Schedule 80 Piping - rated for vacuum service? 4

[si729123]

Is schedule 80 piping rated for vacuum service? I have a drawing with the following pipe number 10"-PL-083005-80-C. This pipe is rated for atleast 70 bar of internal pressure. However, I am encountering a situation where this pipe could see vacuum as well. Is it rated to vacuum such that it will not collapse?

Sada Iyer

 

[LSThill]

si729123 (Chemical)


304.1.3 Straight Pipe Under External Pressure.
To determine wall thickness and stiffening requirements for straight pipe under external pressure, the procedure outlined in the BPV Code, Section VIII, Division 1, UG-28 through UG-30 shall be followed, using as the design length L the running center line length between any two sections stiffened in accordance with UG-29. As an exception, for pipe with Do/t < 10, the value of S to be used in determining Paz shall be the lesser of the following values for pipe material at design temperature:
(a) 1.5 times the stress value from Table A-1 of this Code; or (b) 0.9 times the yield strength tabulated in Section II, Part D, Table Y-1 for materials listed therein. (The symbol Do in Section VI11 is equivalent to D in this Code.)

Leonard@thill.bis

http://www.thill.biz

 

[si729123]

I am talking of pipe under internal pressure. The fluid inside will be at a pressure of 70 bar while the external pressure is 1 bar (atmospheric). The vacuum will be experienced inside the pipe and I want to know if the external pressure 1 bar will crush the pipe.

 

[TD2K]

si, Isthill is giving you the reference to use to check whether the piping under vacuum has sufficient strength.

 

[si729123]

TD2K: No lsthill has not yet given me the reference to check it. However, I am hoping that sombody here will have the judgement to say that if this pipe is rated to handle a differntial of 69 bar (i.e. 70 bar internal minus 1 bar external) then it would be rated to handle a differential of -1 bar (i.e. 0 bar internal minus 1 bar external). Can anybody provide that judgement ?

Thanks

 

[MJCronin]

si729123 (Chemical),

For Schedule 80 carbon steel piping, operating at ambient temperatures,full vacuum protection (ie. internal pressure 0 psia, external pressure 14.7 psia) exists to at least 36&quot; diameter.

There are a couple of SS piping fabricators that supplied charts for FV protection for Schedule 5S and 10S piping. They also included Schedule 40 and 80 in the charts......but I cant put my hand on one now

As for lsthill,.....I have never understood his posts. It seems that he copies things and &quot;pastes&quot; them into his responses to specific questions.....just his style, I guess.

My opinion only

MJC

 

[si729123]

MJC: Thanks for your reply. My pipe is rated to handle fluids upto 170 F (77 C). Any opinions on whether the temperature will make that much of a change?

 

[jte]

si729123 and MJC-

I'll agree that lsthill's posts could use a LOT less copying and pasting (and less advertising). Nonetheless, the reference is correct. Si729123, if you'll look up the reference, you'll find some answers. I realize you are &quot;talking of pipe under internal pressure,&quot; but you are asking your question with regards to that pipe handling full vacuum (aka &quot;external pressure&quot;, aka &quot;negative internal gage pressure&quot: &quot;-1 bar (i.e. 0 bar internal minus 1 bar external).&quot;

If you *had* looked up the B31.3 reference, you would have discovered that you should be designing (with some piping specific stuff) in accordance with Section VIII. If you *had* looked up the referenced parts of Section VIII, you would have discovered that the vacuum charts are in Section IID. If you *had* looked at the charts in Section IID, you would have discovered that for carbon steel materials (thanks for the pipe's line number, but without your project's line class listing, we still don't know what material your pipe is made of or what schedule it is) the allowable compressive stress (&quot;B&quot; factor) doesn't start to diminish until you reach 300°F. So don't worry about going from ambient to 170°F.

jt

 

[StressGuy]

si729123,

What you were asking for was for someone to provide you with free engineering service. While I don't think it's been formally settled, I think there's a large percentage of the users of this site that agree that this is not a place to seek free engineering. The issues of liability for giving engineering recommendations make it a dubious prospect at best.

What we do generally seek and trade back and forth, are answers to questions to allow us to do the engineering work ourselves, with the expectation that most of us are functioning as engineers.

While Isthill could have fleshed his response out some, I think from a content standpoint it was exactly the correct response - a reference to look to in order to determine the answer for yourself.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.

 

[packdad]

Although I'm sure this is not a nuclear-related issue, Section III, Subsection NC-3133.8 and Figure NC-3133.8-1 is another possible design reference source.

 

[dfowler]

Just think about it for a second. If the pipe can handle a delta of 69x atmospheric pressure in the positive direction (with some sort of safety factor I'd imagine) why wouldn't it handle a delta of only a single atmospheric pressure in the negative direction?

David Fowler

 

[jte]

dfowler-

I understand your point. But a person qualified to make the determination wouldn't be asking the question on this forum. What is commonly not understood by folks not in the mechanical engineering field is that there are two different failure modes involved - tensile burst vs. buckling.

Someone who doesn't understand the significance might design a pipe in a structural application to handle a 150 kip load and decide to use 4&quot; XS pipe. No safety factor, but the design would work. Oops, I forgot to mention that it is not a tension member but a 95' long column (k=1). Now it fails by a factor of roughly 69.

jt

 

[LSThill]

si729123 (Chemical) and Team Members

The Piping Classification for the above 10&quot;-PL-083005-80-C question shall include all calculation) before the Piping Classification is issued and approved.

As poing out by the Team Member I do not thank si729123 (Chemical) has a legel Piping Classification Specification for this PIPING CLASS.

Leonard Thill.

 

[bvi]

While schedule 80 NPS 10 pipe is undoubtably good for full vacuum, and a temperature of 150F will not have a significant effect, I would think it highly ill advised to take anonymous advice offered over the internet for engineering decisions with safety implications. Take the advice on how to check it, and check it. It isn't difficult.

 

[si729123]

Hello All:

Thanks for all your responses. Just for clarification, I fully agree with Edward Klein and cb4 that this forum is not meant for free advise or that matters of safety in design should not be taken over the internet.

Two reasons why I posted this

a) To get the appropriate references (thank lsthill)
b) To have a &quot;feel good&quot; factor before I went and verified with the real books.

Our design has been completed and this vacuum situation was not predicted during the design phase. Hence we are having to re-verify.

I want to now request that this thread be closed since I have gotten all the references/advise that I have wanted. This is my first time using this site and it has undoubtedly been a postive experience.

Thank you all once again.

SI729123