Mechanical Strength of Black Iron Pipe

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Discussion Overview

The discussion revolves around the mechanical strength of black iron pipes, specifically focusing on the bending torque required for failure when connecting different sizes of pipes using couplings and reducers. The context includes practical applications and considerations for load-bearing scenarios.

Discussion Character

  • Technical explanation
  • Experimental/applied
  • Debate/contested

Main Points Raised

  • One participant inquires about the bending torque needed before failure when applying a load to a 1 ¼” black iron pipe connected to a 1 ½” pipe.
  • Another participant suggests that the threaded ends of the pipes may be the weak point and emphasizes that black iron pipe is not designed for structural use, recommending load tests.
  • A later reply discusses the specific application of the pipe for a tip-over mast in a rural area, noting that the risk of injury is minimal and suggesting a modification to use solid round stock for added stiffness.
  • One participant proposes that a mechanical engineer could accurately calculate the strength of the pipe and mentions the possibility of using computer simulations for analysis.

Areas of Agreement / Disagreement

Participants express differing views on the adequacy of black iron pipe for structural applications, with some cautioning against its use while others suggest modifications to improve its strength. No consensus is reached on the exact bending torque or failure points.

Contextual Notes

Participants mention the lack of specific mechanical strength specifications for black iron pipe and the need for empirical testing to determine load limits. The discussion includes considerations of safety and structural integrity in practical applications.

autek
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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.
 
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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.
 
pantaz said:
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.
 
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.
 

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