Why the seal is the whole system
Reverse circulation works by pushing air down the annulus between the outer and inner tube, and returning the sample up the inside of the inner tube. The two paths are separated by nothing more than the wall of the inner tube and the seal at each joint.
When that seal leaks, air bypasses into the inner tube. The sample return drops, contamination rises, and the hole effectively stops being an exploration hole — regardless of what the rig's depth rating says.
Leakage is therefore not a maintenance nuisance on an RC string. It is the failure mode that ends the hole.
Where the seal is actually lost
Almost never through the tube wall itself. The four places it goes:
- At the joint seal. The seal between inner tubes at each connection is the highest-cycle interface in the string — it is made up and broken out on every rod change.
- Seal wear from abrasion. Cuttings and dust in the annulus are carried past the seal on every cycle. A seal that is not designed for that environment wears progressively until it no longer seals.
- Inner tube misalignment. If the inner tubes are not concentric and coaxial, the seal is loaded unevenly and fails early no matter how good the material is.
- Non-universal interchangeability. Mixed inner tubes from different suppliers or batches that are not machined to a common tolerance will not seal reliably at every joint.
What the pipe design does about it
| Leakage driver | Design response |
|---|---|
| Seal wear in an abrasive annulus | Custom seals, produced to extend seal life and reduce leakage — not a catalogue O-ring |
| Inner tube misalignment | Precision machining ensuring universal interchangeability of inner and outer tubes |
| Tube fatigue and wear | High-strength alloy material with heat treatment, for long inner and outer tube life |
| Joint strength under pull | Friction welding with stress relief after welding, plus upset pipe ends |
The two that matter most in service are the custom seal and the machining tolerance. A seal designed for the annulus environment lasts materially longer than a standard section, and precision-machined inner tubes with universal interchangeability mean you can mix and replace without losing seal integrity at the joint.
Matching the pipe to the rig
The RC range is built around a set of rigs rather than a single size:
- RC500L — compact, catalogue maximum depth 400 m, 3 m rods in Ø102 / Ø114 mm, 132 kW Cummins.
- RC800L — long-stroke, 600 m maximum depth, 6 m rods, 470 kN pull force.
- RC800A — RC800 configuration with automatic rod handling, 20-rod rack of Ø114 × 6,000 mm.
- RC1200L — high capacity, 1,000 m maximum depth, 570 kN pull force, Weichai 220 kW with a Cummins 360 option.
Rod length, rod diameter and pull force all follow from the rig, and the dual-wall pipe has to match all three. Confirm the rig model, the compressor air supply and the sampling requirement together — sizing the pipe alone will not give you a working setup.
Universal interchangeability is a machining-tolerance property, not a dimension. Two inner tubes of the same nominal OD from different sources can differ enough to compromise the seal at the joint. If you are replacing inner tubes on a mixed string, gauge them before they go in the hole.
Frequently asked questions
Why does RC drill pipe leak?
Almost never through the tube wall. The seal is lost at the joint between inner tubes, from seal wear as abrasive cuttings pass through the annulus, from inner tube misalignment loading the seal unevenly, or from mixing inner tubes that are not machined to a common tolerance.
What is a custom seal on RC pipe?
A seal designed for the annulus environment rather than a standard catalogue section. It is produced to extend seal life and reduce leakage, which matters because the joint seal is the highest-cycle interface in the string — it is made up and broken out on every rod change.
What does universal interchangeability mean on dual-wall pipe?
It means inner and outer tubes are precision-machined to a common tolerance so they can be mixed and replaced without losing seal integrity or fit at the joint. It is a machining-tolerance property, not just a matching outside diameter.
How do I choose between RC500L, RC800L, RC800A and RC1200L?
By target depth, rod length and pull force. RC500L is the compact option at 400 m with 3 m rods; RC800L and RC800A reach 600 m with 6 m rods; RC1200L reaches 1,000 m with 570 kN pull. Confirm the rig, the compressor air supply and the sampling requirement together — the pipe has to match all three.
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Rig model, compressor specification and sampling requirement. We will confirm the complete rig, air supply and sampling setup before quoting.
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