Pipe Schedules Explained — SCH 5S, 10S, 40, 80, 160, XXS

What is a Pipe Schedule

Pipe schedule is a number that defines the wall thickness of a pipe relative to its nominal bore (NB) size. The term comes from ASME/ANSI B36.10 (for carbon and alloy steel) and ASME/ANSI B36.19 (for stainless steel).

Critically: the schedule number is NOT the wall thickness itself. It is a code that, combined with the nominal pipe size (NPS or NB), gives a specific wall thickness in millimetres. For example, a 2-inch (50NB) pipe in SCH 40 has a wall thickness of 3.91mm. The same 2-inch pipe in SCH 80 has a wall thickness of 5.54mm. Same outer diameter — completely different wall, weight and pressure rating.

The outer diameter (OD) of a pipe is fixed for a given NPS regardless of schedule. Only the wall thickness (and therefore the bore/inner diameter) changes with schedule.

The Schedule Number System — How It Works

The original ANSI schedule system was defined so that: Schedule Number ≈ 1000 × (P/S), where P = service pressure in psi and S = allowable stress of the material in psi.

This means higher schedule numbers were designed for higher pressure service. Schedule 40 and 80 are the most common for general process piping. However, for stainless steel pipes, the 'S' suffix (SCH 10S, SCH 40S, SCH 80S) indicates the thinner-wall stainless steel schedules defined in ASME B36.19.

Important: SCH 40 and SCH 40S have the same wall thickness for pipes up to 10-inch NPS but differ for larger sizes. Always specify 'S' for stainless steel to ensure you are referencing ASME B36.19 dimensions.

SCH 5S, 10S, 40S, 80S, 160 and XXS — Practical Differences

SCH 5S: Lightest wall. Used in low-pressure applications — instrument air, cooling water, gravity drain lines. Not recommended for high-pressure steam or process gas.

SCH 10S: Standard for stainless steel process piping in low to medium pressure service. Common in pharmaceutical, food and general chemical plant piping where pressure is moderate and corrosion resistance is the primary requirement.

SCH 40 / 40S: The workhorse schedule. Default for carbon steel process piping (ASTM A106 Gr.B, API 5L) and standard SS process piping. Suitable for most general process applications up to moderate pressure.

SCH 80 / 80S: Heavier wall for higher pressure or elevated temperature service. Also used where erosion or corrosion allowance is needed. Common in high-pressure steam lines, hydraulic systems and slurry piping.

SCH 160: Very heavy wall. Used in high-pressure, high-temperature critical service such as boiler steam headers, HP steam turbine inlet piping and high-pressure hydraulics.

XXS (Extra Extra Strong): The heaviest standard schedule. Used in extreme high-pressure service, often with PWHT. Wall thickness can be 2–3× that of SCH 40 for the same pipe size.

Common Mistakes When Specifying Pipe Schedule

Not specifying 'S' for stainless steel: Ordering 'SCH 40 SS pipe' without the S suffix can result in carbon steel schedule dimensions being applied. Always specify SCH 40S, SCH 10S for stainless.

Confusing NB with OD: Nominal bore is NOT the outer diameter. A 2-inch (50NB) SS pipe has an OD of 60.33mm — significantly larger than 50mm. This matters for flange selection, fitting procurement and structural clearances.

Assuming the same schedule means the same wall: A 4-inch SCH 40 pipe has a wall of 6.02mm. An 8-inch SCH 40 pipe has a wall of 8.18mm. The same schedule number gives different walls for different pipe sizes.

Not checking pressure-temperature rating: The allowable working pressure of a schedule 40 pipe in SS 316L at 300°C is very different from the same pipe at 20°C. Always refer to ASME B31.3 tables for your specific material, schedule and temperature.

Creative Metal Industries Pipe Stock — All Schedules in Vadodara

Creative Metal Industries maintains one of the most comprehensive pipe schedule inventories in Gujarat, Vadodara. Our ready stock covers:

Stainless Steel Pipes (ASTM A312): Grades TP304, TP304L, TP316, TP316L, TP317L, TP321, TP310S, TP347, TP904L in SCH 5S, 10S, 40S, 80S, 160 and XXS — sizes 6NB to 600NB.

Carbon Steel Seamless Pipes (ASTM A106 Gr.B): SCH 40, 80, 160, XXS — sizes 6NB to 600NB. IBR Form III-C available.

Alloy Steel Seamless Pipes (ASTM A335 P11, P22, P91): SCH 40 to XXS — IBR certified.

All pipes are supplied with original Mill Test Certificates from ISMT, Ratnamani, Sandvik, Salzgitter and other approved mills. Cut-to-size, bevel cutting and threading available at our Vadodara facility. Call +91 99982 80619 for current stock and pricing.