Weld then Galvanize,what wire?

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When having something "Hot Dipped Galvanized", any welds seem to swell or grow a bit. If I have finished them off completely flush and smooth, as on the top of a handrail, the galvanizing (zinc) seems to bump up at the welds.  It doesn't do this at spots that were ground but there was no weld.  I was told it was because of the silica in the weld. I am using standard MIG wire 70S.030. Will using 7018 stick be better? Any help or input is appreciated.Just my  opinion, not from a book, just from the road.Howes Welding Inc.www.howesweldinginc.com
Reply:Use a -6 wire. Less silicates, coats better.
Reply:ER70S-6 has MORE silicon (and manganese) deoxidizers in it than ER70S-4 or ER70S-3.AWS/ASME/MIL specs say ER70S-3 is supposed to have 0.45-0.75% Si, ER70S-4 is supposed to have 0.65-0.85% Si, and ER70S-6 is supposed to have 0.80-1.15% Si.As to the OP's original question and problem about the hot-dipped zinc bumping up over the smoothed and ground and cleaned weld areas, I have no idea why.I am curious as to find out why.  Hopefully someone will chime in.
Reply:I am pretty sure ER70S-2 would be better for that applicatioin.  -6 has more deoxadizes.  Silicon (sp?) is one of em.David Real world weldin.  When I grow up I want to be a tig weldor.
Reply:I stand corrected---However, for what its worth and for whatever reason, -6 will hot dip better....
Reply:The Galvanizer didn't have the right number alloy to give me, he did however say to use the LOWEST number of silicon. So, at the moment we have conflicting advise here on the board. I guess this one is going to take a bit more research! As it was explained to me, the bump comes from the acid or pre-galv dip, it washes the silicates out? and make the weld area a bit more porous. This of  course is not a technical explanation just used to help explain the issue at hand.Does anyone know the silicon amounts for stick rod? 7018?Just my  opinion, not from a book, just from the road.Howes Welding Inc.www.howesweldinginc.com
Reply:Silicon is pretty inert.  Most acids won't touch it.  Hydrofluoric acid will, it eats glass, which is mostly silicon dioxide.  Note: hydrofluoric acid is nasty-nasty-NASTY stuff.  Not only is it a strong acid, not only does it dissolve glass, it also dissolves bone after going through the skin and fat and muscle if it gets on you.Anyway, after welding most if not all of the silicon that was in the wire will melt and form those 'glassy' silicon islands on top of the weld bead.  Once you wire brush and grind the weld, that fused silicon is gone.The silicon call-out for AWS E7018/E7018H4R is 0.75% max, E7018-A1 is 0.80% silicon max.
Reply:I have not found out WHY this happens.  To show everyone what does happen, I am posting pics of a 1 1/4" welded pipe with weld 90's. I did not do this work, but it will happen to anyone using -6 wire.Just my  opinion, not from a book, just from the road.Howes Welding Inc.www.howesweldinginc.com
Reply:I am having some galvanizing done for me this week. I will find out more and have some pics of my completed job before and after.Just my  opinion, not from a book, just from the road.Howes Welding Inc.www.howesweldinginc.com
Reply:After further review, I was incorrect.  My apologies...They say the memory is the first to go-----
Reply:NO... memory is said to be the second thing to go!The first, is helped with the V pill.Just my  opinion, not from a book, just from the road.Howes Welding Inc.www.howesweldinginc.com
Reply:I would have to think that the welds were never ground flush to begin with.  There are grind marks on the welds but none on the base metal on either side.  I've welded hundredws  of feet of pipe railing that got dipped and I've never seen that sort of "swelling", only a difference in texture in the zinc coat in the weld area.
Reply:Originally Posted by Alan NI would have to think that the welds were never ground flush to begin with.  There are grind marks on the welds but none on the base metal on either side.  I've welded hundredws  of feet of pipe railing that got dipped and I've never seen that sort of "swelling", only a difference in texture in the zinc coat in the weld area.
Reply:A quote from the 'American Galvanizers Association' booklet titled 'The design of Products to be Hot-Dip galvanized After Fabrication'."Welding rods high in silicon may cause excessively thick and/or darkened galvanized coatings to form over the weld. In smooth products welded together with high-silicon weld rods, the coating over the weld material will be thicker than the surrounding coating, causing a bump in an otherwise smooth product. A very low-silicon, or no silicon, rod should be used."This does nothing more than tell us what we see in the pictures. There is nothing YET, that I can find as to why.Just my  opinion, not from a book, just from the road.Howes Welding Inc.www.howesweldinginc.com
Reply:Here's a little something. I suppose a guy could research the average weld deposition/composition %'s for several fillers to come up with the better of the choices. Of course the actual weldment compositions are dependant on the individual welders technique to a degree. Anyway it appears that the acceptable silicon %'s fall in two different ranges. Odd. http://www.metalplate.com/galvanizing/tis4a.htm
Reply:I believe this page is also appropriate to the above page, click on the underlined "eta layer" link. http://www.metalplate.com/galvanizing/TIS4E.HTMThe higher silicon content causes the alloying reaction to continue, slow cooling rates also allows the alloying reaction to continue. The later is a good thing, normally.
Reply:One more then I'm done  ..There's a chart here showing the effects of silcon in the metal as well as the two differing ranges. http://www.galvanizeit.org/showContent,287,331.cfm
Reply:A few pictures showing what hapens when you use -6 mig wire. Keep in mind, ALL welds were smoth and flush before galvanizing. This rail has beenepoxy painted after dipping.Just my  opinion, not from a book, just from the road.Howes Welding Inc.www.howesweldinginc.com
Reply:Why not just have it properly dealt with and powdercoated?.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:You have to be looking at that pretty hard to see the difference - after a month or two in the rain, you'll never notice any difference. Unless you're a weird guy that washes his gate and fence Fire!, Fire! Oh wait, that's my torch...Lincoln PT-225 TIGLincoln 175 MIG
Reply:Originally Posted by tessdadNO... memory is said to be the second thing to go!The first, is helped with the V pill.