If you have access to AWS D1.1-2004, go to Annex X, follow that through and you will be right on for calibration. I use a KB 35, using a dsc block also, usually get a reference db of about 52, though you can get a difference from a lot of different things-cable,transducer,how hard you press the puck on the block. I use 50% full screen height for my refernce line. The more you use the equipment, the easier it'll get.
I'm at 43db on the IIW with a USN50 and 40%FSH.(70degree)
John Wright
My reference is usually around 50, but your reference may be different depending on what type of transducer you have. Also, if you compare your reference level obtained on your DSC, it will be different from the reference obtained on an IIW block. If you are performing inspections to D1.1, you will want to use the reference level of the IIW block. Compare the dB difference to the DSC block and use a correction factor. That way you do not need to carry the IIW and only need to carry the DSC.
Could anyone tell me what the difference in db is from an IIW block and a DSC block. I know the IIW block has a .060 side drilled hole and the DSC block has 1/32 slot. So if I am right the db level for the DSC block should be higher because it is a smaller reflector than the hole in the IIW block. But then agian I could be wrong stranger things have happened. Just kidding if I get out of bed in the morning the odds of me being wrong greatly increase.
QCCWI
I agree with thekoz about the correction factor between the .06 hole & the .031 notch. The dB difference I have noticed is about 1% to 2%, usually larger from the notch.
BTW, different makes of transducers (& shoes) along with cable type & length, couplant between the transducer & shoe and couplant used on the block(s) will make a difference with your dB reference. I like to color code cables and probes to be as consistant as possible. I have also always used a reference of 80% FSH.
Here is a link to the archives of TNT, ASNT's quarterly newsletter, which you can subscribe to for free! Search through the online editions for some valuable information on UT calibration (and other NDT subjects). Many of your questions will be answered in the 2004 volumes. Good illustrations too.
http://www.asnt.org/publications/tnt/archive.htm
Here is a sample illustration
http://www.asnt.org/publications/tnt/tnt3-3/tnt3-3fyi-figs1.htm
~thirdeye~
I have found the DSC to be about 2 dB higher but I rarely use it. More comfortable just carrying the IIW in the shop. I usually am in the 38 (±2) range for the reference level at an 80% reference level on my Epoch 4 because 80% is where the AWS software is set. In the 80s and early 90s, I believe I used a 40% on USM2s and USK7s. Yes, different cables and wedges will make the reference level change.
How much does your reference level change during the day. Mine will usually climbs about 1 to 3 dB the first hour or so of inspection, and then level out and stay steady. Don't remember it doing that on my USM2. Is that common?
How are you documenting your hours? Do you have a Level III overseeing your NDE program?
I write my hours down and email them to my corporate level III who is about 6 hours away. I see him maybe twice a year. Kind of hard to be self taught in somethings but I am slowly getting there.
You have to have documented classroom hours taught by a qualified level 111 . The best way is to go to a school run by Kraut Kramer ,Panametrics or Stavely etc . Very expensive and 80 hrs long. 40 hrs level 1 and 40 hrs level 11 with the required tests , but its the way if you want to be qualified properly , then look at about 1000 hrs stick time , then take your level 11 practical and nobody will question your credentials
Hi tebrugge,
Welcome to the forum. What is stick time? In 25 years of bouncing sound, I haven't heard that one.
~thirdeye~
I took that as SMAW welding, but I could be wrong. I've been "bouncing sound" for a few years myself now and I'm still learning.
John Wright
Hi John,
I'm still learning and asking questions too. For me, inspection has been a journey, not a destination.
~thirdeye~
I've heard the term, stick time, from airplane pilots as time in control of the aircraft, especially loggable time. So here I assume "experience".
Bill
I have attended and passed both Krauterkramer UT classes. I am just spending time hugged up to my UT machine trying to get all those hours.
I can't remember exactly what AWS D1.1 or D1.5 says but your reference level can be anything as long as you get the signal from the cal block to 80%. If your response from the SDH is 80% at 2dB or 50dB they are both acceptable calibrations. 40 to mid 50's is what I remember though. If you have a transducer that has a reference level of 50dB AWS makes you scan above that depending on the thickness of the plate and this can cause you problems. I remember having to put in lots of dB to scan a weld. I remember 14 dB above reference level in some instances. That's a ton of extra dB and then have to do the calculations to figure out what the actual defect length is. There is no provision in the code to take into account for beam spread. If you know what your beam spread is you can remove that amount from the defect that you are looking at. I don't think you can figure out beam spread from an IIW block.
[quote]I remember 14 dB above reference level in some instances. That's a ton of extra dB[/quote]
(14 dB above) That is the "min" listed in AWS D1.1 :2004 Table 6.2 Statically Non Tubular, and it goes up from there dependant on the SP distance and then in Table 6.3 Cycically Non Tubular it goes as high as 45 above the ref.
John Wright
I highly recommend www.ndt.net. Using the site search you will find numerous papers about UT examination. Some of them may answer your questions. Another good site is www.ndt-ed.org.
Bill
NDT Level III
www.ndt-cgi.com
It appears that you have newly purchased equipment so you shouldn't have too many problems. I am usually in the low 40's db range. You should also keep in mind that AWS D1.1 6.30.3 gives requirements for transducer internal reflections (applies more with used equipment). Your percentage screen height can be anything as long as you evaluate flaws based on that same screen height. I use 50% because it allows you to see the indication in the center of the screen.
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