API 610 – Eleventh Edition (Sep 2010)

6.3 - PRESSURE CASING

CLAUSE 6.3.3:

“The Pressure casing shall be designed to operate without leakage or internal contact between rotating and stationary components while subject simultaneously to the MAWP (and maximum operating temperature) AND the worst-case combination of TWICE the allowable nozzle loads of Table 5 applied through each nozzle.”

Note: The twice-nozzle load requirement is a pressure casing design criterion. Allowable nozzle loads for piping designers are the values given in Table 5, which in addition to pressure casing design, include other factors that affect allowable nozzle loads, such as casing support and baseplate stiffness.

Note 1: In general, the criteria in 6.3.3 result in deflection (strain) being the determining consideration in the design of pump casings with respect to pressure retention and nozzle loads. Ultimate tensile or yield strength is seldom (rarely) the limiting factor.

7.3 – BASE PLATE

CLAUSE 7.3.20:

“To minimize misalignment of the pump and driver shafts due to piping load effects, the pump and its baseplate shall be constructed with sufficient structural stiffness to limit displacement of the pump shaft at the drive end of the shaft or at the register fit of the coupling hub to the values shown in Table 13. These values are the acceptance criteria for the nozzle load test in 7.3.21. Grout shall not be used as a means of obtaining the required stiffness during this test.”

It is recognized that grout can significantly increase the stiffness of the baseplate assembly; by neglecting this effect, the adequacy of the baseplate can easily be verified at the vendor's shop. It is also noted that thermal growth, piping fabrication errors, and alignment error all contribute to the actual deflection values achieved in the field. Adherence to the nozzle load values in Table 5 limits the total deflection at the pump and drive shaft ends to approximately 250 µm (0,010 in) (see Annex F).

CLAUSE 7.3.21:

“If specified, the vendor shall test to demonstrate that the pump and its baseplate assembly, anchored at foundation bolt hole locations, are in compliance with 7.3.20. The pump casing shall be subjected to moments Myc and Mzc applied to either nozzle, but not both, such that the corresponding shaft displacements can be measured and recorded. Myc and Mzc shall not be applied simultaneously to either nozzle. The shaft displacement measurements shall be absolute (not relative to the baseplate). For record purposes, the vendor's test data shall include a schematic drawing of test set-up, the calculated moment loads (Myc and Mzc), and the applied moment loads and their corresponding displacements at the drive end of the pump shaft.”

T a ble 13- Stiff n ess test a c c eptanc e criter i a

Baseplate intended for grouting Baseplate not intended for groutingLoading

conditionPump shaft displacement

µm (in)Pump shaft displacement

µm (in)Direction

MYc 175 (0,007) 125 (0,005) +ZMZc 75 (0,003) 50 (0,002) -Y

Myc and Mzc equal the sum of the allowable suction and discharge nozzle moments from Table 5.MYc = (MY)suction + (MY)dischargeMZc = (MZ)suction + (MZ)discharge

6.5 EXTERNAL NOZZLE FORCES AND MOMENTS

CLAUSE 6.5.1:

“Steel and alloy-steel horizontal pumps and their baseplates, vertical in-line pumps with supports anchored to the foundation, and vertically suspended pumps shall be designed for satisfactory performance if subjected to the forces and moments in Table 5 applied simultaneously to both suction and discharge nozzles in the worst-case combination for the pump in question. For horizontal pumps, two effects of nozzle loads are considered: distortion of the pump casing (see 6.3.3 and 6.3.4) and misalignment of the pump and driver shafts (see 7.3.20).”

CLAUSE 6.5.2:

“Allowable forces and moments for vertical in-line pumps with supports not anchored to the foundation maybe twice the values in Table 5 for side nozzles.”

CLAUSE 6.5.3:

“For pump casings constructed of materials other than steel or alloy steel or for pumps with nozzles larger than OD 400 (NPS 16), the vendor shall submit allowable nozzle loads corresponding to the format in Table 5.”

CLAUSE 6.5.4:

“The coordinate system(s) shown in Figures 21 through 25 shall be used to apply the forces and moments in Table 5.”

CLAUSE 6.5.5:

“Annex F gives methods of qualifying nozzle loads in excess of those in Table 5. The purchaser should be aware that the use of the methods in Annex F can result in a misalignment up to 50 % greater than that based on the loads given in Table 5 and can impact equipment installation criteria. The use of the methods in Annex F requires approval by the purchaser and specific direction to the piping designers for its use.”

6.4.2.6

6.9.1.3

QUESTIONS:

1. Whether Pump Nozzle Load shall be qualified for Design Case?2. What is the allowable for Stand-By Pump?3. What is the allowable nozzle load for Friction case?4. What is the operating parameters for Stand-By Pump?5. Whether alignment check to be performed for Pump Piping?6. Can we use temporary supports for Pump alignment?7. What is the criteria for pumps not anchored to the foundation?8. When loads in one direction is more than allowable, but loads in other directions are

significantly less, how do we ensure the actual load is OK or NOT for satisfactory performance of the pump?

9.

Interpretation:

1. The limiting factor for Pressure casing design criterion is ‘STRAIN’, not the ‘STRESS’.2.

Compressor

2.1.14

2.5