Pressure Balanced Expansion Joint

"Expansion joints are often included in industrial piping systems to accommodate movement due to thermal and mechanical changes in the system. When the process requires large changes in temperature, metal components change size. Expansion joints with metal bellows are designed to accommodate certain movements while minimizing the transfer of forces to sensitive components in the system." (the site I got this from can be viewed here.)

Hence, you use the expansion joint to minimize the pressure fluctuations due to mechanical fluctuations in the pressure system. Hence, the expansion joint absorbes and reapplies the pressure spikes associated with mechanical variations that exist in any system.

If you need to know what they are and what types and/or number of valves to install, then a good engineering firm will gladly take your rmoney to provide you with an answer. The calculations are extensive and specific to the environment.

While the expansion characteristics of most materials are known and available, they are not the only consideration to be taken into account therefore justifying the need for hiring experienced people.

I hope that answers the gist of your question...feel free to toss any other considerations you may need at me and the rest of the forum.

I'm sure there are standards for this type of system, but I'm sure I don't know what they are. But thank you Abdel for confiming my lay understanding. Abdel is a much more experidnced person to consult for this, as I'm just tossing out the basics as I see em.

More specific comments should be directed towards him and I will learn with you as we hear it from a much more experienced implementor. Take it away Abdel...

Please provide pipe size, vertical rise, horizontal run distance, pounds an hour of discharge steam and pressure as it enters the "vent". It is possible that you may not need a exp. joint but if you need one and your vent piping is hard mounted instead of a walking beam set up you could damage equipment.

Listen to him, I looked up the information on expansion joints...he seems to be a much more reliable source.

pipe size is 30" with vertical rise of 3.00meter & horizontal run of 5.00meter. Pressure is 0.35bar, full vaccum.

I agree with Abdel like always he is right on with his answers. I have never seen an expansion joint used for pressure differences they make pop off valves and PRVs for this. I always thought expansion joints were for thermal growth movement of pipes and ducts etc. They also work for isolating stress ( from thermal growth, weight of pipe) from from affecting pumps,turbines and instrumentation.

pipewelder

Short and sweet answer you should not need an expansion joint for your application.

Thanks for the fast info reponse.

Mike

An expansion joint acts as a spring that also is a pressure boundary. The flexibility is used to absorb deflection due to thermal growth. A side effect of this is that the pipe is now "cut" and the longitudinal pressure thrust in the pipe has to be absorbed by external structures to the pipe (anchors, tanks, etc...). If there are no structures that can do this, a "pressure balanced" expansion joint would be used. The pressure balanced expansion joint has an additional chamber that balances and eliminates the thrust while maintaining the flexibility for absorbing thermal expansion.