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Technical Discussions
Nico Nieuwoudt
Nico Nieuwoudt
03:53 Mar-13-2007
TOFD scanning of process piping

I would like to implement TOFD scanning on pipe welded joints at Hawiyah NGL Project, Saudi Arabia. Unfortunately, we make use of ASME B31.3 - Process Piping and I cannot find a correlation between any code and ASME B31.3.

Please be so kind and assist me with an answer to whether I am permitted to use TOFD in lieu of RT under ASME B31.3 and if there is a correlation between BS or EN and ASME B31.3.


 
 Reply 
 
mj
mj
01:09 Mar-13-2007
Re: TOFD scanning of process piping
----------- Start Original Message -----------b31.3 not permitting to use TOFD in lieu of Radiography.. BUT you can use normal pulse echo tech. with your AUT Equipment (based on your equipment)... as per b31.3 amplitude and length is considering to evaluate and interpretate the defect but with TOFD we are not able to find the amplitude of the defect.

------------ End Original Message ------------




 
 Reply 
 
David Mackintosh
Engineering,
Acuren Group Inc., Canada, Joined Feb 2011, 85

David Mackintosh

Engineering,
Acuren Group Inc.,
Canada,
Joined Feb 2011
85
09:02 Mar-14-2007
Re: TOFD scanning of process piping
----------- Start Original Message -----------
: I would like to implement TOFD scanning on pipe welded joints at Hawiyah NGL Project, Saudi Arabia. Unfortunately, we make use of ASME B31.3 - Process Piping and I cannot find a correlation between any code and ASME B31.3.
: Please be so kind and assist me with an answer to whether I am permitted to use TOFD in lieu of RT under ASME B31.3 and if there is a correlation between BS or EN and ASME B31.3.
------------ End Original Message ------------

B31.3 says:
"341.4.1(b)(1) Not less than 5% of circumferential butt and miter groove welds shall be examined fully by random radiography in accordance with para. 344.5 or by random ultrasonic examination in accordance with para. 344.6."

and:

"344.6 Ultrasonic Examination
Ultrasonic examination of welds shall be performed in
accordance with BPV Code, Section V, Article 5."
I believe this is a typo: weld examination is now covered in Sec V Art 4.


 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1282

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1282
02:01 Mar-15-2007
Re: TOFD scanning of process piping
David:
I suspect it may be an old reference and not a typo.
Until the 2003 update of the 2001 Edition of ASME Section V Article 4 was for Inservice inspections and Artcile 5 was for Materials. As of the 2003 update Article 4 was devoted to welds and Article 5 to Materials. ASME B31 committees are separate from ASME Section committees and their respective "updates" do not all occur as nicely synchronised documents. But it may be that B31.3 is now far out of step with ASME BPVCode.
AS for use of TOFD with B31.3... I believe there is a case for it but you will want to be VERY careful because TOFD will be finind a lot more than pulse-echo. In Article 4 T-482.2 states that for non distance amplitude techniques (TOFD) all indications over 40% of the rejectable LENGTH are investigated in terms of the acceptance criteria (ie you look at the length instead of the amplitude to assess the acceptance of the flaw).
Mandatory Appendix III now describes how you MUSt set up a TOFD configuration for ASMEwork.
Ed

----------- Start Original Message -----------
: : I would like to implement TOFD scanning on pipe welded joints at Hawiyah NGL Project, Saudi Arabia. Unfortunately, we make use of ASME B31.3 - Process Piping and I cannot find a correlation between any code and ASME B31.3.
: : Please be so kind and assist me with an answer to whether I am permitted to use TOFD in lieu of RT under ASME B31.3 and if there is a correlation between BS or EN and ASME B31.3.
: B31.3 says:
: "341.4.1(b)(1) Not less than 5% of circumferential butt and miter groove welds shall be examined fully by random radiography in accordance with para. 344.5 or by random ultrasonic examination in accordance with para. 344.6."
: and:
: "344.6 Ultrasonic Examination
: Ultrasonic examination of welds shall be performed in
: accordance with BPV Code, Section V, Article 5."
: I believe this is a typo: weld examination is now covered in Sec V Art 4.
------------ End Original Message ------------




 
 Reply 
 
Mark Badrick
Inspection
Bahrain Petroleum Co, Bahrain, Joined Oct 1999, 11

Mark Badrick

Inspection
Bahrain Petroleum Co,
Bahrain,
Joined Oct 1999
11
02:33 Mar-15-2007
Re: TOFD scanning of process piping
Yes Ed there is a Code Case - B31 Case 181, issued in January I beleive.

