Hi GOKHANYAMAN!
I read your original post and now that I've re-read your description as to how you're feeding the Argon that's only 99% pure (MUST BE LAB GRADE FOR DUPLEX!!!) into the weld groove from the outside, and flowing out through a couple of holes that were made into the soluable paper, is this what you're saying??? I ask this because if it is,then there's big part of your problem right there!!! Without a doubt, this is an inappropriate method of purging this "tie-in joint" PERIOD!!! I'll explain why...
1.) By feeding the gas from the outside of the weld groove, you are creating turbulence (Asymmetric vortices like in fluid dynamics) inside the pipe causing the atmosphere inside, and already present, to mix with the purging gas instead of passing through the soluable paper to be replaced by the argon purge itself!!! Find a different route or location to supply your purging gas into the inside of the groove or weld purge zone!!!
Otherwise you'll end up with problems where the backside of the root pass is showing incomplete penetration throughout the circumference (weld length) in the radiograph then, when the welder gets to the end of the root to close it up, that's exactly where the root will show an unusal indication (caused by the inability of the welder to mitigate the purge turbulence at that location) and as a result, that will be unacceptable in the RT...
Not only this will fail consistently in an RT but also, the amount of O2 contamination present inside the joint purge zone, due to the unusually high level of O2 concentration from the mix of the atmosphere with the not as pure as one would like, argon on the backside of the root(99.998% would be nice if possible but, usually 99.995% is lab grade), will also cause it to fail the corrosion test, even if it passes the mechanical test by chance!!! How the root pass where the tie-in of the beginning of the root pass to the end was acceptable in the first place, is an anomoly to say the least!!!
In this application, turbulence means that the Argon is mixing with the atmosphere, and loitering in the purge zone because there is too much internal pressure building up inside of the joint where the welding is taking place!!! The reason for this is the insufficient emptying of the atmosphere due to your set-up (not enough holes in your soluable paper to let the atmosphere flow through in order to prevent "mixing"!)... In other words, too much flow going in from outside which is creating these asymmetric vortices, and not enough of what was only atmosphere inside the pipe flowing out through the soluable paper to empty out what is left of the initial mix which noramally occurs at the start of the purge!!! This is also causing turbulence in the weld zone (puddle itself), because of too much positive pressure coming out from the internal purge zone which is building up pressure at the root opening, and in turn has the potential to push up the weld puddle, shielding gas up and away from the puddle itself, especially when you reach the end of the weld length!!! (any porosity at the crater?) Therefore,the internal turbulence is not letting the root of the weld deposit to penetrate consistently if at all, and letting the weld become contaminated inside out!!!
2.) Now you did'nt mention at all if you are using an O2 sensor/analyzer/indicator so, it's safe to say that you have no idea of the O2 content in the purge zone itself or how long to purge prior to the start of welding!!! Now if your client expects you to have a root pass that looks like it was polished as it was welded then, I strongly suggest that you monitor the O2 content in the purge zone repeatedly until you're satisfied that the indicator shows you O2 ppm levels no higher than 10ppm's (Why not use the ppm's recommended for Ti as your standard acceptable O2 level)!!! No if's ands or butts!!! Pardon the pun... Duplex & Super Duplex, and Titanium (Ti is a little more sensitive) are almost identical when they react to even low levels of O2 present during welding... Now I do not know which code you are working from but, I can say with confidence that unless you take our suggestions to heart, your welds will not be acceptable according to the three conditions you must meet!!! (Acceptable RT, Mechanical, and Corrosion test which for the most part is initially based on how the backside of the root looks visually, no discoloration whatsoever in the weld root or a HAZ = Heat Affected Zone, and what I used to call a "chemical wipe" on the root pass, both inside and out )... It's slowly coming back to me!!! My distant memory that is... Oh I almost forgot, the face, and HAZ of each pass has to have no discoloration also!!!
Did you increase or decrease the flow rate when you changed from the sponge to the paper? By one not adjusting the flow rate when changing purge ballast mediums then, excessive internal pressure build-up and mixing can occur also!!! As a result, this will probably slow down or increase your travel speed which is sometimes overlooked when one battles with turbulence, causing excessive heat input, and not enough also in certain locations!!! There is more to point out but, I'll just let someone else give you some more pointers to hopefully solve your dilemma
No disrespect but, I'm tired so, I'm going to take a power nap...........
Oh Yeah, I almost forgot!!!
Respectfully,
SSBN727 Run Silent... Run Deep!!!
SS,
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