Holes in 1st layer of weldment

[Nashanas]

Hello everyone,

In the multi-pass welding process (1st layer FCAW, 2-6 layers SAW), if the 1st layer is made using FCAW, and in this layer there are 2 or 3 holes of 3mm diameter. Should these holes be repaired before performing the 2nd pass which will be with SAW? Or the subsequent layers will actually cover the holes and it will have no effect on the welded structure?

In my opinion the holes should be repaired before subsequent welding otherwise they might become subsurface cracks. But my welder who has much more field experience than me told me that these small defects can be accepted because the layers on tops of it will tap it and will cause no structural flaw. Is there any consturction code which can be used to quantify the size of acceptable defects in the first layer of a multi layer welding process?

 

[kingnero]

FCAW shouldn't have any porosities, so where do they come from? Is this FCAW-G or FCAW-S? oil/paint/coolant/... anywhere? Stick-out OK?
What does your experienced welder has to say about the holes?
If you grind away the surface porosities (that's what I assume they are), do you find new ones (sub-surface)?

I agree that SAW will likely remelt quite a bit of the previous pass, but that's not the correct way to deal with defects.

 

[Nashanas]

Its a FCAW-G process. He is unable to answer about origin of the porosity. Since the work load is too much, they refused to grind away the surface and said that the subsequent process will cover it up. I dont like this approach, but before stopping production and eventually causing even higher workload in future. I want to be certain that this process is wrong (or right) either according to a certain construction code or a certain inspection procedure.

 

[kingnero]

Codes don't address interpass hold points/acceptance criteria, they only define the final result.
Is the final result OK? Preferably using RT, as UT won't pick up the smallest of porosities.
VT, PT and MT are basically useless for internal defects.

 

[Nashanas]

Final result is acceptable by VT and PT. The client has not asked for RT or UT so from production perspective, the product is fine. I am worried about the prestige of comapny in the long run. If the product fails the cost will be very high both on economy and prestige.

 

[kingnero]

I believe you just answered your own question.

 

[EdStainless]

I would expect that these would be mostly ground out in the interpass cleaning procedure. As long as they don't leave slag pockets or something like that then they are probably fine.

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P.E. Metallurgy, consulting work welcomed

 

In my opinion the holes should be repaired before subsequent welding otherwise they might become subsurface cracks.

'Go directly to Jail, do not pass Go, do not collect $200'. If you are expecting the subsequent pass to repair the previous pass, you shouldn't be a welder and you shouldn't be attempting welding engineering.

We are not here to remotely diagnose your weld issues. I'll just say that excessive porosity is always a contamination issue. You troubleshoot porosity by starting at the gas bottle, checking one and only one possible source at a time.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[weldstan]

I've seen this type of porosity lead to wormhole porosity in the past in similarly made welds.

 

[mfgenggear]

the best repair is prevention, I agree with ironic metallurgist. trying to repair defects with a weld is going into the rabbit hole. these type of defects have to be drilled or machined out.

 

[kingnero]

I'll just say that excessive porosity is always a contamination issue.

*ahum, ahum* stick-out for FCAW!

I've seen this type of porosity lead to wormhole porosity in the past in similarly made welds.

Yup. Here's a FCAW example.

 

[TugboatEng]

We had a case involving ceramic tape welding and dual shield. The tape was applied the night before and got wet during the morning before welding. The weld had holes clear through the slag. The welders kept going and laid down about 40 feet of bead. At the end of the day, there was much discussion about what to do. It took 2 laborers half a day with 7 inch grinders to remove the bad weld. It took several management level positions $$$ a full day to make that decision.

There is a wide range of performance when it comes to grinding wheels. Make the right selection and you can more than halve the time required on a project.

 

[kingnero]

^^^ but hey, as long as VT and PT is OK, who cares? Volumetric inspection isn't asked for anywayz...

 

[abangbikerz]

The porosity shall be grind of before subsequent weld passes, that is of course the textbook way of dealing with weld defect. However i doubt that properly design equipment will fail just because of very minor porosity left in the weldment. Even most codes will tolerate some porosity/slag to a certain degree. If that equipment fail just because some minor defect, i guess the design itself is problematic.