Mark


----------- Start Original Message -----------
: David:
: I suspect it may be an old reference and not a typo.
: Until the 2003 update of the 2001 Edition of ASME Section V Article 4 was for Inservice inspections and Artcile 5 was for Materials. As of the 2003 update Article 4 was devoted to welds and Article 5 to Materials. ASME B31 committees are separate from ASME Section committees and their respective "updates" do not all occur as nicely synchronised documents. But it may be that B31.3 is now far out of step with ASME BPVCode.
: AS for use of TOFD with B31.3... I believe there is a case for it but you will want to be VERY careful because TOFD will be finind a lot more than pulse-echo. In Article 4 T-482.2 states that for non distance amplitude techniques (TOFD) all indications over 40% of the rejectable LENGTH are investigated in terms of the acceptance criteria (ie you look at the length instead of the amplitude to assess the acceptance of the flaw).
: Mandatory Appendix III now describes how you MUSt set up a TOFD configuration for ASME work.
: Ed
:
:
: : : I would like to implement TOFD scanning on pipe welded joints at Hawiyah NGL Project, Saudi Arabia. Unfortunately, we make use of ASME B31.3 - Process Piping and I cannot find a correlation between any code and ASME B31.3.
: : : Please be so kind and assist me with an answer to whether I am permitted to use TOFD in lieu of RT under ASME B31.3 and if there is a correlation between BS or EN and ASME B31.3.
: : B31.3 says:
: : "341.4.1(b)(1) Not less than 5% of circumferential butt and miter groove welds shall be examined fully by random radiography in accordance with para. 344.5 or by random ultrasonic examination in accordance with para. 344.6."
: : and:
: : "344.6 Ultrasonic Examination
: : Ultrasonic examination of welds shall be performed in
: : accordance with BPV Code, Section V, Article 5."
: : I believe this is a typo: weld examination is now covered in Sec V Art 4.
------------ End Original Message ------------




 
 Reply 
 
David Mackintosh
Engineering,
Acuren Group Inc., Canada, Joined Feb 2011, 85

David Mackintosh

Engineering,
Acuren Group Inc.,
Canada,
Joined Feb 2011
85
05:57 Mar-15-2007
Re: TOFD scanning of process piping
----------- Start Original Message -----------
: I would like to implement TOFD scanning on pipe welded joints at Hawiyah NGL Project, Saudi Arabia. Unfortunately, we make use of ASME B31.3 - Process Piping and I cannot find a correlation between any code and ASME B31.3.
: Please be so kind and assist me with an answer to whether I am permitted to use TOFD in lieu of RT under ASME B31.3 and if there is a correlation between BS or EN and ASME B31.3.
------------ End Original Message ------------

The code case mentioned by Mr. Badrick is below.




 
 Reply 
 
Rohit Bafna
,
TCR Engineering Services, India, Joined Sep 2007, 18

Rohit Bafna

,
TCR Engineering Services,
India,
Joined Sep 2007
18
04:59 May-19-2007
Re: TOFD scanning of process piping
One of our clients has asked us to inquire if ToFD could be used in place of RT in ASME B31.3. The B31.3 does not permit and Incomplete Fusion, but does allow some slag, and we'd like to inquire about how ToFD will detect the same.

Any advise will be appreciated. Have read the earlier posting on this subject and am looking for some explanation. Is there any paper on this subject? I do find that now there is a strong sense of demand to use ToFD and your help on the code interpretation will assist my thought process.

Thanks in advance.


