Davit Cal 2251B (Davit Arm Calculation)
Davit Cal 2251B (Davit Arm Calculation)
Davit Cal 2251B (Davit Arm Calculation)
DESIGN OF DAVIT
In accordance with pressure vessel design manual by Dennis Moss Notation : P Axial Load A Cross-sectional area Z Section modulus r Radius of gyration tp Wall thickness of pipe davit a Outside radius of pipe L1 Length of davit L2 Height of pipe from support fa Axial Stress fb Bending stress Fa Allowable axial stress Fb Allowable bending stress K Stress coefficients R Radius of bent of davit M1 Bending moment in davit at top support M2 Maximum bending moment in curved davit I Moment of Inertia Fy Minimum specified yield stress fv Vertical force fh Horizontal force W1 Weight of davit
kg cm cm cm mm mm mm mm kg/cm
= = = = = = = = =
lbs in in in in in in in lb/in
cm4 psi kg kg kg
3.8943
= 739 = 739 = 35
Size of davit pipe used - OD 88.9mm * 7.62mm thk Weight of blind flange - 293.00 kg Weight of nozzle N2 - 24.00 kg Weight of nozzle N5 - 5.8 kg Miscellaneous weight - 10 kg Hence Total weight of the blind flange is 332.8 kg ~
335
kg
Material Specification of davit pipe - SA-106 Gr B Yield strength of pipe = Fy = 35000 psi Allowable bending stress Fb = 0.6*Fy = 21000 psi Allowable axial stress Fa = 13250 psi (From sec VIII Div 1 Appendix-L, Ed 2007 allowable compressive stress for columns) Axial Stress fa = P = A 17.22 kg/cm2 = 244.78 lb/in
Page 98 Bending moment in davit pipe at top support M1 M1 = fv*L1 + 0.5*W1*L1 + fh*L2 = 27641.42 in-lb
Maximum bending moment incured at davit M2 M2 = M1 (L2 - R) L2 = 5168.72 in-lb Coefficients = tp* R= a = 6 = 5+6* 9 10+12
1.176
0.45
K= 1-
0.6617
12423.11 psi
Combined stress fa + fb = <1 Fa Fb Hence combined stress at M1 0.61 <1 Hence combined stress at M2 0.11 <1 Thus we can conclude that the provided davit pipe is adequate as the combined stress is Lesser than 1.