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Stress analysis method


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Stress Analysis Method , special points to be checked and understood by Piping engineers, Civil and Structural Engineers and especially by Stress Analysis Engineers.

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Stress analysis method

  1. 1. Stress Analysis Method and Emphasis points David Cohen – 29/09/14
  2. 2. • The Most important reason stress analysis is carried out is : SAFETY • This is achieved by designing a Code Compliant System. • There are also Financial Saving to be made: • Correct pipe support spans • Material sizes and thickness which are correctly specified. 2 General Ideal Flowchart
  3. 3. 3 Dangers Good practice engineering, Quality controls, Experienced engineers, and correct installation should avoid dangerous consequences High pressure Flammable
  4. 4. 4 Dangers Buried Pipes : along roads and in civil areas. HIDDEN DANGERS should be considered seriously
  5. 5. 5 • Design and Analysis should take into account also construction feasibility • The designer should run different analyses according to specifying steps.
  6. 6. 6 Codes • Loading Codes: • Seismic Loads: SI-413 • Wind Loads: SI-414 • Traffic and Earth Loads: ASCE-Guidelines for the design of buried steel pipe & Geotechnical Report • Piping Codes: • ASME B31.3 • ASME B31.8 • SI-5664 • NEN 3650
  7. 7. 7 Sources for generation of stress in a Piping System: •Weight •Internal/External Pressure •Temperature change •Occasional Loads due to wind, seismic disturbances, PSV discharge etc. •Forces due to Vibration. 1.Sustained Stresses are the stresses generated by sustained loads. (e.g. Pressure , Weight). These loads are present continuously throughout plant life. 2.Resistive force arising out of sustained stresses balance the external forces keeping the system in equilibrium. Exceeding sustain allowable stress value causes catastrophic failure of the system. 3.As per ASME B 31.3, (clause 302.3.5) “ The sum of the longitudinal stresses, SL, in any component in a piping system, due to sustained loads such as pressure and weight, shall not exceed the product Sh x W ”. Where, Sh=Basic allowable stress at maximum metal temperature expected during the displacement cycle and W=weld joint strength reduction factor. 4.Pressure Stresses are taken care of by calculating and selecting proper pipe thickness. The pressure thickness (t) of a straight pipe can be obtained as per ASME B31.3 from the equation (Clause 304.1.2).
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  9. 9. Seismic Load התאמת
  10. 10. 10 Seismic Load התאמת M.J. O’Rourke X. Liu Lateral Ground Disp High Seismic area: Solutions David Cohen
  11. 11. David Cohen The SI-414 is giving a very detailed method for calculating wind forces on round elements 11 WIND Load התאמת
  12. 12. 12 WIND Load התאמת
  13. 13. TRAFFIC Load התאמת
  14. 14. Soil-Pipe Interaction
  15. 15. 15 Soil-Pipe Interaction
  16. 16. 16 Supports Definition The supports should be in accordance with actual structures, and not “in the air” The supports should be placed correctly
  17. 17. 17 Supports Friction Coefficient of friction factor depending upon the supporting interface (i.e, junction between Top of Steel and Bottom of Pipe or Bottom of Shoe/Cradle) shall be applied at all vertical restraint (+Y or Y supports) locations as mentioned below. Carbon Steel to Carbon Steel: 0.3 Polished Stainless Steel to Polished Stainless Steel/Graphite: 0.15 Teflon to Teflon/ Polished Stainless Steel: 0.10 Concrete to Carbon Steel: 0.4 Pipe to Roll Support: 0.01 Teflon to Carbon Steel: 0.2
  18. 18. 18 Check the Model From Piping design to stress analysis, just check that any design problem will occur. PIPING Redesign will generate a new stress analysis process.
  19. 19. 19 From Soil Report Insert Data Soil Data should be inserted according to soil report , pipe diameter and pipe depth.
  20. 20. 20 ALL Line Numbers should be written Only on main lines (not for vents) Insert Data ALL Supports should be with different name , check duplicity (line stop should be the same support name)
  21. 21. 21 Analysis Settings
  22. 22. 22 Check the highest displacement value : DR Insert Data Check the highest Support/Anchor Reaction Global FR