Consumed Tack Welds 1

[Nubcakes]

My shop doesn't want to inspect their tack welds anymore, so they want to prove that they are consumed in the final weld. I assume they'll be using some sort of macro etch to do so. It's a section 8 shop, but I found some section 4 and section 3 interpretations that say this is allowed, so I am at least considering it. My question is, can I really trust that these tacks are consumed in all cases? I see a considerable variance in size from day to day and person to person. Anybody have experience with something like this?

 

[metengr]

Have you read Section VIII, Div 1, see below

2017 Edition, Section VIII, Div 1
UW-31 CUTTING, FITTING, AND ALIGNMENT
(a) When plates are shaped by oxygen or arc cutting,
the edges to be welded shall be uniform and smooth
and shall be freed of all loose scale and slag accumulations
before welding (see UG-76 and UCS-5).
(b) Plates that are being welded shall be fitted, aligned,
and retained in position during the welding operation.
(c) Bars, jacks, clamps, tack welds, or other appropriate
means may be used to hold the edges of parts in alignment.
Tack welds used to secure alignment shall either
be removed completely when they have served their purpose,
or their stopping and starting ends shall be properly
prepared by grinding or other suitable means so that they
may be satisfactorily incorporated into the final weld.
Tack welds, whether removed or left in place, shall be
made using a fillet weld or butt weld procedure qualified
in accordance with Section IX. Tack welds to be left in
place shall be made by welders qualified in accordance
with Section IX, and shall be examined visually for defects,
and if found to be defective shall be removed.
Provided that the work is done under the provisions of
U-2(b), it is not necessary that a subcontractor making
such tack welds for a vessel or parts manufacturer be a
holder of a Code Certificate of Authorization. The requirements
of UW-26(d) do not apply to such tack welds.

 

[Nubcakes]

The tack welds are being made by qualified ASME welders. The issue is not that the welds are being made by contractors, but that they don't want to inspect them, and to justify that by "proving" that the tacks are consumed.

 

[Mr168]

I find it pretty process dependent. Small tacks made with GTAW are usually consumed by SAW/FCAW. Any of the flux bearing processes I've only seen SAW reliably consume, likely due to the size of the tack itself. I should note that this isn't for vessel fab, but is my experience based on UT sampling of welds for structural plate fab. No 100% guarantees on any of it, and not worth the risk of rework for our organization, who typically deals with out of position welding and smaller wire diameters.

If the issue isn't so much performing the step as it is having to document the inspection, consider making grinding/feathering of the tack a standard work process to be performed and verified by the welder, and work that into your shop manual/quality program.

 

[metengr]

If the tack welds are consumed they are removed. Nothing more needs to be done. Inspections only apply if they are left in place.

 

[david339933]

Metenger: not a statement I was expecting.

I read the excerpt from UW-31 as the tack welds left in place are to be incorporated into the weld (consumed).

 

[metengr]

david339933
I checked and could not find any specific interpretation on the above regarding tack welds consumed. I looked at "left in place" like welds used for alignment bars, clamps etc., not tack welds used in the weld joint itself (root) to temp hold items. I would still perform a visual to ensure no cracks, but the Code does not require it, specifically.

 

[DekDee]

Just my 2 cents worth on UW-31.
If you weld up to a tack and stop before reaching the tack then the tack has served it purpose and can be completely ground out (removed)and welding continues over the previously tacked area.
or
Leave the tack in place, feather both ends of the tack and then weld into and out of the tack - the tack has then been "incorporated" into the final weld.
IMHO, this is what UW 31 is describing as "left in place" - visual inspection should be done. (as metengr stated "What about possibly cracked tacks left in the weld")

Again, IMHO the only process that can guarantee complete consumption of a tack would be SAW due to it's deep penetration characteristics.

As I tried to impress on students many years ago - if you start welding with a lump on your first run (welding over an unground or unconsumed tack) the lump will be evident in every subsequent run. Either remove the tack or tie-in to the tack.

 

[david339933]

Agreed DekDee.
I read UW-31 as stating tack welds must be removed or incorporated. I see nothing allowing tack welds to be left in place, other than to be incorporated in the weld.

 

[oknow]

I understand UW-31 as written. In addition there always seems to be a crack in a Certificate Holders Quality System on what instruction/document or who determines if the tack weld is left in place or removed. It may be noted in the drawing, WPS or on the Traveler/Checklist but has to be resolved because UW-37 indicates every welder who is involved in welding that particular weld (including tack when not removed) must be identified.