How to test the sealing performance of an oxygen cylinder?

How do factories test the airtightness of gas cylinders during production? And how should the airtightness be checked during daily inspections?What should be the frequency of checking for air tightness?
 

  Now, I'll bring you the answer.

I. Air tightness test (water immersion leak detection method)

This is the most intuitive and commonly used detection method, applicable before filling or during regular inspections. 
Operation steps: 
Fix the gas cylinders filled with the prescribed pressure of nitrogen (or fire extinguishing agent) onto the special supports. 
Immerse the gas cylinder completely in the water tank, with the water level ensuring that it completely covers the cylinder body and the valve connection area. 
Maintain the specified pressure (usually the maximum working pressure of the gas cylinder) and keep it stable for a period of time. 
Carefully observe if there are any continuous bubbles emerging. 
Qualification Criteria: 
Within the specified time frame (usually 3 to 5 minutes), no visible bubbles are continuously produced. 
There is no leakage at the valve, threaded connections, weld seams and other parts. 
Applicable scenarios: Pre-production inspection, regular annual inspection, re-inspection after repair

II. Pressure Drop Method (Pressure Holding Test Method)

Operation Steps: 
Fill the gas cylinder with dry nitrogen gas to the specified pressure (such as 4.2 MPa or 5.6 MPa) 
Close the valve and let it stand for a period of time (usually 24 hours) 
Record the initial pressure and the final pressure, and calculate the pressure drop. 
Qualification Criteria: 
The pressure drop within 24 hours shall not exceed the specified value (typically within ±1% range) 
The pressure gauge pointer did not show any obvious drop in pressure. 
Applicable scenarios: Online monitoring, regular inspection, and situations where immersion in water is not feasible.

III. Leak Detection by Spray Application (Local Leak Detection)

Operation Steps: 
Spray the dedicated leak detection liquid (such as soapy water or electronic leak detection liquid) onto the valve interfaces, weld seams and other areas prone to leakage. 
Observe whether bubbles continue to form 
Qualification Criteria: 
No continuous bubbles were generated after spraying. 
Applicable scenarios: Rapidly identify leakage points, conduct on-site maintenance and then verify the results

IV. Helium Mass Spectrometry Leak Detection (High Precision Detection)

Operation Steps: 
Vacuum the gas cylinder 
Inject helium gas into the exterior or interior of the gas cylinder as a tracer gas. 
Detect the leakage rate using a helium mass spectrometry leak detector 
Qualification Criteria: 
The leakage rate is lower than the standard requirement (e.g., ≤ 1×10⁻⁶ Pa·m³/s) 
Applicable scenarios: High-precision requirements environments, pre-shipment inspection, special gas storage cylinders

V. Daily Inspection Method (Pressure Gauge Observation Method)

Operation Steps: 
Check whether the pointer of the pressure gauge on the container valve is within the green normal range. 
Record the pressure value and compare it with the previous check result. 
Criteria for judgment: 
The pressure gauge pointer is within the green zone range (for example, in the 4.2 MPa system, the green zone is usually 3.6 - 4.8 MPa) 
If the pointer goes out of the green zone or the annual leakage rate exceeds 5%, refilling or maintenance is required.