welding to frame

[Henry Ford]

1990 F250 4x4 5spd, 351

I have seen the rails for dump boxes welded to the frame. I recently bought a truck with a steel plate welded to the frame, a farmer style fifth wheel of sorts. It basically extends crosswise across the frame, welded on both sides with a 2 inch ball hitch through the bed of the truck. The plate is about a five eighths of an inch thick or more, about eight inches wide and the breadth of the frame.
Is this ok to do? It looks like a good job. Would the heat from the welding weaken the frame as to be an issue?
The frame is in good condition.
I have been pulled over and into inspection stations before as part of the usual blitzkrieg traffic campaigns to know enough where to look for weak points on the frame. In any case, I would like to install a proper fifth wheel that I can remove.
Any ideas on the matter would be greatly appreciated.

[taisa899]

your frame should be ok. When welding thin steel the heat is lower

[shelbyx1]

just check for small cracks beside the welds(this would indicate the metal was overheated)and if you remove it grind it down abit and insp for porous welds ,and don't forget to cover with a good rust paint after.

[lynger]

I had a whole new section of frame welded into my truck...if it's done right it shouldn't be a problem.