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Technical Discussions
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1304

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1304
02:56 Dec-30-2005
Re: Acceptance of Defect Indications Detected by TOFD.
Luis:
In spite of its many great advantages, one of the big problems that TOFD has encountered in being accepted by the NDT industry is the fact that Codes are poorly written to address non-amplitude-based results. All of the European, Asian and, until recently, North American Codes have been based on amplitude response of UT.

Most recently, fracture mechanics-based acceptance criteria have been developed that make use of the extra information that TOFD can provide. ASME Section II and VIII now has a provision for UT to be used in lieu of RT (Code Case 2235-6). It also specifically allows TOFD (and calls it a non-amplitude based method). This replacement of RT by UT requires that the UT method be capable of providing a flaw aspect ratio (height to length ratio) so vertical extent sizing is mandatory.

In Europe, where most of the TOFD development has taken place, 3 Standards seem to dominate now,
The CEN Technical Specification WI 00121377, WELDING – USE OF TIME-OF-FLIGHT DIFFRACTION TECHNIQUE (TOFD) FOR TESTING OF WELDS
EN-583-6 and
BS 7706.

All three give good instruction on the application of the test method but none provide any acceptance criteria.

I believe there are several regular participants in the NDT.net forum that are part of the TOFD Code development community. Perhaps they can indicate if there are Codes other than ASME Code Case 2235-6 that provide actual "acceptance criteria".

Regards
Ed

----------- Start Original Message -----------
:
: What are the acceptance criteria for defects detected by TOFD?
: What are the codes used for TOFD testing calibration?
: What are the codes used for TOFD defects acceptance?
: An answer from the forum would be appreciated
: Regards
: Luis Marques
------------ End Original Message ------------




 
 Reply 
 
Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 183

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
183
05:49 Jan-02-2006
Re: Acceptance of Defect Indications Detected by TOFD.
Reply by Udo Schlengermann:

A comment and some additional information on the reply by Ed Ginzel on TOFD standards:

I do not agree with the statement, that TOFD sizing of defects is independent of amplitude.
Of course the location of a defect is determinded by time-of-flight information, but the TOFD image is a B-scan which plots colour-coded coded amplitudes in a TOF/position diagram.
The extension of an image in this B-scan depends on the palette and the thresholds used to code the positive and negative amplitudes of the diffracted signals. By simply changing this amplitude dependent code you get changing boundaries of the defect image, i.e varying sizes.
So, for me, TOFD images and TOFD sizing are amplitude dependend procedures.

Some actual information on European Standards on TOFD:

BS 7760:Calibration and setting-up of the ultrasonic time-of-flight-diffraction technique for the detection, location and sizing of flaws
will only be valid until the European Standards ENV 583-6 and CEN/TS14751 will be full standards and no longer Technical Specifications (TS):

ENV 583-6: Nondestructive testing - Ultrasonic examination - Part 6: Time-of-flight diffraction technique as a method for detection and sizing of discontinuities.

CEN/TS 14751:2005 - Welding - Use of time-of-flight diffraction technique for examination of welds

A project on acceptance criteria for TOFD has been started within CEN/TC121/SC5/WG2 in 2005 by WI 00121471:
Nondestructive testing of welds - Time-of-flight diffraction technique - Acceptance levels

Kind regards
Udo Schlengermann
Convener of CEN/TC121/SC5/WG2

European Application Center
GE Inspection Technologies GmbH
Huerth, Germany

----------- Start Original Message -----------
:
: What are the acceptance criteria for defects detected by TOFD?
: What are the codes used for TOFD testing calibration?
: What are the codes used for TOFD defects acceptance?
: An answer from the forum would be appreciated
: Regards
: Luis Marques
------------ End Original Message ------------




 
 Reply 
 
Jan Verkooijen
Director,
Sonovation, Netherlands, Joined Nov 1998, 29

Jan Verkooijen

Director,
Sonovation,
Netherlands,
Joined Nov 1998
29
06:07 Jan-02-2006
Re: Acceptance of Defect Indications Detected by TOFD.
Dear Ed, Dear Luis,

The situation in Europe is as follows:
BS 7706, although a very usefull document for those wishing to avail themselves with some background knowledge of TOFD and very worthwhile having on the shelf for reference, does not fit in the European legislation of the Pressurised Equipment Directive. Therefore, a general standard was prepared on the method, called ENV 583-6. As the main application for TOFD is inspection of welds, Technical Committee TC 121SC5WG2 has prepared a Technical Specification which can be used as a standard within the PED, called TS 14751. It describes the preferred set ups, testblocks to be used, preparation et cetera. At the moment no official acceptance criteria exist on a European scale, but the same committee has drafted a document based on the outcome of the TOFDPROOF project. This document will be sent to the national standardisation committees in the coming weeks for the 6 months enquiry. In the meantime, you can feel free to do TOFD within the PED, as The Netherlands have had acceptance criteria now for many years, which are available since 2003 as National Standard NEN 1822. As The Netherlands is a full memberstate of Europe, these Acceptance Criteria can be used on a European scale until the aforementioned document of TC121 becomes a (pre-)standard.
May I add, that the acceptance criteria are all based upon Good Workmanship, but verified with the use of Fracture Mechanics and Remaining Life Time calculations.

Please contact me if you require any more information.

