mpi/max_pipes is a SAP Parameter attribute which is used to control Maximum number of memory pipes (MPI) information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
The parameter specifies the maximum number of memory pipes.
The default setting only has to be changed for very big systems or for
the Web Dispatcher that has to keep open a lot of parallel connections.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.