NPS 26 Pipe Dimensions

Nominal size

NPS 26

Metric designator

DN 650

Outside diameter

26.000 in (660.4 mm)

Schedules listed

4

Standard weight wall

0.375 in (9.5 mm)

Extra strong wall

0.500 in (12.7 mm)

What NPS 26 is

NPS 26 pipe measures 26.000 in (660.4 mm) across the outside, so here the size designation and the outside diameter in inches are the same number. That holds from NPS 14 upward and for no size below it. The metric designator is DN 650, which is likewise a label and not a measurement in millimetres. Whatever the schedule, the outside diameter stays at 26.000 in (660.4 mm): a heavier wall grows inward and takes the difference out of the bore.

The first size beyond ASME B16.5. Flanges in this size come from ASME B16.47, and the pipe itself is typically made from rolled and welded plate rather than as seamless pipe.

Every schedule in NPS 26

Dimensions are given in inches, with the millimetre equivalent beneath in grey.

Inside diameter is OD − 2t. Weight is calculated for carbon steel as w = 10.69 × t × (OD − t) lb/ft and is the plain-end weight, excluding coatings, linings and fittings. Water-filled weight adds fresh water at 8.3454 lb per US gallon.

Reading the table

B36.10 lists 4 designations in NPS 26, which between them give 3 different wall thicknesses. The lightest is Schedule 10 at 0.312 in (7.9 mm) and the heaviest is Schedule 20 at 0.500 in (12.7 mm). Going from one to the other takes the bore from 25.376 in (644.6 mm) down to 25.000 in (635.0 mm), which cuts the flow area by 3% and raises the weight from 85.68 to 136.30 lb/ft, a factor of 1.6.

Standard weight does not coincide with any numbered schedule in this size. Extra strong equals Schedule 20. Where two designations share a wall they are the same pipe under two names, and either may appear on a mill certificate. The match is specific to the size, so it is the wall thickness in inches that should go on a requisition, not the designation alone.

For handling and support loads, a 20 ft length of standard weight NPS 26 pipe weighs about 2054 lb (932 kg) empty and 6396 lb (2901 kg) full of water. The water-filled figure is the one that governs pipe support spacing and the load during a hydrostatic test, including on lines that will carry gas or vapour in service.

Flow and pressure capacity by schedule

Two questions decide a schedule: how much the bore will carry, and how much pressure the wall will hold. The flow columns give the water flow through each bore at three velocities that bracket ordinary liquid service, from a pump suction line at the low end to a pump discharge line at the high end. The pressure columns are the ASME B31.3 pressure design equation solved for pressure, first on the nominal wall and then on the wall after the 12.5% mill under-tolerance that seamless pipe is allowed.

Flow is velocity × flow area. Pressure is P = 2·S·t / (D − 2·Y·t) with S = 20,000 psi, E = W = 1.0 and Y = 0.4: seamless carbon steel such as A106 Gr B at moderate temperature, with no corrosion allowance and no threading allowance. It is an illustration of the arithmetic, not a design rating.

The method behind both halves of that table is set out in the pipe sizing guide and the wall thickness guide, each with a worked example.

Flanges for NPS 26 pipe

ASME B16.5 stops at NPS 24, so there is no B16.5 flange in this size. Flanges for NPS 26 pipe come from ASME B16.47, which publishes two series, A and B, that do not bolt to each other. The series has to be settled before anything else about the flange is. See large diameter flanges.

Guides and comparisons for this page

NPS 26 in each schedule chart

Adjacent sizes