Tube & hose failures

[Graybeard]

Our plant has several places where plastic tubing (typically Tygon) has been used to temporarily connect 2 lenghts of pipe. This has been done when piping mods were required and the pipe fitters couldn't weld or thread the pipe (due to many reasons). These are low pressure situations (<15 psi). The fitter just pushes a lenght of tubing over the pipe that will fit and uses a hose clamp at either end. We haven't had any failures yet. Neither the tubing or hose clamp manufacturer recommend doing this without using a hose barb type fitting.

I'm looking for some experience based information where someone else has done something like this and has had a failure. Tubing size and pressure type info would be very helpful. Maintenance argues that since we havn't ever popped off a hose, that it's not a problem.

Suggestions?

 

[DonyWane]

We do a similar plant in our plant. I would recommend that you check chemical compatability first. Many organics will rip through Tygon. The temperature of your process fluid will also affect Tygon's performance. As far as I know, we have never had our Tygon slip off in low-pressure situations. I do know that when approaching higher pressure situations, we often double-clamp or barb-clamp.

 

[Graybeard]

Thanks for your response. We have checked the chem. compatibility & for the most case less than 1/2 the stuff we use the plain R3603. One of the things we discovered is that the supplier had been substituting unbranded tubing in some cases for R3603 even when our purchase reqs called out the formulation number. To him &quot;tubing is tubing&quot;. It came as quite a shock to us when we found that much of the tubing was only branded &quot;Made in Taiwan&quot;. Not that there is anything wrong with Taiwan, it's just that we could not provide assurance as to what the formulation was.

My primary concern was putting the tubing on the pipe without using barbed fittings. The folks at Saint-Gobain don't recommend using ever using it without barbed fittings. It's obviously easier just to slide it over the pipe and clamp. One of these days, I'm going to try to find the time to see at what pressure a single clamp starts to be a problem.

 

[saxon]

This type of piping/tubing/hose practice and precedent is a bad one to let get started. Once it's in the plant, it's near impossible to eliminate. I've seen it used quite frequently in air and water services usually operating at less than 75 psi. Normally these things fail at 3;00 am, and then everyone is in a panic and on the phones trying to get the world out of bed to solve a problem that shouldn't have occured in the first place.

The only real solution is to hold the maintenance/piping crews to the piping/tubing/hose specifications religously. The only proper place for hose usage is at the supplied utility stations using the proper hook-up connections for the service supplied at the utility station.

 

[Graybeard]

Thanks for your response. I agree with you that it's a bad precedent. Unfortunately, it's also light crab grass in your neighbor's lawn, bad for him and you, but difficult to control once it gets started. The problem I'm having is stopping it, or at least not letting it spread any further. We have instituted a rigorors inspection program which requires replacement at the first sign of deterioration or every 2 years minimum.

Through much table pounding and chest thumping, I have been able to require double clamps on any line that is not a gravity drain or vent type situation, and currently limit tubing use to 15 psig or less, or in cases on attended temporary transfers. That's the best I could do. So until we burn the plant down due to a failure, I'm afraid we will always have some tubing to contend with.

Fortunately, we haven't had any failures. The problem with this is that it is difficult to be ridgid about establishing limits, when you don't have any failures to point to. If you know of any, whether at 2am or just after the morning coffee break, I would appreciate any info you could provide (without giving away trade secrets or embarrassing details like plant manager's names).

 

[rbcoulter]

I should have checked this post sooner. I have done this, and have had a failure. Here is why it is a bad idea. The hose clamps on a nonbarbed surface, like a pipe, do not hold well in the direction along the pipe.
The failure mode to expect is the hose sliding off the pipe. A pressure surge, slamming a valve shut downstream, or some other event, will eventually make it fail. It only took once for me to learn my lesson, I'll never do it again.

 

[saxon]

Graybeard, Need an example? This was a &quot;temporary&quot;, quick get it installed and the unit running. (ended up as permanent till it failed)hose jumper from a header connection in the instrument air system to a new unit. Hose size 1&quot;, max. wp 200psi, material Buna, hose length 50', end connections double hose clamped onto 3/4&quot; npt pipe threads. When the end connection failed, it knocked the new unit off line, dropped header pressure below minimum required pressure, overloaded air compressor which shut down on overheat, knocked the rest of plant off line due to low instrument air pressure.

The boys back in the shop learned a hard lesson on this one. Luckily the plant was down for only a couple of hours, but more importantly, no one got hurt.

saxon

 

[Graybeard]

Thanks to both RBCoulter &Saxon for your input.
Saxon - You indicate max wp of hose was 200 psi. Any idea what pressure the hose was actually exposed to at failure?

graybeard

 

[JOM]

Graybeard,

You wrote:
&quot;Maintenance argues that since we havn't ever popped off a hose, that it's not a problem.&quot;

I suppose that counts for something, but &quot;it's never happenned before&quot; must be a frequent statement after the catastrophe occurs. Like &quot;But my dog's never bitten anyone before.&quot;

Have you thought about testing a hose & clamp to determine the pressure at which it will fail? Can you ask a State or industry body to perform such tests?

John. Cheers,
John.

 

[JOM]

Here's another thought.

How tight are the clamps? Are they torqued? Any Quality Assurance around that? What if a fitter leaves in place a loose clamp?

Incidentally, can you mention the fluids involved?

Cheers,
John.

 

[saxon]

Graybeard, The header pressure normally runs at about 80 to 90 psig. So the hose was seeing full header pressure. At the units it is then stepped down to about 15 psig for pneumatic instrument use.

Saxon

 

[abeltio]

the hose thing can and will get YOU &quot;hosed&quot;... sorry for the foul language... please check the site's (owner's specs) for piping and tubing...
In my experience flex piping/tubing (that is how is referred in technicalese) made out of plastic, PTFE, rubber etc... can only be used in water and air/nitrogen service up to 75psig.
Any other service flex piping/tubing can be applied if terminated with proper tube-fittings or flanges and has an external sleeve of braided stainless steel.
Swagelok is an example of a supplier that offer all these goods.
HTH
Saludos.
a.