Guide
Cleaning a tank before visual inspection
Internal cleaning is the step every cylinder inspector knows and many dread: essential to see the real condition of the metal, tedious without the right tool. This guide sums up the method, the equipment and the precautions for cleaning a steel scuba cylinder before its visual inspection.
Why clean before inspecting?
A periodic visual inspection means examining the inside of the cylinder with a lamp or an endoscope to detect corrosion, pitting, cracks or deposits. A thin layer of oxidation, scale or dried moisture hides exactly what you are looking for: a corrosion pit under a film of rust is invisible. Cleaning strips the metal bare so the diagnosis is reliable, and removes deposits that would otherwise keep corroding the tank and end up in the regulator.
Equipment
- Two cleaning whips: a standard whip (long, straight strands) for the bottom and side walls, a reverse whip (short, strands curved backwards) for the shoulder and neck. Either one alone always leaves an area untreated.
- A drill or cordless drill with a 13 mm chuck and speed control, set below 1,000 rpm. No hammer mode.
- A tank fixture: cradle, rubber-lined vice or upright stand. The cylinder must not be able to turn or tip.
- An inspection lamp or endoscope to check before and after.
- Safety glasses, gloves, covering clothes.
- Fresh water and dry air for rinsing and drying.
Step by step
- Empty the cylinder completely and remove the valve. Never work on a pressurised tank, even at residual pressure.
- First inspection with a lamp: locate the affected areas, photograph if useful. This is your reference.
- Secure the cylinder firmly, horizontal or upright, with a suitable fixture. Keep bystanders away.
- Fit the standard whip in the chuck. Check the strands (none broken) and the shaft sleeve (intact: it protects the neck thread).
- Insert the whip with the drill stopped, down to the bottom, then start gradually, never above 1,000 rpm. Move slowly in and out along the walls, turning the cylinder a quarter turn every 20–30 seconds.
- Stop the rotation before withdrawing the whip. A whip spinning outside the tank lashes the air at several metres per second: this is the main injury risk.
- Switch to the reverse whip for the shoulder and the area under the neck: same rule, insert stopped, start inside, stop before pulling out. A few dozen seconds are enough. To withdraw it, turn the whip slightly by hand as you pull it out: the curved strands fold back and do not catch in the neck (umbrella effect), which avoids damaging the whip.
- Empty the residue (turn over, tap), rinse with fresh water if the tank was damp or heavily soiled, then dry completely with dry air. A tank closed while damp starts corroding again.
- Final inspection with a lamp or endoscope: the metal should be uniformly matte and clean. Any pit, crack or abnormal area is for the qualified inspector to judge, and where required for requalification.
Mistakes to avoid
- Spinning too fast. Above 1,000 rpm the strands heat up, deform and mark the metal without cleaning better.
- Starting outside the cylinder, or withdrawing while spinning. Never.
- Using a bare shaft. An uncoated shaft touching the neck thread damages it; a marked thread means a condemned tank.
- Forgetting the neck. The standard whip does not reach the shoulder: without a reverse whip, the area most exposed to condensation stays untreated.
- Closing while damp. Drying is part of the job.
- Cleaning an aluminium or composite cylinder with a tool designed for steel without the cylinder manufacturer's approval: light alloys scratch.
How long does it take?
With both whips and a properly secured tank, allow 10 to 15 minutes per cylinder, drying aside. For a club session of twenty tanks, that is half a day for two people: one cleans, the other rinses, dries and inspects.
Whip maintenance
Rinse with fresh water after the session, dry, store flat. Stainless strands wear normally over the years: a whip with shortened or bent strands cleans less well and should be replaced. Check the shaft sleeve before every use.