standard conditions 4

[kagadpencil]

For SCFM purposes is temperature 70 F or 60 F?
I know crane 410 uses 60 F - I wonder why when most other places (HVAC books etc.) I see 70 F.

what is the most common? -- Or is this rookie missing something ?

 

[iainuts]

I've asked this too. Conclusion: different standards use different temperatures. It's always wisest to state your conditions when the distinction is needed. (Our company sells industrial gasses and always uses 70F)

 

[Montemayor]

kagadpencil:

I think you missed it all and must have slept through the thermodynamics class session or chapter that explains that standard conditions are what some people prefer because it suits their needs, preferences, likes, bias, or simply looks good.

There are many threads on these fora on the subject of so-called "standard" conditions. Most of the opinions still rely on there being a supposed International Court of Standard Conditions or resting on the authority of such organizations as SI (in Europe) or ASME, AICHe, & ASHRAE in the USA. No organization in the world can logically claim to impose their "standard" without the necessary "standard police force" - or army - to enforce it. So embracing or following any standard (whether "Normal" or abnormal; I still wonder how anyone can call 0 oC "normal") is all up to you. Intelligent and knowledgeable engineers know this and know as well that any recitation of a so-called standard is useless without stating the necessary and requisite basis for such a standard - i.e., the temperature and pressure basis. The problem starts and persists simply because lazy and incompetant engineers insist on using their version of "standard" and refusing to state their basis.

This is not nuclear science; rather it is common sensical engineering. Everyone is free to use his own standard - as long as he accepts that accurate communications with such a standard is next to nil if he/she doesn't state the necessary basis for the standard conditions.

This is such an elementary subject in freshman engineering level courses, that it would be embarassing to write an FAQ over this subject. Otherwise, someone would do it. It would be analogous to writing an FAQ over the proper use of a bathroom.

Art Montemayor
Spring, TX

 

[zdas04]

Art,
Did this question hit a hot button? As usual, I agree with everything you said.

"Standard" is about as awful a term as has ever been imposed on the physical world. Mostly I need it for natural gas sales, and every one of the hundreds of gas sales contracts I've reviewed over the years has specified the "Standard" conditions (which change considerably from contract to contract). The temperature tends to be 60F, but 70F is there sometimes (not often). Pressure is much more variable. Contracts have specified values between 14.5 psia and 15.025 psia. Funny thing is that the contract that specified 15.025 was for gas sales at 6,000 ft elevation (zero psig = 11.8 psia).

If it ain't in the contract or the law, it better be stamped on the bottle.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Montemayor]

David:

Thank you for following up and contributing what I consider as a perfect example of what I have tried to expound (perhaps unsuccessfully): When one deals with the flow, storage or, more importantly, the custody transfer of gases one cannot assume that there are fixed, legally enforceable laws defining the "standard" conditions of gases for volumetric measuring purposes. You have brought out perfect, practical examples of what takes place everyday in the custody transfer of natural gas - and it is an extremely important point to understand thoroughly (as you are probably well aware) because it can involve literally hundreds of thousands of dollars' difference in invoicing per one standard or another. It makes a big, big difference! And as professional engineers it behooves us to dominate the subject thoroughly.

I studied the subject of standard conditions for gases in high school chemistry and followed it up with additional review of the subject in Freshman Chemistry in College - which, I believe, is mandatory for all engineers. Therefore, I am working on the premise that we engineers all are well familiar (or should be) with the subject of gaseous volumetric measurements. If we are not, I've missed the boat in familiarization with basic engineering training. What I have found is that young graduates are seldom, if ever, aware of the fact that - as you reveal - so-called standard conditons can take any basis that you so desire, like, or lust after. I have worked in all the continents on this planet as an engineer and it would take a lot of paper to list the various standard gaseous conditons I have employed or used in my work. Young grads seem to believe that there is only one - the one they studied in college. Nothing is further from the truth, and it shouldn't present problems to anyone -- as long as the basis for the conditons are stated clearly. This is why I am very critical of engineers who refuse to give their basis when they discuss Scfm, Ncfm, Acfm, etc. They are not communicating accurately and clearly as engineers are expected to.

I didn't respond due to a "hot" button being pushed, and I hope anyone reading this doesn't try to read between the lines. As an engineer, I always try to be as candid and frank as I possibly can because I believe it can only profit the transfer of information to the reader. As you know, we are a breed that doesn't survive on ego or self-importance. A job well done and documented is (or should be) a measure of our profession.

With so many variations available on the definition of gaseous "standard" conditions in the world, I believe it logically stands to reason that the basis for the conditons should always be stated or identified - without exception. Otherwise, we leave ourselves open for mis-information, errors, and mistakes - something that should not be a characteristic of a professional engineer.

Thanks for helping me explain what I failed to do in the first post.



Art Montemayor
Spring, TX

 

[25362]

I may be adding insult to injury to an overly discussed subject in past threads, but I've read that the Compressed Gas Institute uses 20^oC (68^oF) as a standard.

