welding in casting material

[Mous1747]

what will happen if you weld on a casting material that already has a porosity? can you still have a good weld joint even if the parent material has porosity in it?

Thanks all in advance

 

[EdStainless]

It depends on the alloy, but this is done in many materials.
To start with you must grind out all of the porosity. Until a penertrant check comes out clean.
Then you can weld to rebuild the material (provided that the customer allows it)
In some materials you must follow with a heat treatment.

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P.E. Metallurgy, Plymouth Tube

 

[Tmoose]

I think much more info is needed up front, starting with, but not limited to the "casting material" and beaucoup pictures of the porosity defects in question.
Is the requirement a cosmetic repair, sealing against through-the-wall leakage, or a structurally sound repair?

Do I interpret correctly that your intended weld repair is "autogenously" welding (simply remelting) the area that is porous?
Generally serious weld repairs require excavating the bad stuff.

A nice high chrome abrasion resistant iron may crack happily if nearly any weld repair is attempted.

Fancy cast irons reverse Alchemically turn into Lesser csst irons when welded, often with a return to such poor ductility that HAZ cracking is likely to result unless stretchy bronze fillers or expensive, stretchy nickel based fillers and heroic measures to reduce thermal stresses upon cooling are practiced.

 

[metengr]

As always, general questions with blanket answers do not always apply. Porosity can be local or scattered throughout a casting. If a casting meets the acceptance criteria for intended service and a repair is required. Yes, you can repair by removing the porosity locally and depositing sound weld metal. The key is the porosity must be removed before weld repair, otherwise the repair weld can contain porosity.

 

[Mous1747]

sorry for not providing enough info in my original post. the material is A352 LCC. there's no weld repair involved in this scenario. this is a new fitting that will be welded on a pipeline.
i don't trust the chinese supplier he did any PT or MT to the beveled weld end at least, and the part was dropped shipped to the location where it will be welded.
what are the chances the new weld will come out good in the event there's invisible porosity in the beveled weld end of the fitting? full penetration will be an issue i suppose?

 

[metengr]

Perform a PT or wet fluorescent MT of the prepared weld prep on the casting as a sanity check, and if acceptable, the subsequent weld should be fine.

 

[EdStainless]

Don't weld over porosity or you will get voids in the weld.
Inspect them and just use the good ones.

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P.E. Metallurgy, Plymouth Tube

 

[Tmoose]

ASTM A352 has a section on acceptable weld repairs. They vary according to Grade ( LCC in your case) . "Repairs shall be made using procedures and welders in accordance with Practice A 488/A 488M."

 

[geesamand]

If you grind a casting until “all” “porosity” is eliminated, you probably won’t have a part left.

 

[tbuelna]

what are the chances the new weld will come out good in the event there's invisible porosity in the beveled weld end of the fitting?

By "invisible porosity", I'm assuming you mean subsurface porosity with no visible surface indications? If so, you'll need an NDI process capable of detecting subsurface defects (like mag particle) to determine if any exist near the prepared surfaces for your bevel weld. You can always perform a post-weld NDI to locate any discontinuities beyond acceptable limits. But it would seem better to find any defects in the valve material before welding when it is much easier to fix them.

 

[weldstan]

Subsurface casting flaws are not uncommon adjacent to the weld bevel. If you are unsure of the quality of your castings, perform a UT scan of the area in addition to the MT recommended by metengr prior to welding.

 

[gtaw]

I did some work for an aerospace manufacturer that included a statement in the NDE acceptance standard that stated the weld only had to meet the acceptance standard imposed on the base metal.

It makes sense, why should a weld be subjected to acceptance criteria that is more stringent than that of the base metal? Demanding a weld that is "free of porosity" while the casting being welded is permitted to contain porosity makes little sense. If the casting containing porosity will provide acceptable service, a weld containing the same amount/size of porosity should provide the same level of service.

Best regards - Al

 

[Tmoose]

What welding process?

Some SMAW electrodes are inherently slower "freezing." Welding techniques that slow the travel speed allow time for gas bubbles to boil out of the molten weld before it freezes.

http://www.lincolnelectric.com/en-u...to/Pages/high-quality-stick-welds-detail.aspx

 

[EdStainless]

gtaw, often repairs are tested more carefully because you know that there is a defect there, and in doing the prep and weld repair you have made it larger.
The real question is should you repair it at all. If it isn't part of a critical load path, or doesn't cause leakage then maybe leaving it is the best approach. We used to face this issue with pump parts. People wanted them to look better, but for durability reasons leaving visible defects was often the best choice.

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P.E. Metallurgy, Plymouth Tube