Inch Meter & Inch Dia in Piping

In construction projects, both Inch Dia & Inch Metre are generally considered as units for measurement of quantum of piping job (mainly for welding/ Erection of piping/ hydrotest measurements). Former being denoted by ID of (phi)” or ” and inch metre by IM respectively; can be understood as below:

Part1:

Consider an 8 inch NB pipe of length say 100 metres. If there are 5 joints of this pipe to be welded, the quantum of this welding job is calculated as Pipe Dia (in inches) x No. of joints, i.e, 40 and denoted as 40 Inch dia (ID). 

In terms of IM, we say the quantum of job as Pipe Dia (in inches) x No. of Metres, i.e, 800 and denoted as 800 Inch Metre (IM).

Once again, ID is generally taken as unit of measurement (of quantum of job) for Welding, Radiography, DP test etc and are used as units for payment purposes as well.

IM is considered normally to define the quantum of Piping Erection job, Insulation (besides Metre cube) and its payment terms.

part 2

Inch dia in welding is nothing but the multiplication of size of joint x no of joints (of that size) which you need to weld during fabrication. Consider a Piping Spool , Say it has a pipe of 4″ (12 m long), with flange on one end and elbow on another. You are providing a branch connection of 2″ on it.

Welding inchdia in it is:

Total joints of 4″ in it = 1(pipe with flange) + 1(pipe with elbow) + 1 (it is optional – if a pipe purchased is of 6m length then you need to weld pipe to pipe to gain 12m length spool, but if pipe purchased is of 12m length then it is not required).

so inch dia = 4*3 = 12.

Now for branch connection of 2″ on mother pipe of 4″, you need to provide a weldolet, which will add one joint of 2″ size. so inchdia = 2*1 = 2

So Total inchdia involved in fabrication of that spool = 12 + 2 = 14inchdia.