DTH Drilling in Cold Weather: Prevent Frozen Air Lines, Poor Lubrication, and Lost Impact

Direct answer: when DTH drilling becomes unstable in freezing weather, do not assume the hammer itself has failed. Cold conditions can thicken lubricants, increase cold-start stress at the compressor, and turn condensate in receivers, filters, valves, hoses or exposed lines into an airflow restriction. Because a DTH hammer depends on a continuous supply of compressed air and rock-drill oil, a winter problem upstream can appear at the bottom of the hole as weak impact, irregular hammering, poor hole cleaning or a complete stop.

The safest winter approach is therefore system-based: prepare the compressor, remove and control moisture, verify the air-treatment chain, use the hammer manufacturer’s temperature-appropriate rock-drill oil, confirm oil delivery under real airflow, and diagnose pressure loss before changing drilling parameters or dismantling the hammer.

This guide is for surface mines, quarries, water-well and construction drilling crews operating DTH systems in cold or freezing conditions. It is not a substitute for the temperature limits, lubricant table or startup procedure for your specific compressor, rig and hammer.

1. Why Cold Weather Changes a DTH Drilling System

DTH drilling is unusually sensitive to the quality of the compressed-air path because the same air system has several jobs: it powers the hammer cycle, carries lubricant to internal moving surfaces, helps clear cuttings and, in many configurations, manages water and other drilling fluids. A winter disturbance anywhere between the compressor and hammer can therefore affect impact and hole cleaning at the same time.

Atlas Copco’s current cold-weather compressor guidance specifically identifies thicker oil, frozen moisture in lines or valves, cold-start difficulty and unstable output as winter risks. Kaeser likewise recommends draining receiver tanks, protecting condensate drains from freezing and keeping compressor lubricant warm enough for the manufacturer’s allowed operating range.

2. Moisture Control Comes Before Hammer Troubleshooting

Compressed air always contains water vapor. After compression, the air is hot; as it cools through the aftercooler, receiver, dryer, piping and exposed hoses, moisture can condense. In warm weather that liquid may simply collect in drains. In freezing conditions, the same liquid can become an obstruction.

For a DTH crew, the important point is that the pressure shown at the compressor does not prove that full air volume is reaching the hammer. A frozen or partially blocked component can create a large pressure loss only when the system is flowing.

1. Drain the receiver and separators. Remove accumulated condensate before the shift and according to the compressor manufacturer’s maintenance schedule.
2. Check the dryer and drains. Confirm that the air-treatment equipment is intended for the lowest expected exposed temperature. A dryer that is adequate in a warm compressor room may not protect a long outdoor hose or pipe run if downstream air cools further.
3. Inspect low points. Hoses, manifolds and temporary piping can trap liquid. Look for sagging sections, frozen drain bowls and valves that no longer operate freely.
4. Compare pressure under flow. If possible, compare compressor discharge with pressure closer to the rig while the system is flowing. A winter-specific increase in pressure loss points to the air path before it points to the hammer.
5. Keep connections clean and capped. Snow, ice, dirt and scale entering an open drill pipe can create a second restriction after the air system is restored.

3. Cold-Weather Lubrication: Verify Delivery, Not Just Oil Level

DTH hammer OEM manuals consistently treat lubrication as a critical operating requirement. Robit states that the correct rock-drill-oil grade depends on ambient temperature and notes that lubricator delivery changes with viscosity. Rockmore requires pneumatic rock-drill oil for its ROK-series hammers and warns that inadequate lubrication can cause premature hammer damage.

The practical winter lesson is not to copy a universal “winter oil” number from another hammer. The correct grade depends on the hammer manufacturer, ambient temperature, lubricator design and operating air conditions. Instead:

• use only the rock-drill oil grade approved for the specific hammer and temperature range;
• check whether the lubricator is a plunger, venturi or other metering design and confirm its cold-weather behavior;
• verify that oil is actually reaching the drill string under operating airflow, not merely that the lubricator reservoir is full;
• recheck the metering setting after a major temperature change because viscosity affects delivery;
• do not substitute hydraulic oil, engine oil, gear oil, diesel or an improvised additive when the hammer manual does not approve it;
• if water injection or wet drilling is used, follow the hammer OEM’s increased-lubrication instruction rather than assuming the dry-drilling setting is sufficient.

Robit’s current H-series manual, for example, specifies different rock-drill-oil grades by ambient temperature and explicitly states that oil viscosity changes with temperature. That is a useful engineering principle, but the exact grade for your hammer should still come from its own manual.

4. Pre-Shift Winter Checklist for DTH Drilling

Do not use extra feed force or rotation speed to “push through” a winter air-supply problem. If impact energy or return air is unstable, first restore the compressed-air and lubrication conditions specified for the system.

5. Lost Impact in Freezing Weather: A Diagnostic Sequence

If a hammer loses impact only on cold mornings or after a long winter shutdown, use a sequence that separates the air system from the hammer. This prevents unnecessary disassembly and helps avoid treating the symptom instead of the cause.

