LIFTING LUG REPAD 1

[rockyvud]

Hello.
We had a problem when compress was showing error to lift the vessel(30,000 lbs) because the shell (3/8" thick)was weak. So we are using repad with lifting lug.
I need the formula to calculate shell thickness required to make sure the shell is good when lifted. Please help. Thank you.

 

[ash008]

Hi rocky,

There are no formula to find shell thickness while lifting, but u can go for calculation based on external pressure taking the lifting weight(conver it to pressure) as external pressure.

Moreover addition of repads doesnot provide strength to ur vessel.

 

[arto]

Look in Bednar PV Des Hdbk Ch 7 for local stresses @ shell & pad

 

[LSThill]

TEAM MEMBERS

DENNIS MOSS PRESSURE VESSEL DESIGN MANUAL
PAGE 418 and 419

L S THILL

 

[rockyvud]

I appreciate all the replies.
In reply to ash008 i want to double check if there is no formula to find shell thickness while lifting.
Also according to ash i can go for calcuation based on external pressure- what i understand is that external force is compression force on shell and when lifting using lifting lug it is tensile or outward away from the shell. So if tensile is considered can i just calculate pressure on the repad (P=weight of vessel/Area of pad) and find out thickness required of shell using the formula: P(r)/[S(J.E.)-0.6(P). And if the required thickness is less than actual shell thickness then design is good? Please help. Thank you.

 

[rockyvud]

Also i have checked DENNIS MOSS PRESSURE VESSEL DESIGN MANUAL PAGE 418 and 419, it does not talk about shell thickness but only about lug and weld. Thank you.

 

[doct9960]

rockyvud,
If you've never done a rigging/lifting/local stress analysis before, I strongly recommend you seek the help of an experienced vessel engineer. Serious consequences like the loss of lives could happen if your vessel or lugs fail during lift.

ash008,
Wow!!! Where did you get the idea that you can convert lifting weight to external pressure and that repads won't help?

 

[TomBarsh]

COMPRESS uses the WRC-107 bulletin to analyze stresses in the shell at the lifting lug (or EN 13445 for tailing lug on skirt). The bulletin is equally applicable for lifting or operating conditions since it does not consider pressure (of course, if you analyze for the operating condition you need to account for the additional stresses due to pressure, which COMPRESS does); it is simply a method to determine stresses in the shell due to some applied loads. So, the only formula you need to know is to be familiar with WRC bulletin 107.

Ditto to doct9960's comments.

 

[TomBarsh]

By the way, Keith Escoe's new book (just published) "Pressure Vessel and Stacks Field Repair Manual", contains some great information on lifting, etc.

His book "Mechanical Design of Process Systems", Volume 2, also has a very good chapter on design of lifting devices. This is out of print but may be in many design offices or might be found in a used book store.

 

[chicopee]

I am not sure how you are lifting the vessel; however, if you intend to lift it horizontally with a double leg sling, the vessel upper portion will probably be under compression depending on the placement of the lifting lugs, therefore, use a spreader bar to eliminate the compressive force. As far as the lifting lug stress analysis in the vessel use Bednar as suggested above.