[updated:LAST EDITED ON Mar-23-05 AT 07:02 PM (CDT)]Chakra: The information you provided is not much to provide a informative response; however, is it possible that when the 350C stream is suddenly mixed with the 200C stream it causes rapid evaporation of the 200C stream? That could cause significant vibration. David Hendrix The Hendrix Group Inc.

Chakra Basically, in piping where there is a let down from higher pressrue or with high differential temperature there will be vibration problem, Severity depends on the let down in pressure and also in the temperature differential seen in the piping. In your case, both are reported to be occuring. Pressure let down : from higher pressue to lower pressure system will result in flow induced /presssure induced vibration problem inyour piping. Fortunately you are letting down from a 3 " to a 8" size where basic pressure let down vibration will be more. if the same had been reverse that is from 8" to 3" there will be severe erosion and corrosion problem in addition to flow induced / pressure induced vibration. Suggest that you look closely the "T" joint of 3" to 8" where there is a let down from higher pressure to lower pressure for erosion - corrosion. Also in your system there is a temperature difference of 150 deg centigrade which can also cause liquid -vapor impingement . This will result in piping vibration. With liquid-vapor due to temperature differential you will get erosion-corrosion problem unless there is enough built -in straight lengths available at the down stream end of 3" to 8" sizes. Please look carefully the "T" joints and also down stream piping for erosion-corrosion or impingement corrosion problem - due to flow (pressure transition) and temperature transition problems Hope this will help you to solve the problem C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai India March 24 E-mail: nishi@vsnl.com >Not knowing the specifics of your application, the mixing of >two streams with such a temperature difference is generally >not a good idea. > > > > >