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Mixing Up Tube-Fittings

07/18/2011 10:04 AM

dear members/readers.

We are currently in a investigation of a devective hydraulic fitting. It's the type using 2 ferrules as in Parker A-Lock, Swagelok, UNI-lok, BAC-lok etc. etc.

We found out that for 1 (defective) connection, our contractor used a UNI-lok fitting with a BAC-lok nut, the ferrules are not tracable (brand wise).

Does anyone have encountered a defective tube fitting, caused by mixing up diverend brands for 1 connection ? I would like to know your experience.

The defective fitting caused a serious incident, around 600 liters of agressive oil was sprayed over 6 people.

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#1

Re: Mixing Up Tube-Fittings

07/18/2011 11:49 AM

I have known of various fittings to fail, sometimes the cause is from the guy who assembled it, sometimes from a manufacturer defect, sometimes because of bi-metallic corrosion/pitting, sometimes from overpressurization... the list goes on.

What you say could be your answer... The mix/match could have been a no-no.

But I don't know anything for sure... Call in the CSI team.

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#2

Re: Mixing Up Tube-Fittings

07/18/2011 12:45 PM

The solution is to standardize on only one brand and ONLY one brand to avoid potential problems. ALL of the ferrules are proprietary and incompatible with each other (that is where the intellectual property controls are for each company. NONE of the companies will talk about their ferrule designs to ANYONE. And the geometry is such that it does not take much of a tolerance variation to have HUGE effects on sealing and tube retention. Take it from someone who has done some of that design work, there is a lot more to a ferrule design than meets the eye.

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#3

Re: Mixing Up Tube-Fittings

07/18/2011 4:30 PM

As was mentioned, you absolutely can't mix parts from different brands of these types of fittings.

The other thing, perhaps more importantly, is that assembling these fittings properly requires more skill and knowledge than meets the eye. All the parts must go un in the correct order, and in the correct orientation, and then be tightened using a precise series of steps. It's not just like tightening an NPT fitting. Some of the bigger manufacturers will actually send out a representative to your company, along with teaching aids, to give a class in the proper technique. It's about a 30 minute class. It may sound ridiculous, but it's true. It's very easy to get something in the wrong order, or turned around, or over tightened, or undertightened, or inserted too far or too shallow, if you don't know exactly what you're looking for. And an improperly assembled connection looks very much like a properly assembled connection, if you don't know what to look for.

My engineering dept went through it a couple years ago.

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#4

Re: Mixing Up Tube-Fittings

07/18/2011 4:44 PM

Just out of curiosity, what is "aggressive oil"? I suspect this is a translation error. Hot? high pressure? corrosive? (high H2S fraction).

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#5
In reply to #4

Re: Mixing Up Tube-Fittings

07/18/2011 4:47 PM

Oil that doesn't play well with others, and tends to run other oil off the road pipe.

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#6
In reply to #4

Re: Mixing Up Tube-Fittings

07/19/2011 1:44 AM

with agresive oil I mean Firequel, it's a non flameable hydraulic fluid, nasty stuff.

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#7
In reply to #6

Re: Mixing Up Tube-Fittings

07/19/2011 1:50 AM

So, what is "nasty" or "aggressive" about it? (This is possible, but lacks explanation.)

As to the original topic, there might not be any defect with the fitting; for instance, if it was assembled improperly or mixed with other brands of components.

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#8
In reply to #7

Re: Mixing Up Tube-Fittings

07/19/2011 2:01 AM

I spelt it wrong the real name is Fyrquel EHC, it's a synthetic pure phosphate ester fluid. You can find it on the web if your interested

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#9
In reply to #8

Re: Mixing Up Tube-Fittings

07/19/2011 2:43 AM

So, what is "nasty" or "aggressive" about this fluid? Just answer the question, rather than sending us on a wild-goose Web chase.

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#10
In reply to #9

Re: Mixing Up Tube-Fittings

07/19/2011 3:26 AM

The problem of the defective fitting isn't caused by the type of fluid, all materials used in this application are the correct ones, according to temperature, pressure, and medium.

The Issue is; can you use ferrules, nut and fitting body from different brands in one connection (all parts are correct for the application).

And Tornado specially for you, the fluid is:

Trixylenyl phosphate/Butylated triphenyl phosphate/Triphenyl phosphate Mixture

This fluid turns acid when in contact with water, nasty and agressive when sprayed over humans, who are likely te be made out of water for the biggest part.

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#11
In reply to #10

Re: Mixing Up Tube-Fittings

07/19/2011 3:36 AM

Henk, that question has already been clearly answered by myself and a couple of others. No. You can't. They are all proprietary.

