porosity

Date 06-20-2014 01:36

using a wps over 20 tears old, qualified numerous times by numerous welders our x-rays are failing because of porosity. we are welding mild steel 106 pipe and wcb castings using gtaw process. the failure is in an open root pass with eightnth inch gap and seems to be coming from silica build up on the underside of the root boiling at the tie ins. all failures are in 4 locations all in the tie ins. and I have seen it on occasion where the underside slag tries to rise to the top. most failures are to small to see but are getting kicked on x-ray. all normal step to prevent porosity have been taken hydro argon lines, new gas filters, new cups, fans off all doors closed. any tips would be gratefully appreciated.

By swsweld (****)

Date 06-20-2014 01:43

What wire are you using? S2 or S6?
I've always had better results with ER 70S6.

By moontan002 (*)

Date 06-20-2014 01:46

harris er70 -6

By Superflux (****)

Date 06-20-2014 03:40

Change in supplier or brand of your fittings?

By CWI7611 (**)

Date 06-20-2014 15:25

Something you might try, but you probably already have, is to grind and feather the stops on your root bead passes. This may be coming from impurities becoming trapped in the molten puddle as you stop welding. The molten metal when you stop cools from the edges to the center chasing all the impurities to the center of the puddle. Grinding the stop and a little area above the stop then starting above the stop should allow the arc to be hot enough when you get to the stop that you will re-melt and carry the impurities along with you. When you finish the root be sure you grind the stop or start that you are going to overlap or tie in to and then stop past the area up on the previously deposited weld metal. Then if you grind the root you will remove this area.

You probably have already tried this but I just thought I would offer the suggestion. I don't know what code you are welding to or what the thickness of the material you are welding on. Some codes base the size of the porosity on a percentage of the wall thickness.

Good luck!!

By 46.00

Date 06-22-2014 04:09

Is silca islands slag? Can it lead to weld defects? Is it detectable by X-ray? Seems we have debated this subject before!

By 803056

Date 06-20-2014 09:59 Edited 06-20-2014 10:03

Are the fittings dressed to fit by grinding to bright metal? The surfaces of the cast fitting should not be welded with the "as cast" surfaces. The fitting should be ground to fit the run pipe with a consistent root opening and to remove the "as cast" surface to remove any silica remaining from the casting process. That includes the ID and any surfaces included in the groove face.

All tack welds should be feathered before depositing the root bead. Don't forget to feather the weld crater and weld starts by grinding. A light touch with the grinder will prevent imbedding aluminum oxide grit (from the aluminum oxide grinding disk) into the surface of the weld being ground. Aluminum oxide can give the appearance of small porosity in the radiograph (film) because it is not as dense as the steel of the weld or the fitting.

Best regards - Al

By fschweighardt (***)

Date 06-20-2014 10:53

I you suspect silica, try the S-2 wire (.4-.7%) vs .8 - 1.15 for the S6

By welderbrent (*****)

Date 06-20-2014 18:33

This is all good info as I have an occasional GTAW project on pipe 'T's to machined parts that once in a while gives me problems with porosity. Happens so seldom I always attributed it to coolant or other contaminants that got into the joint and not cleaned before I performed the welding. The manufacturer assured me that all parts are cleaned thoroughly before press fit assembly but I still have the occasional problem. Checked my gas, changed tungsten grade, made sure no breeze coming through, couldn't get it to go completely away yet ofttimes it will be only one in a batch of 20 or so. A few times we have had contaminated Ar. The minute you change the tank everything clears up. Those I find when it does 3 or 4 in a row.

Now, wondering about the Tees. They come from about 3 different suppliers. You can tell by the coatings and style of radius and other features. Some definitely weld better than others.

Wondering about this for the OP as well, have parts suppliers changed? Not all parts are created equal.

He Is In Control, Have a Great Day, Brent

By moontan002 (*)

Date 06-21-2014 11:31

thanks for all replys

By Stringer (***)

Date 06-21-2014 19:40

ER70s-2 made by ameritech or inweld makes a difference for me in controlling porosity with mild steel and cast PROVIDED that the Argon is good. I get lousy (OK, contaminated) argon on a too regular basis. All that said, from reading post, I think Al is guiding you to the real issue with the grinding of tacks. A light touch with the proper wheel or one can see too much 'activity' at the tie-ins.