Underground salt dome storage facilities provide a safe and
efficient means of storing hydrocarbons. The corrosion and
abrasion issues related to handling brine, however, create
integrity challenges that impact operational reliability and cost.
A recent project to replace a brine handling system allowed
Pemex to permanently address corrosion and abrasion issues.
The Tuzandeptl Strategic Hydrocarbon Storage Center
(CAE-Tuzandeptl) is an underground salt cavern storage
facility that uses brine to receive, store and deliver excess
crude oil production. The facility plays a vital role in providing
Pemex with operational flexibility. It consists of 12 underground
caverns with a 7.1 million barrel storage capacity and 2 brine
dams with a holding capacity of 12 million barrels. When crude
is deposited into the caverns, brine flows from the caverns to the
brine dams. The reverse occurs when crude oil is taken out of the
caverns. A brine pumping station directs the flow of brine to and
from each salt cavern, and a brine discharge system directs the
flow to and from the brine-holding dams. This system is designed
to displace large amounts of crude oil and brine in a short period
of time, with 16-inch pipelines going to each cavern and 36-inch
discharge pipelines going out.
With average sodium chloride concentrations in brine of
26 percent, the corrosion rate of carbon steel can exceed
200 mils per year (mpy) depending on flow rate and temperature.
The Tuzandeptl facility was originally built of bare carbon steel
with a substantial corrosion allowance to take into account the
expected wall loss due to the corrosive and abrasive nature
of brine used. The corrosion rate is further exacerbated by
turbulence in the flow streams, explaining why a facility like
Tuzandeptl would be prone to high corrosion rates. After years
of operation, actual corrosion loss far exceeded the initial
design of the system. This created integrity problems that
started to compromise the operational reliability of the facility,
requiring regular replacement of pipe sections and service
disruptions due to leaks.
In seeking a solution, the reliability and integrity issues arising
from internal corrosion and abrasion were first addressed with
epoxy paints, high solids epoxy coatings, thick wall steel and
active steel pipe replacement programs. Nonetheless, by 2012,
wall loss due to corrosion had reached a critical level and more
assertive steps were necessary to address the facility’s internal
After analyzing various alternatives, a total thermoplastic coating
system was selected as a comprehensive long-term solution.
A complete reconfiguration project was launched in 2013, and
the new facility was commissioned in 2016 to yield a solution
that will provide Pemex with years of trouble-free operation.
TITE LINER® SYSTEM INSTALLATION
One of the key benefits and appeal of the Tite Liner® thermoplastic
system is the ease of installation in new and existing pipelines.
First, interactive, tight-fitting thermoplastic liners are custom
sized so that the outside diameter of the liner is larger than the
inside diameter of the host pipe. The liner pipe is then delivered
to the jobsite in 45-foot sections that are thermally fused into long monolithic sections equivalent to the pipe section being
lined, up to 6,500 feet in length.
Field installation of the Tite Liner® system is achieved by
sectioning the pipeline and inserting fused liner sections.
A blow-down pig and sizing plate attached to a steel cable
are blown down each section of the host pipeline. The roller
reduction box is used to compress the liner in order to provide
sufficient clearance to pull the liner through the host pipeline.
Once the liner is pulled through, the material expands and
locks itself inside the pipeline providing a tight compression
fit. Although the resulting inside diameter is somewhat
reduced, the flow characteristics and transport capacity
of the pipeline are not affected due to the smoother surface
of the thermoplastic compared to bare steel.
To reconnect the lined pipeline sections, various connection
methods are available, which include flanged and flangeless
connections. Once the system is reconnected, the pipeline
is tested and recommissioned.
Rotational molding, or rotomolding, is a process where a thin
layer of thermoplastic material is applied onto the interior
surface of the fitting to provide a smooth corrosion- and
abrasion-resistant surface. For in-plant piping, wellheads,
headers and other piping systems where a straight liner pipe
cannot be installed, a thermoplastic coating can also be applied
through the rotomolding process. This creates a seamless
one-piece, thermoplastic coating that can be applied to complex
geometries, large pipe assemblies, tanks and process equipment.
During the application process, rotational-grade polymer
resin in granular form is placed inside the metal fitting
and heated while being rotated simultaneously about two
perpendicular axes. During the heating cycle, the polymer
particles melt and adhere to the metal fitting, forming a thin,
uniform layer of seamless thermoplastic coating less than
1/3 inch thick. This coating thickness makes rotationally
molded coatings extremely durable and resistant to abrasive
wear. The metal fitting is then cooled by a combination of
forced air and water mist and the part is then removed from
the machine. Finally, coated end connections are machined
to tight tolerances and finished to be fitted and assembled with
other coated fittings, forming a complete corrosion-resistant
piping system. Rotomolding is part of Aegion’s corrosion
protection solutions through its strategic partnership with
RMB Products, Inc., of Fountain, Colorado.
The Tite Liner® system was designed into 150 sections between
10 and 3,200 feet in length, and ranging in size from 4 to 36
inches in diameter. Engineers employed a computer-generated
design to drive the fabrication, fit and installation of a complex
series of pipeline spools and fittings of various sizes, where
even the slightest dimensional variation could impact proper
fit of the entire system. The general contractor then fabricated
the steel fittings, and Aegion coordinated the fitting of the
system spools and pipelines.
Because of integrity issues and continuous leakage problems,
the first phase of the project addressed replacement of brine
pipelines connecting the dams to the pumping station. For
the second phase, 450 spool pieces were rotolined and then
installed on site. Once the redesigned facility was completed,
a system switchover was executed over a one-week period
with the new system successfully commissioned in May 2016.
Given its complexity, execution of the project involved careful
and detailed planning and coordination by Aegion between
Pemex’s design engineers, RMB Products, Inc., the fabrication
crews and the field installation team. With the successful
completion of this project, Pemex ensured the integrity of the
Tuzandeptl brine handling system by eliminating recurring
corrosion concerns and potential leaks for decades to come.