November 2017
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 thebrine 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 designedto 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 exceed200 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 arisingfrom internal corrosion and abrasion were first addressed withepoxy 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 corrosion issues.
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 customized 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 job site 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 andlocks itself inside the pipeline providing a tight compressionfit. 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.
ROTOLINING PROCESS
Rotational lining, or rotolining, 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 rotolining 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 offorced air and water mist and the part is then removed fromthe 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. Rotolining is part of Aegion’s corrosion protection solutions through its strategic partnership with RMB Products, Inc., of Fountain, Colorado.
PROJECT EXECUTION
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 United 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.
CONCLUSION
Given its complexity, execution of the project involved careful and detailed planning and coordination by United 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.