Which method is NOT a type of requalification for DOT cylinders?

The Electrical Resistance Method is not recognized as a type of requalification for DOT (Department of Transportation) cylinders. In the context of requalifying gas cylinders, the methods generally accepted involve physical inspections and tests that assess the integrity and safety of the cylinder.

The External Visual Inspection Method is a fundamental approach where the cylinders are visually inspected for any signs of damage, corrosion, or deformities that may affect their safety during use. This method is crucial for ensuring that any external faults are identified before the cylinder is put back into service.

The Proof Pressure Method involves filling the cylinder with water and pressurizing it to a level higher than its service pressure. This test is designed to ensure that the cylinder can withstand pressures beyond what it would typically encounter in use, thereby confirming that it is safe for continued operation.

The Volumetric Expansion Method also serves as a requalification technique by measuring how much a cylinder expands under pressure. This method helps to verify the cylinder's structural integrity and ability to hold pressure safely over time.

Each of these accepted methods has specific criteria and procedures outlined by the DOT to ensure the continued safety of gas cylinders.