Liquid Water hammer - Joukowsky Head - advice 1

[jamesbanda]

Dear all,

I've Joukowsky Head method to estimate surge flow for a liquid line. This calculates 130% overpressure. Our internal standard only allows for 100% for lined and plastic pipes. We also plan to increase line capacity
1. Is this normal pratice.
2. What the experience with surge protections (on corrisive service ?) do NRV's work ? if so how effective etc.
3. Ive assumed 1500 m/s for the propagration speed eg water. but it is hydrochloric acid - do you know how to calculate this value ?

Pressure increase (Joukowsky Head, JH.)
JH = d x a x u / 100 000
JH : max. surge pressure (bar)
a : Wave propagation speed (m/s)
d : Fluid density (kg/m3) u : Fluid velocity (m/s)

 

[sshep]

I think you want the speed of sound in hydrochloric acid. This can be calculated by Hook's Law from the modulus of elasticity and the density. Consequently sound speed is a function of temperature. You should check it out online in order to get the units right- if I cite a formula here I will probably get it wrong.

Alternatively, sound speed is a parameter needed in ultrasonic flow meters, and companies like panametrics sometimes include tables for a large number of fluids in their literature.

best wishes,
sshep

 

[davefitz]

There are other tricks that can be used. There has been used dead ended tees with internal compressible bladders to snub the acoustic wave and limit overpressure. Also, dampening the motive valves that initiate the change in fluid momentum is a common practice.

Upon reading the accident report for the 2000 bellingham pipe failure, it seems that it is also common at long pipelines to mechanically prevent total closure of the control valves in the system, so that failure of DCS will not initiate the waterhammer. But in that case, they forgot to install the mechanical stop that would have prevented the waterhammer event when the DCS failed.