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1775 views
04:49 Aug-10-2004

Mike Trinidad

Consultant, API 510 570 & 653
Marine Inspection Service Pty Ltd (MIS),
Australia,
Joined Jan 2003
138
What is a B Scan?

Can anyone tell me what a B scan image should be as I haven't seen one for some time. UT theory states that a B scan is a cross sectional view of the component. Having a cross sectional view would be of some benefit in identifying the damage and for fitness for purpose.

Now many instruments 'claim' to have B scan yet the image is nothing like the actual defect dimensions. Is their no standard for sensitivity of B scans as there is for the other forms of UT?

I would be interested in comments from the fourm regarding this issue as personally having an instrument supposedly doing inspection work that has no resolution should not be marketed.

Obviously there is good equipment out there but their is also not, should there be a standard or is there a standard?


 
04:47 Aug-11-2004

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1197
Re: What is a B Scan? Hello Mike:
B-scan has long been as you described it; providing a cross sectional view of a component. The exposure I first had to this was from the 1959 version of the NDT Handbook edited by McMaster. Then it seemed to be used only in zero-degree tests (immersion or contact).
Since then the imaging terminoly seems to be a bit more cluttered with letters of the alphabet. In the TOFD applications this tends to relate to weld centreline as a reference. THere a B-scan implies probe motion perpendicular to the weld axis and they reserve D-scan for the cross sectional representation where the probe motion is parallel to the weld axis.
But Both are "cross sections" so often get called Bscans.
When we inspect at some angle, time is equated to depth, but we must imagine the results "projected". This, I believe is where the origin of the term "P-scan" comes from (Projection scan).

But as to your comment on sensitivity, that should be taken care of in the setup. More recently we construct our Bscans from the raw Ascan not just some thresholded value of amplitude. As such, these can also be termed "stacked A-scans", i.e. a colour encoded amplitude of every point on a flash capture of each Ascan. If the system does NOT have colour control then we are stuck with a go/no-go system which is not usually very useful.

Since Bscans constructed from captured Ascans are easily manipulated by the computer to display colour levels for the lowest amplitude, we SHOULD have no problems with sensitivity. If the A-scan was used to set detection sensitivity then the colour palette used should indicate amplitudes down to whatever level you require (even down to 1% FSH).

Another issue related to this might be the digitisation frequency. If the probe you are using is 10-15MHz and you are trying to resolve thicknesses accurately then the B-scan that results might not provide the thickness accuracy you are hoping for if it was set up using a 25MHz digitisation frequency.

In your comments you also mention that"yet the image is nothing like the actual defect dimensions". This may not be entirely the fault of the B-scan but merely the method of assessing dimensions.

Regards
Ed

----------- Start Original Message -----------
: Can anyone tell me what a B scan image should be as I haven't seen one for some time. UT theory states that a B scan is a cross sectional view of the component. Having a cross sectional view would be of some benefit in identifying the damage and for fitness for purpose.
: Now many instruments 'claim' to have B scan yet the image is nothing like the actual defect dimensions. Is their no standard for sensitivity of B scans as there is for the other forms of UT?
: I would be interested in comments from the fourm regarding this issue as personally having an instrument supposedly doing inspection work that has no resolution should not be marketed.
: Obviously there is good equipment out there but their is also not, should there be a standard or is there a standard?
------------ End Original Message ------------




 
01:11 Aug-11-2004

Mike Trinidad

Consultant, API 510 570 & 653
Marine Inspection Service Pty Ltd (MIS),
Australia,
Joined Jan 2003
138
Re: What is a B Scan? G'Day Ed

Glad you made it back ok. I understand the sensitivity and capture rate etc can be adjusted to gain an acceptable resolution. My interest is in why there is no standard to what a B scan should or should not be. A lot of supposed B scans are nothing of the sort if what we are after is a cross sectional view. A large number of B scans would not be able to resolve the steps on a V1 block yet there are used in the inspection of pressure vessels, tanks and pipelines everywhere.