 
 Reply 
 
Nigel
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
06:37 May-21-2007
Re: TOFD scanning of process piping
Rohit
I think you are asking how is the TOFD method used to discriminate between different types of defects, e.g. lack of fusion and slag inclusions for acceptance/rejection. Certainly when employing radiography for weld inspection it is important to be able to differentiate between lack-of-fusion (LOF) and slag inclusions as the Code has zero-tolerance of LOF but allows up to twice the wall thickness for slag.

344.6.2. of the Code gives the ultrasonic examination acceptance criteria for flaw length indications with amplitude exceeding the reference level. The test sensitivity is set using the responses from known dimension reflectors in stipulated calibration pieces to derive a distance-amplitude correction (DAC) curve for each probe utilised.

However Code Case 181 of B31 gives alternative ultrasonic acceptance criteria to 344.6.2. Para (i)(1) of the Case states the Data Analysis Criteria and it stipulates the criteria for evaluating reflectors as to their origin, e.g. flaws or geometry and (b) a non-amplitude technique is based on whether or not the indication exceeds a fixed length. If this is exceeded then the indication has to be further evaluated taking into account its location, length, height and, for materials over 25mm thick, its "aspect ratio", i.e. height-to-length.

So TOFD is perfectly acceptable to use as per Code Case 181 and the question of distinguishing between LOF and slag is, I believe, a non-sequitir.

That is not to say that it would not be of great interst to know if TOFD is capable of flaw characterisation and identification. For manual UT, defect location and orientation and the response to multiple probe angle and location interrogation and manipulation (orbital, swivel, rotation, translation) has been the key to defect identification. I believe that for proper defect identifcation a TOFD parallel scan would have to be supplemented by 90 degree scans and perhaps others.

I hope this clarifies the position vis-a-vis the Code, though I feel I have not been of help in the case of defect discrimination using TOFD.


----------- Start Original Message -----------
: One of our clients has asked us to inquire if ToFD could be used in place of RT in ASME B31.3. The B31.3 does not permit and Incomplete Fusion, but does allow some slag, and we'd like to inquire about how ToFD will detect the same.
: Any advise will be appreciated. Have read the earlier posting on this subject and am looking for some explanation. Is there any paper on this subject? I do find that now there is a strong sense of demand to use ToFD and your help on the code interpretation will assist my thought process.
: Thanks in advance.
------------ End Original Message ------------




 
 Reply 
 
Rohit Bafna
,
TCR Engineering Services, India, Joined Sep 2007, 18

Rohit Bafna

,
TCR Engineering Services,
India,
Joined Sep 2007
18
01:22 May-23-2007
Re: TOFD scanning of process piping
Thanks Nigel for your explanation,however my question still remains regarding differntiation between LoF and Slaf while doing ToFD or PA. Ideally I'd like us to move away from Radiography and use the Omniscan.


 
 Reply 
 
J. Mark Davis
Teacher, And Consultant
University of Ultrasonics, Birmingham, Alabama, USA, Joined Mar 2000, 85

J. Mark Davis

Teacher, And Consultant
University of Ultrasonics, Birmingham, Alabama,
USA,
Joined Mar 2000
85
03:02 May-23-2007
Re: TOFD scanning of process piping
First, even with Phased Array, you will still need to analyze the signals using the Ascan Data.

LOF being a planar defect will tend to have a fast rise and fall time, and a short pulse duration.

Slag is a volumetric defect and tends to have a slow rise and a long duration.

Both defects can cause a beam redirection to the OD or the ID.

And, both can look the same depending upon angle of refraction, frequency, etc.

The huge advantage of Phased Array is the ability to sweep the refracted sound beam to the optimum angle while observing the A scan data. Using a Phased Array system like the OmniScan with a true depth calibration will significantly aid in your evaluation by observing the Ascan signal and the collateral image in the sector scan.

Also, after the scan data is frozen, you can analyze along the length of the flaw and look at the signal dynamically as you scroll along the length of the defect observing the rise and fall time, and the pulse duration of the signals.

LOF can produce multipleimages that will apear to ring down and have muliple echos at equadistances. This is due to beam redirction and mode conversion.

A concern I am dealing with now is UT inspectors right out of school who have limited field experience with UT A scan (and have jumped into Phased Array), are trying to analyze Phased Array data (Ascan, B scan, C scan and S scan data) when they don't really understand flaw charcaterization with signal analysis in A scan. I am not being critical, just an recent observation with some younger students.

