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Does hydrostatically testing an aluminum-lined composite cylinder with tap water corrode the cylinder or make the cylinder unsafe?

No. Tap water of varying quality from all around the world has been used to hydrostatically test and retest aluminum and aluminum-lined composite cylinders for more than 30 years without harming cylinders or making them unsafe to use—provided, of course, that the cylinders have been properly dried after testing, as required by regulation. The worldwide safety record for some three million aluminum-lined composite cylinders is excellent, which affirms that tap water is an appropriate hydrostatic test liquid. Moreover, test agencies have an excellent record of properly drying cylinders before releasing them for service. In short, based on Luxfer field experience and user feedback, tap water corrosion of aluminum and aluminum-lined composite cylinders in the field is not a problem.


Should I avoid leaving tap water inside aluminum cylinders made from alloy 6061?

Yes. Do not leave tap water or any other kind of water inside any aluminum or aluminum-lined cylinder—or any steel cylinder, for that matter. Water remaining inside a cylinder is considered a “contaminant.” Luxfer, as well as regulatory authorities around the world, have required for years that cylinders be kept free of contaminants. If a cylinder becomes contaminated with tap water, pure water, sea water, oil, grease or other contaminating substances, the cylinder should be removed from service, properly cleaned, thoroughly dried and diligently inspected before further use. However, in some countries, regulations or standards require that cylinders containing water be condemned and rendered unserviceable (for example, see ISO 10461, Section 14.2). In short, if you find water or other contaminants inside your cylinder, take it out of service and comply with all applicable regulations.

As far as 6061 aluminum alloy is concerned, cylinders made from this alloy have been used for decades in scuba and shipboard service, in which cylinders are periodically exposed to very corrosive salt water and brine. These cylinders have an outstanding record both for service and safety. However, at no time should cylinders be stored sitting or standing in water—they should be stored in a clean, dry place—and water should never be allowed to remain inside cylinders. The only time that cylinders should contain water is during the very brief period required to perform a hydrostatic test (see questions 2 and 3, below), and the cylinders should be immediately dried when the test is completed.


Sustained-load cracking. I’ve heard that Luxfer have closed their plant in Australia and that they are no longer manufacturing scuba tanks. Is that true?

No. Luxfer has not stopped manufacturing scuba tanks. The Luxfer plant in Australia was closed in 2004 during a consolidation of Luxfer’s global manufacturing capacity. However, Luxfer has maintained a sales office and distribution center near Sydney. The Luxfer tanks now sold in Australia are manufactured at the Luxfer plant in California, which produces more aluminium tanks than any other facility in the world. Luxfer also manufactures scuba tanks in England. Luxfer remains fully committed to supplying the highest-quality tanks to the scuba industry worldwide.


Sustained-load-cracking – I’ve seen evidence on the Internet that a Luxfer scuba tank exploded in Perth, Australia, early in 2005. Was SLC involved?

An older scuba tank did, in fact, rupture in Perth in January 2005, and the likely mode of rupture was SLC. The investigation is ongoing. However, the 6351-alloy tank involved in the accident was not manufactured by Luxfer, but by CIG Gas Cylinders, a company acquired by Luxfer in 1997. CIG Gas Cylinders used 6351 alloy to manufacture scuba tanks from 1975 through 1990, and then switched to 6061 alloy. All scuba tanks manufactured in Australia by Luxfer have been made from Luxfer’s proprietary 6061 aluminium alloy, which is not susceptible to SLC.


Sustained-load cracking – how often should my Luxfer 6351-alloy scuba tank be inspected?

  • DOT requires requalification (hydrostatic retesting and visual inspection) of all aluminum scuba tanks every five years, regardless of alloy.
  • Both the DOT and the U.S. scuba industry recommend an annual visual inspection for all 6351-alloy scuba tanks. Luxfer supports this recommendation.
  • For its 6351-alloy tanks, Luxfer has established a manufacturer’s requirement for a visual inspection, including an eddy-current test, at least every 2.5 years.


