What are Inch-Dia and Inch-Meter? Their Significance and Examples (PDF)

Inch Dia and Inch Meter are the terms frequently used in the piping construction industry. Both Inch dia and inch meter are units for measuring the quantum of piping construction jobs for fabrication, erection, and hydro test purposes. In this article, we will explore the significance of Inch Dia and Inch Meter with examples.

What is Inch Dia?

Inch dia and Inch meter are used during the construction of chemical, petrochemical, fertilizer, refinery, power, and oil&gas industries. The progress of piping spool fabrication mainly welding is measured by the term Inch Dia.

In piping welding, the pipe size is converted to the equivalent inch dia and reported. Let’s understand this with some examples,

Assume a 6″ NPS pipe of length 60 m needs to be produced. We all know that pipes are not manufactured with indefinite lengths. Single random length pipes are manufactured in the length of 5 to 7 m whereas double random length has a length in the range of 11 to 13 m. So to make a pipe of length 60 m we have to weld smaller length pipes. So even if we consider a maximum length of 13 m, there will be a minimum of 4 welding joint requirements. This pipe welding requirement is denoted by Inch dia.

As per the above example, the Total required inch dia=Diameter of pipe in inches X No of joints required =6 X 4=24 inch dia.

Similarly, if the pipe NPS is 12 inches and the required number of joints is 6 then the inch dia will be 12 X 5=60 inch dia. The joints with Pipe Spool, Elbow, Tee, Reducer, Flanges, Valves, or other piping components are denoted and calculated using Inch-Dia in a similar way.

So, the equation for inch dia can be represented as below:

Inch Dia=Pipe Size in Inches X Total Number of Joint for that size.

Other than welding, NDT tests like Radiography and DPT requirements are also measured in terms of Inch Dia. The payment for all these construction activities is calculated based on Inch-Dia.

What is an Inch Meter?

Inch Meter is specifically used to measure the progress of Piping erection and hydro-testing. The pipe length that is erected or hydro tested at the construction site is converted to the equivalent inch Meter of erection or hydro testing.

The equation for calculating Inch-Meter is

Inch Meter=Pipe NPS in Inches X Length of Pipe in Meters

Let’s understand the concept of the Inch-Meter with some examples,

Assume a 20-inch NPS pipe of length 100 meters is to be erected at the site. So, the quantum of the piping erection job is 20 X 100= 2000 Inch-Meter.

Similarly, If a 12-inch pipe of 50 m length is required to be hydro-tested the quantum of piping hydro-testing job is 12 X 50=600 Inch-meter.

All piping erection jobs, insulation, etc are converted to Inch-meter for measuring progress for payment purposes.

The estimated inch-dia and inch-meter also help to calculate the required number of professionals and associated cost and time requirements for any project.

Sample Calculation of Inch-Dia

Let’s calculate the Inch dia for the configuration shown in Fig. 1.

In this diagram, the size of the larger pipe is 10 inches NPS and the total number of joints in the 10-inch pipe is 6 (1 with the flange, 4 with the elbows, and one with the reducer). So, the Inch dia for the 10-inch line is 10X6=60 inch-dia.

Now the diameter of the smaller pipe is 8 inches NPS.
The total number of joints in the 8-inch pipe is 2 (1 with the flange and the other with the reducer).
So, the Inch-dia for the 8-inch pipe=8 X 2=16 inch dia.

Hence, the total calculated inch-dia=60+16=76 inch-dia