WRC 107 Analysis for Attachments to Vessels using CodeCalc

[KLee777]

Hi again all,

Thank you for being so helpful in my previous posts. Please pardon the elementary questions, but I am a new engineer (surely you remember what that was like??). No need to worry, all designs are checked...twice.

Now I need to take a look at how the lifting lugs will act on the vessel wall. I have four different vessels, so I won't mention specific thicknesses here. I guess what it boils down to is that I'm looking for is a clarification of the WRC 107 sign convention.

Specifics:
1) I am using CodeCalc for the WRC 107 analysis.
2) I am lifting a horizontal vessel straight up only (2 cranes), and the customer wants lugs, not straps at the saddles.
3) I have two ear-type lugs on top of the vessel with repads.

Here's my question: To determine the stresses caused due to "pullout," how to I enter the loads into CodeCalc? Do I enter the load as a "pressure" load (P) in the negative direction? I'm basing this on the same convention that's used to determine pressure loads (pulling) on a nozzle.

Once this is done (and assuming I'm doing this right), if my stresses between the repad and vessel wall are too high, what's the best way to get them to come down (besides increasing repad thickness & size)?

As always, I'd appreciate any advice.

KLee777

 

[jproj]

KLee777:

The "pull out" stress is a Radial force (the "P" designation is correct). From the CodeCalc manual...

RADIAL LOAD-
Enter the value for the load which is trying to push or pull the nozzle in/out of the vessel. Positive loads try to "push" the nozzle while negative loads try to "pull" the nozzle. The program does not account for the effect of pressure thrust.

With regards to decreasing stress, I normally run nozzle loads and haven't done lugs, but for nozzles you can increase the repad size / thickness, increase the nozzle thickness, or increase the shell thickness.

jproj

 

[codeeng]

The sign convention is negative for a outward radial load (-Pr). WRC is not very accurate on rectangular attachments as the length is limited to 4 times width (thickness). You'd be much better off using FEA such as NozzlePro. Another way to reduce loads is to increase to 4 lugs. Because Code stresses are typically higher than allowable lifting stresses you should apply an appropriate impact factor.

 

[KLee777]

Thanks for your help. I've come to realize CodeCalc is very limited in some areas, but for now it's all I've got. It will apparently only perform FEA calcs for round attachments.

As for decreasing the stresses, I am ending up with this HUGE repad for this tiny little ear lug. Hm. Something isn't right, I agree with codeeng as to the accuracy of WRC for rectangular attachments. I *could* do this by hand, but where do I begin? (I've got lots of books--Megyesy, Moss 3rd ed., Roark's, Blodgett...just don't have time to dig through them all right now.)

I DO have an impact factor of 1.33 in there. Also have each lug bearing 1.5 x's the vessel weight. Results in much bigger lugs than really necessary, but I'd rather overdesign and NOT have us responsible for dropping a vessel. These calcs have to be checked anyway.

Thanks again....I'll get it one way or the other.

 

[waskillywabbit]

I use Codecalc very frequently and have found it very in line w/ accepted standards for lifting lugs/ears. A good place to start is Megyesy's PV Handbook for an idea of what size lug you need then plug it into the Codecalc Lifting Lug portion of the program to see the lug actually works, then do the WRC-107. If you are getting some ridiculous needed thickness and repad size you've probably got a convention/input wrong somewhere.

Try taking a previous set of correct calculations for lifting lugs/repads/WRC-107 and backtracking as the output for Codecalc is very helpful.

CodeCalc is a great program compared to others I've used.

Brian

 

[mechsurd]

why dont you send me your data and have me look at the situations. dont worry i wont charge you nothing.i have lots of time to kill