How Do You Measure Tubing?

How Do You Measure Tubing?

June 24, 2022

Are you wondering how to measure tubing? Tubing is typically measured using the outside diameter, which is specified in inches or a fraction of an inch. Pipes are measured using nominal pipe size. It is related to the outside diameter but is much different. Read on to find more information about how tubing is measured, including wall thickness.

Measuring Tubing

When measuring tubing, always remember that the outside diameter is not the same as the pipe size. For example, a 1-1/2’’ pipe size has an outside diameter of 1.9’’ instead of 1.5’’.

For any size that ranges between 1/8- 12 inches, the NPS corresponds to the nominal inside diameter. However, it differs from the actual inside diameter. Pipe manufacturers, years ago, made the walls in smaller sizes way too thick. When they went to correct this error, the excess from the inside was taken away to avoid changing the sizes of the companion fittings.

For any larger tubing that measures more than 12 inches, NPS refers to the actual outside diameter. The outside diameter will remain constant for each nominal pipe size. The inside diameter is the only thing affected when it comes to wall thickness.

Wall Thickness & Pipe Schedule

Whenever you measure the wall thickness of the tubing, you will always use inches. However, when referring to a pipe schedule chart, you will notice that not all 12 gauges allow a thickness between 0.101 to 0.111. typically, the value is used for calculating section properties.

Pipe wall thickness is more complicated. There are three traditional designations used to indicate wall thickness, including:

  • Standard wall
  • Extra strong wall, which may also be referred to as extra heavy wall
  • Double extra strong wall, which may also be referred to as a double extra heavy wall

The ANSI was published by the American National Standards Institute to standardize pipe dimensions. This standard broadened the range of wall thicknesses. These numbers indicate estimated values of 1000 times pressure-stress ratios.

Various relationships exist between the traditional designations of STD, XS, and XXS, the ANSI schedule numbers, and the actual wall thicknesses. You should know that SCH 40 and STD are the same in size through 10-inch. However, in sizes over 10 inches, STD has a wall of 3/8 inch and XS has a wall thickness of ½ inch.

When referencing pipe wall thickness, this normally means the nominal or average wall thickness. Tubing measurements are important to note. The majority of ASTM tolerances of regular pipe products do state that the wall thickness of pipe at any point is not to be greater than 12.5% under the nominal wall thickness that was specified.

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