Differences among the terms oxygen service – oxygen mixture – nitrox – enriched-air nitrox EAN – oxygen-enriched air

The term oxygen service generally means using pure oxygen (oxygen concentrations of 95% to 100%), but the term is sometimes used more broadly to refer to any gas mixture containing more oxygen than air. The “standard air” we breathe is composed of 20.95% oxygen, 78.05% nitrogen and 1% of trace amounts of other gases, including argon, carbon dioxide, neon, helium, krypton and xenon (the amounts vary depending upon your geographical location, altitude, etc.). For practical purposes, most technical literature rounds off these percentages and defines “standard air” as 21% oxygen and 79% nitrogen.

Oxygen mixture generally refers to gas blends containing between 50% and 95% oxygen.

Oxygen – enriched air, nitrox , and enriched-air nitrox (EAN) are generally used synonymously in the diving industry since all refer to pressurized diving gas mixtures containing various oxygen concentrations greater than standard air. For example, two common mixtures used by divers are EAN 32 (32% oxygen) and EAN 36 (36% oxygen). However, in the gas industry, oxygen-enriched air is sometimes defined more specifically as gas mixtures containing more oxygen than found in standard air, but no more than 50% oxygen.

To avoid confusion, Luxfer prefers using the term oxygen service to refer only to pure oxygen usage and enriched-air nitrox (EAN) to refer to oxygen-enriched breathing mixtures used for diving.

Whatever term you choose, the main thing to remember concerning Luxfer scuba cylinders is that when you fill a cylinder with an oxygen concentration of 23.5% or more, that cylinder must be specially cleaned for oxygen service as though it contained 100% oxygen.


Sustained-load cracking – how can I tell if my Luxfer cylinder is made from 6351 alloy?

The easiest way is to check the original hydrostatic test date stamped on the cylinder crown. Luxfer manufactured 6351-alloy cylinders during the following periods:

  • United States: 1972 through mid-1988
  • England: 1958 through 1995

After the above dates, Luxfer began making cylinders from a proprietary 6061 alloy, which is not susceptible to SLC.

In Australia, CIG Gas Cylinders manufactured scuba tanks from 6351 alloy from 1975 through 1990, and then switched to 6061 alloy. Luxfer acquired CIG Gas Cylinders in 1997, by which time Luxfer was manufacturing all scuba tanks with its own proprietary version of 6061 alloy. All Luxfer tanks manufactured in Australia under the names “Luxfer” and “Luxfer Australia ” have been made exclusively with Luxfer’s 6061 alloy.


Sustained-load cracking – how do I know if the person inspecting my cylinders is properly trained?

  • Luxfer recommends taking your cylinder to an authorized Luxfer service center or to an inspector trained by Professional Scuba Inspectors, Inc. (PSI) or the Association of Scuba Service Engineers & Technicians (ASSET).
  • It cannot be overemphasized that the quality of inspection is far more important than the frequency of inspection! An untrained or improperly trained inspector can look at a 6351-alloy cylinder numerous times without detecting SLC.
  • Unfortunately, many untrained or improperly trained technicians continue to inspect cylinders, and no uniform standards for inspector training and certification exist among regulatory authorities around the world.
  • Luxfer is working with industry groups and government agencies to help establish such standards.


Sustained-load cracking – why is it necessary to have my 6351-alloy cylinder inspected with an eddy-current device?

  • When properly used, eddy-current devices contribute significantly to early detection of hard-to-see sustained-load cracks. However, an eddy-current test is not a replacement for a diligent visual inspection by a properly trained inspector.
  • Eddy-current devices are tools to enhance proper visual inspections.
  • Eddy-current devices currently approved by Luxfer for use with Luxfer 6351-alloy cylinders are Visual Plus, Visual Plus II, Visual Plus III, and Visual Eddy. However, the only eddy-current device approved by Luxfer for use with cylinders made from Luxfer’s proprietary 6061 alloy is Visual Plus III.


Sustained-load cracking – which types of cylinders are most susceptible to SLC-related ruptures?

  • Any type of cylinder manufactured from 6351 alloy could conceivably develop a sustained-load crack over time if subjected to certain conditions.
  • However, a cylinder is more likely to rupture in applications where pressure is higher and where overfilling and abuse occur more often.
  • Historically, the applications most susceptible to SLC-related rupture are scuba and SCBA (life support).