Hi All,

As you all know, during hydrotest, the pressure might drop dramatically in the pressure vessel when the ambient temperature reduced (eg. in a rainy day) accordingly. Do you guys know the theoretical reason behind?

This is my understanding..

According to the thermodynamic first law, assumed the expansion workdone is zero since the pressure vessel is a closed system, the heat released from the system is completely converted from the internal energy of the water molecules. Therefore, the pressure of the water (system) dropped.


In another point of view, the ambient temperature reduced resulted in the contraction of the volume of water and steel. The contraction of water is more than the contraction of steel and caused the water inside the pressure vessel dropped. The pressure dropped could be calculated by referring to the bulk modulus of water.


Sorry for my poor explanation.. Hope somebody is on the same page with me and can understand what I am trying to explain.
Thanks in advance.