Does anyone have experience with welding items that are galvanized prior to welding? Should the galvanized layer be totally removed prior to welding and for what distance should it be removed? I am primarily concerned with stair treads and handrails using SMAW with either E6010 or E7018. The welding is not under any specific Code.
Thanks,
Chris
Chris,
The galvanized layer should be completely removed in the area where weld metal is to be deposited. Removal of the coating reduces porosity caused by entrapment of the zinc vapor. However, in general, a galvanized coating can be welded with 6012 (rutile coating), 6013 (rutile coating), 7016 (titania coating). 6010 and 6011 are suitable for some applications. Electrodes with rutile coating and low silicon content (0.2 % or lower) generally produce welds free of cracks. Conversely, titania electrodes with high silicon content (0.4 % or higher) usually produce cracked welds because of the greater susceptibility of the weld metal to zinc penetration. The trick is to oscillate the arc parallel to the seam with a whipping motion 1/8" to 5/16" ahead of the molten crater. This volatizes the zinc. The welding speed will be 80 to 90% of that compared to uncoated steel. The weld will contain porosity and possibly cracks if the zinc is not completely volatized in the area where the weld metal is to be deposited. Although welding can be done over a galvanized coating, I would not recommend it. Whether cracking will occur in fillet welds depends on factors such as the thickness of the galvanized coating, method of galvanizing, thickness of the galvanized steel, root opening of the joint, joint restraint, welding process, and electrode classification. Either way, watch those fumes. Even though you remove the galvanized coating in the weld area, there will still be fumes produced because the adjacent areas get hot enough from the welding to produce them. I see you're in Wisconsin, so, on a more important note, How bout' them Packers last week!!
As far as the fumes go, I've heard of drinking milk before welding on galvanized pipe reduces the nauseated feeling one gets from exposure. How it works, I don't know. Just have heard many welders who practice this.
the milk trick does work, but I always drank it after. Oh, and welding the stuff overhead is a new experience in pain.
swnorris gave you some great tips.
I would just add that after you remove the zinc and complete the weld, a good way to replace the zinc protection is by applying cold galvanizing compound spray paint or even better, use Galv-A-Bar.
Galv-A- Bar can be purchased at most welding supply stores. It is basically a square rod of zinc, abut 3/8" square and 12" long. It is applied by heating the base metal with a torch up to the melting point of the bar. Then rub the bar on the affected area and spread with a wire brush. Take care not to overheat or the zinc will burn away rather than stick.
Be careful with the fumes as they will make you sick. Good ventilation and a respirator is reccomended. If you do feel nautius afterward, drinking milk helps relieve the symptoms.
Tim
Welding Procedure for Galvanized Steel
Remove galvanizing by grinding
Welding should be made after 100% removal of all galvanized coatings. You can check for removal of the galvanized coating - heating the Steel to 450-600°F will color the Steel Gold-Brown to Blue while leaving the Zinc Silver colored.
Please note galvanizing is more than just zinc. Caution is required due to alloying elements.
genreal Notes on the Effects of Elements in Galvanizing
Iron is not added but dissolves from the steel. It is always present at its saturation. This is about 0.025%. Weekly, a galvanizer will remove excess of ZnFe that has settle at the bottom of his kettle (called bottom dross) from its kettle.
Lead Is added to promote wetting of the steel. Maximum solubility at galvanizing temperature is 1.2%. Lead in a kettle will give spangle on the surface.(the zinc "crystals" you can see on galvanized steel). Some galvanizers prefer a layer of molten lead at the bottom of the kettle. This can make it easier to remove the bottom dross, which is now floating on the liquid lead instead of lying on the bottom of the kettle. Zinc-lead (GOB zinc) is less expensive as SHG zinc (electrolytic grade 99.995%)
Cadmium is a major metal present in zinc concentrates, and in the past (many years ago), it was therefore an impurity in zinc. Due to its toxicity, it is banned almost everywhere. Nobody adds cadmium to his galvanizing kettle but someone who used old (remelted) zinc from a doubtful source can find some Cd in his kettle.
