No Porosity in Process Side of Weld

Take it with a pinch of salt, may be due to difference in temperature gradient, between both sides.

Here are some possibilities:

1. Porosity wasn't available to be detected:

Your assumptions about the root side not being shielded may be incorrect.

A gap is often specified in fitting. One effect of this gap is it makes protection of the root side possible as shielding gasis conveyed by candoa effect. On any subsequent passes, the root side should not reach sufficient temperature to induce porosity.

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Alternately something like a backing ring or plate may have been utlized, which prevented conditions that would lead to porosity.

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2. Porosity was created, but:

You may not have been able to detect any porosity on the root side because you didn't have sufficient access to the root side post-welding,to detect porosity with the available tools.

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3. Porosity was created but:

Even with access to the root side, your inspection might have failed in detecting porosity for any of numerous reasons.

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Don't count on never having porosity at the weld root. Many industrial process specifications call for shielding gas inside the pipe.

Have you done a root pass weld?? If so there would or should be enough gas to shield the root weld and should have no porosity if done correctly, further passes would not require internal gas shielding.

You must have done a good job if there is no porosity.

Your description does not really give enough information.

In the GTAW or TIG process, the shielding gas is added mainly just for "shielding" from air oxygen and avoid oxidation of the weld pool. Porosity can be originated more easily in welding with hygroscopic covered electrodes or fluxes which produce steam which flows through the weld pool while it is solidifying, leaving the pores.

Regards

'....In the GTAW or TIG process, the shielding gas is added mainly just for "shielding" from air oxygen and avoid oxidation of the weld pool. Porosity can be originated more easily....'

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Some avenues to porosity might be equally easy, but nothing can really be much easier than 'Ineffective 'shielding' in TIG, allowing not only O2 but also the remainder of atmospheric components to react with the weldpool. Simple, surefire, ruin.

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Not convinced? See for yourself...when someone is running some test pieces (nothing for certification, something low cost) scrap low carbon would be fine....stand near with a helmet to observe. When they begin, position yourself and adjust your helmet so that you can blow air at the arc. If you are effective, sputtering will occur. If the welder does not stop immediately blow more forcefully, eventually the welding will stop, so that you can check out the certain porosity. If you are sly, the welder might not even know that you are what is introducing the problem....so let them know before toomuch time gets wasterd.

Of course, if you blow the inert gas you will have no protection. TIG and MIG weldings must be wind shielded to avoid that... Or even an inert gas high flow at high pressure can jeopardize the weld.

Porosity is always produced by some gas entrapped in the molten pool when tries to scape while the metal is not able to fill the gas path. It is difficult to find porosity in the root side of one side TIG welding if you take the minimum measures (wind shield and preheat over dew temperature to avoid a wet welding end).

Do you disagree with the statement ....In the GTAW or TIG process, the shielding gas is added mainly just for "shielding" from air oxygen and avoid oxidation of the weld pool?

I do not know other "main" reason to use Ar or He....

Kind regards

I mainly disagree with what is implied by:

'....Porosity can be originated more easily....'

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i.e. that there is any significant level of difficulty in originating porosity through inadequate shielding. It just doesn't get much easier...

...fog a mirror? you can do it.

I cannot fog the mirror while welding... just fog the shielding glass....

Kind regards

Your reply in #9 suggests you are a good sport and not taking offense....

So, I feel pretty safe assuming you won't misjudge my response to your inquiry :

'....In the GTAW or TIG process, the shielding gas is added mainly just for "shielding" from air oxygen and avoid oxidation of the weld pool?

I do not know other "main" reason to use Ar or He........'

There are a couple other main reasons:

-Ease of striking an arc

-Arc stability

-Remove heat from the Tungsten...prevent overheating of the electode.

-Prevent detrimental gasses (not just O2) from reaching the weldpool (porosity/embrittlement)

-Prevent detrimental gasses (not just O2) from reaching solid but still very hot metal in the HAZ which could lead to problems like embrittlement.

No offense at all!!!

I've always thought this is a free forum where we can discuss change our different points of view.

All the things you say are correct. But some of them are lateral aids (chemical composition of the shielding gas...)

If somebody would try to weld with an electric arc between a W non consumable electrode and the part to weld without any gas, all other things (arc stability, porosity, HAZ embrittlement, etc.) really don't matter.

Nothing there to disagree with outright, though I have to say several of the things I listed also fall into the catagory of sine qua non

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....perhaps if I approach this from the other side, you might find it more palatable:

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If the primary purpose of shielding gas in a GTAW process is to keep Oxygen away from the weld pool. Why are several shielding gas mixes available andin use that contain a few percent O2?

Your question re other puposes of shielding gas mixes relate to,

Arc stability

Manipulation of weld pool ie, width ,penitration depth etc, also used in conjuction with electrode polarity.

Different mixes suite different metals re the quality of the weld.

Some gas mixes can be propirity for various companies proceedures.

It is a large field for which I dont have time for more detail and sugesst you do some googling.

You are just catching the tail end of this discussion.

I wasn't questioning to receive information about other shielding gas purposes. I'm reasonably well versed in this area, but your helpful attitude is still appreciated.

My question was more rhetorical, intended to convince Kwetz his assertion (that the predominant and most important function of shielding gas in GTAW is to shield the weldpool from O2) is untenable.

