Strength Of Copper Tube Compression Fitting

[briand2]

Does anyone know where I can find realistic information on the strength of compression fittings for copper tube?

I'm specifically referring to the type of fitting that is common in domestic water installations in the UK. It would appear that the mode of failure under pressure is that the fitting simply gets pulled apart, the "olive" / compression ring leaving scratches on the pipe surface. At what pressure should this occur (for typical R250 / "half hard" tube)? How can it be modelled; is it just friction, or does the "olive" have to actually elastically or plastically deform the pipe as it moves towards the end?

I realise there are several questions here, but I guess they're all variations on the theme!

Thanks in advance for your helpful comments.

Brian

 

[jsummerfield]

All compression fittings are different. The fitting that connects the water to my refrigerator is pretty sorry. Swagelok and Parker can likely provide lots of data. These better fittings are quite strong. I have never seen the ferrules come off the tubing in any metal. I have little experience with copper at high pressure but used some lower quality compression fittings on copper for temporary steam tracing, perhaps only 50 psig steam.

John

 

[krb]

I would second j's recommendations to check with swagelok. I have seen fittings come off of copper tubing, but it was because the fitting was not tightened properly. All fittings are different, but they all should be designed to have the ferrule swage onto the tubing, deforming it and locking the ferrule in place. If properly installed, they only way to remove the ferrule is to cut it off, and companies like Swagelok say that the pipe will burst before the fitting fails. I have seen demonstrations of this as well. Sounds like yours was either of poor quality or not installed properly. Try Swagelok.com for more info.

KB

 

[hacksaw]

If the "olive" ferrule is non-metallic then it was not meant for copper tubing. You may be using a fitting for plastic tubing. Just a thought...

 

[btrueblood]

I've seen very cheesy compression fittings from the local hardware warehouse store fail in two ways - in one, the compression nut splits when someone over-tightens the fitting (to make it stop leaking). In a second case, the ferrule supplied was made of nylon or acetal; this particular fitting was used to replace the outlet tube on an air compressor (which gets quite hot). The plastic ferrule melted, the fitting let go, and fairly good chunk of copper tube "whipped", broke loose, and sailed across a shop.

Swagelok and Parker both make pressure-rated compression fittings. You'll be hard pressed to get any such ratings for "standard" compression fittings.