Mechanical Strength of Black Iron Pipe

[autek]

If you were to mate a 1 ½” black iron pipe to a 1 ¼” black iron pipe using a 1 ½” coupling and a bushing reducer, how much bending torque would be needed before one of the parts or connections failed? That is, if you held the 1 ½” black iron pipe in a fixed position and the applied a force to the end of a length of 1 ¼” black iron pipe how large could the load be before failure. In my case I want to apply a load 8 pounds at the end of 20 feet. I have looked on the web and in my copy of Marks but did not find much on the mechanical strength of black iron pipe.

 

[pantaz]

I don't have any specs, but the threaded ends are going to be your weak point. Also, since that type of pipe is not designed for structural use, you'll probably have to perform your own load tests. I would not use it for anything critical, or anything that may cause injury upon failure.
Just guessing, but I'd expect some major deflection even before hanging eight pounds off of it.

 

[autek]

I don't have any specs, but the threaded ends are going to be your weak point. Also, since that type of pipe is not designed for structural use, you'll probably have to perform your own load tests. I would not use it for anything critical, or anything that may cause injury upon failure.
Just guessing, but I'd expect some major deflection even before hanging eight pounds off of it.

It would be for a tip-over mast for some WX instrumentation in a very rural area away from people and buildings so there is not much risk for injury. In addition the bending moment would be at its worst only when moving it to the horizontal position. The cross sectional area of the instrumentation is not very large so there would not be much torque due to wind loading in the normal upright position. Actually, after talking it over with another person it appears that a better way would be to replace the 1 1/4" pipe with solid 1 3/8” round stock that you could slide several feet into the 1 1/4" pipe which would stiffen the pipe as well as avoid the threads. Based on your comments however, I would also test it with incremental loads first to check the deflection and shorten it some if need be. The 20 foot length is not set in stone. Thanks for taking the time to reply.

 

[FeX32]

Its strength can ba accurately calculated by a mechanical engineer. Since it is a simple connected pipe analytical formulations are possible. Computer simulations are also a possible solution.