Optimizing the Allowable Pipe Load on Rotating Equipment Nozzles
Publication Date: 2012-Jul-18
The IP.com Prior Art Database
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RETHINKING THE ALLOWABLE PIPE LOAD ON ROTATING EQUIPmeNT NOZZLES
Piping Mechanical Principal Engineer
Albert O. Medellin
Manager, Piping Mechanical Division
The M. W. Kellogg Compaay
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It is a consensual belief of piping engineers that the current allowable pipe loads on rotating equipment nozzles imposed by the equipment manufactur- ers are too low. A more realistic allowable should be established to better balance equipment costs against piping engineering and material costs.
This article reviews past practices of equipment nozzle loads and points out inadequacies and inconsistencies of the current standards. It is believ- ed tha the extra manufacturing or engineering cost incurred in providing in- creased allowable nozzle loads for rotating equipment can be compensated by materla]s and engineering savings in the associated piping systems, This paper proposes a set of reasonable limiting allowables and suggests giving credit to equipmeut with higher allowable nozzle loads when a bid is being evaluated.
A piping system has to be designed to satisfy the following rquirements:
(a) Functional Adequacy - The pipe shall be big enough to carry the amount of fluid required for the process." Its material shall be compatible with the fluid it .carries. It is protected from excessive heat loss and from environmental damage such as corrosion, freezing and so forth.
(b) gtructural Integrity - The pipe shall be thick enough to resit
the internal pressure. It is properly supported for weight, wind, seismic, and other loadings. It should be flexible enough to absorb thermal expansion and contraction.
(c) System Operability - The piping shall not cause any excessive de- formation to the connecting equipment thus hindering its proper operation,
Flange leaking, valve sticking, rotating equipment vibration and overheating are some of the problems to be avoided.
While both insuring structural integrity and maintaining "system opera- bility" are responsibilities of piping engineers, the task of maintaining the system operability is more difficult because it involves the strength of the consecting equipment which is beyond the control of piping engineers. What
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a piping engineer can do is to arrange the pipe in such a way that the pipe load applied at an equipment nozzle is less than the allowable load furnished by the equipment manufacturer. Unfortunately in actual practice this is not as easy as it sounds, since the allowable loads are generally very low. It is unusual to select a piping system meeting the allowable nozzle load without going through a considerable number of calculations. Flexible loops and spe- cial restraints are normally needed for hot piping systems to bring the pipe load within the acceptable limit.
It is a eonsensual feeling amont the pipe stress engineers that the current standard allowable nozzle loads should be higher. These low allowables have c...