Steel pipe sizes "Nominal" refers to pipe in non-specific terms and identifies the diameter of the hole with a nondimensional number (for example – 2-inch nominal steel pipe" consists of many varieties of steel pipe with the only criterion being a 2.375-inch (60.3 mm) outside diameter). Specific pipe is identified by pipe diameter and another non-dimensional number for wall thickness referred to as the Schedule (Sched. or Sch., for example – "2-inch diameter pipe, Schedule 40"). Pipe size is quoted as a “Nominal Pipe Size” or NPS. The origin of the NPS numbers for smaller pipes (< NPS 12) is different to the origin for larger diameter pipes. However, all pipes of a specific NPS number have the same external or outer diameter (OD). The internal diameter will vary depending on the wall thickness of the metal. The reason for this is so that the same structural supports can be used for all piping of a specific NPS number regardless of the wall thickness.
Schedules Steel pipe schedules are a way to describe the wall thickness of the pipe. This is a critical parameter as it is directly related to the strength of the pipe and the suitability for specific applications. A pipe schedule is a dimensionless number and is calculated based on the design formula for wall thickness, given the design pressure and allowable stress. Examples of schedule numbers are as follows: 5, 5S, 10, 20, 30, 40, 50, 60, 80, 100, 120, 140, 160, STD, XS, and XXS—with the most common being schedules 40 and 80. As the schedule number increases, the wall thickness of the pipe increases. The schedule number of a pipe therefore defines the internal diameter, as the OD is fixed by the NPS number. The schedule number is roughly calculated as: Schedule = 1000 x (P/S) where P is the internal service pressure of the pipe (psig) and S is the ultimate tensile strength of the pipe material (psi). SCHEDULE = 1000(P/S) P = internal service pressure of pipe (psig) S = ultimate stress of pipe material (psi)
FREQUENTLY USED ASTM GRADES Material
Pipes A106 Gr A Carbon Steel A106 Gr B A106 Gr C
Fttg A234 Gr WPA A234 Gr WPB A234 Gr WPC
Flg A105 A105 A105
Valves Bolts and Nuts A216 Gr WCB A193 Gr B7 A216 Gr WCB A194 Gr 2H A216 Gr WCB
Carbon Steel A335 Gr P1
A234 Gr WP1
A182 Gr F1
A217 Gr WC1 A193 Gr B7