Pipe Wall Thickness

Pipes are produced in various thicknesses that have been standardized. Each pipe wall thickness is given a name pipe in the form of schedule number, not in the form of actual pipe wall thickness.

Initially, the pipe wall thickness is classified into three groups as following below:

-          Double Extra Strong (XXS)

-          Extra Strong (XS)

-          Standard

Currently the naming of pipe wall thickness has been replaced with schedule which providing certain number, starts from 5 and 5S, then followed with 10 and 10S, so in multiples of 10 to Schedule 40 (20, 30, 40), and then have multiple of 20 such as pipe wall thickness schedule 60, 80 , 100, 120, 140, 160.

The pipe wall thickness which has schedule 40 is generally same with schedule STD pipe sizes 1/8 inch up to 10 inch. Likewise, schedule 80 is the same as the schedule XS for pipe sizes 1/8 inch up to 10 inch.

One thing should be considered is the use of pipe that has Schedule 5 and 10 are more widely used on stainless steel pipe. While the pipes which are classified as Small Bore, usually have minimum pipe wall thickness of Schedule 80, although it may have thickness more than that, it's just going to make a pipe becomes excessive strength than is needed.

Pipes are usually produced with having different length depending on the material, size and schedule. But in general the pipes are produced with having average length of 20 feet or 6 feet for pipe Carbon Steel. This length is also called as random length. Sometimes pipe which having length twice than random length are also widely available and include preferred especially for use in the pipe rack. This size is also called as Double Random Length, or equal to 12 meters.

Name Size of Pipe

There are two methods commonly used to name the size of a pipe, namely:

1. NPS: Nominal Pipe Size, widely used in North America, with inch units.
2. DN: Nominal Diameter used by countries in mainland Europe, with millimeters units.

DN and NPS show the size of diameter. Therefore need to know how to find the naming of pipe thickness sizes which is commonly referred to as Schedule. Schedule is the naming of pipe sizes that show the size of pipe wall thickness.

For countries which always use millimeter as their units will commonly confuse if use NPS (Nominal Pipe Size) to naming size of pipe.  The size of pipe in NPS is not always measure and show outside diameter (OD) actually. The difference between NPS and OD is starting from pipe sizes NPS ¼ "up to pipe size NPS 12". But for pipe size NPS above 12 inches show size of outside diameter actually or in other word, size NPS above 12 inch is same with size in millimeter.

In some literatures explained that the difference is more due at the beginning of pipe manufacturing in 1930s are based on inside diameter pipe with 1/16" wall thickness, so the size becomes larger outer diameter 1/8".  Over time, technology of pipe manufacturing is advancing so pipe manufacturer can produce pipe with smaller wall thickness but can maintain outside diameter pipe size.