where expertise comes together since 1996

The Web's Largest Open Access Database of Nondestructive Testing (NDT)
Conference Proceedings, Articles, News, Exhibition, Forum and a Professional Network
All Forum Boards
Technical Discussions >
DGS method Attenuation correction curve for 2.5 mm CRR
General Discussions
Job Offers
Job Seeks
Classified Ads
About NDT.net
Italian NDT Talk
About Articles & News
Special Sessions

Acoustic Control Systems Ltd.
develop and manufacture hi-tech devices for Ultrasonic Testing

Technical Discussions
13:59 May-11-2010
Ramachandran L
3524 views
DGS method Attenuation correction curve for 2.5 mm CRR
I am using DGS method for our job UT examination.

How to draw the attenuation correction curve for 2.5 mm CRR?

I have the following information

1. Beam path & Δv from the probe data sheet

2. Material: Q&T Low alloy steel

3. Probe : Krautkramer probes.

a WB 45 °/2Mhz, 20x22 probe

b MB 4 S-N / 4 Mhz , dia 10mm

To calculate Corrected Δ vg with Attenuation = Δv + ( α k - α s ).

Δv= The gain difference of sound path between 2.5mm CRR & "0 dB" attenuation curve from data sheet.
Alpha K (α k)= Sound absorption at 100mm Using V1 block
Alpha S (( α s) =Sound absorption for the testing raw material

I don't have value for Alpha s ( α s) and Alpha K (α k) for angle probe and normal probe.
Does Alpha s ( α s) of these materials changes w.r.t probe or Probe frequency?

My acceptance standard ask for minimum 1.78mm CRR and 2.5 mm CRR Maximum.

We have USK 7 M/c

I have to manually draw the curve.

Can u please explain with and example

please help me in calculating the curves with respect to' 0' dB attenuation curve from data sheet.

I request you to mail me the details (or) give a reference book to read and understand the method of curve creation.
 
 
20:59 May-17-2010

Swaminathan.S

Engineering, QA/QC/NDT,
NOV (National Oilwell Varco),
Angola,
Joined Mar 2006
35
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Ramachandran L on 13:59 May-11-2010 (Opening).

When I was using different material from which DGS curve given by kk make probes, i will take back wall echo form testing material (Multiple echos when you compress the sweep range) you can see the different thickness and it will look like a curve. You have to plot this in log sheet. Sorry I don't have any example.
SSK

 
 
21:57 May-17-2010

Nigel Armstrong

Engineering, - Specialist services,
United Kingdom,
Joined Oct 2000
912
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Ramachandran L on 13:59 May-11-2010 (Opening).

http://www.bindt.org/Content.asp?ProdCatID=1&ProdID=63

The link is to John Drury's book on the BINDT website, "Ultrasonic flaw detection for technicians". It costs £25 and has a chapter on DGS techniques. Its a good all-round book on UT theory and practice at sufficient level to be of interest to most.

 
 
09:37 May-18-2010

Jon Wallis

NDT Inspector, - ,
Netherlands,
Joined Feb 2010
494
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Ramachandran L on 13:59 May-11-2010 (Opening).

I'm not sure of all the abbreviations you have used but the answer to the question of how to produce a curve for a given flat bottomed hole from a data sheet is as follows:
- note on your data sheet the dB level for an inf. large reflector (∞) - often around 2dB
- choose your flat bottom hole i.e. 2mm and note the amount of extra dB's this gives
- repeat this for several different distances up to the necessary maximum depending
on the wall thickness being examined.
- you will now have a table of distances and dB values which you can now draw on
your screen.

Beware of the following:

- The difference in dB is between the particular fbh and the infinately large reflector, as you move along the data sheet at different distances the base reflector stays the same. So, if your ∞ with a 25mm reflector is 2dB say, this remains 2dB throughout the construction of your curve.
- Δv is the difference between your calibration reflector (e.g. 25mm radius) and an infinately large reflector and can be either gain increase or decrease.
- the horizontal axis is the beam path, not the wall thickness.

This is fairly complicated to explain and an understanding of the principals is necessary. As well as John Drury's book, there is also the blue book by Krautkrämer which will explain this procedure.

 
 
10:43 May-18-2010
Ramachandran L
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Jon Wallis on 09:37 May-18-2010 .

Dear Nigel

Thank you for the DGS Book Link.
Ultrasonic Flaw Detection for Technicians - (DRURULT)

Author: J C Drury
Publisher: Silverwing

I shall get the book and read.

 
 
11:02 May-18-2010
Ramachandran L
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Jon Wallis on 09:37 May-18-2010 .

Dear Jon Wallis

Thank you for basic information.
What you say is good for a Standard CRR 2 or 3mm etc.,
Let me ask you in simple way
When your testing procedure asks for 1.78 mm CRR to 2.5 mm CRR.
How to draw the curve?

I also know about the blue book from KK.
I do not have this blue book by Krautkrämer

I checked with the M/s GE Sales represnetative in India.
Since present m/c are coming with preset curve the issue of hard copy has been stopped.
If u have one copy. Can please mail me the scanned copy,
to my mail ed ID.lrcbama@gmail.com

 
 
11:40 May-18-2010

Jon Wallis

NDT Inspector, - ,
Netherlands,
Joined Feb 2010
494
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Ramachandran L on 11:02 May-18-2010 .

A CRR 2,5mm is not so difficult you simply take the dB value between 2mm and 3mm. You are, after all, using a USK7 (which has dB steps of 2dB doesn't it?) which won't allow an accuracy you would get with a digital unit.

