Steam Piping Schedule Number

The s value of 13,100 suggests that a safety factor has already been accounted for.

Since you have gone to 8" pipe, you may need to (re)calculate wall thickness based on the actual diameter of the 8" pipe.

Schedule 30 is a less common thickness. Schedule 40 may be more available, and maybe even less expensive.

hi. thank you for reply.
The s value of 13,100 is for 900F .. Is this enough for operating temperature of 869.2 F? This is why i am looking for safety factor.. I dont know what temperature i should use to look for allowable stress..

Get a copy of Perry's handbook, and there is a section of assorted pipe schedules on various services = in your case superheated steam.

Solving for the pressure it where it will break when freshly made. The schedules will incorporate a safety factor and a corrosive wear factor that is supposed to deal with using that piece of pipe in that use for, say, 20 years. The pipe is made to resist pinholes as well as bulk failures. You will need to look up your pipe material and determine it's length of life in the service you are going to use it.

the schedules are meant to make sure that whatever you build will last at least that long. Any installation will have a number of test sections, where you can shut down a pair of valves, remove a few feet and replace it will new pipe, and allow you to saw the test section into pieces to look for corrosion. Some modern test procedures allow for sonic or x-ray examination of these test areas while in service.

Modern refineries have an ongoing battle against failure and have a number of ways to test in service.

hi ibrahim!! Good luck.

Your safety factor will be 2.5 times, on your design pressure (665psia). but its also vary for different guideline.

8" Pipe with 40 schedule is not recommended, at least 80 or better if you can use 100 schedule.

thanks for reply :)
actually, I can use any schedule number. But the problem is I have to defend it. I need basis or reference why i should use sch 80 or higher. And may I ask why FOS is 2.5?

Longevity is a very important factor in piping systems, especially those under great stress at high temperatures in a corrosive environment.

We extend the life as well as the safety by the use of 'Schedules', which are charts of expected longevity of various types of piping at various services.

It is often cheaper to make the entire system thicker and stronger than required by various safety factors because a failure might kill people or ruin the system.

It is often very expensive to shut down a system to repair a break that could have been prevented by increasing all pipe from Sch-80 to Sch-100, so to ensure safe longevity they overbuild the system.

That is your defense. Their attack would be we have installed a chemical additive regime that will block pinholes and corrosion for 50 years. Your attack would be to ask what if the man responsible for adding the additive every day, and signing the book, decided that the signing process was all he would do, it was too hot/cold to spend an hour a day adding chemicals. Their defense would be we have samples daily that will show accumulated corrosion ions. Your attack would be that this must be a different person - just in case that man decided to fill his sample bottles from the tap because it was too hot/cold to take that daily sample. Their defense would be that the sampler was a P.Eng. who was a serious professional etc etc.

In short, you need to design a system that will endure, with checks and balances for the expected plant life, against all perils of man and nature.

i found this new formula
SN = 1000*S/P
but im not sure if it is safe to use to know the schedule number.

That can't possibly be a correct formula. Some variables have been transposed, or something.