what is the reason for this phenomenon ?

? what is the reason for this phenomenon 


This answer from alot of people in facebook 

The valve seems to cause too much pressure drop due to very very small opening... ∆P is related to ∆T....that is why the pipe is cooled enough to condense water vapour

      Gas hydrates due to low temperature and high Gas pressure

       This is a gas line , the high reduction in pressure cause a high reduction in temperature. This effect known as Joule–Thomson effect

   Throttling lead to dp and according to joule tomso effect pressure drop cause temp. Drop 0.4 deg for every 1bar pressure loss

When pressure drop. Temperature also drop.

The pressure reduction was much and there was no hydrate catcher. It seems the JT Valve failed

 This is hydration because of press drop which cause temperature drop. To avoid this we can use methanol or increase choke size to decrease press drop

As my friends said and also we should know that the flow direction comes from small pipeline-which have a pressure gauge to the pipeline contains the iced big valve due to joule Thomson effect or enthalpy effect which can be ovrcomed with previous heating or opening the valve more with monitoring the flow required...

Liquid handled at its boiling point ,,, and thus boiling point is lower than the freeze point of water so water vapors at atmosphere reach dew point, condense and freeze on that chilly service ,,,
That pipeline will be exposed internally to hammering problem ,,, due to mixed phase flow liquid + vapour

Normaly the ice on pipe line caused by a fluid has boiling point too much lower than the ambient temp so it evaporate and consume heat from the pipe surface .the other factor is the pressure when it drop and the vapor pressure achived the same process will be occured.examples LNG and liquified nitrogen

Thanks for all