Lifting lugs impact factor/saftey factor as per J.3.8.3 of API 650

[inammanj123]

Dear ALL,

I have confusion regarding interperating J.3.8.3 of API 650.
As per my understanding in this clause API is addressing two diferent factors:
1- impact factor(each lug shall carry weight of complate equipment)
2- allowable stress shall be lesser of 0.6Xyield and tensile stress/4

please explain whether my understanding is o.k or not, because my client says that this API clause means that impact factor(each lug shall carry weight of two equipments) shall be 4 and there is nothing to do with tensile/4

regards,
Inam

 

[r6155]

Your client is correct

Regards
r6155

 

[r6155]

Example: empty weight of the tank= 10.000 kg, 4 lifting lugs.
Each lug shall be designed to support 2 x 10.000 kg/ 4 lugs = 5.000 kg

Regards
r6155

 

[IFRs]

r6155 - how do you interpret "designed to support" - designed with a safety factor, if so what factor, if not, designed to yield or fail?

 

[inammanj123]

r6155, i is understandable that one lug should be able to hold whole equipment, but from where this second equipment come, until you drop a second equipment onto the, which is not possible, there is no way one lug will be dear weight of two equipment.

In clause J3.8.3 API says that lugs should carry twice the empty weight of tank. We have considered impact factor 2, which means that the weight of tank should be considered as double of empty , which will be distributed on 02 no of lugs , which is API understanding & it does not say that each lifting lug should be capable of carrying double of empty weight of the tank. Pl. confirm the same.
After this API says that factor of safety shall be 4. It is a basic engineering principal that factor of safety is applied on the yield or tensile(to get the allowable stress). We have already indicated this in our calculation. see the value of material allowable stress in tension(lesser of 0.6Xyield and tensile stress/4)

 

[r6155]

IFRs: “Designed to support” is designed to carry their share of the applied load

inammanj123: In my example “each lug” is one (1)lug
“Lugs” in API 650 mean total quantity, 4 lugs in my example

Safety factor of 4 is tensile stress /4

Regards
r6155