pvesseleng
Mechanical
Is the lifting lug calculation under the scope of B&PV code?
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Lifting Lug Calculation 1
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meteng, I respectfully disagree with your response. But I have to admit it did make me think for a bit. Then I realized just what a can of worms are opened by this simple question.
First, let's clarify if we're discussing lifting lugs or support lugs:
Support lugs (as opposed to a support skirt, legs, saddles, etc) support the vessel during operation. Thus the local stresses in the shell resulting from the support reactions must be combined with stresses resulting from pressure. These loads from the support lugs are clearly included in UG-22 as loadings to be considered when designing the vessel.
Lifting lugs, however, are intended for temporary use during construction, erection, and placement of the vessel prior to operation. Such lugs are not intended as primary structural supports during operation of the vessel (if they were they would be support lugs). And hopefully no one will try to lift and move a pressurized vessel using temporary "lifting lugs".
Lifting lugs are a temporary attachment that may be removed from the shell before operation. In this sense they are no different than any temporary clip added to facilitate handling during shop fabrication. If left on the vessel during operation then they must meet the Code material requirements for nonpressure parts, UG-4(b).
But this doesn't mean that these lugs need not be "engineered". Nope. When lifting and turning a multi-million dollar tower there had better have been some sophisticated analysis done on every component of the lifting apparatus to ensure life safety and protection of the equipment.
The design of lifting lugs is so general and there are many failure modes to be considered (stresses in shell, shear in the lifting pin, bending in the pin, shear pull-out in the lug, bending of the lug, tension and buckling of the lug, etc) that this is best left for another discussion. (I hope there is some, because I'd like to learn more)
First, let's clarify if we're discussing lifting lugs or support lugs:
Support lugs (as opposed to a support skirt, legs, saddles, etc) support the vessel during operation. Thus the local stresses in the shell resulting from the support reactions must be combined with stresses resulting from pressure. These loads from the support lugs are clearly included in UG-22 as loadings to be considered when designing the vessel.
Lifting lugs, however, are intended for temporary use during construction, erection, and placement of the vessel prior to operation. Such lugs are not intended as primary structural supports during operation of the vessel (if they were they would be support lugs). And hopefully no one will try to lift and move a pressurized vessel using temporary "lifting lugs".
Lifting lugs are a temporary attachment that may be removed from the shell before operation. In this sense they are no different than any temporary clip added to facilitate handling during shop fabrication. If left on the vessel during operation then they must meet the Code material requirements for nonpressure parts, UG-4(b).
But this doesn't mean that these lugs need not be "engineered". Nope. When lifting and turning a multi-million dollar tower there had better have been some sophisticated analysis done on every component of the lifting apparatus to ensure life safety and protection of the equipment.
The design of lifting lugs is so general and there are many failure modes to be considered (stresses in shell, shear in the lifting pin, bending in the pin, shear pull-out in the lug, bending of the lug, tension and buckling of the lug, etc) that this is best left for another discussion. (I hope there is some, because I'd like to learn more)
Tombarsch;
I took the original post as a permanent lifting lug design that would remove a bolted head like on an HP feedwater heater or other type of pressure vessel once placed in service. It is not TEMPORARY. If a temporary lifting lug is used during assembly or erection this is a different matter, I agree with your post. However, any welding of temporary lifting lugs needs to be performed by an ASME or NB stamp holder and must be approved by the AI.
I took the original post as a permanent lifting lug design that would remove a bolted head like on an HP feedwater heater or other type of pressure vessel once placed in service. It is not TEMPORARY. If a temporary lifting lug is used during assembly or erection this is a different matter, I agree with your post. However, any welding of temporary lifting lugs needs to be performed by an ASME or NB stamp holder and must be approved by the AI.
You are correct, the "temporary" nature has nothing to do with this. There are millions of blind flange davits out there permanently attached to the vessel and blind flange. However, they only carry load when the blind flange is removed...and the vessel is not in operation. Again, this load condition is outside the scope of ASME B&PV Code, except that materials welded to the pressure components must meet UG-4(b).
Most vessel owners will expect some calculations for this sort of attachment that is structural in nature but not covered under ASME P&PV Code, unless the attachment is built per their own standard specifications.
So, is "lifting lug calculation under the scope of B&PV code?"...only insofar as that the material, if permanently attached, has to meet UG-4(b). But stress/strength calculations are not under scope of this Code.
Most vessel owners will expect some calculations for this sort of attachment that is structural in nature but not covered under ASME P&PV Code, unless the attachment is built per their own standard specifications.
So, is "lifting lug calculation under the scope of B&PV code?"...only insofar as that the material, if permanently attached, has to meet UG-4(b). But stress/strength calculations are not under scope of this Code.
waskillywabbit
Mechanical
I agree...I think a great deal of the confusion lies in the term "lug" and the difference between a "support lug" and a "lifting lug". UG-22 mentions "vessel supports such as lugs" so I can see the reason for the confusion as I had to go get my UG-22 sheet and read it again.
Brian
Pressure Vessels and Autoclave Systems
The above comments/opinions are solely my own and not those of McAbee Construction.
Brian
Pressure Vessels and Autoclave Systems
The above comments/opinions are solely my own and not those of McAbee Construction.
davidribeiro
Mechanical
We normally call up standard lifting lugs according to DIN 28082. What is important though is that the stresses induced during lifting do not exceed the allowable stresses of the shell times 1,5. A WRC 107 analysis should suffice for this.
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