Aluminum - Between 10 and 100 ppm of aluminum in a galvanizing kettle. It is added as brightener. Without aluminum, the surface of the zinc melt will oxidize much more and a thicker oxidized film will form on the surface. Drainage of zinc from the steel is not so good because of this oxidized film. The surface will no longer be metallic silver but you will see a coloring of the surface when not sufficient Al is present. In literature, you will find zinc compositions with more aluminum (goal is to reduce coating thickness on high Si steel) but none of them is industrially applied in batch galvanizing (a handful of exceptions worldwide excluded)
Copper is an impurity found in all zinc kettles. My guess is that it comes from the steelwork that is galvanized.
Tin -Traditionally an impurity coming from remelted zinc. Tin is used in soldering material for zinc plumbing. Tin is also used to enhance spangle and to promote wetting of the steel. Tin also improves drainage of zinc after removing steel out of the kettle. At higher Sn concentration, it decreases the coating thickness on higher Si steel. Tin, Bismuth & Lead can contribute to Liquid Metal Embrittlement or Liquid Metal Assisted Cracking
Nickel reacts with zinc and iron to form an intermetallic compound. The Zn-Fe-Ni reaction layer that forms on the steel surface is more compact than the normal Zn-Fe layer. This has the advantage that the zinc coating become less thick, especially in Sandelin steels and steels with more Si. Ni gives also a better drainage of zinc, so the galvanizer will have less work to remove zinc from drilled holes in the steelwork.
Bismuth -Promotes wettabilty and spangle much stronger than lead.
An easy way to be sure that all galvanize is removed by grinding ; is that
galvanized does not produce sparks off the grinder, When you finally hit steel the sparks really fly. Just a cursory grinding, while it brightens the coating, is only polishing the galvanized. Keep grinding. Milk works but
grinding is better. Also hold your breath while you're burning the rod, and step back before you raise your hood.
Another caution about grinding is that it loads up on your grinding wheel and as the material is heated from the friction of grinding it remelts and continues to contaminate your material. Not only is there a thick coating to remove but it also has melted into and impreginated the grain of the steel near the surface while it was immersed in the molten zinc bath.
John Wright
A silicon carbide grinding disc will help with that. Still, if it isn't possible to weld on steel with the zinc coating ground back away from the weld area, OSHA permissible exposure limits (PELs) for zinc oxide and lead may be exceeded. A high velocity circulating fan or an air respirator helps too.
AWS D19.0, Welding Zinc Coated Steel is a good procedure reference. It calls for welds to be made on steel that is free of zinc in the area to be welded. Thus, for galvanized steels, the zinc coating should be removed at least 1 to 4 inches from either side of the intended weld zone and on both sides of the work piece.
Well I don't agree with most of this post.
Welding galvanized handrail is normal practice in the building industry.
OSHA and any safety related actions and equipment are important, however that does not mean you have to grind/remove the galvanizing unless specified per your WPS.
Coatings removal for PQR/WPS is an essential variable. If you qualify your WPS not removing coatings, you can weld without grinding. Check AWS D1.1 or AWS D1.3 for normal base material preparation for welds if your PQR/WPS does not specify coatings removal.
If, however, the PQR/WPS specifies coatings removal you must prepare the weld joint and surrounding weld area by grinding or other suitable means.
In general the HAZ is considered sufficient distance for cleaning.
Best Regards,
Vonash
Thought all might find this of interest.
www.sperkoengineering.com/html/articles/WeldingGalvanized.pdf
Steve.
http://www.sperkoengineering.com/html/articles/WeldingGalvanized.pdf
Just a note: adding the prefix "http://" makes the link "clickable"
John Wright
Thanks John, Usually i just copy and paste from the address bar.
Steve
Good link, BTW :)
John Wright
If you indeed decide to grind the galvanizing off of the part before welding, you might try spraying the grinding wheel with WD40, it will definitely keep the wheel from loading up. Good Luck, aevald P.S. use a good quality respirator whenever possible it really is cheap insurance for your longterm health.
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