How to decide nominal thickness

[llaren]

Dear All.
Can anybody reply me to know and calculate nominal thickness. I used pressure vessel plate 516 gr.70 minimum thickness is 28..how should be nominal thickness?
Thank in advance

 

[JStephen]

If you're a fabricator, contact your plate suppliers and see what is available. Otherwise, contact the fabricators that you would be using and see what thicknesses are normally available and used.

 

[gr2vessels]

I assume you mean 28 mm the calculated minimum thickness. I believe the next size up is the 1 1/4" plate (32 mm). That's what you have to select as manufacturing thickness.
Cheers,
gr2vessels

 

[darthsoilsguy2]

think about corrosion allowance and external/internal exposure conditions too or the tank may have a rerating in its future.

 

[blacksmith37]

ASTM A20 has tolerances that apply to most (ASTM) plate specs.

 

[Vinch]

If I understand well your question, you have found, by calculation, the minimum wall thickness required for a given application and you want to know what nominal thickness plate to order.

Mill under-tolerance for plate is no more then 6%. So add that to your minimum thickness and see what is the next available thickness from the supplier.

 

[Duwe6]

and Please!, add a corrosion allowance. If 28mm is the minimum, you build with 28, and the vessel corrodes 0.5mm in the next 5 years [not an unreasonable ammount, just 'high'], the vessel is BAD,. and must be removed from service. Then your customer sues you for the cost of a massive repair, or a rerate to a lower pressure MAWP, than he paid for. I see this all the time.

If your customer needs 28mm and 400°F, and the next standard size is 1-1/4" [31.7], use it or 1-1/2" [38]. Then declare the Design Temp to be 600°F, as 516-70 does not have a strenght derate until >600°F. Now the customer has enough Corrosion Allowance - C.A. - to run for decades w/o needing a thickness-mandated repair, and he can increase his operating temperature without having to pay for an Alteration to increase tne MAWT. Most customers want to increase thoughput after a decade or so of running, so they typically need to increase the Max. Allowable Working Temp.

The inspection, verification of Code calc's, and certification for an Alteration costs about $2,000, without any 'work' being performed on the vessel.

 

[racookpe1978]

The original poster is registered as a Marine engineer, and his other questions on the same day as this one relate to man-rated hemispherical vessels. Corrosion allowance and "factor of safety" must be also addressed in simple vessel thickness decisions. Weld design and weld spec's for the thick-walled joints? PWHT? Hatches, viewports, instrument and actuator penetrations and welds?

As on that thread, I again strongly suggest the original poster get significant additional professional help before committing any people inside his proposed vessels underwater.

 

[GenB]

28mm 1,1/8th? its he commercially available material > your min T or required min T.