Compression Couplings

[TugboatEng]

Are there any systems similar to Swagelok that can be used on pipe? 1/4 pipe to be specific. They used socket weld fittings and pipe for urea solution. Option 2 is rip everything out and replace with 1/2 tube and use compression fittings.

 

[EdStainless]

Swagelok and Parker used to make double ferrule fittings in small pipe sizes. Double check with your local distributor.
They had limited availability, but SS was common.

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[IRstuff]

Actually, I'm only familiar with the 1/4-inch, since that was all of our process plumbing. Nevertheless, the Swagelok catalog claims 1/4-inch:

https://www.swagelok.com/downloads/webcatalogs/en/MS-01-140.pdf

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[TugboatEng]

I was looking for compression fittings that could compress on the OD of 1/4 pipe. I assume pipe doesn't have sufficient OD tolerances to be compatible with metal ferrule type fittings. I figured I would pick the brain pool here before I rip everything out and start over. As always, I appreciate the time you have taken to respond.

 

[IRstuff]

My recollection is that the Swagelok ferrules were sufficiently loose and were able to compress down to the physical OD of the piping. On page 14 of the catalog, you can see the different materials for the ferrules and fittings, one of which might be more amenable to your specific piping.

1/4-in OD is available

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[TugboatEng]

I saw that chart. I believe it's showing the pressure ratings of the NPT connections. I am looking to avoid threaded connections and clamp directly on the pipe. If that is not possible I may have to thread the ends of the pipe and use adapters to tube to span the gap where I cut out the offending union. There is a big crackdown on hot work in the tug industry currently so I'm trying to come up with cold solutions for as many things as possible.

 

[Compositepro]

The outside of a pipe is not a smooth precise surface intended to to create a metal to metal seal. If the pressure is not too great there are compression fittings that use rubber bushings to seal on pipes.

 

[XL83NL]

Not in my area of expertise or experience but have you looked at something like Pyplok? The method used of a weldless pipe coupling or fitting is not unique and applied by other brands as well.
May want to look at

https://www.onepetro.org/conference-paper/OTC-25154-MS

Huub
- You never get what you expect, you only get what you inspect.

 

[TugboatEng]

I did buy the Viega MegaPress system while back. Too bad it only goes to 1/2 inch. I can't see investing in a new system for an uncommon repair. I think I'll remove the entire system and build it in tubing. It's only two 30ft runs.

 

[EdStainless]

I was going to say that one issue with either ferrule systems or ones like Viega or VicPress is the huge range of OD size in pipe. The OD tol on small pipe is about 3x that of tubing.
Switching to tube is a good idea TBE, Just make sure that the size is clearly noted for people in the future (maybe stamped metal tags).

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P.E. Metallurgy, consulting work welcomed

 

[TiCl4]

TugboatEng,

If the OD tolerances for of the piping disallows compression fittings, you may want to consider Victaulic or other grooved pipe couplings. They make as small as 1/4" couplings - it would only require grooving the two pipes to fit the coupling on in order to retrofit your system, assuming the spacing is fine after removing the coupling. If the application is in a high-vibration area, you will not want to use compression fittings anyways - they will fatigue crack. Ask me how I know...

Overall, I prefer the option of running new tubing and using compression fittings if the budget/area conditions allow. Perhaps it's just a personal impression, but I feel that compression fittings will last longer than Victaulics or screwed pipe. I would use a single ferrule fitting unless a double ferrule is required for pressure/temp/etc - it has significantly fewer ways of being installed incorrectly.

 

[TugboatEng]

Good news is, I would be the one doing the install.

 

[EdStainless]

Think of future maint needs.
VicPress or Vieaga require cutting out to remove.
Ferrule and Vitaulic clamp fittings can be broken and remade with simple tools.
I have never had fatigue issues with double ferrule fittings and SS tube, but we made sure that tubing was well supported.
Victaulic clamp fittings require heavy enough pipe and a groove cutter.
I am sure that you can figure out which will work for your application.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[moltenmetal]

OD compression fittings of the Swagelok type DO NOT work on the OD of pipe. The OD tolerance for pipe and the surface finish both are far, far too great to make such a system work.

There are hydraulically crimpable fittings which work on the OD of light wall stainless steel pipe, which use O-rings- made by Victaulic and others.

There are hydraulically crimpable fittings which work on pipe of ordinary dimensions and weight, requiring special tooling to install and which are very expensive, that do not require o-rings. They give you a metal to metal seal. Can't remember the brand name off the top of my head, but they were basically only the sort of thing you'd use as a last resort if you needed a "no hot work" solution in an operating plant as an alternative to a weld.

Neither of these crimp-on options are removable without a saw.

Victaulic roll- or cut-grooved fittings are an o-ring type fitting, not firesafe, but widely used for utility type services. Not something I'd personally use much beyond Category D (nonhazardous) services personally- air, water, drain, vent, lube oil and the like.

 

[moltenmetal]

Forgot to say- for 1/4" NPS pipe, the right solution here would be to use 1/2" OD tube and OD compression fittings. Don't screw around with the other options.

Face seal unions of the sort leaking in the pic are known to be a problem. Unless you are in carbon steel where you can use a brass seating ring, you're likely going to be in trouble over time. In stainless steels they should just be avoided and replaced with flanges.

 

[TBP]

Once upon a time, there was a manufacturer that offered unions that incorporated a spriral-wound gasket between the union halves. I haven't looked for them in years, so I don't know if they're still made.