Storage Tank Piping Stress Analysis as Per API 650 Using Caesar II

STORAGE TANK PIPING STRESS ANALYSIS AS PER API 650 USING CAESAR II Introduction: Tanks are one of the most important equipment for storing large amount of fluids which might be highly toxic, flammable or injurious to environment and failure at any point could result into highly hazardous or fatal accident. So proper analysis of tank connected piping system is required for accurate functioning and safety. In this article I will give emphasis on modeling of tank, load cases for tank piping analysis in Caesar II, tank nozzle load checking as per API-

650.

Documents required for Stress Analysis: Ø Ø Ø Ø

Tank G.A. drawing indicating nozzle elevation, nozzle projection. Allowable load for tank nozzle as per vendor/manufacturer, if available. Piping isometric, Line list, P&ID etc. Soil settlement data of that region as per civil department.

Modelling Procedure in Caesar II: > Model the nozzle flange (10-20) as per tank flange pressure rating. > Model the projection as pipe element (20-30) with same pipe diameter & schedule given in the drawing for the nozzle up to pipe and tank intersection. > For tanks having diameter less than 36 meter model 40-50 and 50-60 in the same way as followed for normal pressure vessels. provide anchor at node 60 with cnode at 61. Add the settlement displacement if any at node 61.

> Following steps to be taken when doing the stress analysis for the lines connected to tank having diameter more than 36 meter: > Engineering/Process data sheet to be obtained from Process team to evaluate parameter (Radial Growth, unrestrained rotation, allowable forces and moments) as per API 650 as shown in the following figure:

Here, Tank Coefficient of thermal expansion and modulus of elasticity can be obtained from API 650 (2007 Edition) Appendix P, ANSI B 31.3, or alternatively from any engineering handbooks. > Temperature change shall be based on the temperature at which nozzle to be checked. If required both can be entered in successive single run to obtain nozzle movement.) > “Start run” option to be executed to get the API 650 flexibility calculation and parameter as shown in the following figure

>Radial Growth, unrestrained longitudinal rotation (as calculated from API 650 spreadsheet) to be inserted in the displacement vector as shown below with correct orientation and direction. (See the sample attached here with).

> In addition to normal load cases, following cases, in general, shall be included for tank piping analysis,L1 W+P1+T1+D1+D3………….OPE L2 W+P1+T2+D2+D3………….OPE L3 W+P1………………….SUS L4 L1-L3………………….EXP L5 L2-L3………………….EXP Where, D1 & D2 represent displacement vector as per API 650 for operating and design condition respectively and D3 represents tank settlement, if any. Nozzle Loading Checking: 

To be checked as per “APPENDIX P” OF API 650 (as shown in Caesar API 650 spreadsheet) for Tanks having diameter larger than 36 M(120 ft).

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For Tanks smaller than 36 m (120 ft) in diameter :  

   

Vendor has to provide allowable load for the connected nozzles To be checked with Nozzle-Pro / WRC 107/ FEA/ WRC 297/ for Tanks