Why do transfer lines fail?

[MichaelVW]

I have a 6890-5975. When I spray air duster in the oven, where the transfer line and column meet, I get nothing. When I spray it between the instruments, near where the MS meets the shroud that protects the transfer line heater - bingo... big leak.

So I guess I'm looking at a new transfer line manifold. I'm curious though why these things go bad. I could understand there being a problem with the o-ring between the instrument and the manifold (and I'd rather pay for an o-ring!) or the treads on the end that stick in the GC. But why do these things need to get replaced every X years?

[James_Ball]

I have only had to replace two in 20 years so far. The transfer line interface is made in two parts, one is identical to the measuring tool they used to send with them to set the column length that goes into the transfer line and that is welded inside a larger tube with the o-ring fitting on it that seals on the side of the MS. I guess that if you repeatedly tighten the column nut super tight without using a wrench on the interface side.(I noticed the new interface doesn't have any flats for a wrench so that makes it worse). Ours was cracked at that weld and had to be replaced. The other one someone had tighten the nut too tight over and over and actually cracked it just past the threads, it was bent upwards for several years before it finally cracked.

I had one analyst who any time they saw an air leak, their first thing was to tighten the nut some more.

[Bigbear]

On a CI system, there are more potential leak points.

[aldehyde]

The transfer line is relatively thin metal to keep the temperature correct, and so overtightening can physically deform the metal especially if it has gone through many temperature cycles.

The other common issue is reusing ferrules or overtightening ferrules. Again once there have been heating cycles the ferrule material becomes more brittle and prone to cracking, or deforming if it is tightened repeatedly.

If you are using the brass transfer line nut I strongly encourage you to invest in a "self tightening" column nut instead. They can be tightened by hand, rather than with a wrench, which basically eliminates the possibility of overtightening. For the most leak tight system possible, replace the ferrule if you remove the column from the transfer line and intend to reinstall it. You can probably get away with retightening it a few times.. but is it really worth the risk/down time?


https://www.agilent.com/en/product/gas- ... uts-for-gc

here's an example of those nuts--you can get them for either the inlet, the MS, or any GC detectors. The newest model has a removable piece that has a septa like material in it which can be used to hold the position of the column nut when it is removed from inlet or detector. Once it is installed back into the inlet/detector you loosen it and remove it (sadly you cant keep it installed bc the oven will damage the septa-like material. Would be awesome if you could keep it on all the time.)

I ABSOLUTELY HATE those brass nuts.. they cause so many problems.

[H.Thomas]

Does anybody know if there are similar self tightening nuts for Shimadzu.GCs?