B31.3 2004, value of "f = 1.2"

Hi,

Can anyone guide me how to incorporate the value of f = 1.2 based on new B31.3 2004 edition.

I know that C2 has option at the bottom stating "f" Allowed Maximum of 1.2 and we can select whether this should be On or Off.

But even after I selected On, the allowable stresses doesn't increase by 1.2 times the original allowable stress.

I know that I am doing something wrong but can someone point me in the right direction.

Based on the information in B31.3 the allowable in Displacement Stress Range, which is Thermal case in C2, has to be multiplied to f = 1.2 but when I check the code stresses, the pipes that were failing are still failing and there is no increase in allowable stress.

Any help will be greately appreciated.

Dharmit

Is your original overstress = 20% or less in the EXP case?????? or is you r system overstressed in SUS or OCC???

It is overstressed 15% in EXP case.

Thanks

Dharmit

You just can't use f=1.2, there are some checks to be made. The Code allows "f" to go to 1.2 if:

(a) the material is ferrous - c2 can't check this one, you have to
(b) the min tensile strength does not exceed 75 ksi, - c2 can't check this one, you have to
(c) the temperature is less than 700 degF.

If you exceed any of these, "f" is limited to 1.0. c2 can only enforce the temperature limit, so my guess is that your over this.

Please read the code before jumping to a hasty and incorrect conclusion and each code issued is different from its predecessor.

Richard,

(a) The material used is A312 TP316 Stainless steel which is ferrous
(b) The minimum tensile strength is 75 ksi as per B31.3 - 2004 edition. I haven't exceeded teh minimum tensile strength but I am on the range.
(c) The design temperature is 120 deg C which is 248 deg F

Please let me know if I am wrong in my understanding of Ferrous material or minimum tensile strength or the temperature limits.

Thanks

Dharmit

John,

Thanks for comment.

Which hasty and incorrect conclusion was drawn by me. Please let me know so that I dont ANNOY someone else in the future.

I have ASME B31.3 2004 code. If the code changed from 2004 till now, please let me know and I will ask my organisation to get one for us so that I dont make a mistake of jumping to hasty and incorrect conclusions by not giving proper justice to the new code which is different from its predecessor.

Thanks John

Dharmit

Richard,

Please let me know if you had problems in interpreting what I said above so that next time I make myself clear and get proper answers. From some other readers comments, I feel that I am missing something in my questions. I would like to get a quality answer (the one that I received from you and some other which points in the right direction) but I also understand that quality answers can only be obtained from quality questions. So this is for my own sake.

Regards

Dharmit

Please send us the job, I need to see this.

Richard,

This is the file that has the problem.

The load case to be looked at is L26.

Please let me know if you need more information.

Thanks

Dharmit

Did you really upload this file? It doesn't appear to be available?

I sure did upload the file last time but dont know why it didnt reach the server.

I am uploading this again. This time, I have trimmed down the fat and the file size is something 12-14 kb.

Hope this time you get it.

I am also attaching the snapshot where it shows the problem area.

Let me know if it doesn't get through.

Regards

Dharmit

Ok, your JPG file is there, but not the "c2". Perhaps you have blanks in the file name - just a guess? To be on the safe side, e-mail it to techsupport@coade.com.

Richard,

I have sent the file at the said e-mail address

Please let me know if you have troubles with that one.

Regards

Dharmit

You didn't enable the option to allow "f" to go to 1.2. On the Allowable Stress Auxiliary Dialog, there is a radio button setting at the bottom. If you want "f" to possibly go to 1.2, you have to turn this on - it defaults to "Off".

Richard,

Even if I turn it ON the allowable stresses doesn't change and the node shown previously fails as shown in the attached figure.

Is there something I am missing?

Regards

Dharmit

The cyclic reduction factor "f" is based on the anticipated number of cycles for the specific range (load case) under consideration. In all versions of c2 up to Version 5.00, you had to explicitly define "f" in the input. So if the range in question was based on T1, the you would define "f1" appropriately. If you didn't define "f1", then c2 defaults this value to 1.0. (Similarly, if the range in question was based on T2, then you would define "f2" appropriately.)

c2 Version 5.00 implements the B31.3 Code change allowing "f" to go as high as 1.2 in certain circumstances, but this is not the default. As in previous versions, if "f" is left blank, it defaults to 1.0 (except if you define the number of load cycles in the Static Load Case Editor).

So, if you want "f" to exceed 1.0, you must:
a) Verify the restrictions discussed in a previous post above.
b) Toggle the radio button on the Allowable Stress dialog to allow this possibility.
c) AND define the value of "f". Again, if you leave this blank it defaults to 1.0 (unless load cycles are defined). Your input didn't define "f" or the number of load cycles - hence c2 defaulted this value to 1.0.


What are these references to "defining load cycles"? We recognized that the "f" factors are more associated with the (EXP) load cases than with the temperature values defined in the input. So with Version 5.00 we made another two changes addressing "f".

New Option 1: Instead of defining "f" directly (as say 0.9 or 1.2), you can specify the number of cycles. If the value specified is greater than 1.2, c2 assumes this is the number of cycles and it will compute "f" as per the Code Equation.

New Option 2: You can leave the "f" fields blank in the input, and define the number of Load Cycles in the Static Load Case Editor. This is actually a better (more reasonable) policy, since it is the load cases that experience the cycles, not necessarily the temperatures. If the number of cycles is defined here, then c2 will compute "f" as per the Code Equation, for that load case.

Thanks Richard,

I will use the path of defining the Load cycles in Static Load Case as you said in your post. This way I will get more control on the actual load cases rather than just the temperature.

Thanks again.

Dharmit