As there appears to be no standard for B scan I would have thought the default would be that the standard zero degree transducer requirements such as resolution should apply?


----------- Start Original Message -----------
: Hello Mike:
: B-scan has long been as you described it; providing a cross sectional view of a component. The exposure I first had to this was from the 1959 version of the NDT Handbook edited by McMaster. Then it seemed to be used only in zero-degree tests (immersion or contact).
: Since then the imaging terminoly seems to be a bit more cluttered with letters of the alphabet. In the TOFD applications this tends to relate to weld centreline as a reference. THere a B-scan implies probe motion perpendicular to the weld axis and they reserve D-scan for the cross sectional representation where the probe motion is parallel to the weld axis.
: But Both are "cross sections" so often get called Bscans.
: When we inspect at some angle, time is equated to depth, but we must imagine the results "projected". This, I believe is where the origin of the term "P-scan" comes from (Projection scan).
: But as to your comment on sensitivity, that should be taken care of in the setup. More recently we construct our Bscans from the raw Ascan not just some thresholded value of amplitude. As such, these can also be termed "stacked A-scans", i.e. a colour encoded amplitude of every point on a flash capture of each Ascan. If the system does NOT have colour control then we are stuck with a go/no-go system which is not usually very useful.
: Since Bscans constructed from captured Ascans are easily manipulated by the computer to display colour levels for the lowest amplitude, we SHOULD have no problems with sensitivity. If the A-scan was used to set detection sensitivity then the colour palette used should indicate amplitudes down to whatever level you require (even down to 1% FSH).
: Another issue related to this might be the digitisation frequency. If the probe you are using is 10-15MHz and you are trying to resolve thicknesses accurately then the B-scan that results might not provide the thickness accuracy you are hoping for if it was set up using a 25MHz digitisation frequency.
: In your comments you also mention that "yet the image is nothing like the actual defect dimensions". This may not be entirely the fault of the B-scan but merely the method of assessing dimensions.
: Regards
: Ed
: : Can anyone tell me what a B scan image should be as I haven't seen one for sometime. UT theory states that a B scan is a cross sectional view of the component. Having a cross sectional view would be of some benefit in identifying the damage and for fitness for purpose.
: : Now many instruments 'claim' to have B scan yet the image is nothing like the actual defect dimensions. Is their no standard for sensitivity of B scans as there is for the other forms of UT?
: : I would be interested in comments from the fourm regarding this issue as personally having an instrument supposedly doing inspection work that has no resolution should not be marketed.
: : Obviously there is good equipment out there but their is also not, should there be a standard or is there a standard?
------------ End Original Message ------------




 
05:37 Aug-11-2004

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
278
Re: What is a B Scan? Its a good discussion Mike and shows how buyers of services fail to specify what they expect. Users should understand that the business end as Ed says is dictated by UT resolution. If you wnat displays to be What you see is what you get thay have to specify this. Its often like pulling teeth to get clients to understand they need to specify and hence why no one comes up with a 'satandard' for a B Scan.

Too many people are blinded by the myriad of software display possibilities without looking at the base resolution and the true question, is what I am looking at a true representation.

A poor display if accurate is to my mind better than 128 colours which is inaccurate.

Simple answer I think is you specify what you want or will dleiver and make people recognise that fact.


 
03:15 Aug-12-2004

Mike Trinidad

Consultant, API 510 570 & 653
Marine Inspection Service Pty Ltd (MIS),
Australia,
Joined Jan 2003
138
Re: What is a B Scan? G'Day John

I just find it odd that B scan has no resolution standard or perhaps it has been considered such a low end offshoot no-one really cared. For every other method there is resolution requirements. For C scan it is normally a flat bottom hole and the encoder sequence has to be taken into consideration.

