Would someone indulge me this somewhat elementary question. It crosses design, shop fabrication and field installation and also relates to isometric generating software.

A typical method and listed practice of dimensioning piping isometrics is centerline to centerline, say for a loop. Alternatively, full dimensioning of each and every element, example spools, fittings and valves, may be applied to an iso – for the assistance of the bill.

How does dimensioning take into account the weld root gaps between pipe spools and fittings? Are the root gaps included in the dimension, thus resulting in each dimension, say, along a pipe being 2mm longer and the center – end dimension for an elbow 1mm longer – for a 2mm root gap. Or are the root gaps ignored entirely. Ignoring the gaps would rely on the usual field adjustments using shims and packers at pipe supports to compensate for the tolerance of pre-fabricated developments.

ISOGEN does have the option setting (tick box) of including / excluding root gaps, but this ultimately then leads back to the above question.

Could anyone give guidance on the usual practice.

Thanks