I'm working on stress analysis for piping connected to outlet of radiant coil of API560 fired heater,radiant coil is supported from top with guide at bottom of coil, there is shear lug on radiant coil outlet which is near to outlet flange and is supposed to work as a support for coil. I model coil and connect the coil model to piping model,I found the support at radiant coil outlet to lift off. I disconnect coil model to piping model and only run coil model, the support at radiant coil still lift off (note: for coil, I use metal temperture). Could somebody give me light for this issue.

Heater connections to API 560 usually have Allowable "Movements" and Loads. Note the term "Movements". It is for the stress engr to check if the stress model containing the connected piping ,its suuports and the coil restraint configurations are conforming to the allowables.

As the radiant coil is top suuported, you would ideally like to have a top "y" at or near the elevation of nozzle connection suupport, in the connected piping to minimise the diff expansion between the coil and piping. The liftoff situation has to be studied with the allowable movements and loads agreed with the supplier.

Make sure you specify the min stiffness of the supports taken from the Heater structure. Else you could have flexible supports (meeting only the project structural criteria) coming with the heater. The supplier may also be requested for an axial restraint on the face of the nozzle penetration(outside the firing area).Hope this helps.

Thanks for your reply. In my case,shear lug on vertical radiant coil near to outlet is +Y support and not Y restraint (axial restraint). if I put Y axial restraint at vertical coil near to outlet in coil model and combined model( piping connected to coil model), the expansion displacement at outlet flange of radiant coil in these models is the same as the allowable displacement at outlet flange which vendor gave. Do I need ask vendor to put real axial restraint at coil near to outlet instead of +Y support? Thanks!

For Fired Heater models, I always follow two things:

1) Do not try to check the nozzle loads w.r.t API 560. The API loads are to be checked at coil -tube interface which requires complete modelling of the heater ring and tubes ,something extremely time consuming,difficult and unnecessary in a pipe stress program.

2) Model the inside of the tubes to the first few supports which typically will be rest+guide type( look at the vendor drg. carefully and talk to your equipment specialist/vendor for additional clarity)and provide the interface flange load /displacement to the vendor for approval. The axial movement is the most critical parameter.

Regards