Also, please realize that as with radiography, you can have several people look at a radiograph and make a slag or a LOF call, and sometimes not all wil be in agreement. The same will hold true with UT and Phased Array.

I teach a Flaw Detection and Characterizatiuon classes and I am the Administrator for the API QUTE Exmination. Many people still struggle with classifcation of slag versus LOF.

If the indication plots to the weld fusion line this probably is side wall lack of fusion. If the indication plots to the weld centerline, line this is probably Slag. Plus, you still analyze Rise and Fall and Pulse Duration.

I hope this helps.

Sincerely,

J. Mark Davis


----------- Start Original Message -----------
: Thanks Nigel for your explanation,however my question still remains regarding differntiation between LoF and Slaf while doing ToFD or PA. Ideally I'd like us to move away from Radiography and use the Omniscan.
------------ End Original Message ------------




 
 Reply 
 
Jarno de Jonge
Jarno de Jonge
00:06 May-24-2007
Re: TOFD scanning of process piping
Dear Nigel,

I am using TOFD and knew about code case 2235 for vessels for quite a while and recently found out about code case 181 for the piping.

So now it seems that the big code issues with TOFD has been dealt with. The question I have is about thicknesses that are not covered in these code cases. Thincknesses below 13 mm are not covered in cc 2235 and now I read (haven't actually had a chance to study the document) that cc 181 is only valid for thicknesses over 25 mm. I would say there is a lot of piping with thicknesses below 25 mm so then we will have the same old problem again. Or not?

Do you have experience with this and how is this problem dealt with in practice?

Thanks for your help in advance.

Kind Regards,

Jarno
----------- Start Original Message -----------
: Rohit
: I think you are asking how is the TOFD method used to discriminate between different types of defects, e.g. lack of fusion and slag inclusions for acceptance/rejection. Certainly when employing radiography forweld inspection it is important to be able to differentiate between lack-of-fusion (LOF) and slag inclusions as the Code has zero-tolerance of LOF but allows up to twice the wall thickness for slag.
: 344.6.2. of the Code gives the ultrasonic examination acceptance criteria for flaw length indications with amplitude exceeding the reference level. The test sensitivity is set using the responses from known dimension reflectors in stipulated calibration pieces to derive a distance-amplitude correction (DAC) curve for each probe utilised.
:
: However Code Case 181 of B31 gives alternative ultrasonic acceptance criteria to 344.6.2. Para (i)(1) of the Case states the Data Analysis Criteria and it stipulates the criteria for evaluating reflectors as to their origin, e.g. flaws or geometry and (b) a non-amplitude technique is based on whether or not the indication exceeds a fixed length. If this is exceeded then the indication has to be further evaluated taking into account its location, length, heightand, for materials over 25mm thick, its "aspect ratio", i.e. height-to-length.
: So TOFD is perfectly acceptable to use as per Code Case 181 and the question of distinguishing between LOF and slag is, I believe, a non-sequitir.
: That is not to say that it would not be of great interst to know if TOFD is capable of flaw characterisation and identification. For manual UT, defect location and orientation and the response to multiple probe angle and location interrogation and manipulation (orbital, swivel, rotation, translation) has been the key to defect identification. I believe that for proper defect identifcation a TOFD parallel scan would have to be supplemented by 90 degree scans and perhaps others.
: I hope this clarifies the position vis-a-vis the Code, though I feel I have not been of help in the case of defect discrimination using TOFD.
:
: : One of our clients has asked us to inquire if ToFD could be used in place of RT in ASME B31.3. The B31.3 does not permit and Incomplete Fusion, but does allow some slag, and we'd like to inquire about how ToFD will detect the same.
: : Any advise will be appreciated. Have read the earlier posting on this subject and am looking for some explanation. Is there any paper on this subject? I do find that now there is a strong sense of demand to use ToFD and your help on the code interpretation will assist my thought process.
: : Thanks in advance.
------------ End Original Message ------------




 
 Reply 
 
Nigel
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
01:54 May-25-2007
Re: TOFD scanning of process piping

Hi Jarno

Unlike Code Case 2235 of ASME, Code B31 Case 181 does NOT stipulate a minimum wall thickness. Table 1 is the acceptance criteria for weld thicknesses less than 25 mm. It is based on two requirements, 1) the defect vertical height is less than about 1/3 of the weld thickness for buried and 1/7 for surface-breaking defects and 2) its length is less then 6.4mm.

