Tank-full for Safety Inspections

While we stay busy in the winter months with classes and Try Scuba’s it’s also that time of the year at the dive shop when all the equipment gets the once over. We keep an eye on all of our equipment throughout the year but during the slower winter months every piece of equipment and gear gets an in depth inspection. It starts with the TANKs. All tanks or cylinders as they are referred to by the US Department of Transportation (DOT) and Compressed Gas Association (CGA) are required to undergo an annual visual inspection. Most SCUBA (Self Contained Underwater Breathing Apparatus) cylinders also need a hydro test every five years.  SCBA (Self Contained Breathing Apparatus) used by HAZMAT teams and Fire Departments as well as Fiber Wrapped Paintball cylinders are often on different Hydro  schedules. 

Last Saturday was tank inspection day.  I try to keep all the tanks that we use at Manta Dives inspected within the same month.  At Manta Divers we maintain 33 tanks.  24 of the tanks are Manta Divers rental fleet as well as 9 customers’ tanks that live at Manta Divers in exchange for letting us use them in a pinch. While most of the tanks are standard Aluminum S80 and S63 cubic ft. with 3000 lb working pressure we also have Steel  63 and 100 cubic ft. cylinders with working pleasures of 3442 lb.  

So why is it important to have tanks inspected annually?  Why is it important to the person filling your tank to do an exterior inspection of your tank and look for that inspection sticker on your tank?  If you could ask Hector Duran of Amigos Del Mar dive shop in San Pedro, Belize he would tell you that damaged tanks rupture and explode when re-filling them.  A twenty year veteran of the dive industry he died in October 2012 when a tank ruptured while he was refilling it.  Its protocol to check the Hydro stamp, Visual Inspection Sticker (VIS) as well as inspect the cylinder for any damage or condition that may of occurred since the VIS.  We look for deep scratches, gouges, dings, scratches, dents or extreme heat damage (fire).  It is still unclear why the tank Hector was filling exploded, but if he skipped any of the usual protocols, it could have led to his death.

It’s not just for the benefit of the person filling the tank to do the prefill inspection.  On September 11, 2011 Russell Vanhorn of St. Petersburg FL. died when the tank he was carrying into his condo exploded.  Although the cause has not been pinpointed all evidence points to a damaged tank that was filled without a prefill inspection or the tank was filled beyond its working pressure.  That’s why we follow the  protocols, OUR  SAFETY DEPENDS ON IT.

So what’s in an inspection?  It breaks down into 3 parts.

#1 - Exterior Inspection 

• Look for scratches, dents, gouges, dings.  Any of these over .015 inch depth  can be reason to condemn a tank.
• Look for heat or fire damage.
• Use a straight edge to check the tank hasn’t bulged from overfilling.
• Remove stickers and inspect the paint to insure that no repainting or repairs have been made
• Remove the boot and clamps to look for pitting or rust that could compromise the cylinder.
• For steel tanks we do a Hammer Tone Test.  Holding the tank off the floor by the valve I strike the tank with a fiberglass hammer. It should sound like a bell.  If it doesn’t the tank is most likely rusted out inside.

#2 - Interior Inspection

• Remove the valve and turn the tank over on a clean paper to determine if there are any particles or contaminates in the tank.
• After turning the cylinder upright “sniff test” the cylinder.  An oily or burnt plastic smell reveals that the cylinder has been refilled at less than a quality refilled station or off of a construction compressor.  Any odor will require the cylinder to be washed and dried to eliminate contamination.
• After inserting an inspection light we look for pitting, oxidation, rust or other issues.  If pitting is present it is tested to determine if it isn’t extensive enough to condemn the tank. In aluminum tanks oxidation dust can be rinsed out in a wash. In steel tanks the rust is removed by tumbling with an aggregate or by whipping with special tools. The interior should be clean and dry.
• A light and mirror is used to inspect the underside of the neck and threads.
• I use a VISUAL PLUS system to inspect the threads. It’s like a microscope that allows the inspector to see every detail of the threads.
• On Aluminum tanks manufactured prior to 1990 it’s a DOT requirement that the threads are EDDY tested every 5 years with the Hydro. Prior to 1990, some tanks were made from a 6359 alloy that was susceptible to thread cracking under a sustained load or pressure.  I EDDY test all aluminum tanks manufacture pre 1990 annually.  During an EDDT test a coil probe sends an electromagnetic current though the conductive threads.  A second receiver coil picks up the current and detects the presence of cracks or flaws.  If it fails the EDDY it’s a condemned tank.
• The last thing we look at is the O-ring gland. It’s a depression in the neck of the tank that the O-ring that seals the valve sits in . It must be clean and free of scratches to seal the pressure in the tank.

#3 - Valve Inspection

• The threads on the valve are inspected for damaged  or missing threads.
• The dip tube is inspected to insure that its tight in place. (  the dip tube protects  you if there was water in the tank for whatever reasons it wouldn’t go in your regulator if you were upside down)
• We check to the burst disc to make sure it’s in good condition and the right pressure.
• We check the operation of the valve to make sure operating smoothly,
• We check both of the O-rings. If either looks questionable we replace.

I hope this was informational about tanks, tank inspections and their importance. More knowledge makes us all better divers, but reading this blog should in no way be considered a class to certify you as a tank inspector or fill operator. Remember to check that your tank has been inspected by a professional and be aware of any damage to the tank.

Thank you for reading. As always, leave a comment and give us some feedback, share the blog on Facebook or tweet us out to your friends. Until next time, cheers.