Hydraulic Collapse Pressure (aka crush depth) 1

[oceanman]

I am trying to design some enclosures for equipment I intend to locate on or near the sea floor at a depth of about 1300 feet. I need to figure out how best to design these enclosures so that they do not implode due the the high ambient pressure. My question is, is there a good reference on the internet, or in a book where this type of design information could be found. Thanks.

Oceanman

 

[arto]

Look in the ASME Boiler &Pressure Vessel Code Section VIII for External Pressure Design.

 

[oceanman]

Thank you Arto for the response. This reference may be a very good one indeed! The description of it seems to be right on. The ASME web site shows it to be a very long and detailed (and expensive) document, so if anyone knows of something more streamlined, that would be good too. I will wait a few days before buying this ASME document in case something a bit less involved is posted. If not, I intend to get it.

 

[arto]

Look in an engineering college library - they should have a set of codebooks. You will probably need Sec VIII Div 1 & Sec II-D for properties & Ext'l Pressure charts.

IHS has it in their online spec service too [

http://www.ihserc.com/

expensive, but worth it if you need a lot of MIL specs or ASME specs]

 

[TYL]

BS5500 is better than ASME 8 for shells under external pressure. There is also an a U. of Strathclyde course on 'Pressurised Systems' by Dr. Nash called 16426/16587 which is explanatory to BS5500, this can be found on the web. If you search under 'submarine design' you will also find useful info.

 

[howkers]

Submarine hulls are stiffened at intervals by hoops. One of the interesting failure modes is a concertina axial collapse.

 

[TYL]

To find Dr. Nash's course just search with Google for '16426'. I came across part of the course under some heading or other, saw the number, then searched under that & Hey Presto!

 

[khardy]

There is a book called "Pressure Vessel Handbook" by Pressure Vessel Publishing. It has a chapter on designing vessles under external pressure. It's alot cheaper than buying ASME VIII and much easier to read.

 

[ncc212]

oceanman,

nothing in your note on the radius you are looking at? Are you sure you want to go for a ring stiffened cylinder?
The section in BS5500 applicable to external pressure is about 20 pages (based on Bill Kendricks work at ARE/NCRE) search for Kendrick and you should get something pretty quick. There is an option of using empirical design curves for pc1-7 etc or you can do the calcs and see what you get by analysis Bresse/Bryant.... There are also (though somewhat dated) some Class society rules for submersibles LR and ABS, may be others. Classically there is interframe buckling and overall collapse and you need to anlyse up to at least mode six. Current thinking is that there is no dicretisation between IF and overall but that the two interact.

At the end of the day i would say that how much you want to spend on the design is liable to drive you. If the application is going to be static then make it simple and use a large gammaI and gammaC on both the cylinder and domes.

 

[oceanman]

Thanks ncc212 for your insight. I will try to find the proper reference that you suggest. Recently, I purchased a computer program called "Under Pressure" which makes these sorts of calculations quite straight forward. The references will be good back up and support for the software.

Oceanman

 

[colinp]

Hi Oceanman,

Can you completely fill the enclosure with a dielectric liquid? This might allow you to simplify the design. If there is no pressure differential between the inside and the outside of the enclosure the structural loads are much less and leakage is less of a problem as well.

If this is impractical, look into using FEA tools to do a buckling analysis as has already been mentioned.

Sounds like fun
Colin

 

[oceanman]

Thanks ColinP. We are doing OK now with our computer program. Thanks for the thought on the dielectric fluid, it is a good one, but I think that our equipment would not do so well in it.

Oceanman