3/5/2008, A Lee1 A Preliminary Result for a Helical Tube Subjected to the Internal Pressure Ang Lee, PPD/MD March 5,2008

3/5/2008, A Lee2 Initial Geometry, Loading and Material Dh=0.5 m/1 m;Wave length = 1.6 m and 2 cycles. Dt (tube )=0.5 m; P=1500 psi (100 ATM) and 750 psi (50 ATM) Assuming the end plate is a perfect circular plate_ its normal vector is lined up with the helical pitch angle=tg-1(1.6/3.14*Dh). Stainless steel 316, Inconel 625 and Inconel 718

3/5/2008, A Lee3 FEA model and Boundary condition A shell element 181 with the element size ~0.5 “ (12.7 mm) The minimum restrains required for the structure __assuming 4 points supports (since there is no design for the end plate and how it will be supported yet ). Internal pressure p=1500 psi and 750 psi

3/5/2008, A Lee4 Stress Criteria (ASME widely used) ASME code, VIII, Div 2, Appendix 4, "Mandatory Design Based on Stress Analysis" as a guide line to classify the stress result based on the primary membrane, bending and secondary stress to satisfy the code requirement for each category: a) Primary membrane stress, Pm < Pa b) Primary membrane + bending, Pm+Pb < 1.5*Pa c) Primary membrane+ bending + secondary stress, Pm+Pb+Pl < 3*Pa Where Pa is the allowable stress given by ASME, II, part D or a similar SF applied if the material is not found in the part D. We used SF=4 based on the tensile ultimate.

3/5/2008, A Lee5 Ansys Stress plot

3/5/2008, A Lee6 Calculation Result for P=1500 psi with Dh=0.5 m and Dt=0.5m

3/5/2008, A Lee7 Calculation Result for P=750 psi with Dh=0.5 m and Dt=0.5m

3/5/2008, A Lee8 Calculation Result for P=1500 psi with Dh=1 m (or ID=0.5 m) and Dt=0.5m

3/5/2008, A Lee9 Calculation Result for P=700 psi with Dh=1 m (or ID=0.5 m) and Dt=0.5m

3/5/2008, A Lee10 Some Simple Verifications We could approximately assume the helical tube is ~ about/similar to toroidal shell solution if the pitch angle is small or Dh is larger with a fixed wave length, then see left

3/5/2008, A Lee11 Conclusion and Discussion from this initial exercise Thickness The initial result indicate that the shell thickness is about 1.25” for ss316 for p=1500 psi. It could be thinner if a high strength of alloy is used (inconel 625, inconel 728). Fabrication and Material Cost Get some rough feedback from either machine shop or outside vender and see if it could be built realistic with such curvature and thickness. Look at both fixture and material cost. The end plate design and placement a) The one used in the model assumes a perfect circle since there is no design/consideration given yet. Next iteration, we should think about it how the helical tube will be ended, as well as the support issue. It will influent the stress result as well as the deflection. b) Whether the end plate has to be “flat”?_ inefficient structure against the bending or it can be “dome” type? It turns the bending to the membrane stress __ much efficient

3/5/2008, A Lee12 Stress for the end plate