Lifting Lug with Shell Corrosion (Codeware COMPRESS)
Lifting Lug with Shell Corrosion (Codeware COMPRESS)
(OP)
Hey Y'all! Looking for a little guidance on designing lifting lugs here. I do this routinely and the lug calcs (by hand) are no problem for me. That said, I'm not a vessel guy, so the local stress on vessels is a bit outside of my wheelhouse. In this case, the client has indicated they have significant, known corrosion issues in the existing vessel.
What I'd like to do is run lug calcs in COMPRESS as if the corrosion had already reduced the vessel wall thickness. However, I want the full weight of the vessel to be used in the calcs to check everything b/c obviously I can't know the true extent of corrosion.
My thought was to "fake" it by using a wall thickness equal to the original minus the corrosion that the client has told us to expect. Then I would take the difference in weight between the original and corroded conditions and apply that as a liner with the density manipulated to make up that difference. If I'm thinking right, that would run the local stress calcs on the thin metal but the lugs would be loaded with the original/uncorroded weight. However, COMPRESS appears to force me to use a min thickness that is greater than what the approx corroded thickness is.
What do y'all think about that, sound reasonable?
Thanks for your help, have a great day and stay safe!
What I'd like to do is run lug calcs in COMPRESS as if the corrosion had already reduced the vessel wall thickness. However, I want the full weight of the vessel to be used in the calcs to check everything b/c obviously I can't know the true extent of corrosion.
My thought was to "fake" it by using a wall thickness equal to the original minus the corrosion that the client has told us to expect. Then I would take the difference in weight between the original and corroded conditions and apply that as a liner with the density manipulated to make up that difference. If I'm thinking right, that would run the local stress calcs on the thin metal but the lugs would be loaded with the original/uncorroded weight. However, COMPRESS appears to force me to use a min thickness that is greater than what the approx corroded thickness is.
What do y'all think about that, sound reasonable?
Thanks for your help, have a great day and stay safe!
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
As far as COMPRESS forcing a (nominal) thickness greater than your input, it sounds like you are using "design" mode and the input corrosion combined with the 'tr' found by ASME Code rules is greater than what you want to use. You can switch to "rating" mode or take a closer view of the report for the support lug to see if your actual condition is investigated properly without artificially ginning up the corrosion.
You could also try contacting the people at Codeware for advice on this: support@codeware.com or call them.
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
@oknow, I'm not sure I follow why the weight during hydro would be important?
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
will close the case quickly. Negligent with the design IMO.
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
FYA, Lifting lugs are normally designed for empty lift with applying certain load factors only as necessary. Designing the lifting lugs for hydro static (water filled) case would cause considerable increase in the cost, thus, equipment would be commercially inefficient.
Best Regards,
Ramil Abbaszade CEng MIMechE, MSc
Pressure Vessel, Pipe Stress and Mechanical-Piping Design Engineer
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
RE: Lifting Lug with Shell Corrosion (Codeware COMPRESS)
The role of an engineer is to use proper judgement in gathering inputs to generate safe and economical designs.
At the outset you must determine what loads are reasonable to occur simultaneously. For example, equipment is not normally designed for 1/50 year wind and 1/50 year earthquake events occurring simultaneously. ASME VIII-2 takes this into account when defining load cases in Tables 5.3, 5.4, and 5.5 for example.
Normal practice in the pressure equipment industry is to not lift a vessel when it is full of water. That is the baseline assumption that 99% of our industry will make.
That's not to say you never need to consider this case, and that comes down to using proper engineering judgement. If for example you are designing water tanks that are to be filled, transported, and unloaded while flooded, then it would make sense to design the lifting lugs for a flooded condition. This is an unusual design case however, and would need to be specified by the customer or end-user.
Cheers,
Marty