Spacing between welds

Date 05-23-2008 05:05

When a carbon steel bracket, 6" wide and 1.5" thick is welded to SS304 pipe 3/8" thick, we would like to add a pad between bracket and pipe.
Does anyone has experience in sizing the pad which would give an indication of the spacing between the weld on bracket to the edge of the pad?
How about a pad size of 9" x 4.5"?
Is the pad size more for visual need or should the size be calculated for strength requirement?
Regards
Boon

By js55

Date 05-23-2008 13:26

Your question should be asked of yourself, and your engineering. In other words, why are you adding the pad?

By Boon

Date 05-24-2008 01:44

I understand it is not a good practice to weld carbon steel directly onto stainless steel pipe, so a pad is added. But there are others who disagree. What is the concern here with the direct weld?
Boon

By G.S.Crisi (****)

Date 05-23-2008 19:21

If the bracket is 6 inches wide and the pad is 9 inches wide, it means that there will be 1.5 inches of pad at each side of the bracket. Sounds OK for me.
What doesn't sound OK is the fact that the pad is 1.5 inches thick and the pípe is just 3/8 inches thick. This isn't good engineering practice.
Good engineering practice says that any structural plate welded to a pressure containing part (a vessel or a piping, for example) should have, as a maximum, the same thickness of the pressure containing part.
Of course, the pad should be made of the same material of the pipe.
Giovanni S. Crisi
Sao Paulo - Brazil

By Boon

Date 05-24-2008 01:39

The 1.5" thickness is for the bracket sitting on top of the pad. The pad should be about same thickness and material as the pipe. In good engineering practice should the pipe thickness be use as maximum or minimum for the pad thickness. Or should it be just the same?
Boon

By G.S.Crisi (****)

Date 05-26-2008 14:25

I'm sorry, I misunterstood your first question.
Now, having understood its right meaning, I agree with the dimensions you suggest for the pad. Good engineering practice says that the pad should not be thicker than the plate it's welded to.
It can be thinner, of course, and the thickness should be calculated.
Now, for small pads as yours, it's easier to adopt a pad of the same pipe thickenss and avoid making calculations.
Giovanni S. Crisi

By js55

Date 05-27-2008 13:46

There is nothing inherently wrong with welding SS directly to CS (or vice versa) with due consideration to metallurgical characterisitcs, proper fillers, and service requirements.