How much are metal PIPES weakened by THREADS?

I can't put a figure on it, but my instinct is that the pipe will be weakened quite a lot by this joint. The threaded collar is pretty short and will therefore not offer much support when the pipe is flexed. It might fail suddenly under load if the thread is stripped, or if the iron coupler isn't ductile enough and cracks. As someone else here pointed out, a plain mild steel pipe wouldn't fail in this manner. You could strengthen the joint by using a longer threaded coupler, or even better a slightly larger mild steel pipe which is bolted to your trailer which the long mild steel pipe slots into (secure it with a pin). The most important question is how serious the consequences of a failure will be.

Hope this helps,

Chris

Iggy Your strength in part comes from wall thickness of the pipe. As you thread you reduce the wall thickness at the root of the thread and this being tapered threads your wall thickness is reduced further. I'm not sure what the stress is on this but if it a bending stress I would not rely on it. I've seen to many pipes break in the threads. lg no neat sig line

Thanks... I might do that...

I regularly use 3/4 inch pipe with PONY clamps. They are common for clamping applications in woodwork. We use them in a steel shop of pulling frames and the like into alignment. The threaded ends often fracture and twist. On my personal clamps I use one inch round bar welded to the pipe so that I have about two to three inches of bar threaded on the outside joined to the pipe. the best arrangement is to put the bar on the lathe and turn half of it down to fit inside the pipe. This makes welding easier and moves the stress point away from the weld. If you have a lathe and a pipe die you are in business. You could rough grind the bar down if you did not have a lathe. Randy