nozzle loads on rotating equipments 1

[Hashim lawati]

Hi all and thanks in advance for your participation

regarding nozzle loads on rotating equipment's, we are following the rule of thumb: twice the values in API 610 table 5.

any reason for this rule ?
are you guys using it ? or you follow other standard ?

pump spec API610
piping spec. B31.3

thanks.
Hashim.

 

[MJCronin]

Where did your rule come from ?

MJCronin
Sr. Process Engineer

 

[racookpe1978]

The NEMA has published old (very old!) nozzle force and moment limitations for turbines and rotating machinery. But all observers challenge those limits - which are based on a nominal diameter of the nozzle and total "area" removed from the casing of the turbine or pump by all nozzles as impractical, overly restrictive, and not based on actual turbine casing strength.

The original limits were drawn up in the 50's based on rules of thumb used at the time, and those equations and their limits have not been updated based on FEA or any real-world analysis since then even though the NEMA document itself have been updated. Use the turbine manufacturer's limits, if those are published.

The API has published different limits based on vessel pressures usually much higher than the steam turbine nozzles and thin steam turbine casings assumed by the NEMA, but I am aware of no such "Use twice the API limit (for pumps and compressors)." Yes, for steam nozzles, the NEMA limits on forces and moments have been tested on actual steam turbine casings for nozzles less than 10 inch diameter. Those steam nozzles tested do resist up to twice the NEMA limit, but you cannot extrapolate that series of tests to "all nozzles made of all materials at all pressures at all temperatures".

 

[Rauf30]

It looks like misinterpretation of API 610 section 6.3.3 a), and 6.5.2

 

[RVAmeche]

API 610 has allowances (see Appendix F) where your equipment is okay provided the individual loads are not > 2x the allowable AND other criteria (various combined loadings) are met.

Note that API 610 says this is acceptable with owner approval; it means there is a higher risk of damage to the pump.

 

[StressGuy]

Agree with Rauf30 and RVAmeche. There's no "rule of thumb" to use 2x API-610. API-610 is the rule for API pumps, unless your contract specifies that the vendors designs the pump for 2x API-610 - which is appropriate is some cases.

Also, keep in mind "rotating equipment" is a broad category. API pumps, ANSI pumps, API centrifugal compressors, NEMA steam turbines, etc. are all "rotating equipment" but all have different standards that govern their nozzle allowables.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.