Annual Cylinder Visual Inspection

 In Services

They say “looks can be deceiving”. It really is. Not just for human appearance, but looks can also be deceiving when it comes to SCUBA and BA cylinders: It’s shiny and clean on the outside. While it may be true for most cylinders we see and use, what is important is the part that we don’t see and is located in the internal structures of the cylinder where it comes in contact with the compressed air that we are breathing.

But how do we determine the cylinders internal condition given the fact that it is totally sealed? Do we use x-ray machines? We are not after concealed substances, like drugs and other prohibited items, that the use of an x-ray machine is significant. Instead, what is needed are the eyes and hands of a highly trained technician.

Cylinder Visual Inspection: The Process

Photo courtesy from

The most logical thing to do to determine the internal condition of Scuba and BA cylinders is to inspect it visually. But how do you do it since cylinders are completely sealed?

Here are the steps in doing a visual inspection:

Before the actual inspection process will commence, you need to fill-out some documents such as the Cylinder Visual Inspection Form. You will need to remove any cylinder accessory (like mesh, boot and cap) as it can possibly interfere with the inspection process.

Recording all cylinder markings is very important. If you found out that the cylinder about to be inspected, has a manufacturers marking which falls under the category of “Cylinders at Risk“, then there is no need to proceed in doing the visual inspection. All cylinders that are considered at risk must be condemned immediately as they may risk of exploding releasing a potential energy equivalent to the power of a hand grenade.

Other factors can also be considered at this pre-inspection phase which will become the basis in condemning such cylinder, as follows:

  • cylinders exposed to heat over 350 F (177 C)
  • cylinders that were repainted and heated to over 350 F (177 C) to dry and cure the paint
  • cylinders that are exposed to direct fire
  • cylinders that shows any torch burns or fire damage 

After initial inspection and verification has been done, you can now commence in doing the cylinder visual inspection.

Step 1: Drain all the Air. We are all taught during our certification course to leave some air in our tank after every use. This is not to help the compressor technician in reducing his airfill time, but rather, it would prevent the entry of water and other contaminants in going inside the cylinder as there is still air pressure. With this, most scuba or BA cylinders that are subjected for a visual inspection still contains some amount of air. So, you need to open the valve to allow air to escape until it is totally drained. But not just opening the valve, but you need to open it in such a way that air is flowing out at a minimal rate. Otherwise, excessive flow of air will increase the potential of damaging the valve itself. Since there are several brands and models of cylinders, it is best to follow the manufacturers recommendation in opening the valve.

Photo courtesy from Scuba Engineer

WARNING: Do not unscrew the valve when there is still air inside the cylinder. By doing so could lead to injury or even death as the valve will be jolted out of its thread like a giant bullet courtesy from the exiting air pressure.

Step 2: Unscrew the Cylinder Valve. This part is quite tricky as it will give you an initial impression that you can use ordinary handyman tools, like a wrench or vice grip, to open such valve. For purposes of safety, we might as well not describe the process on how to unscrew the valve as it might trigger your interest and do it yourself instead.

Step 3: Internal Inspection using a Light stick. Do not use ordinary flashlight or torch as it will only illuminate the outer edges of the cylinder. Instead, a special light stick is used that can easily be inserted inside the cylinder giving you a bright internal light. Observe and record any contaminants you see inside the cylinder, as well as record any metal deformities or corrosion you see inside the cylinder.

  • Condemn cylinders that has internal cracks or distortion in the internal wall

Step 4: Extract all Internal Contaminants. How do you extract? Do you need to do internal scraping? The answer is a BIG NO. All you need to do is invert the cylinder over a piece of clean paper and allow the contaminants to freely feel off. In cases of contaminants being stuck in the metal, holding the inverted cylinder half an inch over the paper then dropping it will allow contaminants to be dislodged. Collect all contaminants and identify their origins if possible. In cases where internal contaminants are stuck hard in the metal or if you see a gummy substance which is an indicator of oil contamination, an internal cleaning should be done.

  • Hold cylinders that have gummy substances which have an offensive odor. The cylinder will be subjected to internal cleaning.

Step 5: External Inspection. Another important element in doing a visual inspection is taking notes on the condition of the external material. The external surface of the cylinder should be smooth, flat and without any bulges, bows, dents, cuts, gouges, scratches and corrosion.

  • Condemn cylinders with dents deeper than 0.060 inch (1.53 mm)
  • Condemn cylinders with dents greater than 2 inches (50 mm) in diameter
  • Condemn cylinders with visible bulges
  • Condemn cylinders with surface cuts, digs or gouges longer than 6 inches (152mm) or deeper than 0.030 inch (0.76 mm)
  • Condemn cylinders with corrosion pits
  • Condemn cylinders with external line or widespread corrosion 

Step 6: Valve Thread Inspection. Careful inspection should also be made on the cylinder valve particularly on thread imperfections which include metal loss, galling, corrosion, folds, cracks, broken threads, cross threads, stripped threads and threads without well defined and sharp peaks.

  • Condemn cylinders that have defective valve threads.
  • Condemn cylinders with valve cracks
  • Condemn cylinders that has an o-ring gland, face cracks or face damage
  • Condemn cylinders that has a folded thread
  • Condemn cylinders with thread corrosion

Special Note: After laying the process of doing visual inspection, you may think that some handyman tools may aid you in performing such visual inspection, thereby giving you an initial impression that you can do it yourself and save money. If this is the case, then we appeal to you not to do so. Allow certified personnel to do their job and please do send your cylinders only to facilities and technicians that are certified to do cylinder visual inspection.



Frequency in conducting Cylinder Visual Inspection

Ideally, on a normal service rate, SCUBA and BA cylinders should be visually inspected once a year. However, there are variations in the frequency in conducting a visual inspection which will depend on the degree of use. For a heavy service (which means a cylinder is filled at least 5 times a week), then the visual inspection should be carried out every four months.

In some extraordinary circumstances, the need to do a visual inspection should be ASAP before continued use. These are some events that may need immediate visual inspection:

  • cylinder was dropped
  • cylinder was struck in an accident
  • cylinder was improperly stored
  • cylinder shows sign of damage
  • cylinder has obvious corrosion, dent, scrape, cut or dig
  • cylinder shows sign of charring or blistering of the paint
  • cylinder shows melting or charring of the metal
  • cylinder wall shows distortion
  • cylinder valve (or any of the valve components) shows melting
  • cylinder is leaking

On a final note, taking our cylinders for a visual inspection would consume our much needed time, effort and budget. But just consider all of these as a safety investment as the consequence of not doing one would often lead to accidents, which in turn, means a higher cost.

Video courtesy from Alec Peirce Scuba

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