ok, let's say one was welding a sqaure tube, end on, to a flat plate - each sdie being a T joint.

would you expect to see the surface of hte plate below melted i.e. full penetration?

presumably just discoloured e.g.

is not good/strong enough?

[Edited on 23/3/09 by 02GF74]

Good penetration = good strength, you just need to cut right through it and measure for peace of mind

Depends on the thickness of the tube wall and the thickness of the plate but I wouldn't be happy with that. There's no penetration!!!

It depends on the relative thicknesses of the materials.

If the tube is thin (1.5mm) and the plate is thick (6mm) theres no way you will get full penetration on the plate without vapourising the tube. In this case as long as you have full penetration on the tube and the same on to the plate then thats as strong as its going to be anyway as the tube will be the weak link.

If both are quite thick, try bevelling the end of the tube first.

I assume you are making engine mounts?

David