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#12
In reply to #10

Re: Mixing Up Tube-Fittings

07/19/2011 3:38 AM

The main issue has already been addressed. If you mix and match different styles/brands of ferrules/nuts/bodies, then not all the parts are correct for the application, as has been mentioned before.

Why use such a fluid? (Yes, there may be reasons, but what about countervailing reasons?)

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#13
In reply to #12

Re: Mixing Up Tube-Fittings

07/19/2011 4:03 AM

first, we are not happy with this fluid.

the main reason why it's still used in our installation, our powerplant has a contract with G.E. and G.E. doesn't allow us to change this, again it's all about money (maybe the incident changes things).

The technical reason for using this fluid; we have a number of regulator valves in our steam and gas lines with hydraulic actuators. These are "hot" valves, normal hydraulic fluid could cause fire if it's leaking.

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#14
In reply to #13

Re: Mixing Up Tube-Fittings

07/19/2011 5:49 AM

Hi Henk klep,

I have sold hydraulic fittings for 40 years and the only failure I know of was a DIN 2354c 38mm OD fitting blowing off the end of a pipe on a fairground ride ( it was one of those spinning cage type rides that is on the end of an arm that lifts the cage vertical and centrifugal force holds you in) the pipe was on the lift side of the cylinder that raised the arm and it dropped down and slightly injured some of the occupants. The ring had been put in the fitting backwards and not checked before assembly!

What pressure was your system working when the fitting failed?

To digress slightly, I was in Germany back in the '70's when there was a "big thing" about 2 bite rings. The benefits of which were lost on the fitting supplier i was visiting at the time (VOSS) for various reasons which I won't go into now.

Anyway, I made up 2 tube assemblies of 20mm OD one with a single bite ring and one with a 2 bite ring, this was to illustrate the 50% increase in torque it required to make a satisfactory joint. It felt like TWICE as much to me making the joint in perfect conditions. The joint was then pressure tested to failure. In both assemblies the tube burst (like a sausage) at 27,000 psi (1837Bar) the fitting has a Maximum Working Pressure of 400 Bar with a 4:1 Factor of Safety.

I hope this illustrates the question I asked above.

Best regards,

John

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#15
In reply to #13

Re: Mixing Up Tube-Fittings

07/19/2011 6:44 AM

Hi again Henk klep,

I spoke to my supplier of 2 ring fittings, he said there is no "Standard"( like they have for DIN2353c fittings) so it is even more of a potential problem if you try and mix and match component parts.

What size fitting were you using?

Best regards,

John

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#17
In reply to #15

Re: Mixing Up Tube-Fittings

07/19/2011 7:35 AM

jesw55

I mailed my responce to your CR4 mailbox, can't use company names in public with this kind of incidents.

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#20
In reply to #13

Re: Mixing Up Tube-Fittings

07/19/2011 11:20 AM

And of course PCB's are not allowed..... what about Silicon Oil? it has an extremely high flash point... consider Dow Corning 710 as a potential alternative, it is good to 500 degrees F.

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#16
In reply to #9

Re: Mixing Up Tube-Fittings

07/19/2011 7:32 AM

http://www.cleanoil.com/images/stories/pdfs/MSDSpdf/MSD%202011%20Fyrquel%20EHC.pdf

My questions is there is no indications given on how long it was in service. Whether there has been any regular inspections on these devices. The oil is a hydraulic foundry oil formulated for high flash point. So in it's requirement in this application what has been done to contain the spray if there is a rupture. As the oil would do damage to personal no matter what it was. As it is in a hot environment and will be hot.

Though the oil is listed as a mild skin and eye irritant I suspect more damage to be done by the heat of the oil.

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#19
In reply to #6

Re: Mixing Up Tube-Fittings

07/19/2011 11:15 AM

I'm guessing a cousin to Skydrol? I've used skydrol many times, and it will eat the bottoms clean off your boots, and turn em into a puddle.

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#18

Re: Mixing Up Tube-Fittings

07/19/2011 9:36 AM

The components of tubing must be by brands, if you use several brands, their component pieces are generally not interchangeable.

Most serious hardware suppliers and manufacturers will advise you that if you want to use different brands, on each connection you use only the components of that brand.

I have seen a number of failures due to mixing the ferrules of one brand for another and then you can have leaks, nuts being damaged and even blowouts.

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#21
In reply to #18

Re: Mixing Up Tube-Fittings

07/20/2011 2:00 AM

Thanks for all your comments/suggestions/advice,I appreciate this.

kind regards

Henk Mensinga

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