By Ocean Eye’s Chris Gabel
Editor’s note: This is part two of an article entitled “Tanks for the Clarification” that ran in the November/December issue of UNDERWATER Magazine.
Steel tanks seemed to be becoming increasingly popular for a while but there has been a lot of change in the industry. Faber still produces steel tanks in both hot dipped galvanized and painted steel versions. They appear to be the current main player in the steel SCUBA cylinder market. PST (Pressed Steel Tanks) was another manufacturer but stopped production in 2002. That said, they have recently renewed their DOT certification for 2018. Stay tuned, things may change. Worthington too got out of the business announcing in 2014 that they closed their Canadian facility and have discontinued their steel tanks.
Steel tanks, by their nature, are heavier than their aluminum counterparts for the most part. The positive buoyancy issues, due to the weight of the cylinder, that can plague aluminum are non-existent. One daily field test is to make sure that any outer corrosion is noted and frequently checked for pitting. Any deep pitting or creasing should be noted and the tank taken out of service until inspected by a qualified technician. Make sure that pressure is kept in the tank. Preferably at or above 500 PSI. If the tank is completely drained, then appropriate procedure is to have the tank immediately visually inspected. I’ve seen tanks that have been drained and not inspected. The inside walls of the tank had rust and the risk of pitting was high. Moisture had entered the vessel in this case. I know I can’t speak for you, but personally I wouldn’t want to breathe air from a rusty cylinder.
As far as composites, the current people to keep looking at is Interspiro. They’ve introduced a series of tanks to the United States called the Divator Lite Cylinder Pack. They are now approved by the DOT for use in the U.S. According to Interspiro, they are authorized for use with compressed air from 0 to 50 Meters (166 Feet). They are manufactured with a carbon fiber filament with an outer wrap of glass fibers. The other fittings are made of acid proof stainless. It’s reported that the working pressure is 300 BAR, or 4350 PSI. They have a test pressure of 450 BAR (6526.71 PSI) and a minimum burst pressure of 900 BAR (13053.42 PSI). If you fill a tank to over 13000 PSI, then you’ve got to know that something bad is about to happen. They also have a Non-Limited Life approval. They have an interesting solution to the issue of varying buoyancy. They use a counterweight that attaches directly to the tank system. Admittedly, I have not been able to see one of these units for myself or dive one.
No matter which type of tank you chose, there are a few things to take note of. Specifically, please avoid putting any decals on your tanks. According to SOP, any decals are to be removed so that they can be inspected for corrosion. The same can be said about repainting. Any repainting of a cylinder means that either the tank needs to be completely stripped of paint or decommissioned. Again, the inspector can’t tell if there is any corrosion under the new paint. Also, be sure to check the o-ring in the valve that mates with the first stage. That seems to be one of the biggest pain points. Another thing to make sure of is that the burst disk is changed at least every 5 years. One humble suggestion I have is to avoid using tank boots. They can trap water and promote corrosion underneath the plastic/rubber devices.
So in conclusion, there are three current choices of tank compositions. Using the right tank composition and size for your use, whether it’s an EGS/ bailout bottle or as a SCUBA application for other uses (such as inspections), is an individual decision. According to PSI, there were about 8 (perhaps more) U.S. cylinder manufactures. So no matter what brand name you purchase, for the most part, they will be manufactured by companies such as Faber, Luxfer, and Catalina. Interspiro may be a good choice to explore as well taking advantage of their light weight. Make sure that you inspect your tanks before every dive and if in doubt, have them re-inspected. I know this is an expense but your life and health are worth it.
As always, take care of your equipment and it will take care of you.
For any questions, please contact Chris Gabel at CGabel@oceaneyeinc.com.