It is possible. If you could explain a little more as to the discontinuities that were found with PT and the code that was worked to.
Pictures help to!! ;-)
Are you talking about polishing the surface post weld?
If this strategy is producing succsess..... I question the method.. If the porosity and cracks are real than the polishing is only smearing the metal to make the indication disappear.. the process control problem would remain.
But lets find out a bit more about what the inspection criteria is... Code? Size and amount of porosity allowable?
And why the RT before the Penetrant inspection? Would save alot of expense if it were the other way around... Assuming the indications are real and not a misinterpretion of the FPI.
I agree with Lawrence. Is the same person inspecting the RT and PT? A basic order of operations might be as follows.
1. Visual inspection. If you see a defect, stop and change your process. If it looks good, continue.
2. PT inspection. If you see a defect, stop and change your process. If it looks good, continue.
3. RT inspection.
As far as you process, check your welding procedure. I would use argon with a 5356 rod (if GTAW) on clean material. And I mean clean. No dirt or grease or waxy film. I would clean the parts right before welding, not days.
I wouldn't pay to have part RT inspected if it didn't look right to begin with.
Good luck.
Welding aluminum can produce very fine cracks on the surface of the base metal adjacent to the weld toe (in the HAZ so to speak). These "cracks" are typically where the surface oxides have been removed by cathodic cleaning. It is sometimes referred to as arc erosion by some welding standards. These "cracks" are only a few thousandths deep and can usually be effectively removed by vigorous wire brushing.
I recommend that the welds and the base metal beside the weld be wire brushed with a stiff bristled stainless steel hand brush before any inspection is performed. Brush in the direction parallel to the weld axis. Do not use a power brush.
Best regards - Al
Are the Indications curved? Do the welders do anything that could cause minor scratches? If polishing is effecting the indication these cant be very deep and smearing is taking place. I have seen many indications that could be called linear but turn out to be grinding marks ( Any Inspector should spot these right away ).
The rounded indications could be poor Cleaning. Did he verifiy his call for you ( I allways verifiey a reject when practical ).
We always DO PT on joints that are to be X-rayed i do the root pass only after back gouging ,MT on the cover pass if the VT Needs enhancer.
If they are Relevant id start doing the PT 1st and be bone with it.
MDK
By hansw3
Date 01-17-2009 21:44
Edited 01-20-2009 04:35
Is it possible to repair weld after dye penetrant has found a crack? I am welding an aluminum fuel tank. I could pressure test it, but perhaps dye would be safer for finding cracks that are not through material.
To clarify- If a crack is detected with dye penetrant must the entire crack and surrounding material be removed for a clean area to make repair or can the penetrant be welded over and still expect a uniform weld?
Penetrant dye is oil based and like any hydrocarbon it will produce porosity in an aluminum weld if it is not completely removed from the defect and surfaces of the base metal before welding.
What you describe is one factor that must considered before using dye penetrants; can you remove it completely if a welded repair is required. If the answer is no, as you mentioned a through wall crack may prevent complete removal of the penetrant from the opposite surface, an alternative to dye penetrant testing should be considered. Even cracks that extend part way through a part can be a problem unless the crack or other defect is completely removed so that all traces of the penetrant can be removed as well.
Penetrant testing is often specified because it is relatively fast and inexpensive, but like any NDT method, there are certain draw backs that have to be given consideration.
Can you flush the inside of the tank with acetone and isopropyl alcohol? If you can, you can probably remove the penetrant after several flushings. It will not be easy to remove all the penetrant if it gets to the inside of the tank or trapped between a tight fitting seam. Sufficient time and possibly some heat may be required to evaporate any remaining solvent.
I've seen jobs that were scrapped because the penetrant could not be completely removed from tight faying surfaces prior to painting. No cracks were found, but the paint was supposed to be white, not pink!
Best regards -Al
