Pipe Schedule
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Pipe Schedule / Schedule Numbers The main function of the pipes is to carry fluid (liquid, gas, fluidized solids, slurry, mixed phase products etc) under pressure (internal, external or both), therefore to sustain the fluid pressure the pipe has to be strong enough to perform its intended duty without failure. Obviously, for pipes containing pressurised fluids the wall thickness, and by implication the pipe’s strength, is the most important parameter. Wall thickness is expressed by “schedules or Schedule numbers“, referred to as pipe schedules. Pipe Schedule or Schedule number is a dimensionless number. Schedule Numbers for pipe size/wall thickness combinations are approximated to get a uniform relationship equal to 1000 times the P/S (P=Design Pressure and S=Allowable Stress) expression contained in the modified Barlow formula for pipe wall thickness. The pipe schedule is abbreviated as SCH. For a given size and schedule the thickness of the pipe is fixed and defined in the applicable ASME standard (B 36.10/B 36.19). Even though Pipe thickness can also be specified in mm or inches to the value corresponding to that specified in the ASME standard, The Schedule Numbers are strictly used as a convenient designation system while ordering piping item. For any given pipe size and varying schedule numbers or thicknesses its Outside Diameter (OD) remains constant and Internal Diameter (ID) varies. With increase in thickness the strength increases but its ID decreases. OD is kept constant to help the support hardware design so that the same support hardware can be used for same pipe size (varying thicknesses). Governing Standards: In the oil and gas and related downstream industries the most common standards are ASME B 36.10 Welded and Seamless Wrought Steel Pipe, and ASME B36.19 Stainless Steel Pipe Nominal Pipe Size: The size of all pipe is identified by the nominal pipe size. The manufacture of pipe NPS 1⁄8 (DN 6) to NPS 12 (DN 300), inclusive, is based on a standardized outside diameter (OD). This OD was originally selected so that pipe with a standard OD and having a wall thickness that was typical of the period would have an inside diameter (ID) approximately equal to the nominal size. Although there is no such relation between the existing standard thickness — OD and nominal size — these nominal sizes and standard ODs continue in use as ‘‘standard.’’ The manufacture of pipe NPS 14 (DN 350) and larger proceeds on the basis of an OD corresponding to the nominal size. So the OD in mm of a pipe NPS 14 or higher can easily be calculated by simply multiplying the NPS (here 14) by 25.4. But for lower sizes the OD calculation is not so easy. Pipe Schedule vs Pipe Size: As For all pipe sizes the outside diameter remains constant. Therefore any variation in schedule i.e. wall thickness, affects only the inside diameter. As the schedule number increases, the wall thickness increases, and the actual bore is reduced. Standard (STD) is identical to SCH 40 up to NPS 10. All larger sizes of Standard have 9.53 mm wall thicknesses. Extra-Strong (XS) is identical to SCH 80 up to NPS 8. All larger sizes of Extra-Strong have 12.70 mm wall thicknesses. Double Extra Strong (XXS) wall is thicker than SCH 160 from NPS 1/8 to NPS 6, and SCH 160 is thicker than XXS wall for NPS 8 and larger. Pipe of sizes and wall thicknesses other than those of Standard, Extra-Strong, and Double Extra-Strong, and Schedule Number were adopted from API Specification 5L.
description
(NPS) for diameter based on inches, and a schedule (Sched. or Sch.) for wall thickness
Transcript of Pipe Schedule
Pipe Schedule / Schedule Numbers The main function of the pipes is to carry fluid (liquid, gas, fluidized solids, slurry, mixed phase products etc) under pressure (internal, external or both), therefore to sustain the fluid pressure the pipe has to be strong enough to perform its intended duty without failure. Obviously, for pipes containing pressurised fluids the wall thickness, and by implication the pipe’s strength, is the most important parameter. Wall thickness is expressed by “schedules or Schedule numbers“, referred to as pipe schedules.
