Maintaining a trouble-free corrosive gas system (such as Cl2 or BCl3) is a function of how clean you keep the gas. Moisture is the#1 enemy of most corrosive gases, and it doesn’t take much to wipe out your system. We’ve been reconditioning gas cabinets for 12 years now and have been around these systems for close to 30 years and we’ve seen systems that last a couple of weeks and others that are still running strong after 10 years. The difference between the two is how the systems are cared for.
Here are a few things you can do to maximize the life of your gas systems:
1. Make sure to adequately cycle purge your gas cabinet when changing bottles. Always use the automated cycle purge function on your gas cabinet and set it to a minimum of 75 cycle purges. This effectively removes the corrosive gas before you open the connection and allow atmosphere to enter the tubing, and then removes the atmosphere effectively after you install the bottle, before you reintroduce the corrosive gas. Your higher quality gas cabinets will pull a vacuum on the pigtail to the primary shutoff valve, before you open the gas cylinder, so you don’t mix spec gas with N2.
2. Make sure that you have the “trickle purge” option for the process purge enabled, and that you quickly change cylinders. The trickle purge allows a small amount of nitrogen to fill the tube during the cylinder change so atmosphere can’t migrate up the pigtail, while the quick cylinder change minimizes the time that the tubing is open to atmosphere.
3. Always use DISS fittings for both the spec gas AND purge gas. No CGA fittings! With DISS fittings, you get a high purity connection as opposed to the friction seal of a CGA, and with the DISS it is also assured you get a higher purity purge gas which lowers the moisture content of the nitrogen.
4. Make sure you get UHP grade spec gas and nitrogen, as the purity is higher therefore the moisture is lower.
5. Keep your cylinders, as well as your gas cabinets, in a climate controlled room. So, for example, if you’re in New York and it’s winter, your cylinders can end up being stored in a cold room. If you hook up that cool cylinder to a warm system, you can easily end up with moisture in the system, which can damage your system in a hurry.
6. Make sure you have a dedicated purge cylinder per gas cabinet. Don’t connect all the cabinets to a house purge or 1 purge bottle. The reason is the potential of contaminating your N2 if you lose a check valve and back stream spec gas into your N2 supply.
Note: If you have a contaminated gas line, you will most likely first see it in the regulator. The pressure will begin to “creep” and the regulator won’t shut off. This is because moisture falls out at the pressure drops, and corrosion starts to build on the poppet at the seat interference area, on the diaphragm and downstream of the seat. Replacing the regulator won’t help as your line is contaminated. At this point you would have to rebuild your gas panel, and quite possibly your gas line to the tool.