1. Confirm the compressor is fully warmed and stable. Record discharge pressure and, if available, airflow or engine/load data.
2. Check pressure loss while air is flowing. A normal static pressure reading can hide a frozen filter, valve or hose restriction.
3. Drain and inspect moisture points. Receiver tanks, separators, filters, drain bowls, manifolds and low hose sections should be checked for water or ice.
4. Confirm rock-drill oil reaches the hammer. Follow the hammer OEM’s verification method. A full lubricator with poor cold-flow delivery is not adequate lubrication.
5. Check the drill string and bit exhaust paths. Make sure pipe bores, connections and bit flushing holes are clear and that return air is not being restricted by a blockage.
6. Then inspect the hammer. If correct pressure, airflow, lubrication and clean flow paths are confirmed but impact remains abnormal, proceed with the hammer manufacturer’s troubleshooting and wear inspection procedure.

Robit’s troubleshooting table lists insufficient air pressure, insufficient or excessive lubrication, blocked bit exhaust holes, contamination and worn parts as separate causes of poor or inoperative DTH performance. That is why a cold-weather diagnosis should not jump directly to a piston or wear-sleeve failure.

6. Shutdown and Restart Matter More in Winter

A winter shift can end with more risk than a summer shift because residual moisture can freeze while the rig is idle. Before a planned shutdown:

• drain compressor and air-treatment condensate according to the equipment manual;
• remove standing water from exposed air lines or approved drain points;
• clean and cap drill-pipe connections so snow and debris cannot enter;
• lubricate and store the DTH hammer as required by its manufacturer, especially after wet drilling;
• protect the lubricator and oil supply from temperatures outside the oil and equipment limits;
• at restart, warm and stabilize the compressor before assuming the previous shift’s pressure and lubrication settings are still correct.

If a component is suspected to be frozen, use the equipment manufacturer’s approved thawing and restart procedure. Do not apply uncontrolled heat to a DTH hammer; Rockmore’s current service guide specifically instructs users not to apply heat during hammer service.

7. What to Send in an RFQ for a Cold-Weather DTH Job

Cold-weather procurement should describe the operating environment, not just the hammer size and bit diameter. Send:

• rig make and model;
• DTH hammer make/model and top-sub connection;
• target hole diameter, typical depth and application;
• rock condition and expected cuttings load;
• minimum expected ambient temperature and whether the air lines are exposed outdoors;
• compressor model, rated pressure and airflow;
• dryer, receiver, separator and drain arrangement;
• air-hose / drill-pipe length and major connection sizes;
• current rock-drill oil and lubricator type;
• whether water injection, foam or wet drilling is used;
• current drill pipe, bit shank and bit face details;
• quantity, destination and required inspection/packing documents.

For the drill string, PerfoMax currently offers a 76 mm DTH drill pipe with API 2-3/8 REG connection and a DTH drill-bit selection page that requires the hammer shank, target diameter, face, buttons and flushing to be confirmed together. Browse the current DTH Tools collection for the available scope.

Cold-weather operation does not change the basic compatibility rule: the rotary-head or saver-sub connection, drill pipe, hammer top sub and bit shank still have to be approved as one system. If you need a quotation, send PerfoMax the rig, compressor, hammer, drill-string and site-temperature information so the configuration can be reviewed rather than guessed from nominal size alone.

8. Common Cold-Weather Mistakes

• Blaming the hammer before checking a frozen or restricted air line.
• Reading only compressor discharge pressure instead of checking pressure loss under airflow.
• Assuming a full lubricator reservoir means adequate oil is reaching the hammer.
• Keeping a warm-weather lubricant setting after a large temperature drop without rechecking delivery.
• Using a dryer or drain arrangement without considering the coldest outdoor section of the air system.
• Leaving wet hoses, receivers or drill pipes idle through a freezing shutdown.
• Increasing feed, rotation or pressure beyond the approved operating range to compensate for weak percussion.
• Changing to an unapproved oil or additive because the original oil flows slowly in the cold.

FAQ

Why can a DTH hammer stop working only in cold weather?

Cold weather can create upstream problems that look like a hammer fault. Condensate can freeze in air-system components, compressor oil can thicken during startup, and rock-drill-oil delivery can change with viscosity. Confirm stable airflow, pressure and lubrication before opening the hammer.

Does a higher compressor pressure solve a frozen DTH air line?

No. A restriction should be located and removed according to the compressor and rig procedures. Raising pressure beyond the approved operating range does not correct ice, a blocked filter, poor lubrication or a restricted drill string.

What rock-drill oil should I use for winter DTH drilling?

Use the grade specified by the DTH hammer manufacturer for the actual ambient and operating conditions. OEM manuals show that oil selection and metering are temperature-dependent; do not copy a grade from a different hammer without verification.

How do I know whether the problem is the compressor or the hammer?

Compare system behavior under flow. Confirm compressor warm-up, drain condensate, inspect filters/valves/hoses, verify pressure closer to the rig, confirm oil delivery and clear the drill string and bit flushing paths. If those checks pass, continue with the hammer OEM’s internal troubleshooting sequence.

What cold-weather information should be included in a DTH tooling RFQ?

Include minimum ambient temperature, compressor pressure/airflow, air-treatment arrangement, hose and pipe lengths, lubricator/oil details, hammer and bit interface, hole diameter/depth, rock condition and whether water or foam is injected.

Technical Sources

• Atlas Copco — How Extreme Temperatures Affect Air Compressor Performance
• Kaeser — Tips for Winterizing Your Compressed Air System
• Robit — H Series DTH Hammers Operation and Maintenance Manual
• Rockmore — ROK Series DTH Hammer Operation & Service Guide