Pipe Schedule or Schedule number is a dimensionless number. Schedule Numbers for pipe size/wall thickness combinations are approximated to get a uniform relationship equal to 1000 times the P/S (P=Design Pressure and S=Allowable Stress) expression contained in the modified Barlow formula for pipe wall thickness. The pipe schedule is abbreviated as SCH. For a given size and schedule the thickness of the pipe is fixed and defined in the applicable ASME standard (B 36.10/B 36.19). Even though Pipe thickness can also be specified in mm or inches to the value corresponding to that specified in the ASME standard, The Schedule Numbers are strictly used as a convenient designation system while ordering piping item.
For any given pipe size and varying schedule numbers or thicknesses its Outside Diameter (OD) remains constant and Internal Diameter (ID) varies. With increase in thickness the strength increases but its ID decreases. OD is kept constant to help the support hardware design so that the same support hardware can be used for same pipe size (varying thicknesses).
Governing Standards: In the oil and gas and related downstream industries the most common standards are
ASME B 36.10 Welded and Seamless Wrought Steel Pipe, and ASME B36.19 Stainless Steel Pipe Nominal Pipe Size: The size of all pipe is identified by the nominal pipe size. The manufacture of pipe NPS 1⁄8 (DN 6) to NPS 12 (DN 300), inclusive, is based on a standardized outside diameter (OD). This OD was originally selected so that pipe with a standard OD and having a wall thickness that was typical of the period would have an inside diameter (ID) approximately equal to the nominal size. Although there is no such relation between the existing standard thickness — OD and nominal size — these nominal sizes and standard ODs continue in use as ‘‘standard.’’
The manufacture of pipe NPS 14 (DN 350) and larger proceeds on the basis of an OD corresponding to the nominal size. So the OD in mm of a pipe NPS 14 or higher can easily be calculated by simply multiplying the NPS (here 14) by 25.4. But for lower sizes the OD calculation is not so easy.
Pipe Schedule vs Pipe Size: As For all pipe sizes the outside diameter remains constant. Therefore any variation in schedule i.e. wall thickness, affects only the inside diameter. As the schedule number increases, the wall thickness increases, and the actual bore is reduced.
Standard (STD) is identical to SCH 40 up to NPS 10. All larger sizes of Standard have 9.53 mm wall thicknesses.
Extra-Strong (XS) is identical to SCH 80 up to NPS 8. All larger sizes of Extra-Strong have 12.70 mm wall thicknesses.
Double Extra Strong (XXS) wall is thicker than SCH 160 from NPS 1/8 to NPS 6, and SCH 160 is thicker than XXS wall for NPS 8 and larger.
Pipe of sizes and wall thicknesses other than those of Standard, Extra-Strong, and Double Extra-Strong, and Schedule Number were adopted from API Specification 5L.
Wall thickness Calculation: The calculation of wall thickness varies depending on usage of code. All codes (B 31.3, B 31.1, IBR, B 31.4, B 31.8, nuclear code etc.) provide equations for calculating the minimum wall thickness based on pressure which the pipe has to withstand. The major parameters involved for thickness calculation are Design pressure, Pipe OD and Allowable Stress at design temperature. After calculation of minimum wall thickness, corrosion and mechanical allowances need to be added with that. After that the actual pipe thickness is selected (immediate higher size thickness of the calculated value) from ASME code tables depending on pipe material (CS or SS)
Pipe Dimension Charts/Tables: The wall thickness associated with a particular schedule depends on the pipe size. Dimensions (OD, ID, Thickness, and Schedule Number) and Weights of CS and SS pipes are given in ASME standards mentioned above. The tables in the respective codes are dimensionally complete for all sizes and wall thicknesses within its scope, but some of the larger, heavier wall sections are beyond the capability of seamless mill production and must be obtained from forged and bored billets or other sources.
Stainless steel pipe is more often available in standard weight sizes (noted by the “S” designation, for example “NPS SCH 10S”). However stainless steel pipe can also be available in other schedules.
Abbreviations used: DN-Nominal Diameter, NPS- Nominal Pipe Size, NB – Nominal bore, STD – Standard, XS – Extra Strong, XXS – Double Extra Strong, ASME-American Society of Mechanical Engineers, CS-Carbon Steel, SS-Stainless Steel.
