All, I thought I should post a solution (work around) I've found.
I found that I can create the same parameter name in the start part as the locked parameter from the linestock, i.e. (OD) and when using the pipe solid command, it would populate the data from the linestock to the pipe part created in the assembly.
therefore, I could create a relation using the OD to populate the DN parameter using IF statements.
because all parameters are in the start part there is no errors.
IF OD == 114.3
PIPE_DN_SIZE="DN100"
ENDIF
and Wall thickness to populate the schedule size using IF, &(AND) (only used when a duplicate WT between sizes and schedules) as well as |(OR) Statements.
/* DN50 TO DN80
IF WALL_THICKNESS == 5.54 | WALL_THICKNESS == 7.62 | WALL_THICKNESS == 8.56
PIPE_SCH="XS"
ENDIF
and having 2 different start parts, one for welded pipe, the other for seamless, and having a fixed parameter (pipe_std) for those,
I was then able to combine them together to form the required description
DESCRIPTION=STOCKNO + ", " + PIPE_DN_SIZE + ", " + PIPE_TYPE + ", " + PIPE_SCH +", " + PIPE_STD
Stockno & Pipe_type are also populated from the linestock when the pipe solid command is run.
Note:
The regenerate command needs to be run after the pipe solid command for the data to be populated.
Hope this helps