Hi everybody I am trying to calc 1

[Misaman]

Hi everybody

I am trying to calculate the required equivalent thickness of a vessel using IMDG 6.7.2.4.7 code but the value I get is way too small.
I need help on how the formula works.

The formula is
e1 = 21.4e0d/(1.8(Rm*A1)^1/3)

e0 = 6mm
d = 2.075m
Rm = 485MPa
A1 = 40%

Thank you

 

[Agent666]

Show your full working and answer...

https://engineervsheep.com

 

[3DDave]

Click on "report" to ask this thread be deleted and ask in the Boiler and Pressure Vessel Engineering section where people who are involved with Pressure Vessels know what all those factors are.

https://www.eng-tips.com/threadminder.cfm?pid=794

If it's a Storage Tank then

https://www.eng-tips.com/threadminder.cfm?pid=1452

If there is a spreadsheet question this is the place. If it's asking how a standard derived a formula, another forum is better.

 

[IDS]

I agree with 3DDave, but a general comment that applies to all calculations, whether on spreadsheet or not:

If you have a code formula with inconsistent units (in this case arising from the ^1/3), it's not enough to use consistent units in your input, you must make sure you are using the same units as used in the code.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[IRstuff]

The equation with your values result in something like 5.5 mm, which does seem a bit thin

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[electricpete]

I agree with IDS' point, in general if the equation is not dimensionally consistent between RHS and LHS, then it's an empirical relationship which means you have to match the units assumed by that relationship.

I was able to track down the reference... it does appear op is using the correct units mentioned in the code paragraph 6.7.2.4.7

fwiw my quick calculation was: e1=2.3mm if I plugged in 0.4 for A1; and e1=0.03mm if I plugged in 40 for A1. The latter is arguably the strict/literal way to interpret a request for numerical input "in percent", by analogy to how the other inputs are requested "in mm" for example... but I don't think that's what they intended.

More importantly, while I was there, I did happen to notice the very next paragraph after op referenced is 6.7.2.4.8, which states "in no case should the wall thickness be less than that prescribed in 6.7.2.4.2, 6.7.2.4.3 and 6.7.2.4.4". So once you do your 6.7.2.4.7 calc, then the next step is to check if those other sections might dictate a minimum thickness higher than the result of 6.7.2.4.7

=====================================
(2B)+(2B)' ?

 

[JoelTXCive]

The formula is
e1 = 21.4e0d/(1.8(Rm*A1)^1/3)

Doesn't the exponent (or root) 1/3 need to be in parenthesis in Excel? If not, then excel is raising to 1st power and then dividing the result by 3?

 

[dik]

What are the units?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[electricpete]

> Doesn't the exponent (or root) 1/3 need to be in parenthesis in Excel? If not, then excel is raising to 1st power and then dividing the result by 3?

Yes good catch. I think my calculations above carried that same error.

> What are the units?

It is an empirical relationship, not unit consistent between LHS and RHS.
The intended units are listed in op and also in the excerpt that I posted above.

=====================================
(2B)+(2B)' ?

 

[dik]

What other numbers need adjusting?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

maybe division by 1000?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[electricpete]

Try putting in A1 = 40 rather than A1=40%
As I mentioned above that part is ambiguous.

=====================================
(2B)+(2B)' ?

 

[dik]

Something like... I have no idea of what was just calculated...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[IRstuff]

hmm... that number looks familiar ;-)

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[dik]

Not to me... never seen it before.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[IRstuff]

IRstuff (Aerospace)19 May 21 00:52
The equation with your values result in something like 5.5 mm, which does seem a bit thin

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[IDS]

In Excel (using my Eval UDF, but really just as easy with standard Excel formula):

The message being (in my opinion), when you have a formula with inconsistent units, just use the units stated and keep it simple.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/