Based on what you have posted, this is how I would start designing the tables and relationships. (remember, this is just a start)
So one Project can have many Drawings, but one Drawings has only one Project.
One Drawing can have many Spools, but One Spool has only One Drawing.
One Spool can have many Joints, but One Joint has only one Spool.
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Adding the Look up TABLES, the relationships look like
I combined "T_Elbows" and "T_Pipes". Then I merged "T_Product_Type" into "T_Products". This may be wrong after looking at dB "3CMA_DATABASE_V0.2"
Here is my attempt at the dB