Which of the following is true about the construction of steel cylinders?

The statement that steel cylinders must meet DOT specifications is accurate because all pressure vessels, including those used for compressed natural gas, must comply with specific safety and manufacturing standards set forth by the Department of Transportation (DOT). These regulations ensure that the cylinders can safely withstand the pressures they will encounter and that they are constructed with materials and design techniques appropriate for their intended use.

Meeting DOT specifications is vital for ensuring both the integrity of the cylinder and the safety of the public. Tests for materials, performance under pressure, and leak resistance are among the requirements that must be adhered to, further emphasizing the importance of these regulations in cylinder construction.

The other options do not reflect accurate information regarding steel cylinder construction. For example, while some cylinders are welded, not all are, as they can also be constructed using methods like seamless manufacturing techniques. Similarly, steel cylinders require rigorous testing to confirm they meet safety standards, rather than exempting them from testing. Finally, cylinders must be made from suitable alloys rather than any metal, as the choice of material impacts the strength, durability, and safety performance of the cylinder under high pressure.