 

[katmar]

I knew there was nothing standard about a SCF, but I always believed that Normal conditions were very well defined. I have even posted here in the past that you can always rely on Nm3 as being referenced to 0 deg C and 1 atm.

However, when I saw Art's comment that there is no organizational body that can fix (and police) a definition it got me thinking about IUPAC (International Union of Pure and Applied Chemistry). Most countries subscribe to their rules, and I thought I would check on their site to make sure that we have got it right.

Imagine my horror when I discovered that I have been laboring under a wrong understanding all these years. Standard conditions are defined (by IUPAC) as 273.15 Kelvin (or 0C/32F for us engineers) and (Oh no!!) 100 000 Pascal (or 1 bar).

On the relevant IUPAC page (

http://www.iupac.org/goldbook/S05910.pdf)

they say that the old pressure standard of 1 atmosphere (101325 Pa or 14.696 PSI) should not be used anymore, and it seems to have been this way since 1990.

I enjoyed Art's comment that there was nothing normal about 0 deg C - well, there is also nothing normal about 100 000 Pascals. It seems that it is time for me to update my gas volume calculator in Uconeer, and to start adding reference conditions every time I use a gas volume (as Art has advocated all along).

Maybe as atonement for my sins I should write the FAQ ;-)

 

[kagadpencil]

Art :

Thanks for your comments. They certainly help this rookie understand the "real" engineering world! ..

 

[25362]

If so, the famous long-lived 22.41 L/mol, is now being replaced by 22.71 L/mol, following IUPAC's "new" STP conditions.

 

[katmar]

Hi 25362,

Yes, that is exactly right. I'm afraid it is going to take me a while to internalize that one! And I don't think I will be alone.

 

[TD2K]

"the famous long-lived 22.41 L/mol, is now being replaced by 22.71 L/mol"

ACK!!!!

Art, as usual, brings up an excellent point. Several times I've been involved in this very issue and made myself unpopular by asking 'what do you mean by standard temperature and pressure'. First, usually, the attempt is made to brush off the question 'you know, standard conditions' and then when we have to actually write down the temperature and pressure everything will be based on the head scratching begins.

 

[rmw]

TD2K,

Ditto.

And, Kagadpencil, I do not consider myself to be a rookie.

rmw

 

[saxon]

Art, Is it a pascal or a psi, a deg. F or a degree Kelvin, or is it a pascal/F or a psi/K? Good question, what is it, and what are we talking about?

As for having to put together SOP's for bathrooms, I've already had to do that. As the old saying goes, "If common sense were a common commodity, the world would be a utopia"
Especially in industry these days.

saxon

 

[Montemayor]

kagadpencil:

I sincerely hope that I succeeded, albeit in a small manner, in describing what is an annoying situation in engineering design and operation: the lack of proper basis identification when stating any gaseous state. I apologize if it took me two posts in making the attempt, but I rest on the capabilities of the rest of the experienced Forum members that came to the front to better explain what I have tried to describe as an existing situation. Please consider that my posts were not meant to highlight your rookie experience level or, worse, to emphasize my background or knowledge. Rather, bear in mind that I, as well as all the experienced Forum members (Katmar, zdas04, 25362, TD2K, rmw, & saxon) have had to go through and work with a cumbersome gaseous measurement and have made our errors, discoveries, and understandings due to our raising the question of what really constitutes "standard" conditions in industry. We all learned by doing just what you have done: raise the question and inquire as to why and how to cope with the various systems. The subject, as I stated, is simple and elementary; however, the employment is awkward and trying at times. However, as engineers we are all trained and tested to be above this challenge; and as you've seen in the various postings, although we don't agree with the system (or among ourselves), we certainly know how to deal with it - whatever the standard or rules. That is the point that I have tried to make clear: we are intelligent and well-trained and can work with anything - as long as we are given the basis.

After working in Industrial gases for many years in the U.S., I worked in Europe and found, to my delight, that working, distributing and invoicing gases in mass units was not only acceptable, but much more practical. Why the U.S. has not adopted the same practice is probably one of bias or simply lack of sincere interest. I certainly favor working with gases in mass units whenever I can. It is more accurate, simpler, direct, and easier to understand and visualize. However, many designs don't allow this unless, again, some temperature and pressure basis is given - such as pipe and compressor design.

Saxon has gone to the absolute heart of the engineering point in all this discussion: "what is it, and what are we talking about?". In short, as an engineer you deserve to know and to be advised exactly what it is exactly that you are supposed to be working on - and that always includes the correct units as well as the correct basis. After many years of having to cover for mine and others' mistakes I am no longer sheepish about asking for the basis directly and frankly. If this comes across as overbearing or demanding, I can't apologize for making sure that my work will be as accurate and reliable as my client deserves. I am sure that the other Forum members all believe in this principle.

Art Montemayor
Spring, TX

 

[MariusChE]

Brilliant. This is one thread worth having on the billboards...

remove.marius_che@yahoo.com

 

[quark]

I have yet to find out which one endorses global warming, either normal or standard conditions...lol. I am sure I didn't miss anything.

Good points by Mr Montemayor.

Regards,