I think he will eventually concede that shielding gas serves manyfunctions, some just as important as keeping O2 away from the weld pool.

Here is all the dope on shielding gas.

Function of shielding gas in GTAW

Joshi, your Google Cheerleader routine is wearing a bit thin.

Most of us have no problem searching with Google.

Sorry, truth is not a compromise. Solution is simple. Turn a blind eye/overlook/don't bother & carry on. I did not specifically address the link to you.

Sorry. My comment was uncalled for.

Hi,

There was a root gap of 1.8mm provided to fill the filler metal (Diameter 1.6mm) in the root region. Moreover, compound bevel was used on this joint due to it's high thickness. Root and hot pass executed by GTAW and remaining thickness filled by SMAW due to space limitation to utilise the commercial advantage of SAW. So, at last, I think, the root gap provided was sufficient to pass Argon gas to provide an adequate shielding region on the bottom portion of the entire root to avoid porosity.

However, I have other doubt to be clarified.

1.Is it really needed to melt the suck back region to push down to correct the root concavity during hot pass welding? I found that, good welders are capable to correct suck back during hot pass .If melting required to correct suck back during hot pass welding,then why there is no porosity on that region though there was no back purging to protect process side?(If no melting required, then there is no question about porosity)

Thanks

1.Is it really needed to melt the suck back region to push down to correct the root concavity during hot pass welding?

Of course welding is an art learned by good practice.

You might consider closing the root gap to same diameter as the electrode, this gives you the advantage of resting your electrode in the gap without push through and can give a more consistent weld once the technique has been mastered.

garth,

Here the question, why there is no porosity on the corrected suck back region of PROCESS SIDE (BOTTOM PORTION OF ROOT)?If there is no proper shielding of argon/helium gas during GTAW ,you will get cluster of pores in the weld(upper side).But bottom portion of root had no shielding from argon during suck back correction!I couldn't find pores on the bottom portion of corrected suck back region!What is the reson for this miracle, I hope, now the question is more clear.

Hi forum members,

How are you?Are you running out of ideas?Any link,research paper,article to find the answer for my query?

'.... I found that, good welders are capable to correct suck back during hot pass....'

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I'm pretty sure this is where your thinking is going astray. A good welder isn't going to create a suckback problem on their root pass. Additionally, running subequent passes hot enough to remelt the root pass is unlikely to correct suckback, will probably creat a problem or make an existing problem worse.

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Also note that steel beings to loose structural integrity and can be reshaped easily at temperatures far below what is necessary to cause porosity.

I would have agreed up to some extent with your statement, "A good welder isn't going to create a suck back problem on their root pass" if there was no space shuttle Columbia failure. It is still believed to be the Space shuttle was constructed and operated by world's best brains! Unfortunately, space shuttle Columbia failed! So, compared to space shuttle failure, it is not a major issue for a good welder to make a single suck back mistake in his/her entire life time. But the point which I noted, once the temperature keep on increasing the yield strength of steel will come down (atoms will vibrate more!). So the arc force during hot pass can penetrate the root pass and capable to make some cosmetic changes (even capable to correct small scale suck back!) of the root pass without melting the process side.

Ok, just for argument sake.....

....lets say there is a competent welder who believes that suck back can be corrected by running hot passes (immediately following the root pass), sufficiently hot that the slumping and contraction cause enough thickening in the area to offset any depression....

My main question would be, does he just assume that he screwed up every root pass, and cook the hell out of all the subsequent root passes (HAZ be damned)?

Or is each radiography performed after each root pass? If this is the case, I'd be very interested in seeing how the Weld Inspector reacts to the whole idea of root passes sufficiently hot to noticably shorten the joint.

The Space Shuttle Colombia did not go down because someone failed to apply excessive heat to a joint on the off chance their root pass had suckback.

Stringent heat input control is to avoid grain coarsening during welding heating and cooling cycle and it is applicable only when stringent charpy impact toughness required for the welded joint. As long as the joint is not going to take any kind of impact load and no toughness requirement, then heat input is not a major problem in welding of low carbon steel. Practically it is not possible to accept a welder who is continuously creating suck back problems.But,I feel,it is unfair to reject a skill proven welder based on a single suck back problem created in a non critical joint.

You know what?

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You are on the right side of this argument and I am wrong.

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You are exactly correct in pointing out my inappropriate aversion to significant additional heat. It is simply not that big of a dealin the situation you describe.

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Much of my welding related education and also much of my welding realted real world experience has been focused on highly stressed thin wall stuctures. In that world, excess heat is can easily cause damage from which a work piece cannnot recover.

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Apparently I allowed my aversion excess heat to spill beyond the bounds of utility.

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So, please forgive my over reaction and the over emphasis I placed on avoiding excess heat.

No problems.Yes of course, in thin walled structures the main problem is distortion due to the heat generated from welding. Controlling distortion is really a headache for welding professionals. Distortion is a major problem in thin walled pipe spool fabrication, especially in austenitic stainless steel pipes due to it's high coefficient of thermal expansion (Metallurgical reason also involved in selection of less heat input process in austenitic stainless steel welding.) So, stringent heat input control is mandatory in this situation. Moreover, if we are trying to correct suck back in a very thin walled pipe by using the method which I mentioned above, I think, burn through will be the result!