Approximately 36 percent of nitrogen gas supplied by gas companies is delivered in high-pressure cylinders. At first, it would appear to be a fairly simple method of supply, requiring a cylinder, pressure regulator and piping to deliver nitrogen gas to the application.
However, the following checks and procedures must be carried out every time a cylinder is exchanged and the pressure regulator re-fitted and re-connected to a gas system to ensure safe operation. It is also important to understand that when an individual is charged with the responsibility of connecting and disconnecting high-pressure cylinders to an application, they could be personally liable if anything goes wrong.
Three safety inspections for high-pressure cylinders
When taking delivery of cylinders, it is essential that the three safety inspections listed below are carried out each and every time a cylinder is changed over.
1. Colour coding and labels
Although cylinders are colour coded, this should not be relied upon to identify the contents. The label affixed to the cylinder must always be used as the primary means of contents identification. Cylinders without labels or where the label doesn’t match the colour coding should not be used. They need to be set aside or quarantined and returned to the supplier. It is essential to refuse acceptance at the point of delivery if any cylinders do not have identification labels attached.
Having determined the contents of the cylinder, it is then necessary to check that the gas is suitable for the application. The pressure of the gas in the cylinder should not be more than the regulator fitted, and the cylinder needs to be secured so that it can’t topple over — ideally in a purpose-built cylinder rack or store.
2. Cylinder valve
The cylinder valve comes fitted to the cylinder when it is delivered. It is basically an open or closed valve operated with a key/spanner. The pressure regulator is then fitted to this. If the valve is on a newly filled, unused cylinder it should have a factory sealing cap in place. Checks should be carried out to ensure the fitting is undamaged and contaminate free. It is essential that there are no signs of solvents, oils, greases or PTFE tape, and it must be clear of dirt and moisture. Note that PTFE sealing tape should never be used as the pressure regulator has its own rubber seal. PTFE can cause fire/explosions if used with certain gas species.
3. Pressure regulator
- Check it has a date stamp or code and is within its inspection period of usually 5 years.
- Check to make sure the identification and rating label is in place along with the manufacturer's name and or logo and that it is suitable for the gas type.
- Check that it complies with the local standards for pressure regulators and gauges are marked to comply with the appropriate local standards, such as ISO 2503 for regulators and ISO 5171 for pressure gauges and not modified or undergone an unauthorised repair.
- Check for general signs of damage or unauthorised modifications.
- Externally check that the pressure relief valves are undamaged and free from modifications or unauthorised repairs. Internally check that they are free from obstruction.
- Check the cylinder connection to make sure it is free from oils, greases, solvents, debris, PTFE and that it is perpendicular to the regulator body.
- Check to see if the regulator gauges are in place and of the correct type for the gas and scales suitable for the gas pressures. The clear covers should be in place with the needles correctly reading zero, not below the stop bar or bent.
- Check that the pressure rating is suitable for the cylinder pressure. For example - if you have a 230 barg cylinder, then a 230 barg maximum inlet pressure regulator should be okay, right? Maybe not, and here's why: Cylinders are filled with gas to a set pressure using a reference standard. This is normally indicated on the cylinder label. It will read something similar to "pressure at 20°C". So, if the 230 barg cylinder filled at 20°C is in an environment where the ambient temperature is approximately 40°C, located in full sun, what would be the pressure in the cylinder be? In this scenario, would a 230 barg maximum inlet pressure regulator be safe to use? Gay-Lussac’s Law applies here: If a gas’s temperature increases, then so does its pressure, if the mass and volume of a gas are held constant. This is exactly the conditions inside the nitrogen cylinder in our example. Therefore, the answer is no, it would not be safe to use because the pressure would most likely be above the 230bar SWP.
- Check to make sure the tightening nut at the inlet and outlet is the correct thread, undamaged and free from modifications or unauthorised repairs.
- Check that the pressure adjustment screw stays fixed to the body and that it moves freely, covering the full adjustment range.
- Externally check to see if the pressure relief valves are undamaged and free from modifications or unauthorised repairs. Internally check that they are free from obstruction.
- Check that the outlet pressure adjustment range is suitable for the application and downstream equipment pressure rating.
- Finally, check that the backs are in place and the pressure relief covers are not out of place due to an over-pressurizing incident.
Now, you should be good to go!
Alternatively, an on-site nitrogen generator can be used and will alleviate all the hazards and risks associated with high-pressure nitrogen gas cylinders. The Parker NITROSource generator, for example, offers a unique design and advanced energy-saving technology that requires less compressed air to generate more nitrogen. Substantially lower servicing costs, reduced downtime, and longer working life make it the most cost-efficient nitrogen supply available. Additional benefits include:
Watch this video to learn more about the Parker NITROSource on-site nitrogen generator.