Table 2 gives acceptance crieria for the cases where welds are between 25 and 64 mm thick, or between 100 and 100 to 300mm thick. The Code says that fro materials between 64 and 100 mm thick interpolation can be used.

Asme V code case 2235-9 allows alternative acceptance crieteria on thicknesses 13mm and greater.

In my opinion both Code Cases are convoluted and difficult to understand documents. Plus defect acceptance/rejection is based on defect through-thickness height against length. Surface and defect interaction rules are typical of those found in API 1104 for AUT but again they hold pit-falls for those unfamiliar with their requirements.

I may also have given the wrong impression to those who have not read either Code Case- they are not specifically about allowing TOFD or AUT or Phased Array systems, rather they deal with alternative Fitness-For-service (FFS) acceptance criteria, which I presume are based on Crack Tip Opening Displacement test results for typical ASME materials.

The Code Cases require demonstration of the ability of the systems to detect both surface-breaking and sub-surface flaws of the maximum allowable size. Due to the lateral wave top surfcae blind spot this may need some special data manipulation for TOFD to achieve.

I hope this helps

Nigel


----------- Start Original Message -----------
: Dear Nigel,
: I am using TOFD and knew about code case 2235 for vessels for quite a while and recently found out about code case 181 for the piping.
: So now it seems that the big code issues with TOFD has been dealt with. The question I have is about thicknesses that are not covered in these code cases. Thincknesses below 13 mm are not covered in cc 2235 and now I read (haven't actually had a chance to study the document) that cc 181 is only valid for thicknesses over 25 mm. I would say there is a lot of piping with thicknesses below 25 mm so then we will have the same old problem again. Or not?
: Do you have experience with this and how is this problem dealt with in practice?
: Thanks for your help in advance.
: Kind Regards,
: Jarno
: : Rohit
: : I think you are asking how is the TOFD method used to discriminate between different types of defects, e.g. lack of fusion and slag inclusions for acceptance/rejection. Certainly when employing radiography for weld inspection it is important to be able to differentiate between lack-of-fusion (LOF) and slag inclusions as the Code has zero-tolerance of LOF but allows up to twice the wall thickness for slag.
: : 344.6.2. of the Code gives the ultrasonic examination acceptance criteria for flaw length indications with amplitude exceeding the reference level. The test sensitivity is set using the responses from known dimension reflectors in stipulated calibration pieces to derive a distance-amplitude correction (DAC) curve for each probe utilised.
: :
: : However Code Case 181 of B31 gives alternative ultrasonic acceptance criteria to 344.6.2. Para (i)(1) of the Case states the Data Analysis Criteria and it stipulates the criteria for evaluating reflectors as to their origin, e.g. flaws or geometry and (b) a non-amplitude technique is based on whether or not the indication exceeds a fixed length. If this is exceeded then the indication has to be further evaluated taking into account its location, length, height and, for materials over 25mm thick, its "aspect ratio", i.e. height-to-length.
: : So TOFD is perfectly acceptable to use as per Code Case 181 and the question of distinguishing between LOF and slag is, I believe, a non-sequitir.
: : That is not to say that it would not be of great interst to know if TOFD is capableof flaw characterisation and identification. For manual UT, defect location and orientation and the response to multiple probe angle and location interrogation and manipulation (orbital, swivel, rotation, translation) has been the key to defect identification. I believe that for proper defect identifcation a TOFD parallel scan would have to be supplemented by 90 degree scans and perhaps others.
: : I hope this clarifies the position vis-a-vis the Code, though I feel I have not been of help in the case of defect discrimination using TOFD.
: :
: : : One of our clients has asked us to inquire if ToFD could be used in place of RT in ASME B31.3. The B31.3 does not permit and Incomplete Fusion, but does allow some slag, and we'd like to inquire about how ToFD will detect the same.
: : : Any advise will be appreciated. Have read the earlier posting on this subject and am looking for some explanation. Is there any paper on this subject? I do find that now there is a strong sense of demand to use ToFD and your help on the code interpretation will assist my thought process.
: : : Thanks in advance.
------------ End Original Message ------------




 
 Reply 
 
jarno de jonge
jarno de jonge
09:44 Jun-05-2007
Thanks nigel
Hi Nigel,

Almost forgot about my post here. Thanks for your comprehensive answer.

