On brackets fabricated from 304L SS, rust is appearing on the weld metal only (not the base metal) after about a month in the shop. The welds are fillet welds made using TIG with 308L filler.
I would appreciate comments from anyone who has encountered this problem, or who can suggest solutions.
Thanks for your help.
I would first check out your cleaning methods. Were only stainless steel brushes/tools used during fabrication. If so, were they ever used on carbon steel before?
That was my first thought too, but I was assured by the welder that they use separate tools for cleaning stainless
First let me understand your question clearly. Have you checked all your welds exactly and you’ve found just rust on your welds?
I’ve asked this because as Groberts mentioned maybe you didn’t clean your welds by a stainless steel brush and if so, there must be some rust on base metal even in a very narrow zone and near the weld toe. But if rust is just on weld metal, you should doubt your filler.
Have you ever welded an E6013 electrode on a stainless steel plate? In this case weld metal appears like a stainless steel.
The rust was just on the weld. If the weld was cleaned with contaminated tools, then there should be a fairly wide band of rust, but this was not the case.
My second thought was that the filler metal may be the problem. I asked the question because I was wondering if anyone else had had a similar problem that was found to be caused by poor quality weld metal.
If your rust is all truly just on the weld metal, the weld metal itelf would indeed be suspect. However, you would have to have pretty bad weld metal to get rust in a shop environment. Since the chrome level for 308 is 18-21, it would have to be seriously off to rust since stainless steel is considered to be containing 11% Chrome or more. As George pointed out, if you used a carbon steel electrode and get 30% dilution from the base metal, the deposit would be only 5.4 % Cr assuming 18% Cr in the base metal. To get down to 11% Cr, the filler would have to have only 9.3% Cr, almost half of the required level. This could probably only happen if the manufacturer used the wrong core wire or some major screw up like that. The easy way to check would be to deposit an all weld metal pad and have it analyzed at a lab for correct chemical analysis.
Actually the "easiest" way to determine chemistry for bare wire is to do chemical analysis of the bare wire itself instead of welding a weld pad. When we procure welding material, we always specify chemical analysis of the bare wire for solid wires.
Marty
You're right, I'm more used to SMAW or FCAW chem checks, so I forget about that. It's probably best though to check with the lab and see what equipment they have. They may not have equipment for one method or the other.
Hi
Also a potential problem would be the lack of pickling and passivating. In this case, you would also typically have corrosion problems in the HAZ.
Regards
Niekie Jooste
It’s been my experience that there can be two pretty common reasons for a 300 series weld to exhibit rusting such as described and one not so common.
One as already stated would be that the wrong filler or out-of-spec filler was used but I’ve only experienced this a few times in many years.
The second and most common reason I’ve found is that the weld was held at an elevated temperature too long. Period! Too high of a welding current could have been used initially in relation to a slow speed of travel. The welder could have “wash-passed” the weld once or twice without adding filler and this is just about a guarantee to promote rusting.
I’ve observed welders time and time again making (free-hand) GTAW butt welds on both 308L and 316L where the fabrications were left laying outside overnight and just the dew alone causing rusting to appear on the weld’s surfaces literally overnight!
The investigated and subsequently proven cause- OVERHEATING during welding!
Seldom will you see this condition on a properly applied “cup-walked” weld.
The third cause (about as common to find as out-of-spec filler) can stem from using a CO2 contaminated cylinder of argon. This can happen when somebody uses a cylinder of CO2 and argon and mixes their own gas for a semi-automatic process without backflow prevention. The argon cylinder always runs out before the CO2 cylinder so CO2 is allowed to enter the argon cylinder. The argon cylinder is returned for refill and is not evacuated correctly or completely prior to refill. The cylinder’s next stop could be at a GTAW job where SS is being welded. The welds somehow turn out strangely discolored or dirty looking and though the welder wire-wheels the discoloration off and they look acceptable to him, the welds will exhibit rusting later.
Is this caused by carbide precipitation? If so, would laying a smaller bead so the weld cools faster help.
The joint was welded using 308L rods. Shouldn't use of low carbon filler material reduce the liklihood of this problem? Or could there be sufficient dilution with the 304 base metal that carbide precipitation occurs despite the low carbon filler?
Yes, carbide precipitation definitely promotes and offers an environment for the type of surface rusting you described. I purposely didn’t use the term initially because I didn’t know your level of knowledge and wanted to clearly state the cause/effect in straightforward, understandable terms. In addition, yes, small narrow beads certainly will help minimize the condition by maintaining an appropriate interpass temperature as will applying forced cooling measures such as water or oil-free air. My experience and entire career comes from the chemical industry where my plant site has extensive history (over 100 years) with the austenitic stainlessness’ and many of the nickel-based alloys so that the damaging effects promoted by carbide precipitation and SCC are widely recognized and documented as detriments to my old site’s plant operations. The vast majority of the alloy piping at our site commonly consists of sch10 and sch40 with diameters through 16”.
The use of a low carbon electrode or filler will help minimize the chance of carbide precipitation but it’s use isn’t a “cure-all” and won’t overcome the effects of poor or unsupervised welding practices or lack of understanding why there is an interpass temperature list in the welding procedures and why it needs to be adhered to.
As you’ve found and it’s been my experience as well, that if you have a wire-wheel or wire brush concern look further then the finished welds cap and HAZ area. If it’s a contaminated brush or wheel or one was used that wasn’t SS, the area of rust will normally extend well beyond the weld zone and is easily recognizable.
Check to see if the brushes were constructed from type 302 stainless.
If the welder did a power brushing operation, the welds and the base metal on any area the bristles touch, will rust in a heart beat. 316L brushes work very well, but are special order and somewhat hard to get.
Best thing to use when working with stainless steels is Scotch-Brite type abrasives. One last point if you have 302 stainless brushes and you do a hand brushing operation you won't have the problem; you don't get as much heat on the end of the bristle, and that combined with the high carbon content of 302 is the root of the problem. Good luck,
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