Now, with a well-prepared foundation in place, it’s time to move on to the next stages of the installation process: deploying the liner, creating leak-proof seams, and securing the liner’s perimeter. From careful handling of the liner panels to precise seam welding and secure anchoring, each step requires attention to detail and adherence to best practices.
Liner Deployment: Handling and Placement
Panel Unloading and Handling
Beginning at the manufacturer or fabricator, liner panels must be handled carefully at each stage to prevent damage during transportation, unloading, and on-site storage.
Transportation
Transport liner rolls or panels using appropriate vehicles and secure them correctly to prevent shifting or damage during transit. Protect the liner material from exposure to sharp objects, excessive sunlight, and extreme temperatures. Reputable suppliers will ship liners in protective packaging to shield them from abrasion and other damage.
Unloading
Large panels used in frac pad installations can be large and very heavy. Use appropriate equipment, such as forklifts or cranes, to carefully unload the liner rolls or panels. Avoid dragging or dropping the material.
Storage
Store liner rolls or panels on a clean, level surface, free from debris, rocks, or other sharp objects. Protect the material from direct sunlight and precipitation using tarps or covers. If storing rolls, ensure they are adequately supported to prevent deformation.
Panel Layout and Alignment
Once the site and subgrade are prepared, it’s time to install the liner. Sometimes, liners can be shipped in a single, custom-fabricated piece. Other times, individual panels must be carefully laid out and aligned according to the design specifications.
Positioning
Lay out and align the single-piece liner or individual panels, ensuring proper overlap and minimizing wrinkles or creases. The shop drawings prepared by the supplier will provide a detailed layout that minimizes field seaming and optimizes panel sizes for the project. Overlaps should be sufficient to allow secure seam welding and prevent gaps in the liner system.
Alignment
The liner or individual panels should be aligned to create a smooth, continuous surface. Avoid excessive stretching or bunching, which can stress the liner material and lead to premature failure.
Securing
Temporarily secure the panels using stakes, sandbags, or other weights to prevent the liner from moving during installation. This allows you to make adjustments as you go and prevents wind from displacing the panels.
Seam Welding: Creating a Leak-Proof Seal
Seam welding is arguably the most critical step in frac pad liner installation. During seaming, individual liner panels are permanently joined to create a continuous leak-proof barrier. The specialized welding techniques for RPE and XR geomembranes ensure exceptionally strong and durable seams.
Welding Equipment and Techniques for RPE and XR Geomembranes
Hot-Wedge Welding
Hot-wedge welding is the most common technique for seaming RPE and XR geomembranes. It uses a heated wedge to melt overlapping edges of the liner panels, fusing them under controlled pressure. Hot-wedge welding creates a rugged and reliable seam that can withstand the stresses and chemical exposure typical of fracking operations.
RF Welding (Radio Frequency Welding)
XR geomembranes are uniquely suited for RF welding, which uses high-frequency electromagnetic energy to generate heat and fuse the geomembrane layers. In this process, overlapping liner panels are placed between two electrodes, and a high-frequency electric field is applied, causing the molecules in the liner material to vibrate rapidly. This molecular friction generates heat within the material. This localized heat melts the polymer at the seam interface, fusing the panels under pressure.
Which is Better: Hot-Wedge Welding or RF Welding?
RF welding offers advantages in terms of speed, consistency, and greater seam strength. However, it can only be used on XR geomembranes. It also requires specialized equipment and training.
Hot-wedge welding creates tough, reliable seams, and it’s a more established technique, meaning the equipment and experienced operators are more readily available. Ultimately, the manufacturer’s recommendations and project specifications should guide the choice of welding method.
Extrusion Welding
In extrusion welding, a specialized tool applies a molten polymer bead along the seam. When pressure is applied to both sides of the seam, it creates a weld that bonds the panels together. Extrusion welding is especially well-suited for corner seams, repairing damaged sections, or welding around penetrations. It provides a flexible, secure seam that can conform to uneven surfaces or complex geometries.
Key Considerations for Seam Welding
Several key considerations must be taken into account during the welding process to ensure strong and durable seams:
Surface Preparation
The surfaces of the geomembrane panels being joined must be clean and dry. Any dirt, moisture, or debris can weaken the seam and permit leaks.
Pressure Application
Adequate, even pressure must be applied across the entire width of the seam while the material is still molten to ensure proper fusion and bonding of the geomembrane layers.
Welding Surface
The bottom surface on which the welding is performed should be flat and smooth for even contact and pressure distribution during the welding process for a consistent and reliable seam.
Heat Application
In hot-wedge welding, sufficient heat must be applied to create a visible bead of molten material extruded from both edges of the seam. This visible bead indicates the material has reached the proper melt condition for a successful chemical bond between panels.
Seam Testing and Quality Control
Liner seams must meet specified strength standards in order to withstand the stresses and pressures encountered during operation. These standards may be defined by site engineers or mandated by state regulations.
With everything that hinges on flawless seaming, Testing is a crucial step in verifying the integrity of the welds and identifying even tiny leaks. Several common testing methods are used for seam testing.
Air Pressure Testing
This method involves pressurizing the seam with air and checking for pressure which would suggest a seam leak. Alternatively, a soapy water solution can be applied to the seam. If bubbles form, they indicate air is escaping. Air pressure testing is non-destructive, relatively simple to perform, and can be effective for detecting larger leaks.
Vacuum Testing
In vacuum testing, a vacuum is applied to the seam. Similar to air pressure testing, the vacuum is monitored for changes. A rise in pressure indicates air is entering the vacuum chamber, signaling a leak in the seam. Vacuum testing is a non-destructive testing method that’s effective for identifying small leaks or pinholes that may not be visible to the naked eye.
Destructive Testing
In destructive testing, a small section of the seam is cut out, and the weld is visually examined for correct fusion and weld penetration.
While this method provides direct evidence of the weld quality, the removed section must be repaired afterward to restore the liner’s function. Keep in mind that this testing method is limited in scope, as it only assesses a limited portion of the seam. It is typically used along with non-destructive testing methods.
Other Testing Methods
Depending on the liner material, other specialized testing methods may be employed, including ultrasonic testing or destructive methods like shear or peel testing.
