Enter Dimension Values into Part Description

I am trying to enter a dimension value, such as d1 into a parameter such as "Part_Decription."

I have tried using a relation statement like: Part_Description = "PIPE" + istr(@d1). All that this gives me is: PIPE istr(@d1)

What I am trying to do is extract the ID and OD from a tube and place it into my part description. I would also like to do the same thing for the length of the pipe.