Analysis of pump nozzle loads is covered by API Standard 610 "Centrifugal Pumps for General Refinery Service". The requirements of the 6th edition, issued in January of 1981, and those of the 7th edition, issued in February, 1989, can be evaluated using CAESAR II's ROT program. The requirements of the two editions differ slightly; those of the 6th edition are described first: API Standard 610 basically presents reference tables of nozzle loads which a specified size pump nozzle must be good for. The 6th edition of the standard provides separate allowables for two types of support/base plates:
The "heavy duty" pump is typically a reinforced standard pump which can withstand higher piping loads. (The criteria necessary to meet the requirements of a heavy duty base plate/ support are discussed in paragraph 2.4.6 of API 610, 6th Edition.) All force components acting on each nozzle of a heavy duty pump must be less than two times the value shown in Table 2 for that specific load component. For pumps with heavy duty base plates, this is the only requirement. A copy of Table 2 (from the 7th edition) is shown in Figure 3-58.
The "standard" API 610 pump has a slightly more complex scheme for compliance:
1 - In no case shall any of the individual force or moment components on either the suction or discharge nozzles exceed twice the allowable value for the component as shown in Table 2.
2 - Providing that the first is satisfied, the pump passes if the resultant forces and moments on both the suction and discharge nozzles are within the allowables given in Table CI, shown in Figure 3-59 (note that resultant allowables are included in Table 2 of the 7th edition).
3 - If the pump passes the first requirement, but fails the second, the pump may still pass if both conditions described below are satisfied as well:
CONDITION 1 CRITERIA a) The ratio of the applied resultant force to the allowable resultant force from Table CI for each nozzle is less than or equal to 2. b) The ratio of the applied resultant moment to the allowable resultant moment from Table C1 for each nozzle is less than or equal to C; where C=2 for nozzles 6 in. and smaller, and C=(D+6)/D for nozzles larger than 6 in. c) For each nozzle, the sum of the force ratio and the moment ratio found in (a) and (b) above must be less than 2. CONDITION 2 CRITERIA The summation of the forces and moments from both the suction and the discharge nozzles, taken about the base point (which is the intersection of the shaft axis and the pedestal centerline), must be less than the sum of the force and moment resultant allowables for both the suction and discharge taken from Table CI. The 7th edition of this standard modified the requirements to a small extent. The differences in the 7th edition are:
1 - this edition does not recognize separate provisions for heavy duty baseplates; the methodology for evaluating any pump under this edition is the same as that for as standard base plate pump under the 6th edition
2 - different allowables are provided for vertical in-line pumps that are supported only by the attached piping
3 - there is no difference in the allowables for tension and compression loading on top nozzles
4 - the allowables for larger diameter nozzles have been increased in some cases
5 - Tables 2 and C-l have been combined into a single Table 2
An example of an API 610 analysis (if evaluating under the 6th edition, the pump is considered to have a standard base plate) is shown in Figure 3-60. For this example, the suction and discharge piping were analyzed in separate models — the 8-inch suction piping was analyzed in a job called "INLET3" and the 6-inch discharge pipe was analyzed in a job called "DISCH3". In both cases the pump nozzles were modeled as anchors. The forces and moments acting on these anchors, as printed in the CAESAR II output report, are the nozzle forces and moments (with the same sign) that should be entered into the rotating equipment input spreadsheets. These reactions are shown below:
When running the API 610 portion of the ROT program, there are three input spreadsheets upon which descriptive and load data must be entered, which in this case would be filled out as shown in Figure 3-61.
The program then performs the compliance check, as described above. The two page API 610 output report for this particular example is shown in Figure 3-62. The results first show the status of the individual nozzle checks — each of the load components on both the discharge and the suction are within twice the Table 2 allowable; however, the resultant moment on the suction nozzle exceeds the allowable from Table C-l. Because of this failure, Conditions 1 and 2 must be checked. Since both of these conditions are satisfied, the pump meets the requirements of API 610 — despite the one failure.
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