Vacuum service - wall thickness? 2

[Freon66]

Would appreciate to formula(s)/charts to measure minimum wall thickness for:
1) cylindrical shell (4 feet long), diameter 36"
2) flat plates/disks (to be used as ends) matching the cylinder OD (will be welded to shell ends).

Operating vacuum 0.05 psia
Material of construction SS304
flat plates welded to shell will be used as small brine reservoir at 0.05 psia and -40 to 50 degrees C

 

[JoeTank]

If you are asking about DESIGN of this tank, please refer to ASME VIII, UG-28 for the rules for external pressure. I would guess that it would not take much for 36 OD at 0.05 psig vacuum.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[kenvlach]

I would expect serious corrosion using concentrated brine up to 50^oC in a welded 304 SS vessel. The –40^oC limit suggests that you using a 30 wt% CaCl₂ solution. I am not familiar with this solution (perhaps, an inhibitor can be used?), but even for seawater, 6% Mo superaustenitic SS is recommended. Superaustenitic SS grades with PREN’s (Pitting Resistance Equivalent Numbers) above 50 are UNS S31266 & S32654. A less expensive alternative is N08367 (AL-6XN), which is often used to replace 304 & 316 that have suffered chloride SCC. See
The PREN: how to measure the pitting resistance of stainless steel
faq338-285

 

[Freon66]

Thanks SteveBraune and kenvlach

The vacuum is almost 14.65 psig, not 0.05 psig (it is 0.05 psia)

The brine solution is chromate inhibited. -40 to 50 C are the extreme ends, normally it is 0 to 35 C. The brine is lithium bromide 50 to 60 wt% with 0.3% chromate.
No experience with how to access ASME VIII, UG-28...is any internet access available or do I have to purchase reference/registration.

Due to the fact that our maintenance dept has already access to many SS304 shells and plates of various thicknesses, We just didn't want to overkill on the thickness..thus the question on the minimum...which we will likely add 1/8th to.

 

[JoeTank]

The ASME Code must be purchased. Check out

http://www.asme.org.

Check out the pressure vessel design software websites and you may find a free demo or two to get you thru this one problem.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[mgp]

You should not play games with personnel safety by designing a (external or internal) pressure vessel out of the blue. If you have no experience with vessel design, get hold of someone who has.

By the way flat end plates will probably be thicker than your stock plates for a 36" vacuum vessel

Regards
Mogens

 

[jproj]

Freon66:

There are formulas for calculating tank thickness required for external pressure in Eugene Megyesy's Pressure Vessel Handbook. Only problem is that it doesn't include the calculation for flat heads, only hemi, 2:1, and ASME F&D heads (which would be MUCH thinner than the required thickness of a flat plate). Listen to the advice others have given you.... look in the ASME code or pay someone to calculate it for you. The cost will be much cheaper than the liability risk of a poorly designed vessel.

jproj

 

[arto]

Look on the National Board list for a "U" stamp holder near you:

http://www.nationalboard.org/scripts/main_search.asp

 

[MikeONeill]

A safe way to go would be to purchase ASME code 2:1 elliptical heads as opposed to welding plates. Brighton Heads (don't have the web address) can supply them.

Mike

 

[MJCronin]

Steve, freon,

I agree with the above comments about either getting an ASME VIII vessel designed for FV and/or at least using ASME VIII methodology....

kenvlach's comments and cautions abou the use of 304SS in brine of cours, are correct....and I agree

Freon, when all is said and done, you will find out that you need a wall thickness just in excess of schedule 10S for a cyinder of this size, material and operating temperature range.... I suggest you purchase schedule 40S pipe and ellipsoidal end caps for this service.....you will meet the ASME criteria ( You should still go through the calculations and/or certification)

My opinions only....

MJC

 

[roaling]

After a lot of experts, I try to give my personel little contribution to your question.
I am used to apply the following finger rule in calculating vessel thickness under full vacuum: 6 mm every 1000 mm OD.
For flat discs calculation I suggest formulas of Roark book. That's all.

 

[Freon66]

Thanks roaling and MJC, your replies were useful.
As per the reference/data below what would be the difference between yielding and buckling for "flat end caps", or are they nearly one and the same due to the symmetry?
Thanks again,
Freon66

----------------
Roger Cortesi (SM Mechanical Engineering MIT)
21-Jun-02
Only Change Values in BLUE
References:
Woods Hole Oceanographic Institute Technical Memorandum 3-81
Failure Curves of Cylindrical/Spherical Pressure Vessels and Flat End Caps.
By Arnold G. Sharp, August 1981.

Roark's Formulas for Stress and Strain, 6th Edition
By Warren C. Young 1989 McGraw-Hill

Material Properties Used:
Youngs Modulus Yield Stress Poissons Ratio
[Pa] [Pa]
1.90E+11 2.05E+08 0.27


Depth Yielding Buckling Endcap Yielding [T/OD]
(m) T/OD T/OD T/OD
0 0.000 0.000 0.000
250 0.006 0.018 0.061
500 0.012 0.023 0.086
750 0.018 0.026 0.105
1000 0.025 0.029 0.121
.... .....

------------------------

 

[roaling]

Your data are not clear to me. Anyway, this is my suggestion for calculating flat ends.
Refer to Roark's formula for flat circular plate of constant thickness with uniformly distributed load (vacuum) and fixed edges.
Another way is to weld two or more vertical ribs to each flat plate and apply the equivalent Roark's formula for rectangular plate. This solution allows to reduce the plate thickness.
Good work.