 after
three years
of CP-only
protection.
A v e r a g e
rates of
metal loss
dr opped
from a range of 16.7 to 33.3 mm per
year (mil/yr, or mpy) over the initial
three-year period to a range of 6.3 to
7.5 mpy in 2019. Table 2 compares
the results of the 2014 inspection
with those from 2019, showing significantly
fewer corrosion indications.
Such results demonstrate an effective
solution for drastically reducing
corrosion rates through the addition
of CorroLogic VpCI to the tank-bottom
protection equation. It was very
significant that the 2019 inspection
only identified 11 corrosion indications
following the application of CorroLogic
VpCI in 2014. This provided
the confidence needed for the terminal
operator to have MESA perform
additional CorroLogic VpCI installations
on tanks taken out of service
for inspection. This project also provided
significant data that VpCI and
CP interacted well together with an
overall result of significantly less external
tank-bottom corrosion. A further
observation is that, since 2014
sand analysis identified the possibility
for MIC, it is reasonable to assume
that the CorroLogic VpCI chemistry
and application method played a role
in mitigating this problem.
The road to protection
The Cushing terminal tank project
is an excellent example of how CP
TABLE 2. CORROSION INDICATIONS AND MPY FROM 2014 AND 2019 CUSHING TERMINAL
TANK INSPECTIONS
2019 inspection indications, 5 years
after VpCI application
Remaining
thickness
0.200
0.195
0.190
0.185
0.180
0.175
0.160
0.150
Totals
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
11
JANUARY 2023
Total number
of corrosion
indications
10
1
Average metal
loss over 8-yr
period, mpy
6.3
n/a
7.5
n/a
n/a
n/a
n/a
n/a
can be supplemented with CorroLogic
VpCI to counteract the perennial
issue of external corrosion on
AST bottoms. CorroLogic VpCI is a
relatively non-invasive technology
that can be applied at any stage of
a tank's service life to provide corrosion
protection as a standalone solution,
or as a supplement to CP. When
properly applied, CorroLogic VpCI
technology can potentially reduce the
frequency of repairs and even inspections,
which themselves are timeconsuming
and expensive (although
costs vary depending on tank diameter,
cleaning out crude oil sludge for
inspection alone can easily exceed
$1 million for larger crude-oil storage
tanks). Finally, CorroLogic VpCI offers
an additional means of avoiding
the danger of tank-floor bottom leaks
and failures, as well as the need for
premature tank-bottom replacement,
which can incur costs easily reaching
the million-dollar range. Corrosion
prevention is clearly preferable to performing
repairs, and at the Cushing
oil terminal, CorroLogic has opened
up a new road to slow the overall soilside
corrosion process and extend
tank service life.
■
Edited by Mary Page Bailey
Authors
Tim Whited (Email: tim.whited@
mesaproducts.com) is an engineering
specialist with MESA
Products. He has extensive experience
with corrosion control in the
oil-and-gas industry, especially in
the area of AST bottom protection,
and holds special certifications
through the Association for Materials
Protection and Performance
(AMPP, formerly NACE), including NACE CP Specialist
#3245 and NACE Impact Plus Navigator #3. He is currently
the document project manager of the AMPP committee
finalizing Standard SP21474 on the " External
Corrosion Control of On-Grade Carbon-Steel StorageTank
Bottoms. "
Ana Juraga Oluic (Email: ana.
juraga@ecocortec.hr) is corporate
communications manager at Cortec
Corp. She has been a content
writer at Cortec for 10 years. Besides
dealing with media relations,
she collaborates with Cortec's
engineers and chemists in creating
informative technical content.
Julie Holmquist
(Email:
jholmquist@cortecvci.com) has
been a content writer at Cortec
Corp. for more than seven years.
She specializes in writing about
corrosion-inhibiting technology for
concrete,
turing,
electronics, manufacoil-and-gas,
and many
other industries.
43
http://WWW.CHEMENGONLINE.COM
Chemical Engineering January 2023

Table of Contents for the Digital Edition of Chemical Engineering January 2023
