SWL's on "C" shaped pipe hooks 2

[tnteng]

Has anyone used the "C" shaped pipe hooks for lifting pipe. We have some from both Newco and Rigmaster. Newco has indicated that the SWL of the hooks is based on a sling angle of 30 deg. (included angle from horizontal). Rigmaster's SWL is based on a 45 deg. angle. Does anyone have experience with how this SWL would need to be derated if the hook is used at some other sling angle.

My findings are that the stresses on the hook will not increase if the sling angle is increased (i.e. if the pipe length is shorter). If the sling angle is decreased (longer pipe), the bending stresses in the hook would be the same but the tensile stresses would increase. Thus requiring a reduction in the SWL.

Thanks in advance for any help.

Tony Billeaud
Mechanical Engineer

 

[desertfox]

Hi tnteng

Looking at the 'c' hooks I would have thought as you change the angle of lift you alter the angle at which the force acts on the 'c' hook this in turn would alter the the bending moment on the hook and hence the stresses.
I would think to analyse this situation you would need to consider asymmetric bending on the 'c' shape and find the neutral axis after which you can find the stress distribution.

regards

desertfox

 

[vonlueke]

tnteng: I agree with your findings; I got the same thing. Extreme fiber stress on the upper leg of the C increases only slightly due to the increased tensile stress as the cable angle is decreased. However, the tensile stress on the lug eye, on the other hand, increases directly in proportion to 1/sin(theta); so, the lug eye might govern the derating (for angles less than 45 deg), in which case this would imply load_derating_factor = sin[min(45 deg, theta)]/sin(published_swl_angle), where theta = sling angle.