Q. Regarding Allowable Nozzle Loads and Moments in HI 9.6.2 vs. API 610

[djfkaos123]

Dear colleagues,

I would appreciate your insight on the following questions related to allowable nozzle loads on centrifugal pumps, particularly in the context of API 610 and HI 9.6.2 standards:

1. Why are the allowable nozzle loads specified in API 610 typically lower than those in HI 9.6.2 (especially under similar flange sizes and conditions)?
   For example, for a 6" end suction nozzle, the API 610 Table 5 values are significantly more conservative than those shown in HI 9.6.2 Equation Set 1. What is the rationale behind API’s more restrictive approach?
   e.g. )
   API 610 Table 5 : 6" End nozzle Fx, Fy,Fz = 700, 560, 460 lbf ( x 2 = 1400, 1120, 920)
   HI 9.6.2 Set1 table : 6" Suction nozzle Fx, Fy,Fz = 2700, 1350, 1500 lbf
2. If a pump vendor provides allowable nozzle loads that are even lower than both API and HI standard values, how should this be interpreted? Is it a limitation of the specific pump design, or are vendors applying conservative margins? How should we respond in terms of stress analysis and equipment design review?
3. Why do many pump vendors only provide allowable loads based on individual forces/moments (single load conditions), and not for combined load scenarios?
   Since HI 9.6.2 provides methods for evaluating combined loads (Equation Sets 2–5), is there a reason vendors avoid referencing these in their drawings or documentation?

Any practical experience, clarification, or best practices would be greatly appreciated.


Thank you in advance.