The Truth Behind True Schedules (of Pipe)

By John Brady
October 2018

When talking about carbon steel pipe and pipe fittings it is often assumed that Schedule 40 and standard weight are the same thing; likewise, that schedule 80 and extra heavy are the same thing.  These assumptions, however, are incorrect and can lead to the wrong material being installed at the jobsite.

Take a look at the wall thicknesses (in blue) on our pipe chart Look closely at the two columns for schedule 40 and standard weight.  Up through a 10-inch pipe size the wall thicknesses are the same, and the terms schedule 40 and standard weight are very often used interchangeably.  But once we start dealing with pipe and fitting sizes larger than 10-inch you can see that the wall thicknesses diverge.  The wall thickness of the standard weight pipe plateaus, remaining the same at the 12-inch size, while the wall thickness of the schedule 40 pipe continues to increase with pipe size.  You can see this divergence in the following graph:

Graphical representation of the wall thickness divergence of schedule 40 and standard weight pipe starting at 10-inch sized pipe.

The same is true for schedule 80 and extra heavy pipe and pipe fittings, except that these two diverge at 8-inch sized pipe, where the extra heavy wall thickness remains the same.  This divergence is shown in the below graph:

Graphical representation of the wall thickness divergence of schedule 80 and extra heavy pipe starting at 8-inch sized pipe.

Since schedule 80 and extra heavy share the same wall thickness with smaller pipe and fitting sizes, there is often some confusion when quoting customers on pipe sizes above the point of wall thickness divergence.  Above these points of wall thickness divergence, it is especially important to read customer specifications carefully and clarify as necessary. 

Other Related Posts:

For a true story about how knowing how to read this Pipe Chart could save your hide, read: A Story about Pipe & Having our Customer’s Back

For an easier introduction to our Pipe Chart, you might enjoy: How to Read the Standard of New England Pipe Chart

Helpful Hints & Tips:

Terms often used when talking about pipe:

ANSI – American National Standards Institute

ASME – American Society of Mechanical Engineers

API – American Petroleum Institute

NPS – Nominal Pipe Size

NPT – National Pipe Thread

OD – Outside Diameter

STD – Standard

XH or XS – Extra Heavy or Extra Strong

XXH or XXS – Double Extra Heavy or double Extra Strong

ASME/ANSI B 36.10 – Welded and Seamless Wrought Steel Pipe

ASME/ANSI B36.19 – Stainless Steel Pipe

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