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:
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:
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.