A stainless steel pipe schedule identifies a standard wall-thickness series for a particular nominal pipe size. It does not state the pipe’s pressure rating, grade or manufacturing method. Engineers and buyers must therefore specify the nominal size, schedule, material grade and product standard together.
Key takeaways
- A higher schedule generally means a thicker wall for the same nominal pipe size.
- Pipe schedule alone does not determine allowable working pressure.
- Matching pipe, fittings and welding requirements prevents site and fabrication problems.
What a pipe schedule tells you
Nominal Pipe Size, or NPS, is a naming system rather than a direct measurement of the bore. For most sizes, two pipes with the same NPS share the same outside diameter. Changing from Schedule 10S to 40S or 80S increases the wall thickness and reduces the internal diameter.
ASME B36.19M standardises dimensions for welded and seamless wrought stainless steel pipe. It also explains that the S suffix distinguishes schedules listed under B36.19M from those in the carbon and alloy steel pipe standard, ASME B36.10M. Some dimensions coincide, but engineers should not assume that they always do.
How 10S 40S and 80S differ
Schedule 10S is relatively thin-walled and can reduce material weight, welding time and cost where the design conditions permit it. Schedule 40S provides a heavier wall and is widely specified for general industrial piping. Schedule 80S is thicker again and may be selected where the design requires greater mechanical strength, additional allowance or higher pressure capability.
These descriptions are only a starting point. Actual thickness changes with nominal size, and the same schedule number does not represent one fixed thickness across every diameter. The drawing, bill of materials and request for quotation should state both NPS and schedule.
Steelmor stocks welded and seamless stainless steel pipe in commonly used 304L and 316L grades. Welded pipe is available in Schedules 10S and 40S, while the seamless range also includes Schedule 80S.
Why schedule is not a pressure rating
Wall thickness is one input into pressure design, but it is not the final answer. Allowable pressure also depends on pipe diameter, grade, temperature, manufacturing tolerance, corrosion or erosion allowance, weld quality and the design code used for the system.
ASME B31.3 covers the design, fabrication, inspection and testing of process piping in industries that include chemical processing, pharmaceuticals, power generation, pulp and paper. The responsible engineer must apply the relevant code calculation rather than choosing a schedule from a general pressure table.
How schedule affects the rest of the piping system
A thicker wall changes the pipe’s internal diameter, weight and welding preparation. It can affect flow calculations, support loads, weld volume and installation handling. Buttweld fittings should match the pipe wall or have a documented transition that can be prepared correctly for welding.
Schedule also influences availability. A design that uses standard sizes and schedules can usually be sourced more easily than one that combines unusual diameters, grades and wall thicknesses. Confirming stock and fabrication capability before issuing final drawings can prevent late substitutions.
What to include when requesting a quotation
State the nominal size, schedule, grade, ASTM or ASME material specification, welded or seamless construction, length, quantity and certification requirements. Add end preparation, testing, surface condition and fabrication requirements where they apply. These details allow the supplier to quote the intended product rather than infer the design.
Specify the complete pipe requirement
Pipe schedule is a dimensional designation, not a complete engineering specification. Reliable procurement starts when the schedule is paired with the correct grade, standard, construction method and design conditions.
For help confirming available sizes, schedules and processing options, contact Steelmor.