Dear Users

I have a question about the calculation for the thickness of the shell course. I can`t verify the used design stress for courses 3-5.
The temperature: 100C (App M required) and we use API 653

The input:
TANK SHELL COURSE MATERIALS

Shell Course # 1 Material Name ........................ St37-2
Shell Course # 1 Design Stress [Sd] .......(KPa ) 0.14586E+06
Shell Course # 1 Hydro Test Stress [St] ...(KPa ) 0.16048E+06
Shell Course # 1 Minimum Yield Stress .....(KPa ) 0.18700E+06
Shell Course # 1 Minimum Tensile Stress ...(KPa ) 0.34000E+06
Shell Course # 1 Maximum Thickness ..............(mm. ) 25.400
Shell Course # 1 Material Grade ....................... C
Shell Course # 1 Material Group ....................... 1

Shell Course # 2 Material Name ........................ St37-2
Shell Course # 2 Design Stress [Sd] .......(KPa ) 0.14586E+06
Shell Course # 2 Hydro Test Stress [St] ...(KPa ) 0.16048E+06
Shell Course # 2 Minimum Yield Stress .....(KPa ) 0.18700E+06
Shell Course # 2 Minimum Tensile Stress ...(KPa ) 0.34000E+06
Shell Course # 2 Maximum Thickness ..............(mm. ) 25.400
Shell Course # 2 Material Grade ....................... C
Shell Course # 2 Material Group ....................... 1

Shell Course # 3 Material Name ........................ St37-2
Shell Course # 3 Design Stress [Sd] .......(KPa ) 0.16048E+06
Shell Course # 3 Hydro Test Stress [St] ...(KPa ) 0.16830E+06
Shell Course # 3 Minimum Yield Stress .....(KPa ) 0.18700E+06
Shell Course # 3 Minimum Tensile Stress ...(KPa ) 0.34000E+06
Shell Course # 3 Maximum Thickness ..............(mm. ) 25.400
Shell Course # 3 Material Grade ....................... C
Shell Course # 3 Material Group ....................... 1

Shell Course # 4 Material Name ........................ St37-2
Shell Course # 4 Design Stress [Sd] .......(KPa ) 0.16048E+06
Shell Course # 4 Hydro Test Stress [St] ...(KPa ) 0.16830E+06
Shell Course # 4 Minimum Yield Stress .....(KPa ) 0.18700E+06
Shell Course # 4 Minimum Tensile Stress ...(KPa ) 0.34000E+06
Shell Course # 4 Maximum Thickness ..............(mm. ) 25.400
Shell Course # 4 Material Grade ....................... C
Shell Course # 4 Material Group ....................... 1

Shell Course # 5 Material Name ........................ St37-2
Shell Course # 5 Design Stress [Sd] .......(KPa ) 0.16048E+06
Shell Course # 5 Hydro Test Stress [St] ...(KPa ) 0.16830E+06
Shell Course # 5 Minimum Yield Stress .....(KPa ) 0.18700E+06
Shell Course # 5 Minimum Tensile Stress ...(KPa ) 0.34000E+06
Shell Course # 5 Maximum Thickness ..............(mm. ) 25.400
Shell Course # 5 Material Grade ....................... C
Shell Course # 5 Material Group ....................... 1

Output:
The following material properties have been modified in
accordance with API-650 (and API-653 where applicable).

Course Material Design Test App M
Number Name Stress (Sd) Stress (St) Reduction
(KPa ) (KPa )
1 St37-2 0.13225E+06 0.16048E+06 0.9067
2 St37-2 0.13225E+06 0.16048E+06 0.9067
3 St37-2 0.13564E+06 0.16830E+06 0.9067
4 St37-2 0.13564E+06 0.16830E+06 0.9067
5 St37-2 0.13564E+06 0.16830E+06 0.9067

I can verify course number 1&2 but not 3-5 for the design stress
I kindly request your comments.

Thanks in advance .

Regards,

As per the definition of "S" in API-653 4.3.3.1, the determination of the allowable stress for courses 3 and above differs from that of courses 1 & 2.

I have do that. than I have a "S" of 160.48MPa (see the input by design stress, the min of {0.88*187; 0.472*340}) If I multiply 160.48MPa with the reduction factor of 0.9067 than we have 145.507 MPa and not 135.64 MPa! If I do that with courses 1 & 2 with the right "S" than it is okay. Witch stress you take for courses 3-5 or forget I a reduction factor?

Regards,

I agree, you should be getting 145.5. Send you input (.tki) file in to Tech Support so we can look at it.

Ok, here is what is going on:

Y = 187000 kpa
T = 340000 kpa
Reduction = 0.9067

Sd = Reduction * ( 0.80 * Y, 0.472 * T )

S1 = 0.80 * Y = 149600
S2 = 0.472 * T = 160480

Minimum is S1 = 149600

Sd = 0.9067 * 160480 = 135642.32


Note the 0.80 in the above equation instead of 0.88. See API-653 Section 4.3.10.1.1.a for details. (You're in "analysis mode" (an existing tank) and API-650 Appendix M is applicable.)

Aah okay
I don't have give consideration to an exception of the rule
thank you!!

Regards,

Yes, and it would be really nice if the "exceptions" were somehow associated with the portion of the Code they affect. Then we wouldn't miss things.