Replumbing gas lines GC/MS

[MSCHemist]

Hi all please forgive my kind of basic questions. I am an LC chemist that switched recently to GC/MS.

Anyways I just started at a rather cash poor lab with a 6890N-5975MS. All the 1/4 in steel lines have really bad brass swagelok fittings that are cobled together with tons of ptfe tape and don't seal to well. Needless to say I am anxious to replumb the system properly. Could someone point me to a place where I can get new tubing and fittings.

Also what are the steps to cutting and deburring the lines. Can I use a basic 1/4 tubing cutter and bender from the big box hardware store and just debur with a file or do I need the high priced lab grade tools.

[Peter Apps]

Where you can get tubing depends where you are. If you have only a few instruments and no long runs from cylinder to instrument then go for 1/8 inch copper which is readily avialble from chromatography suppliers, and is easy to work and join.

You can use ordinary tools, but do not be tempted into using ordinary plumbing or refrigeration grade tubing.

Peter

[MSCHemist]

Where you can get tubing depends where you are. If you have only a few instruments and no long runs from cylinder to instrument then go for 1/8 inch copper which is readily avialble from chromatography suppliers, and is easy to work and join.

You can use ordinary tools, but do not be tempted into using ordinary plumbing or refrigeration grade tubing.

Peter

I am having the most difficulty trying to find the proper ferrules. I see two piece brass (which is what is currently on there) and steel and 1 piece graphite ferrules. I am not sure if I need to replace the nuts as well. We are currently using 1/4 steel tubing so I believe we will stick with that. I see Resek has most of what we need. It is mainly the fittings that are tripping me up.

[iainconlin]

If you are using stainless steel piping you are best to use stainless steel fittings. If Restek is your preferred supplier they will supply them or you could go to swagelok directly. You need a front and rear ferrule you can normally reuse the nut if the thread has not been damaged.

If you contact a Restek (or other supplier) directly they will be more than happy to help you out. If you have a maintenance contract for the instrument, I'm sure they would be happpy to point you in the right direction too.

If the fittings are not already cleaned you are best to clean them in some solvent then dry them off in an oven (don't use a chlorinated solvent though).

Hope this helps.

Iain

[Peter Apps]

Brass fittings on steel tubing is poor practise to put it mildly. Your best way forward is to cut the tubing behind the existing nut - what is on there already has probably distorted the tubing so that it will not now make a good seal - and then make the joins from scratch using 1/4 inch stainless unions - you can get these from Swagelok (Crawford) or Parker, and probably some others (but beware cheap imports !!) and the major chromatography companies will also supply them. Do not mix fitting types - the ferrules are different shapes. Each fitting comes fully assembled with nuts and ferrules.

Given the history of the system I would be seriously concerned that the tubing is contaminated, which will cause major problems.

Stainless fittings cost a lot more than brass ones, and depending on tubing lengths and how many connections there are it might work out cheaper to replace the whole system with 1/8 inch copper and brass fittings.

Peter

[MSCHemist]

Thanks for all the advice so far. I ordered some new 1/4" line, some proper stainless steel ferrules, their deburring tool and their hi-duty tubing cutter. the only part I am having a bear finding is this fitting that is female and screws onto the he Regulator's 1/2" threads and the other end is female and recieves the 1/4 tubing with ferrule and has threads on the outside for the nut.

[Peter Apps]

Thanks for all the advice so far. I ordered some new 1/4" line, some proper stainless steel ferrules, their deburring tool and their hi-duty tubing cutter. the only part I am having a bear finding is this fitting that is female and screws onto the he Regulator's 1/2" threads and the other end is female and recieves the 1/4 tubing with ferrule and has threads on the outside for the nut.

Swagelok SS-400-1-8 or SS-400-7-8 are probably what you need, depending if the regulator outlet is male or female. Double check the regulator outlet thread size; 1/4 inch is more common than 1/2 inch. NB that the size is not the diameter. If they really are 1/4 inch then change the final 8 to a 4.

Peter

[MSCHemist]

Thanks for all the advice so far. I ordered some new 1/4" line, some proper stainless steel ferrules, their deburring tool and their hi-duty tubing cutter. the only part I am having a bear finding is this fitting that is female and screws onto the he Regulator's 1/2" threads and the other end is female and recieves the 1/4 tubing with ferrule and has threads on the outside for the nut.

Swagelok SS-400-1-8 or SS-400-7-8 are probably what you need, depending if the regulator outlet is male or female. Double check the regulator outlet thread size; 1/4 inch is more common than 1/2 inch. NB that the size is not the diameter. If they really are 1/4 inch then change the final 8 to a 4.

Peter

Thanks does it matter if the part is steel or brass. The regulator and line is steel but I have five of the brass adapters and I'll be using a steel ferrule/fitting.

I would replumb the system with Cu but it is also feeding an old HP 5890-5971 and I read 1/4" should be used to reduce pressure dropoff.

