The most accurate means of evaluating a piece of equipment for anticipated nozzle loads is to perform a test. In lieu of a test, the next best method may be a finite element analysis, if operability failure (as opposed to stress failure) can be accurately determined from the model. In the absence of either of these, the pipe stress engineer can often specify that the equipment meet a recognized standard, which provides for evaluation of nozzle loads. This standard, which may provide look-up tables or simple calculations, becomes a common reference between the manufacturer and the pipe stress engineer — a promise that the equipment can stand at least a certain set of loads, which the pipe stress engineer can then ensure that the piping loads remain below. It should be noted that these loads are minimum loads—in most case, the standards do not provide a means of actually evaluating the capacities of individual pieces of equipment.
Equipment can be modeled in the piping problem in a number of ways. The nozzles can be considered to be rigid anchors, or entire pieces of equipment can be built-up from an assemblage of rigid elements, with varying degrees of complexity. In either case the forces considered when evaluating the equipment are those forces which the pipe stress analysis shows are acting at the equipment connection. The load cases for which the nozzle loads are to be checked are the greater of those from the cold and the hot cases — that is, from the sustained and the operating load cases (except when cold spring is considered, in which case the cold case would be sustained plus the effects of cold spring). Read Also the types of pipe loading conditions.
Typically suction, discharge and extraction lines are included in separate pipe stress models. Once all of the loadings on a particular piece of equipment have been computed, the equipment can be evaluated to determine whether these loads are acceptable (i.e., in accordance with the governing standard).
CAESAR II provides the ROT program, which may be accessed from the main menu, to automatically evaluate piping nozzle loads against the requirements of a number of these standards. Equipment (and standards) covered include:
Steam Turbines — National Electrical Manufacturer's Association (NEMA) Standard SM23
Centrifugal Pumps — American Petroleum Institute (API) Standard 610
Centrifugal Compressors — API Standard 617
Air Cooled Heat Exchangers — API Standard 661
Closed Feedwater Heaters — Heat Exchange Institute (HEI) Standard
In order to use this program, the user is required to enter some description of the equipment (geometry, nozzle sizes, etc.) and the applied loads. Specific requirements of these standards (and the corresponding use of the ROT program) are described below.