Which Pipe Schedule to Use

Not available? I would go with schd 40...

http://en.wikipedia.org/wiki/Nominal_Pipe_Size

Can you explain a bit why would you go for Sch 40 pipe..?

With a wall thickness of .280 it is the next available option....without going to more expensive custom order...

.203 = 5mm.

Sch Std: 7.11, then use Standard

Use the schedule that has a wall thickness ≥ the calculated requirement.

There is another possible answer to the "three dots"

http://www.pipingdesigners.com/downloads/pipechart.htm#choice

This version of the pipe wall thickness chart has blank boxes instead of the three dots. However it does have the same wide range of wall thicknesses listed. So this suggests that it IS available.

I think the three dots (or the blank) actually means that there are special wall thicknesses available but do not "fit" into the generally accepted classifications of schedule numbers (40, 60, 80, 129, etc) or the "Std, XH or XXh" designations. These other three dot wall thicknesses may be available from some pipe suppliers but may also be much more expensive.

If .203 wall is available but is more expensive you may want to move up to the more common but less expensive sch 40.

Only your local pipe supplier can answer this question.

• Use the next greater commercial pipe wall thickness found from Table 2 of ASME B36.10M "Dimensions and Weights Of Welded And Seamless Wrought Steel Pipe" to be 0.280 inch which corresponds to 6" NPS, Sch. 40 (or STD).

• For more details, see the solved example at my post #1 of CR4 Thread: Schedule of pipe.

In the "Down and dirty" world of practical Chem Engineering and Pipefitting the common practice is: If the specified pipe schedule is not available, too costly, too long a delivery, too expensive, etc., go with the next thicker wall schedule. This is a conservative approach to the problem by going in the pessimistic direction with its better properties and not taking the chances involved with a thinner wall thickness. This approach has worked for hundreds of years and reduces the risk of an unplanned and perhaps harmful event.

As an aside, many times a thicker wall schedule such as 80 vs. 40 is used to extend the time between anticipated repair or failure events simply because there is more wall to be erroded before failure. This is especially true in steam and steam condensate service, a particularly harsh application. The cost of the next set of replacement parts of the thinner materials, the labor cost and especially the cost of process equipment down-time is much greater than the cost of using the more expensive thcker wall (higher schedule) materials initially.

Good Luck, Old Salt

Good answer "Old salt"....

Most piping systems in use are schedule 40 ( or Standard wall)

Student, what are you going to do about flange and valve ratings ???? ?

What is your design temperature and pressure for the system and why do you not have piping specifications ?

Don't you need to add corrosion alowance to your calculated thickness before looking for the standard schedule no.?

After adding corrosion alowance, take the schedule number of the nearest next thickness from the sch. table.

(...) these dots means those thicknesses are also coverd under the standard but are not available commercially. To reduce the commercial inventary, standard schedule number pipes are manufactured and used in industry with sufficient margine of safety.