Aluminium Pipe Size Chart: SCH40 and SCH80 Dimensions and Weights

How NPS and schedule numbers work

NPS is a name, not a measurement. From NPS 1/8 to NPS 12 the actual outside diameter is larger than the nominal size: a 1 in pipe has an OD of 1.315 in (33.4 mm), and a 2 in pipe 2.375 in (60.3 mm). From NPS 14 upward, OD equals the nominal size in inches. Because OD is fixed for each NPS, all schedules of a size fit the same fittings and clamps; only the bore changes.

The schedule number sets the wall thickness. Higher schedule means a thicker wall, a smaller inside diameter, more weight and a higher pressure rating. Aluminium pipe dimensions follow ASME B36.10M (Schedule 40 and 80) and ASME B36.19M (Schedule 5S and 10S), and the aluminium product standards ASTM B241 (seamless pipe) and ASTM B429 (structural pipe) reference these dimensions.

A note on the "S" schedules: up to NPS 8, Schedule 40 and 40S are identical, as are 80 and 80S. At NPS 10 and 12 they differ (for example, NPS 12 Schedule 80 is 0.688 in, but 80S is 0.500 in). Always state which one you need on the order.

Aluminium pipe outside diameters by NPS

Outside diameter is the same for every schedule of a given NPS.

Wall thickness chart: Schedule 5, 10, 40 and 80 (inches)

Wall thicknesses below are the nominal values from ASME B36.19M (5S, 10S) and B36.10M (40, 80). Schedule 5 and 10 are light walls used for low-pressure lines and lightweight structures; Schedule 40 is the general-purpose wall; Schedule 80 is used for higher pressure, threading and heavy-duty structures.

NPS 10 and 12: Schedule 40S walls are 0.365 in and 0.375 in, and Schedule 80S walls are 0.500 in for both sizes. Schedule 5S and 10S are not defined for NPS 1/8 – 3/8 in all tables.

SCH40 aluminium pipe dimensions and weight

Weights are calculated from nominal dimensions using a density of 0.098 lb/in³ (2.71 g/cm³), the value used for 6061 in aluminium pipe tables. 6063 pipe weighs about 0.5 % less. Actual weights vary with wall tolerance.

SCH80 aluminium pipe dimensions and weight

Schedule 80 walls are roughly 35 – 70 % thicker than Schedule 40, which raises pressure capacity and leaves more metal under threads.

NPS 10 and 12 values above use Schedule 80 (B36.10M). For Schedule 80S (0.500 in wall), weights are about 18.9 lb/ft for NPS 10 and 22.6 lb/ft for NPS 12.

Which alloy for aluminium pipe?

Minimum properties summarised from ASTM B241 and B221 for typical wall ranges; thicker walls and other product forms may have different limits. The mill certificate states the guaranteed values for your lot.

6061-T6 is the default where strength matters; 6063 is chosen for appearance, bending and anodising. For seawater and cryogenic service, 5083 and 5086 pipe keep their strength after welding. High-strength aerospace alloys such as 2024 and 7075 are usually supplied as tube to OD × wall rather than in pipe schedules.

Estimating the pressure rating of aluminium pipe

A first estimate of internal pressure capacity uses Barlow’s formula, P = 2 × S × t ÷ D, where S is the allowable stress for the alloy and temper at the design temperature, t the minimum wall (nominal wall less the mill tolerance, typically 12.5 % for seamless pipe), and D the outside diameter. Allowable stresses come from the design code, for example ASME B31.3 for process piping, not from the tensile strength.

• Welding reduces strength. The heat-affected zone of 6061-T6 drops to near annealed strength, so codes give lower allowable stresses for welded 6xxx pipe.
• Temperature matters. Allowable stress for 6xxx alloys falls significantly above about 100 – 150 °C.
• Threads remove wall. Threaded joints use Schedule 80 so that enough metal remains under the thread.
• Use seamless pipe for pressure. Specify ASTM B241 seamless; B221 and B429 structural pipe may contain extrusion seams.

Supply range and processing

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