Dear all,

I've a question about heater CONVECTION and RADIANT tubes: this part of the heater is not governed by the ASME B31.3 but by API 530, consequently I think CAESAR is not the best way to analyze this systems.

Anyone has experience of furnace coils analysis? Which program is used for this kind of job? (maybe a finite element software is the best approach?)

NOTE: Analyzing, for example, a convection coil with CAESAR II one of the major problem encountred(my experience) is the friction that doesn't allow the convergence of the solution, so it must be omitted for a considerable number of supports, altering the precision and the relibility of the results.

Someone agree with this statement?

Thanks in advice.

any comment?

I have used Caesar II for reformer furnace piping up to 1100 deg C, both hot wall and refractory lines, no particular problems.

With regard to the Code, it's essentially the Owner's responsibility to define. I have mostly used B31.3.

Hi MoverZ,

Thanks for reply.

Any advice about problems with solution convergence while modeling CONVECTION HEATER internal tube (I mean that when I model this part of the heater I ALWAYS need to remove friction for a relevant number of supports ----> intermediate and end supports)

How can I solve the issue?

TY.

There are several different issues that can cause non-convergence. A suggested methodology to determine the cause and obtain results is:

1 - Get results to evaluate the trouble.

2 - Focus only on the Load Case that is presently not converging.

3 - Find a simple Open/Close situation and make it linear – NOTE THE CHANGE.

4 - Rerun.

5 - Remove more of these simple Open/Close situations if necessary to get convergence.

6 - Check the “error” in the results for this load case.

7 - If still no solution and only friction remains, select a friction support and either 1) lock down the node or 2) remove mu at that node (again, simplify, make it more linear – all you want is a look into the results to decide).

8 - Note that if you have to remove several nonlinearities, you may be able to reinsert some of them when you finally pick the right one.

So, linearize and review the impact.

Thanks Richard for your advices.

MoverZ,

You mean that stress analysis of heater coil (convection-external crossover-radiant) are usual in heater design; I was convinced that all this stuff is not useful due to the extreme flexibility of the coils so just a waste of time (in addition to all the other problems listed above).

Maybe I'm wrong, It's common to model in Caesar this part of the heater tubes?

What's the main intent of this kind of anlaysis?

TY.

Dear,

As MoverZ said, it's essentially the Owner's responsibility to define, but CAESAR can be used for this modelling, checking special features which the analist consider must be checked.

I normally model part or full coil lines, adding vendor supports.

In this moment i am calculating a box heater with arbor coil, connected to 3 reactors. Internal modelling done to check several peculiarities as foundation loads (done by our civil department), manifold connections stresses, etc.

Regards.