An oilless bearing in drilling equipment is normally a bronze or high-strength brass body with a solid lubricant — usually graphite-based plugs or an impregnated graphite pattern — embedded in the working surface. As the shaft or pin slides, the lubricant transfers to the counterface and forms a film. No oil or grease is applied in service, so none can leak onto the deck, wash into the sea or bake onto a hot surface.

The mechanism has a cost. Without a fluid film, friction is higher than in a hydrodynamic bearing and the heat has to leave through the shaft and housing rather than with circulating oil. That is why the envelope is defined by PV — contact pressure times sliding velocity — and why these bushings belong on slow, heavily loaded joints.

Fire water and seawater pumps are a deliberate contrast: their wear rings and bushings are maintenance-free because the pumped fluid lubricates them, not because they run dry. They are often grouped with oilless parts in a bill of materials, but the selection logic differs — see aluminum bronze wear rings for fire water pumps and aluminum bronze plate.

Across this group, dry PV limits commonly fall around 1.0–1.6 MPa·m/s, dry friction coefficients around 0.10–0.20, and temperature capability is usually quoted at −40 °C to +300 °C (−40 °F to 570 °F). Treat these as first-pass figures; the material certificate governs. Part forms supplied into this sector are listed under oil and gas industry solutions, and testing under quality inspection and life evaluation.

Onshore and offshore: what differs

On land the driver is usually access and contamination. A wellhead or a beam pump is visited on a maintenance round; if a joint needs greasing between visits and does not get it, the joint fails. Drilling fluid, dust and sand make grease films worse, because grease holds abrasive particles at the contact. Temperature swings matter too: a grease chosen for desert service will not behave the same way in arctic conditions.

Offshore adds three things. Salt spray and immersion attack the bearing and the surrounding steel, which is why aluminum bronze and correctly specified tin bronzes appear so often in deck equipment; see sliding bearings for marine and offshore service. Access costs more, since any intervention competes for crane and deck time. And lubricant reaching the sea is regulated, so a joint that cannot leak is worth something beyond the maintenance saving. The same reasoning covers oil-free slide bearings and cantilever skidding plates.

Limits: when an oilless bearing is the wrong answer

• Rotating shafts with real surface speed. Above the PV limit, dry bronze wears quickly and generates heat it cannot shed. Keep the oil or use a rolling bearing.
• Sour service. Copper alloys react with sulfur and are generally restricted where hydrogen sulfide is present. Confirm with the materials engineer before specifying bronze there.
• Abrasive slurry at the contact. Drilling fluid carrying solids cuts both bushing and pin. Sealing, flushing or a harder pairing is the fix.
• Heat that must be removed continuously. Without circulating oil, heat leaves through the shaft and housing; a light housing or long duty cycle overheats it.
• Very low friction is required. Where energy loss or precise positioning matters, a full fluid film beats dry sliding by a wide margin.
• High-frequency, low-load motion. Too little load to generate the transfer film makes wear behaviour less predictable.
• Failure would be sudden and unmonitored. Dry bushings wear gradually, then faster. Plan an inspection interval or accept the risk deliberately.

Selection and installation notes

1. Record the present duty: load range including peaks, stroke or oscillation angle, cycles per hour, temperature range, and what contacts the joint — drilling fluid, seawater, sand, chemicals.
2. Calculate PV at the worst case and keep margin below the limit for the selected alloy.
3. Specify the counterface. A hardened pin or shaft is normal practice, commonly 300 HB or harder, with a finish around Ra 0.4–0.8 µm (16–32 µin).
4. Choose the alloy for the environment as well as the load: aluminum bronze for seawater and splash zones, leaded bronze where conformability matters and the market permits it.
5. Deal with galvanic corrosion. Bronze coupled to steel in seawater needs insulation, coatings or cathodic protection designed in, not added afterwards.
6. Set fit and clearance. A press fit in an H7 housing bore is usual, with running clearance typically 0.1–0.25% of shaft diameter, widened for thermal growth — see oilless bearing specification.
7. Run in at reduced load for the first few hundred cycles so the transfer film forms before full duty.
8. Document the supply: material certificates, dimensional inspection, and traceability to the heat for safety-critical joints.

Frequently asked questions

Are oilless bearings used in oil and gas production?

Yes, mainly on slow, heavily loaded, hard-to-reach joints: wellhead and valve linkages, blowout preventer hinge points, pump linkage, pipe-handling guides, artificial-lift beam bushings and offshore deck equipment. They are not used on the high-speed rotating shafts of a rig, which stay oil-lubricated.

Do these bearings work submerged in seawater?

Yes, with the right alloy. Aluminum bronze and selected tin bronzes run in seawater, and the water removes heat and carries away wear debris. Water-lubricated parts are a different selection case from dry-running ones and should be specified as such.

How does a solid-lubricated bushing behave in sour (H2S) service?

With caution. Copper alloys react with sulfur and are generally restricted in sour environments. Raise the question with the materials engineer before any bronze is specified there, and record the decision on the drawing.

Can an existing greased joint be converted directly?

Sometimes. It works when the duty is inside the PV envelope, the pin or shaft is hard and smooth, and the housing holds its shape. It fails when a conversion is made to remove a maintenance task without checking load and speed first.

What is the maintenance requirement once installed?

No lubrication. The work shifts to inspection: measure wear at a defined interval, watch for temperature rise and debris around the joint, and replace when the measured clearance reaches the limit set for the installation.