Cryogenic Pump - Flexible Connections?

What does it say in the user manual for this pump?

It does recommend to use flexible piping, however does not give an explanation.

Good. The manual is to hand. In the manual will be the telephone number for the pump manufacturer's telephone helpline. The next action is trivial...

I have contacted the manufucturer multiple times. In accordance with their manual they recommend us to use the flexible piping. However, they are not sure whether not using flexible pipings will cause the problems we are having. As there could be other reasons as well (too low temperature seal, multiphase flow), I had hoped that someone has experience with not using flexible connections.

Too much is left to the imagination here for us to help you.

You'll need to look at the coefficient of thermal expansion of the materials that make up the piping to determine the total amount of movement possible.

Remember, everything was probably fitted at ambient temperature, so running at cryo temps will make everything shrink, depending on length of runs and materials of construction.

The supplier didn't suggest flexible connections without a reason.

Without the flex connections you are transferring the vibration to the pump...Install the recommended flex connections and repair the damage....You should also have vibration eliminators on feet...

this ass_ly (~259 kg ) ruin base by start and get hydraulic shock by stop it should have

soft connections and accumulator or pipe loop

We have several cryogenic pumps in our installations, and having flexible pipe connections is a must... not only as a vibration damper but also to alow for pipe contraction and expansion. Other factors for your problems could be incorrect mechanical seal adjustment...A high suction pressure could also be placing unwanted pressure on your seal.. place a pressure safety valve on your suction inlet. (please note that this is not a pressure control valve it is the last resort if all else fails..)

Make sure that you are cooling the pump prior to running.. some mechanical seals are tightened with contraction in mind... running the pump without sufficient cooling will cause premature failure of your seal..

Check your motor to pump couplings to insure that there is flexibility to allow for suficient axial movement due to the contraction.. finally make sure that you have a return valve that opens to allow the cryogenic liquid to escape when the pump is switched off or you will have very high pressure..

I agree, we use flexible pipes on all of our cryo pumps.

GA to comment#8 from Porky.

Dear Peter, why do you want to go against the recommendations of OEM? Provide flexible pipe for suction as well as discharge. We have at least 20 cryogenic pumps all fitted with SS flexibles. You have not given enough information. Some times a Z shape piping arrangement could be a solution. Can you give following information:

1. Liquid handled & its boiling Point.

2. Suction & discharge pressures and temperatures.

3. Suction & discharge pipe material, sizes and shapes (length and orientations).

4. Pump size (capacity/ drive kW/ speed)

5. What modification you did in piping?

Dear Pritam a.o.,

Thank you for the suggestions and recommendations so far. Below some more information on our system.

0. We did not deliberatly go agains the recommendations of the pump manufacturer. At the time the facility was designed and build we did not have sufficient knowledge and experience

1. Currentely we're using LIN which boils at roughly -196 degrees C. We will start using LNG once we've finished this test series

2. The pump is located about thee meters lower than then the supply. Hence, the suction pressure is the hydrostatic head from roughly 3 meters LIN (NPSH required is 0.63). The pressure increase over the pump is roughly 300 mbar for normal operating conditions. For normal operation, boiling of the LIN is avoided by pressurizing the complete system with N2. When pressurized to, say 3 barg, the LIN is still roughly around its 0barg boiling point (-196), however the boiling point for 3 barg is roughly 15 degrees higher.

3. The suction line is 3", the discharge line is 2", pipe schedule 10s I believe. The suction line is a straight pipe of three meters with at the end two bends; one to the supply tank and one to the pump. The discharge line is much shorter and has several out of plane bends before it goes to the remainder of the facility.

4. Diameter impellor 200 mm, power 5.5 kW, speed 25 Hz (I think)

5. The pipe from the LIN supply (the tank that is located about three meters higher than the pump) has been replaced with a vacuum insulated one. (Armaflex insulation before.)

Thank you in advance for your time and thoughts.

"Currently we're using LIN which boils at roughly -196 degrees C. We will start using LNG once we've finished this test series"I'm confused here. Is this a new installation meant for handling LNG but under testing with LIN at the moment? Who is pump OEM, they didn't help in installation and testing?

One more confusion, you say- "The pressure increase over the pump is roughly 300 mbar for normal operating conditions" but suction pressure is 3 barg when pressurised.

With the above confusions, I can make following comments:

1. Installing a vacuum insulated tank is a good sign for cryo systems.

2. Introducing flexibles at suction & discharge is must. In exceptional case discharge side you may fore go if there is a 'Z' shaped bend immediately near pump with at least 2 m straight pipe between the bends. Thermal stresses to be avoided to protect pump.

3. 3 m long suction pipe to be insulated (check). Reduced suction length is better.