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Participant

Join Date: Nov 2015
Posts: 1

ASME II D Subpart 3 Charts and Tables for Determining Shell Thickness

11/11/2015 7:03 PM

I have a question about the chart in the back of the 2010 ASME II D subpart 3 for determining shell thickness of components under external pressure; chart for figure ( G) page 748.

L / Do=90/180=1/2 and Do/t =180/.25=720 and to determine factor ( A ) . To read the chart they say to look to the left of the chart go vertical up the chart to .5 , then move horizontally to the right until it falls between 600 and 800 of Do/t, then move down vertically to the bottom. In my study book the answer is .00015

I am studying for the API / 510 exam and don't understand how they get .00015 at the bottom of the chart.

please help, I've scratched my head so much I'm going bald

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Guru

Join Date: Oct 2008
Posts: 39909
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#1

Re: ASME II D Subpart 3 Charts and Tables for Determining Shell Thickness

11/11/2015 11:00 PM

I'm looking at page 748. Seems normal to me.

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Guru

Join Date: Jul 2005
Location: Stoke-on-Trent, UK
Posts: 3888
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#2

Re: ASME II D Subpart 3 Charts and Tables for Determining Shell Thickness

12/03/2015 5:26 AM

I don't have ASME II, but why do you think you should be able to see how they get it? I assume the figure 0.00015 is used in a formula or something to give shell thickness. If there was a formula for factor A there'd be no need for the chart. But I'm not keen on charts like that as it's easy to get a decimal point out.

I had a case many years back with a pressure vessel 2m dia, design pressure 8 barg and had to be good for full vacuum. The designers did the calcs and said it was good for 2 bar external. I didn't know enough to question it, but my then boss said "load of f*****g b*****s, if it's 8 bar internal no way is it good for 2 bar external" and he was right, they were a point out and it was just about OK for 1 bar.

If you want to do a cross check, you could use a formula from eg Roark, but probably need a safety factor (on pressure, not thickness) of 3 - 4.

BTW if you posted this question in Mech Eng you might get more response.

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