The carrying pipe It is installed inside a sheet pile driven into the ground using supports, centering devices, skids, spacers, or guidance systems that keep the pipe aligned, protected, and centered during internal pushing or pulling. The goal is to prevent damage to the pipe, ensure the intended slope or geometry, maintain the clearance from the casing, and allow the pipeline to function properly throughout its service life.
In projects of pipe ramming y infrastructure crossings, the liner acts as a protective barrier beneath roads, railways, waterways, utility lines, or sensitive areas. The utility pipe—for example, a water, sewer, gas, power, or utility line—is then installed inside the sleeve using a support system compatible with the pipe’s diameter, material, load, slope, and operating conditions.
Difference between a casing and a production pipe
| Element | Function | What Influences Its Design |
|---|---|---|
| Tucked-in Shirt | Protect the crossing and build the underground shelter | Outer diameter, embedment depth, thrusts, geotechnical engineering, external loads, and construction method |
| Carrying pipe | Carries the fluid, wiring, or end-user service | Diameter, pressure, slope, material, leak-tightness, durability, and maintenance |
| Centers or skates | They separate, guide, and protect the carrier pipe | Available clearance, weight, friction, slope, accessibility, and installation length |
The liner does not necessarily replace the service pipe. At many intersections, the liner allows the work to be carried out WITHOUT digging a trench and subsequently protects the active pipeline.
What to Check Before Installing the Carrier
Before installing the carrier pipe, check the following:
- Actual inner diameter of the sleeve.
- Ovality, alignment, and slope of the sleeve.
- Total length of the intersection.
- Interior condition, cleanliness, and presence of obstacles.
- Water table or water inflow.
- Material, diameter, and weight of the carrier.
- Stiffness and sensitivity of the outer layer.
- Hydraulic gradient or alignment requirements.
- Need for expansion, insulation, or cathodic protection.
- Minimum clearance between the carrier and the sleeve.
- Installation method: push, pull, section-by-section installation, or insertion from a shaft.
- Access points available from the starting point and the finish line.
- Need to seal the ends or fill the annular space.
When the shirt is featured as part of a work of microtunneling in terrestrial and subway applications, these checks must be coordinated with the design of wells, joints, slopes, and guidance tolerances.
Systems for Centering the Carrier Pipe
| System | Main function | When to use |
|---|---|---|
| Circular Centering Devices | They keep the pipe separate from the jacket along the entire perimeter | Joints where regular centering and coating protection are required |
| Skates or skids | They support the pipe and reduce friction during installation | Heavy-duty pipes or long runs |
| Temporary rollers | They make it easier to move the equipment during assembly or transport | Facilities with access and control from manholes |
| Adjustable dividers | They allow you to adjust clearances or correct positioning | Sleeves with tight tolerances or variable geometry |
| Bottom guides | They maintain elevation, slope, or longitudinal support | Gravity-fed pipelines or slope-sensitive pipelines |
| Clamps with slides | They secure the support system to the carrier | Metal pipes, FRP, HDPE, or other materials, depending on compatibility |
The selection depends on the available clearance, the weight of the load-bearing structure, the length of the span, the material, the slope, the radius of curvature, external protection, and the possibility of subsequent inspection.
How the installation is performed
The installation usually follows a controlled sequence:
- Internal inspection of the liner.
- Removal of debris, sludge, water, or obstacles.
- Checking alignment and slope.
- Check the available inner diameter.
- Installation of centering devices, slides, or spacers on the carrier pipe.
- Protection of coatings, joints, and edges.
- Gradual installation by pushing, pulling, or assembling in sections.
- Control of friction and applied force.
- Verification of position, slope, and continuity.
- Sealing of ends or treatment of the space between the jacket and the carrier, if required by the project.
- Leak, pressure, or service tests, depending on the type of pipeline.
- Final installation documentation.
In pipelines with a steep gradient, special attention must be paid to the final elevation during installation. In pressurized pipelines, priority is given to mechanical protection, leak-tightness, continuity, and compatibility with the lining.
What Risks Should Be Avoided?
An installation that is not properly centered or lacks adequate supports can result in:
- Damage to the pipe's outer coating.
- Excessive friction during dragging.
- Hydraulic head loss.
- Direct contact between the carrier and the sleeve.
- Concentration of loads at a few points.
- Deformation of flexible pipes.
- Damage to joints.
- Difficulty with inspection or maintenance.
- Corrosion due to unintended contact.
- Problems with expansion or thermal movement.
- Water, fine particles, or animals entering through unsealed openings.
- Issues with pressure or leak tests.
At crossings under roads, railways, or critical infrastructure, these risks must be analyzed in conjunction with the infrastructure owner’s requirements and the pipeline’s operating conditions.
Sealing of Ends and Annular Space
Once the carrier pipe is installed, it may be necessary to seal the ends of the casing to prevent the entry of water, backfill, animals, gases, or the entrainment of fine particles. Depending on the project, the space between the casing and the carrier pipe may be ventilated, drained, partially sealed, or backfilled with compatible material.
The decision depends on:
- Type of service.
- Need for future inspection.
- Risk of water or gas buildup.
- Corrosion protection.
- Requirements for the infrastructure operator.
- Hydraulic or environmental conditions.
- Compatibility with the carrier's expansion and movement.
It is not always advisable to completely fill the annular space. In some cases, maintaining accessibility, ventilation, or the ability to drain water may be preferable; in others, sealing or filling is required for safety, durability, or to protect the crossing.
Information Required for Design or RFQ
When designing or reviewing the installation of a carrier pipe within a driven casing, the following information should be provided: the casing’s inside diameter, the carrier pipe’s outside diameter, the length of the crossing, the required slope, the material of both pipes, the weight of the carrier pipe, type of lining, operating pressure, type of joint, available clearance, installation method, access from manholes, radius or deviations in the alignment, need for centering devices, skids, or rollers, sealing requirements, drainage, ventilation, corrosion protection, final testing, and as-built documentation.
CTA: Request a Technical review for installing and centering a carrier pipe inside a driven casing before specifying diameters, clearances, centering devices, seals, or assembly procedures.
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