Hi All,

Can you explain whether same allowable forces/moments at nozzle terminals of API-560 fired heater connection is applicable for both sustained, max. operating, occasional - all load conditions ?

If we want to use maximum allowable movements at nozzle terminal, will we have to keep the terminal connection free in all six (X,Y,Z,OX,OY,OZ) directions & meet the allowable movements in Table 7 of API -560. Why is this not implemented in Caesar-II ?

Please correct my understanding that both the allowable forces/moments & allowables movements are not simultaneousely applicable & the first approach used by Caesar-II is one acceptable approach where no allowable movements are to be met at nozzle terminal.

regards,

sambhu

API Standard 560 Paragraph 5.2 states, in its entirety: "Heater terminals shall be designed to accept the moments and forces, or the movements listed in Table 7, unless otherwise specified by the purchaser."

CAESAR II simply compares local forces and moments to allowable loads based on tube size. There is no check on movement.

The standard does not specify the source of the load therefore, I would suggest all structural loads (e.g. installed & operating) should be kept below these limits.

I guess some of the trouble here is the deflection limit. But note that the code states load OR movement must be less than Table 7 - not AND. So if you model the connect as a free end (and no load) you can check deflection. But what about rotation? I would suggest you should hold that free end against rotation and axial deflection and check transverse deflections, axial load and moments. But that free translation may produce excessive movement even though the stiffness of the connection would reduce it. You may want to "guess" at the translational stiffness, then, by dividing the maximum load by the allowed deflection.

Why aren't the movements checked in CAESAR II? What's there to check? Transverse limit for radiant terminals is +/- one inch and the limit for convection terminals (horizontal tubes only) is +/- a half inch.

Dear Dave,

Thanks for the following clarification in your reply.

'I guess some of the trouble here is the deflection limit. But note that the code states load OR movement must be less than Table 7 - not AND.'

Why I raised this query is that many analysts meet both the local foce/moment limit & movement limit by modelling some portion of fired heater internal tubing with tube support configuration, thereby having a flexible nozzle stiffness. If it meets the fired heater vendor's requirement, it makes the life of piping analyst's a bit easy. With some thermal movement DX,DY,DZ at nozzle terminal & zero 0X,0Y,0Z values as read from heater internal drawing, it is very difficult to meet API 560 force/moment allowables.

regards,

sambhu