Filling Compressed Gas Cylinders

Due to the vast diversity of uses and requirements associated with compressed gas cylinders, a prefill inspection of each cylinder is a necessary precaution. This should indicate any corrections or repairs that are required prior to filling. The following paragraphs describe operations that should be included in the prefill process. 

DOT and TC regulations specify that cylinders cannot be filled without first determining the ownership of the cylinder. This can be established by means of the cylinder marking and/or written permission of the owner on file at the filling location. 

B — Detachable pressure connection C — Pressure indicating gage D — Pressure recording gage (optional) E — Pressure surge chamber F — Cylinder shut-off valve G — Pressure relief valve H — Pressure valve 

Retest periods may vary depending upon use, material of construction, and the cylinder specification. Many steel cylinders must be retested every five years. DOT and TC regulations allow for Specification 3A and 3AA cylinders to be retested every 10 years provided the cylinder meets the regulatory criteria in 49 CFR 173.34, which are summarized in CGA P-15, Filling of Industrial and Medical Nonflammable Compressed Gas Cylinders [1] and [23] Aluminum cylinders must be retested every five years and fiber-reinforced high pressure cylinders every three years. 

A cylinder valve inspection must be performed on each cylinder to ascertain that the valve is suitable for use and the intended gas service. The valve should be free of oil or other hydrocarbon substances that will present a filling hazard, particularly with oxidizing gases. The valve should operate properly and smoothly. The outlet should be in good condition with undamaged threads and seat. 

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