Question on "As Fit-Up" tolerances in Figure 3.3/3.4

Date 03-22-2012 10:18

That's for the actual fit up of the pieces during fabrication.
For example if the joint calls for a 1/4 RO with a 45 degree bevel, the actual RO could be 3/16" (minus 1/16") because they give you a little tolerance knowing that when building parts things aren't always exact.)

The same for the bevel angle. If 45 degrees is called for you can have on your part +10 and -5 so a 45 can range from 40 degrees to 55 on the actual piece.

The "as-detailed" is for the detailer making the drawings, they have a range they can work with on the drawings that helps the shop get the fit up where it needs to be. If the detailer took the 45 degree as called for in the joint designation, then added 10 degrees to his drawing to account for a certain fit up situation or access the drawing will say 55 degrees (45 plus the as detailed 10 allowed), now the "as fit up" can still be applied on top of that as long as the detailer took it into account on the drawing as a starting point.
Hope this helps.

By allenliao (*)

Date 03-23-2012 05:18

Hi eekpod,

If acc. to "As Detailed", the minus RO tolerance is set to be "-0", will "-1/8" in "As Fit-Up" be applicable or not?

thanks.

By eekpod

Date 03-23-2012 11:31

technically no because you are out of the variables allowed.
Having said that, it's not uncommon to have that situation and still allow the joint to be welded depending on the thickness of the material, position and skill of the individual.

Is there a specific joint designation your referring to?
I ask because a quick look at some do allow -1/8 in fit up but not all.

By allenliao (*)

Date 03-23-2012 15:28

I am studying on AWS D1.1, but feel difficult to get the key point of this standard because of experience insufficiency.

Please refer to Joint designation of "B-L1b"(for SMAW) in Figure3.4 Page 94 of D1.1 2010, for my question.

By fschweighardt (***)

Date 03-23-2012 19:16

So you get .5 x plate thickness for your beginning dimension and your root opening (basic) is 1/8.

The detailer can open it up 1/16" (to 3/16"), minimum is still 1/8

As fit-up, you can open it up to another 1/16" (to 1/4"), and in theory,go down 1/8" from where you started. If you started at 1/8" and didn't change anything at the detailer level, it seems like you would be allowed to go to a zero root opening.

By eekpod

Date 03-23-2012 19:26 Edited 03-23-2012 19:29

OK let's see here this is a CJP weld with a square groove, which means the ends of the members are left square and are not bevelled just like the picture.
Also the L means the joint is "limited" in the material thickness and in your case for SMAW the material can not be thicker than 1/4" in order to stay within the pre-qualifed limitations.
So for example lets say you are using 1/4" plate, your root opening should be T1 divided in half so that's a 1/8" RO (1/4" divided by2= 1/8")
Your shop drawings should call for this joint and the root opening should say 1/8". Now the "as detailed" tolerance is -0 so on paper your RO can't be less than 1/8". You can go +1/16" for a 3/16" maximum on paper RO.
But in reality in the shop the "as fit-up" can be -1/8", which results in no root opening. Which is OK because of the note in the tail that requires backgouging. Which means you'll need access to both sides of the joint to use this joint designation.

With 1/4" material and SMAW process your total root opening range can be;
On the shop drawings and WPS a maximum 3/16" (1/8" plus as detailed tol of 1/16") to a minimum of 1/8".
On the shop floor the actual parts can have a maximum RO of a 1/4" (3/16" + 1/16" as fit up tol) down to a 0 root opening minimum.

Be aware of the footnotes d,e,j, they always come into play as well.

Hope this helps.

Oh abd be sure to look up 3.13.1 on page 62, where it says "may be applied to the dimension shown on the detail drawings" is how the code tells you you can "add" the two tolerances together. That's very important alot of people don't always understand how that works and incorrectly work the tolerance. I did it wrong for a long time because it wasn't never expalined to me, I had to learn the hard way.