pinholes with GMAW,no pinholes SMAW

By - Date 03-21-2005 00:43

Knight,
A number of things can cause porosity when using a shielding gas. You already took moisture out of the equation, and 45-50 CFM shouldn't be causing a vortex, so there are a few things that can cause your problem. First of all, it is possible that your gas can be contaminated (moisture). Also, your liner can have moisture in it. An E90C is not prone to hydrogen cracking when welding an A514 carbon steel properly, so that shouldn't be the problem. Only preheating to take the moisture out of the base metal is a good idea, but the base should be cleaned form any possible foreign, or nonmetallic substances. If your base metal is clean and dry, and your gas is not contaminated, and your equipment is clean and dry, you should not be getting pinholes. You didn't mention if you were "pushing" or "pulling your torch. Pushing will help eliminate porosity if everything isn't exactly perfect more so than pulling. Hope this helps. Oh, one more thing...Make sure your filler metal is also clean and dry. Good luck.

Peace B2U

CM <><

By knightour (*)

Date 03-21-2005 12:03

The metal used for the weldment is sent through a shot blast to remove any contaminants such as rust,etc.The wire was pushed.If there was moisture in the gas line,I would assume the welds just prior to the weld discussed would also have pinholes.The metal can be considered to be clean and dry as the weld discussed is one of the last welds to be done on the weldment and the weldment is inside a building far enough from the doors to not reasonably be affected by any moisture from the outside such as snow or rain.This problem occurs at random to any welder of any skill level.

By jwright650 (*****)

Date 03-21-2005 12:57

Voltage? in relation to amperage. Usually the culprit is something like the things that have already been mentioned(moisture, cleanliness of material(make sure greasy pieces haven't been blasted prior to blasting this last piece, shot gets contaminated), improper gas flow(not enough or too much cfh). But too much voltage has been know to draw in atmosphere. Might check that parameter also. Keep after it because something isn't right. Let us know what you find out is causing it.
John Wright

By - Date 03-21-2005 13:02

That is sounding sort of out of the ordinary now. Aside from all of what we've discussed, too much or too little gas flow, improper arc length, poor gas quality, or defective equipment is possible. Good luck, because it appears that you've covered all the bases.

CM

By - Date 03-21-2005 13:41

Jwright is certainly right ( a little play on words here) about excess voltage and contaminated shot. If all of the obvious things are correct, it appears it could be operator "error" such as too long of arc length or maybe torch angle. Yes, please let us know what you find out, but remember, sometiimes things like this "magically" solve themselves. Again, good luck.

Peace B2U all,

CM <><

By knightour (*)

Date 03-22-2005 10:30

Excess voltage may be a possibility,as most welders I work with tend to run the voltage towards the higher end for general applications.The three possibilities I came up with on this is that the preheat wasn't high enough to get the moisture removed from the faying surface or that air is being pulled in and contaminating the weld from the other side of the weld pass which only has tacks needed to hold the part in place.The plate being welded is about 1/4"(6mm),which could be why this situation doesn't show up on thicker material. GMAW may tend to penetrate deeper than SMAW,which could be why SMAW works and GMAW doesn't.

By - Date 03-22-2005 11:58

I agree with all you say except one thing...I believe your weld process, especially in the GMAW process, will determine the weld penetration. I believe you will find that "pushing" will give more penetration than "pulling". But, I agree that the voltage, in relation to the material thickness, can certainly have an adverse effect if not adjusted properly. In a carbon steel, due to the metallurgical structure, the preheat to remove moisture can be up to 200-250 Deg. F. to ensure complete moisture removal. Naturally, the material thickness will determine the moisture removal temperature. Now, as far as air being pulled in, that is pretty unlikely unless you have your shielding gas so high that you're creating a vortex effect in the weld zone. Again, I wish you luck and would like to know what the final solution is.

CM

By jwright650 (*****)

Date 03-22-2005 12:24

CM,
[quote]"Now, as far as air being pulled in, that is pretty unlikely unless you have your shielding gas so high that you're creating a vortex effect in the weld zone."[/quote]

I know he mentioned that he was running around 50cfh and most of the GMAW I have been around is more in the 30-35cfh range depending on a couple of things. While 50 is towards the upper end, it may just be too much flow for what they are doing. Joints that run along close to an edge may need that kind of flow for good coverage but then if boxed in a tight corner it may cause a turbulance if ran that high.

He also mentioned fit up and if there is a nice size crack between the plates, he may be getting air sucked in from the backside.

I had problems here when a particular welder would run his voltage in excess of what the FCAW wire mfg recommended and all those porosity problems mysteriously went away when we reeled his parameters back in.

Preheat is extermely important on thicker materials but as long as you follow the preheat guidelines (in D1.1:2004, Table 3.2) he should be OK, unless the materials have an unusual amount of moisture on them.

Hopefully he'll be able to put his finger on it and find his problem. I know those mysterious problems are worrisome to figure out when they come and go.
John Wright

By - Date 03-22-2005 23:46

Hi There my Friend,
Like I said, we were only given partial information, as we both know. I would bet that if we, either one of us, had been there to visually assess the problem it might have been different. 50 cfh is a little high, but I had no idea what conditions he was welding in. A slight breeze or around an open door, etc., then kicking up your shielding can be beneficial. Other wise, it's probably unnecessary or even not recommended. All the things you said make sense based on the scenario you put forth, but is that the conditions he was welding under? I don't know. To be perfectly honest, I think it had to do with moisture somewhere, either on the base metal, on the roll of wire, contaminated gas, or maybe moisture in his liner. That's my opinion based on his original question.

Chuck

By knightour (*)

Date 03-24-2005 09:47

There wasn't any noticible breeze outside.As the door was closed and at least 50 feet away, the shielding gas being affected did not seem to be a factor.The fit between the plates was metal to metal,as far as I could visually tell.The reason for the porosity has been determined.There was contamination in the shielding gas line for the welding machine used for the weldment.The line of the wire feeder was purged and the problem cleared up.

By whiteyford M1A1 (**)

Date 04-05-2005 00:28

Hi Knight
I've reviewed the replies and agree with the approaches to the problem, however I noticed a few things that weren't addressed.
Are you getting this problem with different welding machines?
Could the gun liner be contaminated from the lubricant manufacturers apply to aluminum wire?
Could the wire be contaminated from storage/lubricants?
Are you using anti spatter or wire lubrication pads?
Is the gun set up with tip recess, (1/16-1/8)?
What about electrode stickout, (1/2-3/4)?
Is preheat measured with a tempstic and maintained? 1/4" will cool off fairly quick.
Have you verified gas flow at the nozzle? I watched a pair of maint. fellows spend most of a day sorting out a similar problem. You could start a bead then it would turn to swiss cheese after 10-20 seconds.
Turned out someone sabotaged the gas line by inserting a foam ear plug.
What are your parameters for this application?
Just a few thoughts on the problem.
Randy