Walk into almost any steel warehouse, fabricator, or OEM and you will see a variety of different steel products. One of the most common items is pipe and tube. Steel pipe and tube are great in a multitude of different applications – from a sprinkler overhead protecting you from harm, to wonderful architecturally exposed structures waiting to be explored. Wait…did you catch something there?! Those are two very different applications that are oftentimes lumped into the same category.
What are Steel Pipes?
Steel pipes can be found everywhere you look and everyone (even those not in the steel industry) know what a pipe is. Round in shape, pipes are used as a vessel to transfer liquids and gases safely across long areas. Furthermore, pipes are used both above ground and underground in a wide variety of applications. Some of the common applications that use steel pipe include:
- Fire Sprinklers
- Oil and Gas
- Chemical Plants
- Plumbing
- HVAC
- Irrigation systems
How do you typically order steel pipe?
Steel pipe is ordered, or called out in their “NPS” size, or “Nominal Pipe Size” and “Schedule.” The nominal pipe size was established in 1927 by the American Standards Association to replace “Iron Pipe Size.” This system designates wall thicknesses based on smaller steps between sizes and the “Schedule” to specify the nominal wall thickness. On pipe sizes, 12” and under, the size loosely refers to the inside diameter (ID) of the pipe itself. So, while you may think a 1” pipe is actually a 1” outside diameter (OD), that 1” is closer to the ID of the pipe. In fact, schedule sizes designate wall thicknesses, so a schedule 5 will have a thinner wall thickness than a schedule 40.
Things get a little “gray” when you get into the larger pipe sizes such as 10” and above. As an example, for the larger sizes (anything above 12”), the NPS – which was closer to the inside diameter of the pipe before as we just learned – is now equal to the outside diameter of the pipe. Why is this? When the standard was created, the NPS was tied to the same inside diameter based on the standard wall thicknesses at the time. As those have evolved, based on processes and applications, the inside diameters developed to a point where the ID and OD were only indirectly related.
What about Schedules?
Depending on size you are looking for, steel pipe is called out with schedules. Also, it can be called out as a standard wall (STD), extra strong or extra heavy (XS or XH), and double extra strong or double extra heavy (XXS or XXH). These terms, that were in the original Iron Pipe Sizes (IPS), are still a part of the steel pipe language that is used today.
Frankly, the schedule designations were introduced in the hopes of phasing out that terminology. Because they are still in use today, some of the schedules do not always align with the former “standard” and “XS”. As an example, Nominal Pipe Size 12” sch 40 is a 12.75” OD round pipe with a .406” wall thickness. But, a standard (STD) schedule, or 40s, has a wall thickness of .375”. When in doubt, it is always best to refer to a pipe size chart to ensure you are ordering and receiving the size you need.
What are the Common Specifications for Steel Pipe?
When you need steel pipe for an application that is transporting liquids, chemicals, or gasses, in addition to ordering a specific NPS and schedule, you should factor in the specification you desire. In fact, some of the more common pipe specifications include:
ASTM A53
API 5l
ASTM A587
ASTM A795
These are typically produced using an ERW method of manufacture, or Electric Resistance Welded, by various manufacturers.
