What is Direct Pipe?
Direct Pipe (DP) is an innovative trenchless method that combines microtunneling and pipeline installation into a single, simultaneous operation. A microtunnel boring machine (MTBM) is attached directly to the leading end of the product pipe. As the MTBM excavates forward, the product pipe is pushed behind it from a jacking frame at the entry pit — eliminating the separate pilot bore, pre-reaming, and pullback steps that HDD requires.
Direct Pipe is particularly well suited to large-diameter pipeline river crossings and crossings in loose, water-bearing soils where HDD is impractical due to instability or frac-out risk. Drive lengths of 1,000 m or more are achievable, and the method is used extensively for oil, gas, and water transmission pipelines.
Why Drilling Fluids Are Critical to Direct Pipe
The fluid system in a Direct Pipe installation must perform two distinct functions simultaneously — and getting either one wrong can stall the drive or damage the surrounding formation.
- Annular lubrication — A low-viscosity, thixotropic slurry is injected at multiple points along the pipe through annular ports. This fluid fills the annulus between the pipe OD and the borehole wall, reducing skin friction and lowering the jacking forces needed to advance the pipe. Without effective lubrication, jacking forces can escalate rapidly and the pipe string can become locked in place.
- Face slurry — The MTBM uses a pressurized slurry to support the tunnel face, preventing collapse in unstable soils, and to transport excavated cuttings back through the slurry circuit to the surface separation plant.
- Pressure management — The annular slurry must be designed with the right density and gel strength to maintain positive pressure in the annulus without over-pressuring the formation, which could cause ground heave, surface uplift, or loss of slurry containment.
- Fluid compatibility — In river crossings and environmental sensitive areas, slurry additives must comply with local environmental regulations and must not contaminate groundwater or waterways.
How NorthStar Supports Direct Pipe Projects
NorthStar has supplied fluid programs for Direct Pipe installations across North America and South America, including long-reach river crossings in challenging soils. Our engineering team works from the project planning stage to design annular lubrication volumes, mix formulations, and injection pressure recommendations specific to the pipe diameter, drive length, and ground conditions.
Because jacking force is directly tied to annular friction, our lubrication programs directly impact project economics — a well-lubricated drive requires less hydraulic capacity and reduces the risk of a locked string. We also assist with slurry circuit design, including separation plant chemical treatment programs to recycle and clean slurry for continued use throughout the drive.
Our products are available in bulk quantities and can be staged at the entry pit to match the injection rates required for the drive speed. On-site technical support is available for the duration of the project.
Key Products
Recommended additives for direct pipe installations.