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Up Topic Welding Industry / Inspection & Qualification / CLUSTER POROSITY IN UT SCAN
- - By wiggles8879 (*) Date 06-03-2008 21:28
Hello all

We are doing a UT scan of a part and we are seeing some clustered porosity throughout the whole part.  We have to raise the gain up really high to be able to see it, you cant really see it under normal UT conditions.  My question is this:  If the porosity is below 1mm in diameter is it still considered a discontinuity?  there is a bunch of holes throughout the weld but i cant really see any that are bigger than 1mm.  If you take the sum of all of the holes it would probably be out of spec but I think you only count the ones bigger than 1mm.  Any insight into this would be greatly appreciated.  We have checked everything to make sure that the robot isn't getting any air movement that would affect the cover pass of the weld and it is still happening.  I am quickly running out of options as to why this would be happening and it is frustrating me greatly.  thanks in advance to any input that anyone can give me.
Parent - By raptor34 (**) Date 06-04-2008 01:09
Im not sure what code you are referencing but i would be calling that a reject, if one isnt out of spec you might be able to call aqumulations of imperfections. It is a discontinuity, as is anything in the weld that isnt metal.  Have you tried any other inspections on the part in question? 
Parent - By Steve.E (**) Date 06-04-2008 10:22
Don't know about you but I start getting real edgy when UT operators start turning up the gain to find the discontinuity's.
Parent - - By CWI555 (*****) Date 06-04-2008 11:08
Well, the first thing that jumps in my mind is the gain. jumping the gain up is never a good thing. Most codes have a specific gain level to run at, going any hotter gives you a good chance of false indications. If at the prescribed scanning DB, it is acceptable, that is usually it, it's acceptable.

Then there is the nature of the indication you refer to. Rounded indications are omni directional reflectors. Consider the 1.5mm hole in the IIW block.
It makes a nice target and reflection. If you had a pile of them in any weld, I'd find it hard to believe that each of them could be sized individually from a simple physics of the waveforms standpoint.

I suggest being careful with this one, you may be setting yourself up for failure.

Regards,
Gerald
Parent - - By Bill M (***) Date 06-05-2008 12:19
Every NDT method has pluses and minuses.  The weld must have some importance or UT would not be required in the first place. 
I realize RT isn't cheap but is it viable to get a shot of the questionable area to get an idea what these UT reflectors might be?
Parent - - By js55 (*****) Date 06-05-2008 13:59
Am I again catching hints of a philosophy that looks for reasons to reject something?
Do those who are looking for reasons to reject have an understanding of the mountains of engineering and research behind the levels of acceptable 'discontinuities'. Not that they are necessarily always right, I am willing to admit.
And do we intend on dispensing with this 'fitness for service' thinking and impose a more stringent criteria of no discontinuities whatsoever?
Have we lost sight of the fact that even in research level single crystal metallic materials there are discontinuities? Or that actually some discontuities make a material stronger? For example, solid solutioning that actually causes a matrix discontinuity.
Parent - - By CWI555 (*****) Date 06-05-2008 14:11
Not from me your not.
Parent - - By js55 (*****) Date 06-05-2008 14:25
Gerald,
I knew that.
Parent - - By wiggles8879 (*) Date 06-09-2008 12:21
hello all

i didn't mean to make this a philosophy discussion or anything.  I am a CWI and want to make sure that I give the customer what they are paying for and not try to give them a part that would affect the parts function in any way.  I understand the philosophy of acceptable vs unacceptable but wanted to make sure what the general consencus was before trying to make a rushed decision or an irrational one.  I am starting to train on the UT machine so that all the weld inspections come through me one way or another so that I can be confident in the parts we send the customer.  Thanks for the responses to my question.  I take my job very seriously and try to stay out of the gray areas of being a CWI but it doesn't always work out that way.
Parent - By js55 (*****) Date 06-09-2008 13:29
You never know which direction these threads will take. Sometimes for the better, sometimes for the worse. Mostly for the better.
Parent - By CWI555 (*****) Date 06-09-2008 14:59
If your just starting your UT training, I strongly advise you learn how to read the A scan screen recitified and unrectified (RF wave) and not the automatic data from the modern machines. Those auto functions are great for productivity, but remember they are a crutch when it comes to interpreting data, a crutch with a crack in it.

I would also advise learning as much as you can about waveforms/echo dynamics.
Parent - - By g32141 (**) Date 06-10-2008 07:15 Edited 06-10-2008 07:24
Every time we calibrate with an AUT scan we do it on a known reflector between 71% and 99%. My system anyway. Depending on the code the scan dB is increased to look for stuff like porosity. We can't just jack up the gain to reject something.

Everything the UT operators do is audited. It is looked at by a 3rd party.

Usually we have to calibrate before a weld scan and calibrate after without changing any settings. If we cal in and out without changing anything why would we go back to add gain to reject something? We want things to go smooth. Good welds = a fast shift. No one wants repairs. Not the welders and not the inspectors.

We do pick up and reject stuff that RT fails to see. Stuff like cracks and linear defects we can pick up with our probes for slag that RT won't get.

If I find a cracked weld I'll scan it a few times to be sure. After the 2nd time I am sure.
Parent - - By CWI555 (*****) Date 06-10-2008 10:56
There are people out there calling themselves inspectors who "want" rejects. I won't call those people inspectors.
Parent - By Bill M (***) Date 06-10-2008 16:39
I have seen too many welding inspectors with the attitude..."when in doubt, throw it out!"
Up Topic Welding Industry / Inspection & Qualification / CLUSTER POROSITY IN UT SCAN

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