# What does Pipe Schedule Mean? Pipe Size Chart and Pipe Schedule 40 thickness

The pipe Schedule describes the pipe wall thickness. With an increase in pipe schedule number pipe thickness increases. 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 pressurized fluids the wall thickness, and by implication the pipe’s strength, is the most important parameter. Wall thickness of Pipe is expressed by “schedules or Schedule numbers“, referred to as pipe schedules or Piping Schedules.

## What is a Pipe Schedule?

Pipe Schedule or Pipe Schedule number of a Pipe is a dimensionless number that is related to Pipe Wall Thickness. Piping Schedule Number for a specific pipe size is a pipe thickness designator for that pipe size.

## How to Calculate a Pipe Schedule?

Schedule Numbers for pipe size/wall thickness combinations are calculated (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. So,

## Characteristics of Pipe Schedule

For a given pipe size and schedule the thickness of the pipe is fixed and defined in the applicable ASME standard (B 36.10M/B 36.19M). 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 items.

For any given pipe size and varying schedule numbers or thicknesses, its Outside Diameter (OD) remains constant and Internal Diameter (ID) varies. With an 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 the same pipe size (varying thicknesses).

Pipe Schedule numbers can be same for different pipe sizes but that does not mean the pipe thickness is same. It may be same or vary with respect to pipe sizes. For example, 6 inch schedule 40 pipe have 7.11 mm thickness, while 8 inch Schedule 40 pipe have 8.18 mm thickness means thickness is increasing even though both the schedule 40. Again, 15 inch Schedule standard and 16 inch schedule standard both have same 9.53 mm pipe thickness.

## Pipe Schedule 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

## What is 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

For all pipe sizes, the outside diameter remains constant. Therefore any variation in pipe schedule i.e. wall thickness affects only the inside diameter. As the pipe 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 (STD Schedule) 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.
• The double Extra Strong (XXS) wall is thicker than SCH 160 from NPS 1/8 to NPS 6, and SCH 160 is thicker than the XXS wall for NPS 8 and larger.
• With an increase in pipe thickness internal diameter of the pipe reduces as the pipe outer diameter remains constant.

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.

## Pipe Schedule / Pipe wall Thickness Calculation

The calculation of wall thickness varies depending on the 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).

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## Pipe Schedule Chart: Pipe Size Chart

A pipe size chart or pipe schedule chart is a tabular representation of pipe NPS and their thicknesses with respect to various schedule numbers. 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:

• STD – Standard,
• XS – Extra Strong,
• XXS – Double Extra Strong,

Pipe Schedule chart or pipe size chart is provided in the following table with respect to nominal pipe size and pipe thicknesses.

## Pipe Schedule 40 Pipe Dimensions

The following table will provide an example for Schedule 40 Steel Pipe Dimensions.

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

## 11 thoughts on “What does Pipe Schedule Mean? Pipe Size Chart and Pipe Schedule 40 thickness”

1. Engineer's Chaupal says:

Yes For any given pipe size and varying schedule numbers or thicknesses its Outside Diameter (OD) remains constant and Internal Diameter (ID) varies. i am satisfied with this article. Thank You For This Valuable Article

2. Robert C. says:

If all of a given diameter pipe holds the same outside radius, why does the outside radius not used as the pipe size? 3″ pipe is always 3 1/2″ diameter, but the internal clearance is only close to 3″ as sch. 40. Why not call it 3 1/2″ pipe?

3. Michael Kominski says:

I have a question:
You are given two pieces of pipe. The pipes have the following characteristics.
Pipe One is 3.5 inches in outer diameter.
Pipe Two is 4.0 inches in outer diameter.
Both pipes are marked as schedule 80.

What is the same about these two peices of pipe.

Thank you!

4. Safal Agarwal says:

NPS (Nominal Pipe Size) and DN (Nominal Dia) are easy to remember that is why these were introduced. If you see the outside diameter up to NPS 12, it is very difficult to remember. As the outside diameter is in decimal, it is not a whole number.

That is why Pipes are defined as per NPS, not the outside diameter.

And NPS 14 and above Pipe OD is the same as NPS.

5. Safal Agarwal says:

Nothing is common between a 3.5″ and 4″ OD, schedule 80 Pipe.

For 3.5″ OD, Schedule 80 Pipe, Pipe Wall Thickness is 0.3″. So the ID of the Pipe is 3.5-0.6=2.9″.

For 4″ OD, Schedule 80 Pipe, Pipe Wall Thickness is 0.318″. So the ID of the Pipe is 4.0-0.636=3.364″.

I hope the above explanation clarifies your query.

6. kandaswamy says:

I have a question:

Pipeline material X60 using thickness 7.11 mm. equivalent to sch.40. my lead says don’t put sch.40 tell as 7.11mm Thickness. so what is the difference?

thickness or sch. which one to follow. if any standards to be advise

7. MARIO CUBILLOS says:

Thank you for information.
I traslated to use with my partners.

Regards

Mario

8. a.aLAM says:

one pices of pipe
od is 1.33″
id 1.06″
what is shedule

1. Umarfarukh Sabkhan says:

You can calculate by the formula…
OD-2(Thickness)=ID
0.135

9. P.Sathishkumar says:

Has pipe schedule Sch.HVY matches with any other standard pipe schedules either XS or XXS?

10. AASIF says:

Dear colleagues,
Can anyone tell me why pipe schedule std and Pipe schedule 40 have same thickness upto 10″