A CRR 1,78mm sounds to me as if this is a conversion from imperial to metric up to 2 decimal places. Personally I would create a curve to CRR 1,5mm this very slightly more sensitive than 1,78 so would fulfill the clients requirements and the difference is so small as to be negligible for practical purposes.

If you can get hold of a digital UT unit with pre stored curves, you can call up a curve accurate to 1 digital place for a given probe (CRR 1,7mm, say).

I'm not sure what your client means when he requests a maximum and a minimum in his acceptance standard. An acceptance standard is a single level above which a discontinuity is not acceptable.

 
 
01:59 May-19-2010

Neil Burleigh

Sales,
Krautkramer Australia Pty Ltd,
Australia,
Joined Dec 2002
102
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Ramachandran L on 11:02 May-18-2010 .

Hello Everyone,
The Krautkramer "Blue book" is now out of print the author Udo Schlengermann is a frequent subscriber to these forums. I still have a couple of copies of the "Blue book" which we are keeping for prosperity (for trivia buffs this book was actually white for a while).
I have been in discussions with GE, the owner of the rights to this book, to produce an electronic copy of the "Blue book" I will bring the matter up again when I am in Europe next month and let you know how I get on.

We also keep copies of John Drury's book here in Australia.

Regards
Neil Burleigh

 
 
06:29 May-19-2010
Ramachandran L
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Jon Wallis on 11:40 May-18-2010 .

Dear Jon wallis,

Your information was useful.
Thank you for the update.
I have USK 7 as you said I can interpolate and get the 2.5mm CRR.
But my material of testing is different from IIW V1 or V2 block steel.
It is Q&T Low alloy steel.
The attenuation properties will vary from IIW V1 or V2 block.

Take into consideration of this attenuation losses.

I hope this these losses are

Alpha K (α k)= Sound absorption at 100mm Using V1 block
Alpha S (( α s) =Sound absorption for the testing raw material

How to generate a curve for 1.78 mm and 2.5 mm CRR.

 
 
06:34 May-19-2010
Ramachandran L
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Neil Burleigh on 01:59 May-19-2010 .

Dear Neil,

Thank you so much for the concern.
If you can take up the issue with KK.
A electronic copy will a useful information for researchers.

I located the Book from my library.
Author: J C Drury
Publisher: Silverwing

Awaiting for you mail and reply after favorable discussion with KK

 
 
09:44 May-19-2010

Jon Wallis

NDT Inspector, - ,
Netherlands,
Joined Feb 2010
494
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Ramachandran L on 06:29 May-19-2010 .

As I recommended in my last post, use a CRR of 1.5mm.

I don't know what Q&T low alloy steel is, maybe someone else can help you there? If the attenuation of the material is different from that in the calibration block then you cannot perform the examination without custom made blocks and the data sheets will not be correct.

I don't think you can make a correlation for the difference in attenuation between materials and simply correct the dB values because the 'shape' of the curve will be different. Do not forget, the purpose of a transfer correction (difference in dB between cal. block and examination material) is to compensate for surface roughness and coupling differences, not for material attenuation.

Regards, Jon

 
 
13:33 May-19-2010

Nigel Armstrong

Engineering, - Specialist services,
United Kingdom,
Joined Oct 2000
912
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Neil Burleigh on 01:59 May-19-2010 .

Neil

Trivia can be fun! I thought the Blue Book always was white as printed, just it came in a blue plastic protective sleeve.

 
 
13:15 May-21-2010
Ramachandran L
Re: DGS method Attenuation correction curve for 2.5 mm CRR
In Reply to Jon Wallis on 09:44 May-19-2010 .

Dear Jon Wallis,
According to J.C.Drury
DGS curve
Types of Losses to be considered:
1. Transfer losses.
• Couplant losses
• Surface roughness (between the reference block and the work piece)
3. Attenuation losses.
Example:
Material thickness 100mm, One Near field distance 21mm.
If there were no attenuation losses,
The dB difference between a 1st back wall echo and 2nd back wall echo should be 6dB
(i.e., Amplitude is inversely proportional to Distance beyond about 3 near field).
Suppose actual difference measured is 13dB, then the extra 7 dB would be due to attenuation of the beam.
Therefore the attenuation of the material is 7dB / 200mm = 0.033 dB/mm (i.e. 33 dB/meter).
DGS curve for compression wave
For example: Assume a defect at a depth of 84 mm, the gain of the flaw would be on the 32dB line for a 2mm CRR. If the attenuation loss of 0.033dB/ mm is considered, then of that 32 dB
Say, Depth of defect x 2 x Attenuation of the material
84 mm x 2 x 0.033 mm= 5.5 dB
(32dB -5.5dB) = 26.5dB was the real ‘GAIN’ of the flaw.
If we go back to the DGS curve and see this 4 th Near field Distance(21mm NF x 4=84mm), the Flaw size would be 3mm CRR for 26.5dB instead without attenuation losses the 32dB gain level would be 2mm CRR curve.
We will under estimate the Flaw size.
When attenuation losses are ignored.
From the above, we conclude Attenuation losses should be considered.
Similarly, Considering the attenuation losses of the material to be tested, how shall we create a DGS Curve for 1.78mm and 2.5mm CRR?

 
 
Your Email Address: You will receive an email when a new message of this topic appears


© NDT.net   |Advertise|   |Contact|   |About Us