Pipe schedule calculation

Dear CMS Engineer,

Please correct your statement that pipe is know by its Nominal Pipe Size diameter and not as "nominal inside diameter". 12" dia NPS diameter means 12-3/4" Outer Dia and 16" NPS means 16" outer dia. When thickness increases internal diameter reduces. Your rest of the statement is correct. Still your answer is not according to the needed reply of question that is "does any one know the formulae of converting Schedule thickness into inches or millimeter". The answere is - there is no formulae. You have the formulae to calculate thickness, diameter and pressure etc but there is no formulae to convert 2" dia Sch: 80 into 0.218" w.t. and 20" dia Sch: 80 into 1.031" wall thickness.

Dear AbdulWasay

The statement of our friend CSM Engineer "pipe is known by its nominal inside diameter" is a correct statement, and it means that its Nominal Pipe Size NPS. Most of piping handbooks said that. That is because the pipes with sizes lesser than 14" NPS have its internal diameter at standard thickness (Sch. 40) very closer to its NPS.

For example, a pipe with 10" NPS, Sch. 40 (Std.), its actual OD = 10.75 ", its wall thickness 0.365" where its inside diameter ID = 10.02" which is very closer to NPS 10", and that what we call nominal inside diameter. Now, the term nominal inside diameter is replaced with nominal pipe size, NPS to include all sizes of pipes.

There MUST be a logical formula, for this, anyone know what it is ?

You wish.

I agree with CSM. Most of these sizes were determined by mills before standards existed.

According to the historical articles I read many years ago, the wall thickness of wrought steel (and iron) pipe had much to do with the quality of materials that were available for making seamless and welded pipe. As the materials were continually refined over several decades the wall thickness was reduced until it became what we have today.

And the other comment is correct concerning the decision to not change the outside dimensions. But I am not aware of any linear formula(e) to determine the correct wall thickness for the pressure/shock application for all sizes.

Best Regards,

Ing. Robert Forbus

OK dear sir,

you mentioned 'P' as internal pressure...Kindly clarify .. what happens when external pressure acts on the system.... also one small updation on that formula you mentioned .. ie Thickness of the pipe is T_m = T + C

Where "T" is above mentioned formula... (that u mentioned already)

C= C₁ + C₂

C₁ = Corrosion Allowance

= 1.6mm for general Carbon steel

= 0 for stainless steel..

C₂ = Depth of thread

Regards

Skarthee

No one can decide exactly that there is a fixed figure for corrosion allowances for different piping materials when used to convey different fluids. The corrosion allowance depends on the pipe material, type of fluid and its concentration, and temperature, all of these define the corrosion rate (mm/year). Depending on the corrosion rate, we have to decide the Depreciable Life (year), upon which we can determine the corrosion allowance of the whole piping system along its depreciable life.

Corrosion Allowance (mm) = Corrosion Rate (mm/year) x Depreciable Life (year)

Note. We have to take the erosion (if occurred) in the calculation of corrosion allowance, i.e the expected erosion rate shall be added to corrosion rate in the equation.

Guest is right.

If you look at the pipe schedule tables you will see that each schedule of pipe is rated to a certain pressure. We in the nuclear industry use these pressure values for calculating which size (schedule) of pipe we need for a particular application.

Usually steam generator/boiler applications.

Guest, please register and let us know who you are.

UFG

Hi Fellow CR4ers,

Thanks for the answers so far, but the holy grail still eludes me.

If you had a theoretical pipe of Diameter 'D', what would be the wall thickness for Schedule 30?

I am lead to believe that there is no relationship that can answer the question exactly; what a wonderful industry we work in !

Regards

Ian

Hi Zaphod:

From the Delaval Engineering Handbook, Third Edition, McGraw-Hill, page 2-26

Schedule No. = 1000X(p/s) Where p= internal pressure (psig), and s= allowable fiber stress (psi).

Now, BE Careful! Use the ASME code B31.1 to be sure your wall thickness is adequate for your conditions.

Hank

Thanks Hankt!

This was just a curiosity question from a customer, and now I have an answer to satisfy their (and my!) curiosity.

I spend a lot of my time explaining to customers that were are a pipe and fitting supplier, not an engineering house, and questions such a 'How much pressure can we put in this pipe?' is beyond the scope of what we do.

For one thing, they don't pay me enough to do those calculations!

Cheers

Ian

My dears Zaphod2Headed and Hankt,

I don't think in any equation to calculate the schedule directly like this one: Schedule No. = 1000X(p/s).

Please refer to the following thread for finding the actual pipe thickness and schedule : High Pressure Steam Pipe

Thanks Abdel !

The reply given by CSM Engineer as it relates to steel and stainless steel pipe is very good. And it demonstrates the industry's lack of refinement of these old values and methodology. The plastics industry is trying to remedy the situation as it applies to their products. They have chosen to rate their pipes by the SDR method. If the pipe is, for instance, SDR21, that means S idewall D iameter R atio. Therefore, the SDR21 pipe has a sidewall thickness to diameter ratio of 21. However, they, too, still use the old Schedule designations. They have schedule 40 and 80 pipe, but are striving for some semblance of uniformity in their industry.

