API-650 Tank Nozzle Allowable Load

Hi,
For the API-650 Tank diameter less than 36m ( dia.3m or even less) ,will the Nomogram check method be applicable for the Nozzle load check?

As per API-650, Annex P.1 shall be used (unless specified otherwise by the Purchaser on Line 29 of the Data Sheet) for tanks larger than 36 m (120 ft) in diameter, and only when specified by the Purchaser for tanks 36 m (120 ft) in diameter and smaller.

& W.2(5)says,Unless specified otherwise by the Purchaser, whenever the tank diameter exceeds 36 m (120 ft), shell stiffness coefficients, maximum unrestrained radial deflection, angle of rotation of bottom course shell nozzles, and the nomographs for moments and forces that these nozzles can safely sustain from connected piping shall be provided in accordance with provisions of Annex P. Alternate analysis techniques, such as the finite element method, may also be used to satisfy this requirement.

Experts ,kindly reply
Rg, MVS

Hello mvs123,

As stated in the code, the analysis of tanks 36m diameter and over in accordance with Annex P is not mandatory unless required the purchaser. I think that is fairly clear. The next point is: Does Annex P accurately compute the flexibility of the shell wall or not. I look at it this way; do the nomograms indicate the stress is outside the boundary defined by the nomograms. If it is outside the boundary, then FEA could be considered.

Other software such as NozzlePRO (available from Intergraph) could be use to refine the analysis. Alternatively, the WRC 107 Bulletin could be used to assess the stresses in the shell wall.

If you have the PV Elite programme, then it can to the WRC 107 analysis.

You can also activate the PVP-1279 option. This will implement the methodology from this PVP paper for the nozzle stiffness computations for tanks smaller than 36M (I believe it address tanks as small as 10M). Read the "help text" on this option.

Thanks Ray & Richard for your valuable reply.
Rg, MVS

Hi Ray & Richard ,

I tried with the API-650 Appendix-P Nomogram method for the Tank Dia < 36m.
For my case Tank Dia. were < 10 m ( 2.5m, 3m like that )after applying the Nomogram Check method it is found that stresses are out of the boundary.

Foces +Moments are,
Axial load , Fr lb) =63.823
Longitudinal. Moment, ML (lb-inch)=4098
Circumferencial. Moment , Mc(lb-inch)=45734


following out comes values ,
a/(Rt)0.5= 0.66

YL,Coefficient obtained from FIG.P-4A = 3.200
YF,Coefficient obtained from FIG.P-4A = 1.100
YC,Coefficient obtained from FIG.P-4B= 2.750

are very small.
after applying the Nomogram Check method it is found that stresses are out of the boundary. Even I reduce the forces moments to 10 lb & 10 lb-in its out of the boundary.
But for the same forces + moments with the increased tank Dia to 36m. the stresses are coming within boundary.

That means for 36m< tank Dia. Nomogram check method is not applicable .

Please reply.

Rg, MVS

If I remember well, in the derivation of the method of Nomogram it was assumed that shell thickness is proportional to tank pressure. On tanks where the thickness is governed by other criteria, that is not true. You might look up the two technical papers referenced in Appendix P to understand where the 36m limitation came from.

Hello mariog,

The thicknesses are based upon the actual metal thicknesses available.