Sizes and Dimensions of Butt Weld Pipe Fittings

How are butt weld pipe fittings measured ?

  • Butt Weld Pipe Fittings are measured by their diameter, wall thickness (known as “schedule”), and shape or configuration. (Butt Weld Pipe Fittings are also defined by their material grade and whether they are welded or seamless.)
  • Diameter refers to outside diameter of a pipe or fitting.
  • The North American standard is known as Nominal Pipe Size (NPS). The International Standard is known as Diameter Nominal (DN). Pipes and fittings are actually made in similar sizes around the world: they are just labeled differently.
  • From ½ in to 12 inch “Nominal Pipe Size”, outside diameters are slightly larger than indicated size; inside diameters get smaller as schedules grow.
  • From 14 in and larger “Nominal Pipe Size”, outside diameters are exactly as indicated size; inside diameters get smaller as schedules grow.
  • As with other North American standards (inch, foot, yard, mile, …), many pipe standards (diameters up to 12 inch and wall thickness) are based on historical precedents (a toolmaker’s dies during US Civil War) rather than a “scientific” method.


What does “schedule” mean for butt weld pipe fittings ?

What is schedule 40, sch80 ?

  • Schedule, often shortened as sch, is a North American standard that refers to wall thickness of a pipe or pipe fitting. Higher schedules mean thicker walls that can resist higher pressures.
  • Pipe standards define these wall thicknesses: SCH 5, 5S, 10, 10S, 20, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160, STD, XS and XXS. (S following a number is for stainless steel. Sizes without an S are for carbon steel.)
  • Higher schedules are heavier, require more material and are therefore more costly to make and install.

Why are butt weld pipe fittings sometimes thicker and heavier than pipes to which they are connected ?

  • Butt weld pipe fittings are sometimes thicker than their connecting pipes to meet performance requirements or due to manufacturing reasons.
  • Due to butt weld pipe fittings geometry, stress is very different when compared to a pipe. Using extra material is often necessary to compensate for such additional stress, especially for tees and tight curve elbows.
  • Butt weld pipe fittings manufacturers may not always stock plates or pipes for all metal grades or sizes. When responding to an order, manufacturers always use the right metal or alloy, but sometimes made with next-higher available plate or pipe size while still respecting specified inside diameters.

What does 45 SR or 90 LR mean for butt weld pipe fittings ?

  • 45 and 90 refer to angles for changing direction of pipe flows: 45 degrees or 90 degrees. Most elbows are 45˚ or 90˚.
  • SR means Short Radius; LR means Long Radius. Centerline radius of long radius (LR) elbows is smoother than of short radius (SR).
  • In SR fittings, radius equals nominal diameter size. A 6 inch pipe will have a 6 inch radius center-to-end, giving it a sharp curve.
  • In LR fittings, radius equals 1.5x nominal diameter size. A 6 inch pipe will have a 9 inch centerline radius, for a smoother curve than SR.7FAQS_CS5

What is the difference between a 3R and a 3D elbow?

  • There is no difference between 3R and 3D. Both have a centerline radius of three times the nominal diameter size. Both have a smoother curve than an SR or LR.
  • (In fittings, 3D does not refer to modeling software or screens.)

What does 3D or 6D mean for butt weld pipe fittings ?

  • Larger numbers have smoother curves.
  • Centerline radius is calculated based on diameter and number that precedes it. For example, a 10″ 6D has a 60″ centerline radius.
  • Smoother curves are often used for applications with higher pressure, abrasion or corrosion.

What is the difference between concentric and eccentric reducers ?

  • A concentric reducer is symmetrical: both ends are aligned along the center.
  • An eccentric reducer is not symmetrical: ends are off center of one another.7FAQS_CS5

What is a lateral tee ?

  • A lateral tee separates one line into two; the second line branches at a 45˚ angle.


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