Load Rating of Overhead Davit and Hoist System

[Rich03]

We have a self-fabricated swinging davit with a small electric hoist attached to it to support loading hoses in a chemical transfer operation. Question came up regarding proper load rating. Engineering calculations have yielded differing answers. Is there an empirical way to determine safe working load? It was suggested to lift up increasing amounts of known weight until slight permanent deformation (permanent sag from horizontal) is noted, then reducing that weight by a safety factor. Would this work/is this a proper method, and if so, how does one choose a safety factor?

 

[Lutfi]

I question why engineering calculations yielded different results! If the member sizes, material grade, weld sized, simple analysis should give permissible load.

During analysis, one must use proper safety factors, and impact loading.

 

[Kishku]

Most structural engineers would be able to come up with a suitable design approach once you provide them with the configuration and functioning of the davit. You can look up Dennis R.Moss, "Pressure Vessel Design Manual", Chapter 6. Related equipment, for some guidance on Davit Design. The load rating of the electric hoist would be the start point, I guess.

The method of applying loads and observing deflections appears to be a bit crude, in these times.

 

[Ron]

It is generally accepted in many applications to load test to a safety factor of 2.0, based on the maximum anticipated working load or the rated load. If this load provides no permanent deformation or observable distress (cracked welds, flaking paint, etc.), and the deformation measurements show full recovery, then the item is considered to be be safe for use within the bounds of the test.