Pl. guide me for the following problem:-

I am designing a horizontal vessel of following design conditions:
ID=6500mm, TL to TL=21000mm, Design Pressure=3.5 barg, Temp.=225 deg C and MOC-SA516 Gr 70.
I am taking head as a stiffner i.e. Saddles are at 1200mm from tangent line.
Thicknesses of shell courses of 2500mm at the portion of Saddles are 20mm and rest shell course thickness is 14mm. Saddle Contact Angle=155 deg.

It is passing in operating condition but in hydrotest condition it is failing in Bending Stress, Sb=(M*C1/I)
where M=Fh * d and d = B-R*Sin(theta)/theta
As in hydrotest condition, allowable stress can go upto 0.9 * Yield Stress, but in PVElite output it takes 2/3 * yield Stress. If I consider 0.9 * Yield Stress, it is passing.

Can I use the above my stated option.

Thanks in advance
Regards
Saurabh Gajwani
Engineer - Mechanical

Hi Saurabh,

You are referring to the bending in the saddle due to the splitting force. The allowable as it is shown in the Moss book is 2/3rds of the material yield strength. Since this is a structural and non-pressure induced type stress, you could check the AISC Structural Code and try to determine an allowable for this stress.