Jarno

----------- Start Original Message -----------
:
: Hi Jarno
: Unlike Code Case 2235 of ASME, Code B31 Case 181 does NOT stipulate a minimum wall thickness. Table 1 is the acceptance criteria for weld thicknesses less than 25 mm. It is based on two requirements, 1) the defect vertical height is less than about 1/3 of the weld thickness for buried and 1/7 for surface-breaking defects and 2) its length is less then 6.4mm.
: Table 2 gives acceptance crieria for the cases where welds are between 25 and 64 mm thick, or between 100 and 100 to 300mm thick. The Code says that fro materials between 64 and 100 mm thick interpolation can be used.
: Asme V code case 2235-9 allows alternative acceptance crieteria on thicknesses 13mm and greater.
: In my opinion both Code Cases are convoluted and difficult to understand documents. Plus defect acceptance/rejection is based on defect through-thickness height against length. Surface and defect interaction rules are typical of those found in API 1104 for AUT but again they hold pit-falls for those unfamiliar with their requirements.
: I may also have given the wrong impression to those who have not read either Code Case- they are not specifically about allowing TOFD or AUT or Phased Array systems, rather they deal with alternative Fitness-For-service (FFS) acceptance criteria, which I presume are based on Crack Tip Opening Displacement test results for typical ASME materials.
: The Code Cases require demonstration of the ability of the systems to detect both surface-breaking and sub-surface flaws of the maximum allowable size. Due to the lateral wave top surfcae blind spot this may need some special data manipulation for TOFD to achieve.
: I hope this helps
: Nigel
:
: : Dear Nigel,
: : I am using TOFD and knew about code case 2235 for vessels for quite a while and recently found out about code case 181 for the piping.
: : So now it seems that the big code issues with TOFD has been dealt with. The question I have is about thicknesses that are not covered in these code cases. Thincknesses below 13 mm are not covered in cc 2235 and now I read (haven't actually had a chance to study the document) that cc 181 is only valid for thicknesses over 25 mm. I would say there is a lot of piping with thicknesses below 25 mm so then we will have the same old problem again. Or not?
: : Do you have experience with this and how is this problem dealt with in practice?
: : Thanks for your help in advance.
: : Kind Regards,
: : Jarno
: : : Rohit
: : : I think you are asking how is the TOFD method used to discriminate between different types of defects, e.g. lack of fusion and slag inclusions for acceptance/rejection. Certainly when employing radiography for weld inspection it is important to be able to differentiate between lack-of-fusion (LOF) and slag inclusions as the Code has zero-tolerance of LOF but allows up to twice the wall thickness for slag.
: : : 344.6.2. of the Code gives the ultrasonic examination acceptance criteria for flaw length indications with amplitude exceeding the reference level. The test sensitivity is set using the responses from known dimension reflectors in stipulated calibration pieces to derive a distance-amplitude correction (DAC) curve for each probe utilised.
: : :
: : : However Code Case 181 of B31 gives alternative ultrasonic acceptance criteria to 344.6.2. Para (i)(1) of the Case states the Data Analysis Criteria and it stipulates the criteria for evaluating reflectors as to their origin, e.g. flaws or geometry and (b) a non-amplitude technique is based on whether or not the indication exceeds a fixed length. If this is exceeded then the indication has to be further evaluated taking into account its location, length, height and, for materials over 25mm thick, its "aspect ratio", i.e. height-to-length.
: : : So TOFD is perfectly acceptable to use as per Code Case 181 and the question of distinguishing between LOF and slag is, I believe, a non-sequitir.
: : : That is not to say that it would not be of great interst to know if TOFD is capable of flaw characterisation and identification. For manual UT, defect location and orientation and the response to multiple probe angle and location interrogation and manipulation (orbital, swivel, rotation, translation) has been the key to defect identification. I believe that for proper defect identifcation a TOFD parallel scan would have to be supplemented by 90 degree scans and perhaps others.
: : : I hope this clarifies the position vis-a-vis the Code, though I feel I have not been of help in the case of defect discrimination using TOFD.
: : :
: : : : One of our clients has asked us to inquire if ToFD could be used in place of RT in ASME B31.3. The B31.3 does not permit and Incomplete Fusion, but does allow some slag, and we'd like to inquire about how ToFD will detect the same.
: : : : Any advise will be appreciated. Have read the earlier postingon this subject and am looking for some explanation. Is there any paper on this subject? I do find that now there is a strong sense of demand to use ToFD and your help on the code interpretation will assist my thought process.
: : : : Thanks in advance.
------------ End Original Message ------------




