Lifting Lugs with Vessel Corrosion 1

[ColinPearson]

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!

 

[r6155]

In order not to waste time, ask your customer for the manufacturer's original calculations. Also the current thickness measurement report.
Is vertical or horizontal vessel?

Regards

 

[JStephen]

In a lot of cases, corrosion will be non-uniform, so if they didn't check right around the lifting lugs, you may find conditions there better or worse than the "average" conditions.
Check the approach used for local stresses in the vessel. Bednar has an approach for line loads on a vessel, if that is what is used, it's also quick and simple to do by hand.
In a lot of cases, the weight distribution won't much matter for lifting lug analysis, just the total weight.

 

[ColinPearson]

@r6155 : Probably not available to us as we are bidding the work but don't have it yet. Vessel will ship horizontally but will be installed vertically.
@JStephen : If we get this work, we will definitely UT the lug locations. I'll check Bednar for sure.

Thanks folks!

 

[r6155]

The client is responsible for supplying the information that you request.

Be careful If the inspection is included in the scope of work. A complete inspection plan is required before transportation and erection. After erection some examinations are required.

Good information in “Pressure Vessel Design Manual” 4th edition, by Dennis Moss

Regards

 

[ColinPearson]

@r1655: Agreed that they need to provide information to contractors, but as we don't have the work awarded yet, they're not really our client yet. I think that info would become available if we get the job so we can review/finalize any early plans before any actual work happens. Depending on whether they can produce an R2 regarding an apparent re-rating they have done on the vessel, the inspection required may vary quite a bit (obviously much more if we need to run the code calcs and produce an R2 capturing the previous re-rate, which I think we'd have to do before completing our work which would fall under and R1). It was originally hydro'd in the shop, and my understanding is that in the state of WA, we would need State and AI approval to perform NDE in lieu of hydro. And if we are going to wind up responsible for the R2, then since it had originally had no RT required, we'd be RTing all round seams and verts. Definitely keeping an eye on the inspection side, it's going to get hairy on this one. Thank again for your feedback!

 

[SnTMan]

However, COMPRESS appears to force me to use a min thickness that is greater than what the approx corroded thickness is.

Downside to "expert systems". I'm not a COMPRESS guy, I don't know how to properly lie to it. I'd suggest tech support.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[ColinPearson]

@SnTMan almost literally laughed out loud at that! Definitely a good skill to know how to lie to your software sometimes!

 

[SnTMan]

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[MJCronin]

You know that for any vessel it is probably possible to either:

1) Add additional lifting lugs, perform an analysis using a lift with additional points of support

2) Remove the existing lugs, grind smooth and replace them with a large rolled plate, weld the plate all around and install new lifting lugs

3) Consider robust plate reinforced lifting trunions

Share more information with us ...

More information = better answers

Post drawings/sketches of the lugs, outline drawings of the vessel

Also, how about pictures ???

MJCronin
Sr. Process Engineer

 

Definitely a good skill to know how to lie to your software sometimes!

Why not, software lies to us all the time.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[ColinPearson]

@MJCronin: all the things you suggest I would agree with. I like trunnions myself for most heavy lifts (well, semi-heavy; like 100k# to 500k#). No existing lugs to remove but I would remove them if they were there and start with new ones anyway. Rolled plate is definitely a good reinforcement option, but in this case, I was just trying to get comfy with a prelim lug design before my COMPRESS dies next week. The IT Dept assures is that when we roll to the new version this coming week, everything will be seamless BUT I’ve learned to never believe IT! I am 100% not worried about the actual lift; this post was mostly an attempt to find out if I could persuade COMPRESS to do what I wanted it to do. Thank you for taking the time for such good suggestions though, like I said, I really do agree with all of them. Cheers!

 

[0707]

Lifting lugs in a vessel is the point where all of the shit is accumulated in a refinery, cans, bottles, trash and sometimes shit in the real sense of the word. If not periodically cleaned, these are points for corrosion to develop. Another important point is the water accumulated during the raining station. Normally designers forgot the drainage of the lugs and when one needs to remove the tower or the vessel for some reason, they discover that the lugs are corroded and need to be recalculated to see if they withstand the lifting for removal.

luis

 

[ColinPearson]

@0707 Agreed. I always have the field remove lugs/trunnions that I've designed. I don't need some yahoo coming behind me in 15 years trying to lift the whole vessel using my lugs/trunnions when I only replaced the head...

 

[r6155]

Try to avoid lifting lugs / trunnions, especially for heavy weight pressure vessel: use nozzles if possible.

Regards