API 653 minimum thickness vs API 650 design thickness

[jharris3]

Why does API 653 provide a higher allowable stress than API 650? The equations are equivalent except for E which is = 1.0 for butt joints.

The tank i am inspecting was constructed to 650 edition 9 appendix F.
It was NOT constructed to Appendix A.
It is 60 ft dia 32 ft tall (4 rings).
t = 0.216 for API 653 and
t = 0.232 for API 650.
The design specific gravity is = 1.5.
A-36 material
Ambient Pressure and Temperature

 

[brubakerj]

The minimum thickness per API 650 would be 0.25 in per Section 3.6.1

That being said, they do have larger allowable stresses for A36 in API 653. I think the reason being service history they feel they can cut into the margin?


Anyway, I put an API 650 calculator online and was looking for feedback. I placed it at

http://www.novanumeric.com/samples.php?CalcName=APITanks

Any constructive criticism/feature requests would be useful.

Regards,
Jeff Brubaker

 

[Duwe6]

"Houston, we have a problem"

Using my handy-dandy 653 calculator, I get 0.313" for A36 at 23.2 kips [1-ft method]

brubaker's calculator spit out 0.3026"

Nobody is close to your .216"/.232"

 

[IFRs]

Hmmm - I used brubaker and got 0.2914 and by hand and got 0.312 - hmmmm

 

[brubakerj]

I matched his numbers in my calculator for course 2.

API 650
Calculating Thickness Per 1FT Method on Course1
Course1
D:60.0
G:1.5
S:23200.0
E:1.0
Cas:0.0
currentHeight:32.0
2.6xDx(H-1)xG/(SxE)+Cas=0.312672413793
Min Plate for 60.0, 0.25
Calculating Thickness Per 1FT Method on Course2
Course2
D:60.0
G:1.5
S:23200.0
E:1.0
Cas:0.0
currentHeight:24.0
2.6xDx(H-1)xG/(SxE)+Cas=0.231982758621


API 653
Min Plate for 60.0, 0.25
Calculating Thickness Per 1FT Method on Course1
Course1
D:60.0
G:1.5
S:23200.0
E:1.0
Cas:0.0
currentHeight:32.0
2.6xDx(H-1)xG/(SxE)+Cas=0.312672413793
Min Plate for 60.0, 0.25
Calculating Thickness Per 1FT Method on Course2
Course2
D:60.0
G:1.5
S:23200.0
E:1.0
Cas:0.0
currentHeight:24.0
2.6xDx(H-1)xG/(SxE)+Cas=0.231982758621

 

[brubakerj]

API 653 (I pasted API 650 twice above)
Min Plate for 60.0, 0.1
Calculating Thickness Per 1FT Method on Course1
Course1
D:60.0
G:1.5
S:24900.0
E:1.0
Cas:0.0
currentHeight:32.0
2.6xDx(H-1)xG/(SxE)+Cas=0.291325301205
Min Plate for 60.0, 0.1
Calculating Thickness Per 1FT Method on Course2
Course2
D:60.0
G:1.5
S:24900.0
E:1.0
Cas:0.0
currentHeight:24.0
2.6xDx(H-1)xG/(SxE)+Cas=0.216144578313
Min Plate for 60.0, 0.1