[Peter Apps]

Thanks for all the advice so far. I ordered some new 1/4" line, some proper stainless steel ferrules, their deburring tool and their hi-duty tubing cutter. the only part I am having a bear finding is this fitting that is female and screws onto the he Regulator's 1/2" threads and the other end is female and recieves the 1/4 tubing with ferrule and has threads on the outside for the nut.

Swagelok SS-400-1-8 or SS-400-7-8 are probably what you need, depending if the regulator outlet is male or female. Double check the regulator outlet thread size; 1/4 inch is more common than 1/2 inch. NB that the size is not the diameter. If they really are 1/4 inch then change the final 8 to a 4.

Peter

Thanks does it matter if the part is steel or brass. The regulator and line is steel but I have five of the brass adapters and I'll be using a steel ferrule/fitting. there is a chance that the force needs to compress the stainless ferrules will distort a brass fitting, but it is worth a try.

I would replumb the system with Cu but it is also feeding an old HP 5890-5971 and I read 1/4" should be used to reduce pressure dropoff.

I have 3 GCs fed by 1/8 inch copper with the cylinders on the other side of the wall. How far are your instruments from the cylinders ?

When it comes time to check for leaks do not use Snoop liquid or anything similar with soap in it, which will contaminate the connectors and lines. First do a pressure test - fill the lines to 5 or 6 bar, with the instruments shut off, then close the cylinder valve and see hat happens to the pressure at the regulator. It should show "no" drop. If it drops you have a leak that you need to trace. With pressure in the lines put a few drops of a 1:1 mix of isopropanol and water where the tube meets the fitting nuts. If there is a leak you will see bubbles, tighten no more than 1/8 turn then check again, Do not be tempted to go around tightening everything willy nilly. Ideally you need a leak seeker - every GC lab should have one.

Peter

[MSCHemist]

The GC's are about 5 feet from the cylanders. I already bought the parts and have cut off the old brass fittings. It was a real horror show. I had fittings with no back ferrule, fittings with the back ferrule backwards, all held together by layers upon layers of ptfe tape and a nice squeeze bottle of soapy water by the instrument (poor mans snoop). It actually tuned and passed the air/water check the when I first came in on the first day but then we changed a He cylander and it all fell apart and I inspected it more closely.

Any ways I read from swagelock 1/4 inch fitting finger tight then exactly 1and 1/4 turn and for 1/8 3/4 of a turn past finger tight so I will do that.

[MSCHemist]

It looks like there are a few places I'll have no choice but to mix materials. At the end of the 1/4" line it comes to a copper T and emerges into a 1/8" Cu tubing then another 1/4" section to another Cu T and also emerges with 2 1/8" lines. Would I be better off using steel or brass ferrule sets where the steel tubing meets a Cu fitting?

At the very least I'll be able to minimize the mixing and make the swageloks proper so they seal without ptfe tape.

[Peter Apps]

It sounds like you have inherited a real mess. If your predecessor was using soap on leaky fttings then your existing pipes are contaminated. You absolutely must put gas scrubbers on each instrument to protect the columns and the MS.

If I understand your description properly, I would go from 1/4 inch SS to 1/8 inch copper at the first T, and then stay with 1/8 inch copper from then on. There is no sense at all in going back up to 1/4 inch and then down again to 1/8 inch.

Peter

[MSCHemist]

Yep I'll take your suggestion and have it 1/4" steel to the first T then 1/8" Cu after it splits to the 5890 and 6890.

In summary my tubing starts 1/4" steel line with steel ferrules through the purrifier and moisture trap then it splits off into two 1/8" Cu tubes one for each instrument. The only way I can see to accomplish it is to have the 1/4" steel line come to a brass swagelok T and emerge into 2 1/8" lines? Is there a better way?

[tphase]

Based on your descriptions, I would not trust anything - I'd replace everything from the regulator to the GC's. If the regulator is old, your local safety regulations may require it to be replaced. If not, at least install a new outlet fitting. I would go with 1/8" copper tubing and brass fittings all the way and get rid of the 1/4" tubing. If you have inline traps, replace them too.
Mixing brass and stainless fittings is not best practice. I do it in some situations but only ever put brass nuts on stainless fittings, *never* the other way around.

[Peter Apps]

Yep I'll take your suggestion and have it 1/4" steel to the first T then 1/8" Cu after it splits to the 5890 and 6890.

In summary my tubing starts 1/4" steel line with steel ferrules through the purrifier and moisture trap then it splits off into two 1/8" Cu tubes one for each instrument. The only way I can see to accomplish it is to have the 1/4" steel line come to a brass swagelok T and emerge into 2 1/8" lines? Is there a better way?

From what you tell us of the state of the connections, the purifiers are almost certainly exhausted and will need to be replaced. You can get the new ones with 1/8 outlets, and then have a short piece of 1/8 inch copper to an 1/8 inch brass T splitting to the two 1/8 inch lines to the GCs.

The more I hear the more convinced I am that you need to bite the bullet and run new, clean 1/8 copper all the way. Speak nicely to the connector supplier, they might trade in the the 1/4 SS connectors you have already, as long as they are still in the original sealed package. If not, hang on to them, they will come in handy for something one day.

Peter