 
 Reply 
 
pcdutta
pcdutta
08:02 Jul-21-2007
Re: TOFD scanning of process piping
----for your informaion------- Start Original Message -----------
: Rohit
: I think you are asking how is the TOFD method used to discriminate between different types of defects, e.g. lack of fusion and slag inclusions for acceptance/rejection. Certainly when employing radiography for weld inspection it is important to be able to differentiate between lack-of-fusion (LOF) and slag inclusions as the Code has zero-tolerance of LOF but allows up to twice the wall thickness for slag.
: 344.6.2. of the Code gives the ultrasonic examination acceptance criteria for flaw length indications with amplitude exceeding the reference level. The test sensitivity is set using the responses from known dimension reflectors in stipulated calibration pieces to derive a distance-amplitude correction (DAC) curve for each probe utilised.
:
: However Code Case 181 of B31 gives alternative ultrasonic acceptance criteria to 344.6.2. Para (i)(1) of the Case states the Data Analysis Criteria and it stipulates the criteria for evaluating reflectors as to their origin, e.g. flaws or geometry and (b) a non-amplitude technique is based on whether or not the indication exceeds a fixed length. If this is exceeded then the indication has to be further evaluated taking into account its location, length, height and, for materials over 25mm thick, its "aspect ratio", i.e. height-to-length.
: So TOFD is perfectly acceptable to use as per Code Case 181 and the question of distinguishing between LOF and slag is, I believe, a non-sequitir.
: That is not to say that it would not be of great interst to know if TOFD is capable of flaw characterisation and identification. For manual UT, defect location and orientation and the response to multiple probe angle and location interrogation and manipulation (orbital, swivel, rotation, translation) has been the key to defect identification. I believe that for proper defect identifcation a TOFD parallel scan would have to be supplemented by 90 degree scans and perhaps others.
: I hope this clarifies the position vis-a-vis the Code, though I feel I have not been of help in the case of defect discrimination using TOFD.
:
: : One of our clients has asked us to inquire if ToFD could be used in place of RT in ASME B31.3. The B31.3 does not permit and Incomplete Fusion, but does allow some slag, and we'd like to inquire about how ToFD will detect the same.
: : Any advise will be appreciated. Have read the earlier posting on this subject and am looking for some explanation. Is there any paper on this subject? I do find that now there is a strong sense of demand to use ToFD and your help on the code interpretation will assist my thought process.
: : Thanks in advance.
------------ End Original Message ------------




 
 Reply 
 
Mathew Alexander
NDT Inspector, ASNT NDT Level III
PETROCHEM-ITSS, Saudi Arabia, Joined Aug 2009, 8

Mathew Alexander

NDT Inspector, ASNT NDT Level III
PETROCHEM-ITSS,
Saudi Arabia,
Joined Aug 2009
8
09:57 Oct-14-2009
Re: TOFD scanning of process piping
In Reply to Nigel at 01:54 May-25-2007 .

Dear friends,

Can anybody help us to explain the code Case 181-1 acceptance /rejction with an example from Table 2? It is confusing a/l, a/t etc. Is "a" considred as flaw height? Or how to calculate "a" ?

Please help.

 
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