Which type of cylinder container is specifically required to be tested every 5 years?

The requirement for testing every 5 years specifically applies to DOT steel cylinders. These cylinders, which are often used for the transport of compressed gases, are regulated by the Department of Transportation (DOT) under specific guidelines. The periodic testing is crucial to ensure safety and reliability in the storage and transport of gases, as the structural integrity of these cylinders can be compromised over time due to factors like corrosion, impact, and wear.

In contrast, ASME cylinders, which are designed according to the standards set by the American Society of Mechanical Engineers, follow a different maintenance and inspection schedule. HDPE containers and polypropylene tanks, typically used for storing liquids and not necessarily under pressure, have different guidelines and testing requirements that do not align with the strict 5-year testing regulation for DOT steel cylinders.