Glad to see that at least someone is trying to make sense of things!

In the steel pipe industry, so I am led to believe, the schedule system was introduced (in 1939!) to replace the 'old school' std, XH and XXH, but due to the inertia of the industry, the std, XH & XXH never were phased out. So now we have the situation of having two different systems for defining wall thickness!

P.S. I see in the forward to ASME B36.10 it says the intent of the original ASME Committee was to establish the schedule numbers fro pipe size/wall thickness combinations which would have an approximately uniform relationship equal to 1000 times the P/S expression contained in the modified Barlow formula for pipe wall thickness as defined in the appendix to this standard.

Only problem is, there IS no appendix to the standard! Doh!

Dear Zaphod,

You must not be embarrassed because you do not know the logical formula to calculate thickness of pipe. Firstly one should bear in mind that thickness mentioned by Schedule is only applicable in pipe or pipeline. This means one should not refer schedule thickness of M.S. plates converted to fractional or decimal measurement of thickness. When it is proved that schedule of thickness is only applicable in pipe or pipeline, then logic leads to conclude that it must be related to pipe, pipe strength or pipeline capability to hold pressure. Now! When it is proved that thickness is related to pipe capability to hold pressure, (there are many other factors to increase capability of holding pressure in pipeline) then it leads to ponder about the hoop-stress which is created by pressure in the pipe or pipeline. When you know that hoop stress is main factor and hoop stress is generated more in larger dia pipe than small, then you give more thickness to larger dia pipeline than the small. This is what the Schedule-Thickness-Chart depicts. For instance 2" dia, Sch::80 is equal to 0.218" will thickness of pipe and same Schedule (Sch:;80) for 20" dia pipe equals to 1.031" wall thickness.

To my knowledge Schedule System of mentioning pipe wall thickness is the adoption of ANSI since the time back, when pipe was being manufacture mostly seamless and seamed pipe was not being considered for high pressure pipeline or piping. Many reliable testing of material and process of manufacturing pipe and its treatment afterwards proved that seamed pipe could also be useful manufactured under tight quality control, which Japan is doing who claim pioneer of seamed pipe. Since then API adopted mentioning wall thickness in decimal and varied thickness of are being introduced and beeing manufacture in the World for designers convenience.

Dear AbdulWasay

That is exactly what I'd like to say. Thank you.

To find the pipe schedule, you have to proceed a full design, may be carrying out stress or finite element analysis to the case under consideration. And I don't agree with whom using the equation Schedule No. = 1000X(p/s) to find the pipe schedule.

To whom saying that the schedule of piping is governed by an equation Schedule No. = 1000 (P/S). The following paragraphs are extracted from "ASME B36.10M-1996" under title "FOREWORD":

Quote

In March 1927, the American Standards Association authorized the organization of a Sectional Committee on Standardization of Dimensions and Material of Wrought Steel and Wrought Iron Pipe and Tubing for the purpose of unifying the standards of these commodities in force in this country. The American Society for Testing and Materials and The American Society of Mechanical Engineers were designated as sponsors, and

the first meeting of the Sectional Committee was held in Pittsburgh, Pennsylvania, on May 18, 1928.

The dimensions of commercial pipe in general use in the United States at the time conformed rather generally to those recommended by the ASME Committee on Standard Pipe and Pipe Threads published in 1886 (ASME Transactions, Vol. VIII, p. 29). On these standards an enormous industry has been built and the satisfactory use of this product proves the soundness of the original design and specification.

Increasingly severe service demands at the time of the Committee's organization had been met by using the nearest available pipe or tubing for heavier sections such as casing, mechanical tubing, etc., with resulting uneconomical multiplicity of wall thicknesses.

Subsequently, the Committee, with the cooperation of the industry, made a survey of existing practice as the logical starting point for the development of an American Standard. From this survey, a table was designed to provide a selection of wall thicknesses of pipe to cover the power piping requirements of industry where strength to resist internal pressure governs selection and was later expanded to include pipe diameters and thicknesses used in other industries.

The original intent of the Committee was to establish a system of Schedule Numbers for pipe size/wall thickness combinations which would have an approximately uniform relationship equal to 1000 times the P/S expression contained in the modified Barlow formula for pipe wall thickness as defined in the Appendix to this standard. The resulting Numbers departed so far from existing wall thicknesses in common use that the original intent could not be accomplished. The Schedule Numbers were then adopted strictly as a convenient designation system for use in ordering.

In all cases, the designer must base his selection on the rules and allowable stresses set by the code which governs his particular construction.

Further revisions were made by the Sectional Committee. The list of specifications in Table 1 was revised where necessary and slight revisions in wall thicknesses of some of the large sizes of the heavy schedules were made where P/S values were out of line.

