Dresser Couplings & Flex Hose 1

[meca]

I have seen many dresser couplings used in pipeline terminals. They seem to hold up well over time, but I am interested in seeing if anyone else has some experience with these couplings.

As an alternative to dresser couplings, some people have recommended a flex hose. I can't find any information about the axial and lateral deflection that this hose can take. Anybody have a recommendation on using flex hose for thermal growth and pump isolation?

 

[butelja]

BEWARE of flex hoses in situations where there is ANY axial movement. The interior convolutions of a metal flex hose depend upon the squeezing ("chinese handcuff&quot effect of the braided outer cover for lateral stability. This squeezing effect is caused by the overbraid resisting the axial tensile force caused by internal pressure. If a metallic convoluted flex hose is subjected to ANY axial compression, it can lose lateral stability due to the loss of squeezing by the overbraid. This will result in lateral buckling that can break the convolutions and cause catastrophic failure.

While the so-called "pump isolator" flex hoses may be widely used in HVAC or other NON-CRITICAL applications, they have no legitimate use whatsoever in any process or safety critical applications.

In my opinion, the reason that so many applications are able to use them without catastrophic failure is due to the lack of fixed supports in the piping system. This ensures that the isolator is in tension, because there is no support robust enough to resist the pipings natural movement in response to internal pressure and thermal expansion.

 

[meca]

Thanks Butelja, this information is very appreciated.

Do you have any experience with the dresser couplings? What has been your practice in pump piping at a tank to handle thermal expansion, pump vibration, and soil settlement?

 

[butelja]

Meca,

I don't have much experience with dresser couplings outside of pneumatic conveying lines. However, they should not be used in any flammable service. This is because the rubber sealing elements will disappear under fire conditions and lead to massive leakage, adding fuel to the fire.