I have a question on the allowable forces and moments ( external piping loads) for API 560.

According to API 560,"Heater Terminals shall be designed to accept the moments and forces or the movements in Table 7".

Now "Terminal" acccording to API 560 is defined as " welded or Flanged connection to and from the coil, providing for inlet and outlet of Fluids".

Does that mean, we have to compute and check the forces and moments at Tube-Header connection , based on Tube Diameter or compute and check the forces and moments at External Piping-Header connection, based on Header Pipe Diameter?

I always used to model the fired heater connected systems upto the interconnection point with the Equipment and included a small portion of the heater inside to model the tube supports.I always reported the loads at the Flange connection point with external piping and checked the loads against API 560 allowables.

Recently I was reviewing a vendor drawing for Fired Heater where the outlet nozzle is 18".Vendor has specified "5 times API 560 " allowables. Since API 560 does not address 18" nozzle, I started going through this document ( API 560 ) once again and came out with this question.

Solicit advise from members of this forum.Also I would appreciate if I can get to know the procedure that is used by other consultants to model fired heater systems.

Regards

Kindly advise.

Hi Anindya
The "movements" are the imposed movements by Piping on the Heater Terminals and are limited usually by the vendors based on their deisgn.

You are correct in your modelling approach on including a portion of the heater internals in your stress model, as the end conditions at an initial vendor drawing stage does not guarantee a reasonable fixity. Mostly you may have to ask for axial stops at the convection area (outside the heating area, this agian is consultant specific).

I would check the vendor allowable loads at the face of the flange terminals, but in most cases case the anlaysis would be governed by the imposed movements of piping on heater terminals.

Raja,

Thanks for your reply.

My main question is still unanswered. Your view on the same will be highly appreciated.

First : The nozzle allowables mentioned by the vendor as 5 times API 560 , when the nozzle size is 18" ( kindly refer my earlier question).This gave me a feel that since 18" is not addressed by API 560, perhaps over the years I have misunderstood the term " Terminal" according to API560 Terminology.My understanding is: "Terminal" is the External Piping-Heater Flange connection. Now I have started to think that this may not be the same as what API 560 indicates i.e." welded or Flanged connection to and from the coil, providing for inlet and outlet of Fluids".Kindly let me know your interpretation on the same.


Thanks and Regards

Anindya

I agree with your understanding:................

" welded or Flanged connection to and from the coil, providing for inlet and outlet of Fluids".

Eventhough you may meet the allowable Forces and Moments at the Terminal face, the proprietary design of the vendor at the Convection/Radiation wall junction will be factor in the Analysis.

All vendors may not allow the suggested "Movements" defined in API 560. Is the piping in discussion in the Convection/Radiant section and is it top/bottom supported in Radiant section.

Caution: Make sure the supports provided by the heater vendor on heater structure have sufficient rigidity.

Hi,
The terminal connection should be taken as piping interface with heater coil or header ( as the case maybe ) and the loads shall be checked at the battery limit interface only.
Regarding the 18" size mentioned by vendor please be aware that sometimes vendors overlook the size limits of the applicable code e.g. quite often I am in receipt of vendor drawings quoting API-610 for 18"-20" nozzle sizes whereas API-610 table is only applicable upto 16" size.You may have to reconfirm with your vendor about the allowable loads.

Regards.

Rajesh and Raja,

Thanks to both of you. The connection is in Radiant Section.

Rajesh, I fully agree with your suggestion. There is something wrong about the vendor information, which I will find out.

The question is ( Raja also agress to this) that if the API allowables are at the Header- Tube connection only, is the check at the External Piping Interface , which I have always done and perhaps many of us do, is correct?

I think the correct methodology for us will be to model the inside to reach the "real Terminal" as defined in API 560, check for the forces and moments there as per API 560 Or give the interface loading to the vendor to check if they are ok.

Like to get your views on the same.

Regards

Hi,
In my opinion it has to be checked at the battery limit flange only.
However, in case of any doubt for the header type construction vendor could be asked to provide allowable loads ( which in most of the cases will be according to API-560 ) at the battery limit flange with initial thermal growths.

Regards.

Anindya

Thanks for bringing up this discussion, which I beleive will be useful for many.

From an external piping connection point of view, the flanges or Welded End connections offered by the heater vendor are the "Terminals".
However the heaters case is that with a Flexible Coil (in Convection or Radiant section), the fixity (of the terminals) is not final, unless the analyst imposes some fixity in the form of axial stops on the teraminals. Having done that ,to have a reasonable Stress model with Good end conditions, the focus will be to check the Forces/moments at the terminal face and also the "MOVEMENTS" imposed by the External piping on the Heater terminals. This sometimes may be very negligible based on Heater proprietary design of the Sealing joint.