Problem In Stress Analysis Of Piping

You may need an accumulator or snubber on your discharge system.

Is it single screw pump or multi screw pump?

How do you achieve the capacity control?

One thing I would suspect is cavitation.

what's cavitation you mean. is it pipe cavitation or some thing else .

can you pleased to give more details

(when pumps work with 50% of their capacities we have no problem but when they are going to 75% of their capacities the pipes start to shaking .)

First you have to differentiate between pipe hammering and pipe shaking

for pipe hammering, Its Momentarily noticeable while pump transfer from running to stop condition and vice versa. If it's your case, It can be solved by installing hammer arrestor like other members advise .

If it's continuous shaking at 75% of pump capacity, It's a pump vibration resonance which transfered through pump body to pipe lines.

In such case , It's advised to install vibration isolators for pump foundation

or pipes vibration isolator as shown below

for more details continue here

.http://en.wikipedia.org/wiki/Vibration_isolation

First, Is your pump a "True Screw Pump" or is it a Progressive Cavity Pump such as a Mono mfg design? They have very close tolerances.

If it is a PCP check the compatibility of the Stator Elastomer and Rotor materials with the fluid your pumping.

If you exceed the suction capacity of the fluid that is available you could be running the pump dry, causing the pump to bind up causing the shakes.

Normally in screw pumps piping vibrations happens only due to poor supporting or poor suction. However, discharge dampening bottle may help you in reducing line vibrations. Further you have to see the direction of vibration so that proper anchoring of the line in the particular direction can be done to arrest vibrations.

Thanks for all answers

I should say:

1-There is no cavitation because we don't have any noises in pumps and the Pressure gauge before of pump indicates 0.4 barg

2-Type of pump is Progressive Cavity (single screw)

3-Accumulator is not applicable and support solution can't be adequate (it has been tested)

4-Medium is produce water with temp. of 95c

5-The piping material is GRE.

It should be noted shaking create as a wave on suction of pump and moved to discharge.

I would look at cavitation again. Water at 95°C is cavitation waiting to happen.

cavitation needs the vacuum but we have positive pressure before pump and we tested suction of pump there is just liquid without vaporization mentioned that cavitation produces noises

Cavitation does not require a vacuum; it only requires that the liquid pressure drops below its vapor pressure at the obtaining conditions.

How did you open up the line and actually see that no liquid was vaporizing?

you are right i mean that we have the required head.

What is discharge head and speed of your pump. Is there any strainer in the suction of the pump?