Answer Posted / www.islamqa.com

# Flashing: it's formation of vapour bubbles in liquid
stream as valve cause pressure drop to the liquid below its
vaporization pressure.

# Cavitation: it's formation and collapse of vapor bubbles,
collapse occures due to pressure recovery at valve
downstream which cause bubbles to implode, giving microjets
and very high pressure waves (in range 100000 psi).

# Noise: is a result of turbulent fields generated through
the flow stream caused by many parameters:

- pipeline restrictions (orifice, valves, ..)
- pressure fluctuation
- unstable flow and very high flow velocity

and the noise radiation depends on pipeline material and
diameter and thickness.



# Here is the main guidelines to avoid flashing and
cavitation:

# To avoid flashing:
====================

1 - valve selection with high Fl.
Fl:valve pressure recovery coefficient, and this introduced
by MASONILIAN as: Fl=(P1-P2/P1-Pvc)^.5 - and Fl max is 1.

where FISHER introduced Km =(P1-P2/P1-Pv) - and this is a
valve parameter presented by vendor and it's calculated by
lab tests, and usin Km we can get allowable(P1-P2) which
will not cause flashing.

2 - using anti cavitation trim, which generate multi vena
contracta points in the presuure profile, and this prevent
pressure drop below Pv.

3 - To cool down the process material to make Pv very low.

4 - To change the valve position to another place with high
pressure, to make pressure drop through the valve away from
PV.


And anyway if there is no escape from flashing, it's better
to sustain flashing within the valve to assure that we will
not have a cavitation when pressure recover, and liquid can
be recovered and bubbles can implode any other place away
from the valve.

and this can be achieved by heating up the process liquid
so we raise Pv, and a good indication for us to be sure
that flash will be sustained is p2, as we can know P2 at
downstream pipeline and make sure that it's below Pvc of
the process liquid.

Regards,

Ahmed Sabry
Control and Instrumentation Engineer
GPC - General Petroleum Company
ahmedsabry.online@gmail.com
CELL.: 00 2 0121367310

what is the criteria to decide conductor size of a cable ?

1857

---

how 3 out of 2 Logic/interlocks works? give brief explanation with help of diagram.

2298

---

how can be calibrate flow indication transmitter (rosemount) it shows excess milli amps nearly about 24 ma on full scale, but its scale was set on 20ma on full scale..???how can be simiulate..???

2402

---

How INtools is useful for routine Instrument maintenance?

2075

---

Hi Friends , i need one urgent help , i am preparing for M.tech entrance examination , i need some obejective questions related to instrumentation field. where can i get those ? can anyone help me pls ?

1933

---

where proximity sensor installed on tank in loading arm application

2257

---

Explain the burnout feature.

966

---

Why boiler chimney area  oxyden sensor fixing? 

2476

---

Please asked me How calculate DCS controller memory.

2770

---

why I need valve guard and whats different between guard and positioner ??

1388

---

Describe the typical instrumentation used in monitoring the performance of a shell and tube heat exchanger.

2072

---

What is difference between differential pressure & delta pressure?

1080

---

How servomotor controls throttle valve of TURBINE?

1945

---

please send the drdo exam paper

2383

---

Pressure tx shows 1 mbar but we need 1000 mbar at this process condition .. how can we sort it out .

1696

---