Please understand that all the replies come from the experience on the similar/same applications.

This type applications require very close relationship between process and stress engineer. Stress engineer finds that the allowables can not be achieved with the available route. Process engineer does not want to increase pipe length and introduce more fittings to the systems not to increase resistance. Thease are all normal for this applications. Sometimes the process engineer/vendor may accept that the pump can cavitate.

There are other things that stress engineer should consider for this applications. The suction line should be as short as possible to reduce the flow resistance and thermal expansion in the system. Keep the horizontal supports as minimum, or do not introduce unless it is essential. Watch the location of vertical supports not to cause additional bending moment at nozzles and pump flanges, put low friction vertical supports if necessary.

The horizontal support that you introduced are the source of the problems in case there is a temperature case. You added too many bends and increased the suction line length, this increased pipe and local friction losses in the pipe. Additionally, when you create new pipe route you need to watch the maintenace and removal access to the pumps.

Start analysing the original route without horizontal supports. Add them if they are necessary. In case this does not satisfy the allowables, and pipe code requirements, you consult the process engineer to plan new locations for the pumps in case you can not change the elevations. Do some stress analyses fpr your proposal before going to process engineer. Talk to the designers for other restrictions as well.

I guess this is sufficient for the moment.

Regards,

Ibrahim Demir