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- since 1996 -

Zawada NDT
Suppliers of instruments to test steel wire ropes in-situ, using magnetic, non-destructive method.
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Technical Discussions
General
General
01:07 Nov-30-2004
Sizing Defects

When sizing a defect according to ASME you take the maximum amplitude and then get the length ccording to the 6 db drop. But according to ASME it has to be over DAC and a certain length to be rejectable, so I have a question about determing length.

Do you only consider the signal portion for length if it goes over DAC, ie; I maximize on my signal and it is over DAC (but not by much), I move laterally to determine length by 6 db drop but before I get to the 6db drop location the signal is now below DAC. SO do you only consider the part of the indication that goes above DAC for determining length or is it 6db drop regardless?

If I size by the 6db drop it may exceed length by code and be rejectable but if i size with the portion that is above DAC it may be acceptable. I can see arguments for both ways.

What is the correct way?


 
 Reply 
 
Chris Jones
Chris Jones
07:46 Nov-30-2004
Re: Sizing Defects
Hello,

I have not worked on compliance testing for some time and when I did I rarely worked to ASME codes.

However, I do remember one rule that was commonly applied to protect the UT operator and that was ->

If in doubt - Knock it out.

Best Regards,
CJ

PS I hope the welders and ECA engineers that I now frequently work with aren't reading in?

----------- Start Original Message -----------
: When sizing a defect according to ASME you take the maximum amplitude and then get the length ccording to the 6 db drop. But according to ASME it has to be over DAC and a certain length to be rejectable, so I have a question about determing length.
: Do you only consider the signal portion for length if it goes over DAC, ie; I maximize on my signal and it is over DAC (but not by much), I move laterally to determine length by 6 db drop but before I get to the 6db drop location the signal is now below DAC. SO do you only consider the part of the indication that goes above DAC for determining length or is it 6db drop regardless?
: If I size by the 6db drop it may exceed length by code and be rejectable but if i size with the portion that is above DAC it may be acceptable. I can see arguments for both ways.
: What is the correct way?
------------ End Original Message ------------




 
 Reply 
 
Dent McIntyre
Consultant, NDE Manager NDELevel III/3
NDT Consultant, Canada, Joined Nov 1998, 250

Dent McIntyre

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
250
03:59 Nov-30-2004
Re: Sizing Defects
I suggest that you post this question on the ASME forum for discussion.
https://cop.asme.org/COP

I agree with the philosophy "if in doubt..cut it out"

----------- Start Original Message -----------
: When sizing a defect according to ASME you take the maximum amplitude and then get the length ccording to the 6 db drop. But according to ASME it has to be over DAC and a certain length to be rejectable, so I have a question about determing length.
: Do you only consider the signal portion for length if it goes over DAC, ie; I maximize on my signal and it is over DAC (but not by much), I move laterally to determine length by 6 db drop but before I get to the 6db drop location the signal is now below DAC. SO do you only consider the part of the indication that goes above DAC for determining length or is it 6db drop regardless?
: If I size by the 6db drop it may exceed length by code and be rejectable but if i size with the portion that is above DAC it may be acceptable. I can see arguments for both ways.
: What is the correct way?
------------ End Original Message ------------




 
 Reply 
 
charlie jackson
Engineering
MBINSPECTION, United Kingdom, Joined Aug 2003, 7

charlie jackson

Engineering
MBINSPECTION,
United Kingdom,
Joined Aug 2003
7
05:04 Nov-30-2004
Re: Sizing Defects
hello
I think you will find that all indications 20% of ref DAC are to be investigated ( ref + 14dB ) if the discons are LOF / Crack they can be classed as defective at this stage and marked for repair. If they are slag then you are allowed the specified amount dependent on thickness ( set at DAC ref ).

Two points to remember which are important are 1 - transfer correction and 2 - there also is a requirement to record all discons within 6dB of the ref DAC.

The important point is that without sufficient gain the interpretation of discons may be flawed.

You can use 6dB on length but will find this flawed when the discon is shorter than the beam ( small defects on thin wall items ) suggest you use 20dB or max amp and give reasoning on the report.

Kind Regards Charlie

Kind Regards Charlie Jackson

----------- Start Original Message -----------
: When sizing a defect according to ASME you take the maximum amplitude and then get the length ccording to the 6 db drop.But according to ASME it has to be over DAC and a certain length to be rejectable, so I have a question about determing length.
: Do you only consider the signal portion for length if it goes over DAC, ie; I maximize on my signal and it is over DAC (but not by much), I move laterally to determine length by 6 db drop but before I get to the 6db drop location the signal is now below DAC. SO do you only consider the part of the indication that goes above DAC for determining length or is it 6db drop regardless?
: If I size by the 6db drop it may exceed length by code and be rejectable but if i size with the portion that is above DAC it may be acceptable. I can see arguments for both ways.
: What is the correct way?
------------ End Original Message ------------




 
 Reply 
 
General
General
02:47 Dec-01-2004
Re: Sizing Defects
I also agree with the cut it out philosophy but there should still be a correct answer IAW the code.


----------- Start Original Message -----------
: I suggest that you post this question on the ASME forum for discussion.
: https://cop.asme.org/COP
: I agree with the philosophy "if in doubt..cut it out"
: : When sizing a defect according to ASME you take the maximum amplitude and then get the length ccording to the 6 db drop. But according to ASME it has to be over DAC and a certain length to be rejectable, so I have a question about determing length.
: : Do you only consider the signal portion for length if it goes over DAC, ie; I maximize on my signal and it is over DAC (but not by much), I move laterally to determine length by 6 db drop but before I get to the 6db drop location the signal is now below DAC. SO do you only consider the part of the indication that goes above DAC for determining length or is it 6db drop regardless?
: : If I size by the 6db drop it may exceed length by code and be rejectable but if i size with the portion that is above DAC it may be acceptable. I can see arguments for both ways.
: : What is the correct way?
------------ End Original Message ------------




 
 Reply 
 

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