×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Hi everybody I am trying to calc

## Hi everybody I am trying to calc

(OP)
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

### RE: Hi everybody I am trying to calc

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.

### RE: Hi everybody I am trying to calc

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/

### RE: Hi everybody I am trying to calc

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)' ?

### RE: Hi everybody I am trying to calc

#### Quote:

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?

### RE: Hi everybody I am trying to calc

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

### RE: Hi everybody I am trying to calc

> 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)' ?

### RE: Hi everybody I am trying to calc

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

-Dik

### RE: Hi everybody I am trying to calc

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

### RE: Hi everybody I am trying to calc

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

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

### RE: Hi everybody I am trying to calc

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

### RE: Hi everybody I am trying to calc

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

### RE: Hi everybody I am trying to calc

#### Quote:

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: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

### RE: Hi everybody I am trying to calc

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/

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!