I agree the client or the purchaser should be more discriminatory. I have been fortunate/unfortunate to have had something to do with ultrasonic B scan development over the past 7 years and in particuliar analog versus digital problems especially in the latter. In my naivity at the beginning I expected digital to be far superior to the older analog systems which were not for various reasons such as what Ed mentioned earlier.

One point is that if conducting a B scan of a pipe or vessel then at minimum the usual plate testing codes would apply in terms of resolution?


Mike Trinidad


----------- Start Original Message -----------
: Its a good discussion Mike and shows how buyers ofservices fail to specify what they expect. Users should understand that the business end as Ed says is dictated by UT resolution. If you wnat displays to be What you see is what you get thay have to specify this. Its often like pulling teeth to get clients to understand they need to specify and hence why no one comes up with a 'satandard' for a B Scan.
: Too many people are blinded by the myriad of software display possibilities without looking at the base resolution and the true question, is what I am looking at a true representation.
: A poor display if accurate is to my mind better than 128 colours which is inaccurate.
: Simple answer I think is you specify what you want or will dleiver and make people recognise that fact.
------------ End Original Message ------------




 
05:41 Aug-13-2004

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
278
Re: What is a B Scan? Your last line sums up what is the real problem. people have to remmber that no matter how fancy the displays the core resolution and specification compliance is what matters.

The number of computer Gurus who think that they should be exempt from standard UT testing and qualification procedures abounds.

In the past people would have said no need for a display standard as it was 'niche' parts of the UT market. That has significantly changed.


 
05:07 Sep-26-2004

David Hermanutz

Consultant,
Hbndt.com,
China,
Joined Jul 2012
85
Re: What is a B Scan? Hi Mike and others,

B-Scan use and misuse has grown significantly with the onsite of portable digital equipment. Most petroleum codes stipulate "A-Scan" calibration and resolution requirements as a minimum accepted level for corrosion and flaw detection. Production and record minded managers often stipulate B-Scan for corrosion searching as it is seen as a faster method of inspection, provides a hard copy and is seen as 1 step over the legal requirements for inspection.

Most field technicians use a Step Wedge for all corrosion calibrations, the probe that is used falls within the standard requirements and procedures for corrosion. So as long as the operator is not exceeded the minimum travel speed (I believe most standards use 6 inches per second), and is using an A-Scan for primary inspection, using the B-Scan for data-recording everything should be OK.

However, the B-Scan problems all start when the technology starts to override the minimum requirements of code. A few ideas to think about:

B-scanonly display; unless qualified with a proper calibration/resolution block at the actual scan speeds being performed in the field, the inspection will be compromised due to missed data from the returned UT signal and sampling rates.

Loss of couplant issues; is the absence of backwall being alarmed? B-Scans often miss tank floor flux leakage equipment due to rounded geometry of the ID pit.

Coverage issues; are the scan overlaps being adhered to? Anything less than an auto or semi-automated rastor scan may miss what you're looking for.

Operator competence issues; B-Scan imaging is seen as a simpler method of viewing the problem and junior operators are often assigned to the repetitive tasks of B-Scans. Is the operator aware of the underlying UT that is generating his data? Quite often this can be overlooked when the "simple" display is being used for primary inspection. How often has a tank floor thickness come out at the same acoustic time as the delay wedge when someone hits the Dual/single crystal button?

In short,

B-Scans don't replace A-scans, they are supplemental and extra technology to our scanning also adds extra problems to be aware of.

All the best,

David Hermanutz
RTD Quality Services
Pipeline Integrity Division

----------- Start Original Message -----------
: Your last line sums up what is the real problem. people have to remmber that no matter how fancy the displays the core resolution and specification compliance is what matters.
: The number of computer Gurus who think that they should be exempt from standard UT testing and qualification procedures abounds.
: In the past people would have said no need for a display standard as it was 'niche' parts of the UT market. That has significantly changed.
------------ End Original Message ------------




 


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