We rarely show weights on our isometric drawings, usually thats handled through a more traditional BOM. All the same, it would be useful in some cases, like isometrics for the stress engineers. Given the option, I'd like a couple of different possible weight values in an isometric BOM: one for per-component weight, and another for total weight for that entry. As your example, the line for components (e.g. elbows) would be similar to:
1 4" ELBOW, 90 DEG LR, SCH. 80, ASTM A-234 GR. WPB 5 10 50
... where the 5 is the unit count, 10 is the weight-per-component, and 50 is the total. Having the option for one, or the other, or both, is useful for the usual "where did this number come from?", "how much for just one?", and "how much for everything?" questions from engineers and purchasing.
As your example for pipe, it would be similar to:
1 4" PIPE, SMLS, SCH. 40, ASTM A-106 GR. B 1205mm _ 50
... where _ is the per-length-unit weight and 50 is the total weight for that length. I don't see a need for a per-length-unit weight for linear components like pipe.
Also, when there is weight values available it is nice (but not essential) for sub-totals and totals in the BOM: fabrication, erection, miscellaneous; supports; and so on.
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