6dB Drop is Not Great for Flaw Length Sizing

It's hard to pick a nice title for a video where all you do pick on 6dB drop for 5 minutes straight. That's the best I could come up with.

[@coryharrison9659]

Paul your videos are an invaluable resource for many techs who don’t have access to continued education. Thanks for all you are doing to spread quality technique and general flaw detection information.

[@aerialrescuesolutions3277]

How does a tech not have access to continuing education? There are numerous opportunities to learn more about UT.

[@coryharrison9659]

@@aerialrescuesolutions3277 is that a serious question? You can’t imagine a single scenario in which quality online resources like this one are valuable to a tech in the field?

[@bacelismael8687]

Thanks so much for your great videos as always, I love your easy to digest, and easy to understand content, I really admire your continuous efforts for developing and teaching UT/PAUT techniques 🙏🏻.
best of luck!
And by the way, Nice T-shirt you've got here, VEO3 is surely awesome 😉.

[@levibrown668]

Awesomeness,cant believe i was not aware of your RUclips channel,so happy i stumbled upon this. You are like the Master Roshi of ultrasonics. Love it

[@courtneykadel9492]

Thankyou, your videos are a great help to better understanding ultrasonics!

[@geemarino6066]

Thankyou for the nice video sir. Paul :)

[@Pattern_seeker202]

The disregard level is basically too small to be rejectable; very practical.

[@jb512137]

Here I thought I was the only one who noticed this. Great explanation - this should not be considered the gospel it often is in the industry.

[@alswanny]

It's a 6db drop that's been around forever its not a must use, but yes great video great information.

[@anushm3405]

Really informative,
Thanks

[@anthonywilliams9508]

Paul if you would in PAUT please do a video explaining when to do multiple index scans and why. I would like to hear a better explanation as to at what thickness do we go to multiple index scans.

[@hollowayndtengineeringinc.5201]

I'll add it to the list!

[@robertrobinson1454]

In theory, the areas beyond the -6dB points would have already been scanned prior to getting to the max amplitude. Wouldn't that area be accounted for prior to scanning the rejectable indications?
EX: So if you're scanning the weld and the max signal is say 90%FSH and you do a -6dB technique and you scan either side until you get 45%FSH. When you go beyond that, wouldn't you have already scanned the area where the amplitude picks back up? I guess what I'm getting at is the -6dB drop is assuming that the rest of the weld is clean and/or there's some other part of the code that covers how much distance has to be between indications to consider them separate or it would be lumped up already with the rejecteable indication. Making the -6dB technique legit.
I'm not saying I'm not, I'm throwing something out there and hoping to get clarification. Thank you in advance.

[@pascaldainelli7763]

Hello Paul,
Thanks for sharing knowledge and ideas !
In your presentation do you assume that the real flaw length is > to the sound beam width (let's say -6dB sound beam width) ? What's your advice regarding small flaw length sizing of heavy thick parts (forgings, or weld between two forgings) with sound path of a few hundred mm with "standard" probes for this kind of components (B4S / B2S, WB45-2 ...) ?

[@ehsanmohebbi2998]

nice, thank you

[@geemarino6066]

If your evaluation is lack of fusion what technique would i be using? Coz you said earlier LF is a bit tricky
Thankyou for the answer Sir

[@dinho9492]

Thanks

[@Harry001989]

Real flaw length yes, but if acceptance criteria are based on amplitude and length then even if you leave some flaws still it will be acceptable.

[@Xarius01]

Wouldn't the max amplitute method over estimate the length?

[@hollowayndtengineeringinc.5201]

No it shouldn't. If there is a small spike on the indication you are picking up and peaking, that belongs to the flaw, and it's the last one, then you should be right at the end of it.

[@robertrobinson1454]

If I get a rejectable signal, I'm going to do the 6dB drop. At that point, I'm going to follow it until there's no signal left. Regardless of amplitude. Is that ok?

[@hollowayndtengineeringinc.5201]

Depends how long it is. If you have a 10ft weld with a trail of slag the whole length, and it peaks in the middle at 4dB over your acceptance level, but the rest of it is 2dB under, are you going to still call the whole thing? Probably not. You call what fails the acceptance criteria, so you use fixed amp technique.

[@robertrobinson1454]

@@hollowayndtengineeringinc.5201 thank you.

[@SantoshKumar-ru7xd]

What about height sizing? Can u please make a video about it.

[@hollowayndtengineeringinc.5201]

6dB for height sizing is useless

[@hollowayndtengineeringinc.5201]

www.ndt.net/forum/thread.php?msgID=80965#80965

[@user-ij2zg9tk4j]

❤❤

[@MrJammydodger20]

Just X-Ray it. :-)