Where should i put the weld to the top of the pipe or to the bottom? 2

[mrcasper]

I need to join a 19feet 8" pipe to another piece of 8"pipe. The pipe is to be vertical with at least 15ft in the water.
It is being used for geotechnical survey.
I am only getting 19ft lengths and i need a total length of 23ft.

The pole would be subjected to drag force due to water. The lower horizontal snub would form a pivot.

Should i weld the pipes together at the top A above the water or below the water at B. Please see attached image.

 

[metengr]

At the top A.

 

[mrcasper]

Thank You for your quick response.

Why are we putting it at A as opposed to B? This is my trend of thought, the pole would be subjected to a bending moment about the fulcrum/pivot.
By putting the weld close to the bottom, am I minimizing the chance that the pole would break at this point?

 

[metengr]

Why introduce a weld at a location where you have exposure to corrosion from immersion in water + bending loads.

 

[mrcasper]

Good point.

The pole would be in the water for roughly 6 weeks and would be painted, so corrosion should be minimal

With respect to the bending loads, won't it be subjected at more bending load at A rather than at B?

 

[kingnero]

That shouldn't matter: a full-pen weld, well executed, is at least as strong as the base material. Assuming normal steel, the weld won't form a "weak spot" (HAZ with reduced properties) in the pole nor a (much) higher risk of fatigue cracking.

 

[mrcasper]

Thank You Gentlemen, you have put my mind at ease

 

[SnTMan]

Might not matter much but you could pre-fab the top part before joining to the lower. Might make for a little easier handling.

Regards,

Mike

 

[gtaw]

You might find it a mite tricky welding the pipe underwater.

Sorry, I couldn't resist poking this one with a sharp stick.

Best regards - Al