comparison of cs schedule 80 pipe with stainless steel pipe 2

[pradeep4u]

Dear all,
If i want to replace cs pipe schedule 80 pipe with stainless steel pipe say ss304 with fluid may be water or air or other non corrosive fluid. what schedule of ss pipe will be appropriate. What is basic difference betwen two apart from corrosion resistance property.
Thanks
A.Pradeep

 

[MJCronin]

There is no simple and responsible answer to your question ... You have given us almost zero information.

We do not know if your piping is 1 INCH diameter or 100 inch diameter.. .... Operating temperatures of 80 or 800 F ????

Your fluids seem to be "water or air or other stuff".... perhaps, but you do not seem to care

You are asking a question about piping system design and you seem to not understand the substantive issues involved...

But, since you seem to be insisting on a quick answer, I would like to offer that you are probably safe substituting seamless Schedule 160S stainless steel piping for Schedule 80 Carbon Steel piping in most applications... My opinion only

Strongly suggest that you reevaluate the pipe support scheme for the massive increase in weight ..

Cost is not a factor in your country, right ???



MJCronin
Sr. Process Engineer

 

[EdStainless]

What Code, What temp? What pressure?
What is the water quality? You may need something a lot better than 304 or 316 for it.
Sch80 for service lines in ridiculously heavy.
It might be that you need the pressure rating, and you will need to use sch80 or 160 in SS.
Or there may have been a generous corrosion allowance and you can use sch40 or even sch10 in SS.


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P.E. Metallurgy, consulting work welcomed

 

[pradeep4u]

Dear sir
Suppose pipe is 3" diameter carrying water at 50 degree celcius,pressure 20 kg/cm2. i just want to know that if in above condition cs pipe sch 80 is replaced with ss pipe then what schedule of pipe will be enough. Is it schedule 10,20, or 40. If schedule of SS pipe for same conditions decrease then why or if schedule remains same or increase then why? I am asking because i was asked same question in interview.
Regards
A.Pradeep

 

[EdStainless]

A reasonable answer would have been to ask them the list of things that MJC and I asked you.
That is a fairly low pressure, so my first question is why on earth is it in sch80 to begin with.

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P.E. Metallurgy, consulting work welcomed

 

[GD2]

Pradip,

If you know and understand the Hoops stress, you can easily know the answer.
Assuming Pressure and Diameter same, the thickness of pipe will be inversely proportional to the pipe material allowable stress, which is usually say 2/3 of yield strength.
In general, yield strength of carbon steel is higher than 300 series austenitic SS.

From this concept, you can easily tell which pipe will require greater thickness or schedule.

GDD
Canada

 

[pradeep4u]

Dear EDstainless
If mentioned cs pipe is schedule 40, then what will be your reply. The real intent of this question is for same pressure and temperature conditions of fluid inside pipe,Whether SS pipe is of same schedule to be used or lesser schedule.if so then why?
Regards
Pradeep

 

[TugboatEng]

Is this a marine or shipboard application?

 

[LittleInch]

It wasn't a great question to ask in an interview unless they wanted to see how you would approach the question.

The answer would be "it depends on the details". If the CS pipe was at the limit of stress due to pressure then the SS schedule would go up as most SS pipe available has a lower S value in B31.3 than say A105. Until you know how the CS pipe was calculated you won't know.

SS schedules are the same up to 10", but start to vary at 12" and above.

But if there was corrosion allowance on the CS then that would not apply for SS.

Also in smaller sizes you can buy sch5S and 10S which you can't get in CS.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MJCronin]

Let us continue this protracted torture !!!

We all understand where he is going and what he is trying to get.....

Because his MBA boss insisted, he is fishing for a statement or rule that says:

-- "It is acceptable to substitute Sched 10S SS piping for Sched 40/80 CS pipe with certain restrictions" ---

Either his technical inexperience or his cultural limitations on language prevent him from formulating this direct question

Instead, let us continue to slowly ask question after question after question to this dull normal poster ....until

Well, until he slowly realizes that competent piping system design and engineering is complex.

and in the final analysis ..... you can't always get what you want !



MJCronin
Sr. Process Engineer

 

[pradeep4u]

Dear MJ Cronin air
I agreed that iam incompetent,dull and inexperienced person and these questions may be dull and unworthy for you but not for incompetent and novice like me. Asking questions should be encouraged not discouraged otherwise I cannot get knowledge from you people.
Regards
Pradeep

 

[LittleInch]

Don't worry about MJC too much.

But we do expect you to do some work and investigation before asking the questions.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[FacEngrPE]

I once had a supervisor ask me to write down all of the codes and other information needed to design piping systems. Since my AOR at the time ran from concrete drainage piping to HP steam, the list quickly became large enough that he told me he did not want to know that much. We all get MBA ish questions, sometimes from engineers that should know better.

 

[weldstan]

Whether sch 10S SS pipe can be used to replace sch 40 or 80 CS pipe can be easily calculated under the Code to which the piping is designed based on pressure and temperature alone. Whether the thinner pipe requires greater supports and whether the costs of the SS pipe warrant replacement is another matter.

 

[davefitz]

Not enough information.

For some types of SS, there is a concern regarding chloride stress corosion and also MIC microbiological induced corrosion. If the pipe is "sensitized" and operates above 140 F and a stress exceeds 11.ksi then SCC stress corrosion cracking may be a concern. If the water velocity is below 7 fps and iron is available in solution then MIC can occur. SS pipe can accept a much higher allowable water velocity if there is adequate pump driving head available , as carbon steel pipe will erode/corrode for water velocities above 12 fps, espescially at bends , entrances and vena contractas. CS is much less costly than SS. CS is usually extruded while thinner wall SS may be rolled and welded with a much thinner thickness for the stainless schedule .There also exists a large difference in thermal expansion coefficient and in yield stress between CS and SS, so transitions can be troublesome.


"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[david339933]

Wow, tough crowd.
All things being equal, same schedule will suffice. The stress values are roughly the same...especially when only comparing "Carbon Steel" to "Stainless Steel"....with no actual specification or type. Small bore piping (1.5 NPS or less)if threaded requires Sch 80 pipe for Carbon Steel, while stainless requires only Sch 40S.