Pipe diamter transitions

[jimrcasper]

I current have a 1/2" diamter stainless steel pipe that transitions to a 1/4" diameter steel pipe via a compression fitting. When flowing at steady state the connection emits a low frequecy hum and causes gases to come out of solution. the operating pressure is approximately 20 psi. I have not been able to find a reference that specifies the length of the taper required to minimize the effect of the diameter change, any help would be greatly appreciated.

 

[CRG]

How was the pipe cut?
Was it de-burred afterwards?
What is the fluid?
What is the velocity?

 

[jimrcasper]

How was the pipe cut? The pipe was cut with a bandsaw.

Was it de-burred afterwards? I believe it to have been deburred afterwards.

What is the fluid? Water
What is the velocity? 1/4" pipe velocity is approx 392 ft/min.

The fluid is also being cooled from ambient room temperature to 32 degrees. The connection is sumberged in a freswater ice bath.

 

[CRG]

I would have thought that at this low velocity the most likely source of the noise would have been that the pipe was cut with a wheel pipe cutter and not reamed afterwards. However, you said that the pipe was de-burred after cutting. The velocity does not seem excessive so I would open up the joint and visually verify that the pipe was properly reamed after it was cut. It seems to me that any quality manufacturer’s fitting would work for this application without excessive noise.

Is the pipe supported where a small flow induced vibration is exciting the pipe or one of its supports at its natural frequency?

 

[desertfox]

Hi jimrcasper

I am no expert on this however I was just thinking wether
or not you could do a Bernoulli calculation on this and find out the pressure drop between the small and large diameter ie 1/2" to 1/4", I wondered if you have a slight
cavitation problem particularly as you are cooling the fluid
below ambient.


regards desertfox

 

[chicopee]

I would not be surprised that if you inserted a tapered fitting, the noise would disappear.