Calculating the piping fabrication works

[chakaad]

- I've encountered problem in my first estimation of the piping fabrication works. For estimation of quantity of welding works (and maybe threaded works) a unit named "inch-dia" is used. I couldn't find any reference for calculation of "inch-dia"s of piping (for pipes, fittings, valves, flanges, ...). I know it considers both the no. of the welds (or threaded joints) and the pipe size. But is it eaxctly equal to the product of the No. of the joints and the pipe size? If yes, how is the effect of pipe thickness is included in the "inch-dia" calculations? For obtaining the total "inch-dia" for piping works, can we simply combine all the "inch-dia" s calculated for various spools, or there might be some restrictions in combining the "inch-dia"s?

- Is there any method to estimate the "inch-dia" for the piping only using the data from piping plans (no isometric dwg is available at this stage)? How should we estimate the number of welds for the pipes? (for the fittings, flanges, valves it can be stright forward). It will depend on the length of the pipes used in fabrication. Is the estimation method different for different pipe sizes?!

Thanks

 

[quark]

That is a general convention(atleast at my place) to use the term inch-dia when you have multiple pipeline sizes. All the pipe sizes are reduced to equivalent length of 1" pipe. For example, if you have 12 meters of 1" piping and 6 meters of 2" piping then you generally estimate the work to be 18meters inch-dia.

This term is useful, particularly, when you charge(or pay) the fabrication cost based on pipeline length in running meters and not on individual welds. Also the thickness of all the pipes being same. As the linear length of the weld is a multiple of pipe diameter, the cost becomes more or less same.

Regards,