Frequently asked questions about the effects of tap water on aluminum and aluminum-lined cylinders made of alloy 6061

1. Question: Should I avoid leaving tap water inside aluminum cylinders made from alloy 6061?

Answer: 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.

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

Answer: 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.

3. Question: Will my aluminum-lined composite cylinder have a shortened life from being hydrostatically tested with tap water?

Answer: No. The field record of cylinders in use for many years shows no evidence of reduced service life from periodic hydrostatic testing with tap water. This test is normally conducted quickly, and the cylinder only holds tap water for a few minutes. After the test, the cylinder must be dried. As long as this procedure is properly followed, there is no cause for concern.

4. Question: Are special coatings needed to protect aluminum cylinder interiors from tap water?

Answer: No. Special internal cylinder coatings are sometimes used with certain kinds of gases, but they have nothing to do with protecting a cylinder from tap water or any other kind of water, nor are they required or recommended for that purpose.

5. Question: Should I be doing anything different for my aluminum alloy 6061 composite cylinders than I have done in the past?

Answer: If you have properly maintained, used, tested and stored your cylinders in accordance with applicable regulations and manufacturer recommendations, the answer is no. If you continue following these proper procedures, your cylinders should provide many years of dependable service.

For more information about proper care and maintenance for your aluminum and aluminum-lined composite cylinders, please see the “Support” section of the Luxfer website at www.luxfercylinders.com.