Hi I am doing some 3D modeling and getting pressure class error.If I create a tank in equipment block it is giving tank 300lb flanges.I am using CS150 spec which has 150lb flanges in it's spec.If I try and route pipe I am getting error:Cannot find flange in CS150 spec Pressure Class 300Flanged connection failed due to properties mismatchIf I try and modify equipment it will not allow me change 300lb to 150lbfor flanges on equipment block.Anybody know a fix for this?

You might try asking your question over at the AutoCAD Discussion Groups in the Plant3D section.  You'll probably get more help there.

I have figured this out. Some equipment blocks allow you to modify flangesand some do not. This may because I am using a student version.Pumps can be modified but tanks cannot be modified. If you clickon block you should see a brown pencil symbol which allows youto modify block and pressure class rating. If no pencil then no modify.

It has nothing to do with the fact you are using a student version.  As AutoDesk plainly states on its website student versions of their programs are fully functional meaning they operate the same way as the retail version.

On the tank, hold the CTRL key down and select the nozzle. Then you'll get the pencil and can edit the nozzles pressure class.