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API Storage 650 Tanks - Nozzle Loads

API Storage 650 Tanks - Nozzle Loads

API Storage 650 Tanks - Nozzle Loads

I would be interested to hear of fellow engineers thoughts and experiences on nozzle load design / application to API 650 Storage Tanks.
I typically try to remove all nozzle loads to tanks as far as possible in agreement with our piping stress people - who are sometimes very reluctant to do so.
I advise them to ensure that piping anchors are as close as possible to the Tanks to keep loads to a minimum.

In our speciifcation we typically state the following:
Nozzle Loads
The Purchaser will supply details of loads resulting from connected piping. Vendor is to check these loads in accordance with API 650 - Appendix P or where tank diameter falls outside of the Appendix P limit vendor shall propose a suitable method of analysis for Purchaser approval.
Approval will only be granted where Vendor is able to demonstrate that the calculation method is appropriate to the tank and nozzle geometry, loadings and boundary conditions.
Vendor shall advise nozzle translations and rotations due to tank hydrostatic loading that shall be accommodated in Purchaser's pipng design.

However Appendix P of API 650 is recommended only for tanks > 36 metres in diameter.
What happens when you have tanks < 36 metres in diameter? What would be the basis for checking nozzle loads on these smaller  tanks?


RE: API Storage 650 Tanks - Nozzle Loads

Hi Joe,

interesting question....

For very small tanks, I have used WRC-107 as the basis for the check.  This is limited because of the ratios between shell and nozzle diameters.  You could also use FEA, I suppose, but it'll be expensive.
Although recommended for tanks>36m, I suppose one could apply the Appendix P for smaller tanks with the proviso that it is accepted by the purchaser (given that there is a potential abscence of other design rules).  In any case, though, I agree wholeheartedly with your approach to eliminate as much as possible the nozzle loads on the tank wall.  We have similar problems with pressure vessel design, where people will specify horrendous loads on nozzles which affect the thicknesses of the shells/heads.  One then supplies a "very big, expensive pipe support-and not a vessel/heat exchanger".  For some reason, though, piping & project management guys don't seem to see the humour in this statement .

RE: API Storage 650 Tanks - Nozzle Loads


Your nozzle loading question has been around for a very long time. I remember it being raised in the early 1980s with regard to Condensate Storage tanks on a Nuclear power plant....The methodology detailed in API-650 actually only applies to a very few tank nozzles.

WRC 107/297 has been used in the past for nozzles within it's range of sizes. There are also finite element programs geared specifically for detailed nozzle evaluation (Nozzle/pro by the Paulin Research Group)


Another approach is to establish a "company wide" conservative acceptable loading chart with estimated forces/moments in three coordinates. This would only apply to API-650 tanks.

You will find that loads of about ~250D (forces) and ~300D (moments) are generally acceptable for nozzles of 4inch to 16 inch NPS  ( where D is the nozzle size in inches and forces are in lbs.; moments in ft-lbs) This is just a rule of thumb....if nothing else is available

Just my opinion....


RE: API Storage 650 Tanks - Nozzle Loads

MJCronin (Mechanical)and roca

I agree with MJCronin (Mechanical) regards to WRC 107/297 has been used in the past for nozzles within it's range of sizes. There are also finite element programs geared specifically for detailed nozzle evaluation (Nozzle/pro by the Paulin Research Group)

Nozzzle PRo. , Also FE-PIPE has the API 650 TANK NOZZLE included.


RE: API Storage 650 Tanks - Nozzle Loads


Expect to see some changes or alternatives to API 650 Appendix P sometime in the future (anyone know when the next edition is due?).

Take a look at a paper by Lengsfeld et. al. published at the 2002 Pressure Vessels and Piping conference:
Stiffness Coefficients for Nozzles in API 650 Tanks Authors: Manfred Lengsfeld - Fluor Daniel Inc.
Kanhaiya L. Bardia - Fluor Daniel Inc.
Jan Taagepera - Valero Refining Co.
Kanajett Hathaitham - Fluor Signature Services Inc.
Donald G. LaBounty - Fluor Daniel Inc.
Mark C. Lengsfeld - Lengsfeld Crane Valves
You can purchase the entire volume, PVP-Vol. 440, or for $15 you can get a .pdf of the paper from


The paper covers nozzle loadings in tanks for 6" thru 48" nozzles in 30' to 300' diameter shells.


RE: API Storage 650 Tanks - Nozzle Loads

Well, I got my question answered. The next edition (well, addenda anyway) of API-650 was published in October. I haven't got my hard copy yet, but I did check IHS and they have updated theirs already. The new section is Appendix P.3 "Alternate Procedure for the Evaluation of External Loads on Tank Shell Openings" with a footnote stating that it is based on the paper published in 2001 by Lengsfeld et. al., not the 2002 paper as I had assumed.


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