Unquote

This post #19 send by me, Thanks

Abdel Halim

I gave this post a good answer since you weren't logged in on #19.

Nice work in finding the info.

Thank you ddk,

Only I like to explore the facts.

dear sir,

our thread #6 as mentioned 'P' as internal pressure...but he is not sure about .. what happens when external pressure acts on the system.... also one small updation on that formula you mentioned .. ie Thickness of the pipe is T_m = T + C

Where "T" is above mentioned formula...

C= C₁ + C₂

C1 = Corrosion Allowance

= 1.6mm for general Carbon steel

= o for stainless steel..

C2 = Depth of thread

Regards

Skarthee

Hi everybody. I'm from germany and my english is not that good, but i try my best.

The answers to this questions are quite interessting, but i'm looking also for a "simple" formula to calculate the wall thickness of a pipe from a schedule.

There must be a relation between the wall thickness and the schedule independent from the stress. Because there are many tables for this.

You know...is there any formula like t= 5*(diameter)/2*(Schedule)

(this relation is just an example with nonsense values ;))

Read post 19 by Abdel Halim Galala

There is no formula. Just inertia.

I hope this helps you.

Regards,

Ghule

Hi

yes there a simple way to do it.

Most people are using " application software" for that.

You also look in B3`1.3 for the right method.

Pat

In sizes from 1/8-inch thru 12-inch, pipe is known by its nominal inside diameter, which differs somewhat from the actual inside diameter. Early pipe manufacturers made the walls in the smaller sizes much too thick, and in correcting this error in design they took the excess from the inside to avoid changing the sizes of the companion fittings. To distinguish pipe sizes from actual measured diameters the terms iron pipe size (IPS) or nominal pipe size (NPS) are usually used. For sizes larger than 12-inch, pipe is known by its actual outside diameter. In all pipe sizes the outside diameter (OD) remains relatively constant; variations in wall thickness affect only the inside diameter (I.D.).

To distinguish different weights of pipe, three long standing traditional designations are used: standard wall (Std., extra strong wall (XS) and double extra strong wall (XXS). These last two designations are sometines referred to as extra heavy wall (XH) and double extra heavy wall (XXH), respectively.

For the purpose of standardizing pipe dimensions, the American Standards Association (ASA), sponsored by the American Society for Testing Materials (ASTM) and the American Society of Mechanical Engineers (ASME), published ASA. B36.10. To broaden the range of wall thicknesses, schedule numbers from schedule 10 (S.10) thru schedule 160 (S.160) were adopted for steel pipe. These schedule numbers indicate approximate values for 1000 times the pressure-stress ratios. Later, stainless steel schedule numbers from schedule 5S through schedule 80S were published in ASA B36.19 for sizes thru 12-inch. The addition of the letter S after the schedule number identifies it as pertaining to stainless steel.

Certain relationships exist among the traditional designations of Std, XS, XXS, the ASA schedule numbers and the actual wall thicknesses. Std and S.40 are the same in sizes thru 10-inch; in sizes above 10-inch, Std has a wall of 3/8-inch. XS and S.80 are the same in sizes thru 8-inch; in sizes 10-inch and above, XS has a wall of 1/2-inch. XXS has no corresponding schedule number, but in sizes thru 6-inch, XXS has a wall twice as thick as XS. Stainless steel schedules 40S and 80S are identical with carbon steel designations Std and XS, respectively, thru 12-inch.

Weighs for carbon steel pipe are based on a density of 0.2833 pounds per cubic inch; for wrought iron pipe the density is 0.2777 pounds per cubic inch. Since wrought iron pipe is made to steel outside diameters and steel weights per foot, the wall thicknesses of wrought iron pipe are necessarily slightly greater than steel pipe to compensate for this difference in densities. Wrought iron pipe is referred to as Std, XS, and XXS and not by schedule numbers.

Unless otherwise designated, references to pipe wall and thickness always mean the nominal, or average, wall thickness. Most ASTM tolerances on regular pipe products specify that the wall thickness of pipe at any point is to be no more that 12-1/2% under the nominal wall thickness specified. This means that a minimum wall of 0.875 times the niminal wall could apply for regular mill rolled pipe.

Dear Friend,

Here is your answer

1. Weight Steel Pipe in kg/m = (Od - Wt) x Wt x 0.02466

1. Weight Steel Pipe in lb/f = (Od - Wt) x Wt x 10.68

OD – Outside Diameter

Wt – Wall Thickness

All the best!!..

Rahul Patel.

Check this link:

http://www.elinox.com.br/index.php?option=com_content&task=view&id=34&Itemid=86&lang=us

Rahul patel...you have given a very good formula for calculating schedule of pipe with weight. It means that we are again beating around the bush. cause we need to see the table to calculate the weight of pipe. Or probably intelligent people like you will calculate the weight of the pipe by multiplying density of metal with volume.