Best regards,

Jan Verkooijen

----------- Start Original Message -----------
: Luis:
: In spite of its many great advantages, one of the big problems that TOFD has encountered in being accepted by the NDT industry is the fact that Codes are poorly written to address non-amplitude-based results. All of the European, Asian and, until recently, North American Codes have been based on amplitude response of UT.
: Most recently, fracture mechanics-based acceptance criteria have been developed that make use of the extra information that TOFD can provide. ASME Section II and VIII now has a provision for UT to be used in lieu of RT (Code Case 2235-6). It also specifically allows TOFD (and calls it a non-amplitude based method). This replacement of RT by UT requires that the UT method be capable of providing a flaw aspect ratio (height to length ratio) so vertical extent sizing is mandatory.
: In Europe, where most of the TOFD development has taken place, 3 Standards seem to dominate now,
: The CEN Technical Specification WI 00121377, WELDING – USE OF TIME-OF-FLIGHT DIFFRACTION TECHNIQUE (TOFD) FOR TESTING OF WELDS
: EN-583-6 and
: BS 7706.
: All three give good instruction on the application of the test method but none provide any acceptance criteria.
: I believe there are several regular participants in the NDT.net forum that are part of the TOFD Code development community. Perhaps they can indicate if there are Codes other than ASME Code Case 2235-6 that provide actual "acceptance criteria".
: Regards
: Ed
:
: :
: : What are the acceptance criteria for defects detected by TOFD?
: : What are the codes used for TOFD testing calibration?
: : What are the codes used for TOFD defects acceptance?
: : An answer from the forum would be appreciated
: : Regards
: : Luis Marques
------------ End Original Message ------------




 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1304

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1304
04:40 Jan-03-2006
Re: Acceptance of Defect Indications Detected by TOFD.
Udo:
Thank you for your added weight to this discussion.
I hope the acceptance criteria document is soon available to provide an option for those in North America to look at.

As for "amplitude" and TOFD, I suppose the wording used by ASME that it is a "non-amplitude based method" originates from the big difference between TOFD and Pulse-echo. In pulse-echo techniques we generally have an evaluation threshold and sizing and disposition are usually related to amplitude of the peaked signal relative to a reference amplitude. In TOFD the operator needs to identify patterns that may be un-noticed on the A-scan but just faintly detected by the "pattern" on the B-scan.

I agree, TOFD also requires a diffractor to have some amplitude response in order for it to be evaluated. EN-583-6 gives several methods to establish this threshold.

Also, the colour pallette is also important.
Both EN-583-6 and BS7706 call for a MINIMUM of 64 level greyscale. All of the TOFD displays I have seen use Greyscale and it seems to provide the most user-friendly display.
But perhaps someone can explain the limit of 64 levels.
In most automated UT systems we use at least an 8 bit Analogue to Digital conversion. That provides 256 levels of amplitude over the screen height. But 256 levels of grey are not possible. This has to do with the black and white we start with...other colour schemes (e.g. thermal pallettes and rainbow pallettes) could all have more colour changes, yet the 64 grey levels are adequate.

Regards
Ed

----------- Start Original Message -----------
: Reply by Udo Schlengermann:
: A comment and some additional information on the reply by Ed Ginzel on TOFD standards:
: I do not agree with the statement, that TOFD sizing of defects is independent of amplitude.
: Of course the location of a defect is determinded by time-of-flight information, but the TOFD image is a B-scan which plots colour-coded coded amplitudes in a TOF/position diagram.
: The extension of an image in this B-scan depends on the palette and the thresholds used to code the positive and negative amplitudes of the diffracted signals. By simply changing this amplitude dependent code you get changing boundaries of the defect image, i.e varying sizes.
: So, for me, TOFD images and TOFD sizing are amplitude dependend procedures.
: Some actual information on European Standards on TOFD:
: BS 7760:Calibration and setting-up of the ultrasonic time-of-flight-diffraction technique for the detection, location and sizing of flaws
: will only be valid until the European Standards ENV 583-6 and CEN/TS 14751 will be full standards and no longer Technical Specifications (TS):
: ENV 583-6: Nondestructive testing - Ultrasonic examination - Part 6: Time-of-flight diffraction technique as a method for detection and sizing of discontinuities.
: CEN/TS 14751:2005 - Welding - Use of time-of-flight diffraction technique for examination of welds
: A project on acceptance criteria for TOFD has been started within CEN/TC121/SC5/WG2 in 2005 by WI 00121471:
: Nondestructive testing of welds - Time-of-flight diffraction technique - Acceptance levels
: Kind regards
: Udo Schlengermann
: Convener of CEN/TC121/SC5/WG2
: European Application Center
: GE Inspection Technologies GmbH
: Huerth, Germany
: ----------- Start Original Message -----------
: :
: : What are the acceptance criteria for defects detected by TOFD?
: : What are the codes used for TOFD testing calibration?
: : What are the codes used for TOFD defects acceptance?
: : An answer from the forum would be appreciated
: : Regards
: : Luis Marques
------------ End Original Message ------------




 
 Reply 
 
John O'Brien
Consultant, -
Chevron ETC , USA, Joined Jan 2000, 280

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
280
06:25 Jan-03-2006
Re: Acceptance of Defect Indications Detected by TOFD.
Gentlemen

be cautious about a generic discussion.

The Code Acceptance approach only applies to new construction. The decision then is clear - does your code or some form of waiver such as the ASME Code Case address TOFD. If so then you can proceed. If not the answer is no you cannot use it.

The concept that because there is a lack of unified guidance under the European PED and one country has a national standard that does address TOFD means you can use that code anywhere in the EU is not always true.

If you are sizing in-service flaws then the original code of construction often may not apply and an FFS approach where you calculate acceptable flaw size may be taken. In that assessment you can also determine POD and POS of the technique such as TOFD and set your own acceptance criteria.


 
 Reply 
 
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Bill
09:48 Oct-09-2006
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