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Technical Discussions
Frank
Frank
05:00 Sep-02-2007
TOFD

I have seen a couple of companies coming out with TOFD seervices. These companies are accepting/rejecting indications based on TOFD only. They are using the aceptnce criteria in ASME B31 Case 181. They do no investigating at all. In fact, they don't even bring Manual UT equipment on site with them and the TOFD techncians are sometimes not experienced with manual UT.
My other problemis they are ignoring the dead zone. No backup inspections are being done. One company uses MPI to do this. Not for investigating indications but as a tool to pick up the dead zone. They indicate that theoretically MPI (AC) can penetrate 3-5 mm in the piece. Well I disagree. ASME considers MPI as a surface examination only.
This is not all companies now. I have seen a couple of companies that I have alot of confidence in.
But I have a problem with these companies that are selling TOFD as a stand alone inspection technique and the project teams are accepting this without knowing what they are accepting .
Anyone else have any thoughts on this?
If I am wrong, someone please enlighten me.


    
 
 
Charlie Jackson
Consultant, - Trainer/Inspector
Northern NDT Ltd, United Kingdom, Joined Sep 2006, 6

Charlie Jackson

Consultant, - Trainer/Inspector
Northern NDT Ltd,
United Kingdom,
Joined Sep 2006
6
01:06 Sep-03-2007
Re: TOFD
Frank
For many years now TOFD has been sold as a stand alone technique for the inspection of new welds which it is not. The main technical issues raised by the use of TOFD alone as you say is the near surface blind zone caused by the lateral wave and also the blind zone on the lower root edge caused by any misalignment. the procedure should include the use of primary and secondary creep waves to investigate these areas. The operator should also be a fully approved Ascan technician to enable interpretation of indications.

Simple answer would be to ensure encumbent inspection companies include above in procedures prior contract commencment and the equipment setup is capable of locating defects of concern.

Hope this helps and kind regards Charlie Jackson

PS Used together there are few defects that TOFD and PE can locate and position accurately but seperately they have deficiencies.


----------- Start Original Message -----------
: I have seen a couple of companies coming out with TOFD seervices. These companies are accepting/rejecting indications based on TOFD only. They are using the aceptnce criteria in ASME B31 Case 181. They do no investigating at all. In fact, they don't even bring Manual UT equipment on site with them and the TOFD techncians are sometimes not experienced with manual UT.
: My other problemis they are ignoring the dead zone. No backup inspections are being done. One company uses MPI to do this. Not for investigating indications but as a tool to pick up the dead zone. They indicate that theoretically MPI (AC) can penetrate 3-5 mm in the piece. Well I disagree. ASME considers MPI as a surface examination only.
: This is not all companies now. I have seen a couple of companies that I have alot of confidence in.
: But I have a problem with these companies that are selling TOFD as a stand alone inspection technique and the project teams are accepting this without knowing what they are accepting .
: Anyone else have any thoughts on this?
: If I am wrong, someoneplease enlighten me.
------------ End Original Message ------------




    
 
 
Frank
Frank
01:43 Sep-03-2007
Re: TOFD
----------- Start Original Message -----------
: Frank
: For many years now TOFD has been sold as a stand alone technique for the inspection of new welds which it is not. The main technical issues raised by the use of TOFD alone as you say is the near surface blind zone caused by the lateral wave and also the blind zone on the lower root edge caused by any misalignment. the procedure should include the use of primary and secondary creep waves to investigate these areas. The operator should also be a fully approved Ascan technician to enable interpretation of indications.
: Simple answer would be to ensure encumbent inspection companies include above in procedures prior contract commencment and the equipment setup is capable of locating defects of concern.
: Hope this helps and kind regards Charlie Jackson
: PS Used together there are few defects that TOFD and PE can locate and position accurately but seperately they have deficiencies.
:
: : I have seen a couple of companies coming outwith TOFD seervices. These companies are accepting/rejecting indications based on TOFD only. They are using the aceptnce criteria in ASME B31 Case 181. They do no investigating at all. In fact, they don't even bring Manual UT equipment on site with them and the TOFD techncians are sometimes not experienced with manual UT.
: : My other problemis they are ignoring the dead zone. No backup inspections are being done. One company uses MPI to do this. Not for investigating indications but as a tool to pick up the dead zone. They indicate that theoretically MPI (AC) can penetrate 3-5 mm in the piece. Well I disagree. ASME considers MPI as a surface examination only.
: : This is not all companies now. I have seen a couple of companies that I have alot of confidence in.
: : But I have a problem with these companies that are selling TOFD as a stand alone inspection technique and the project teams are accepting this without knowing what they are accepting .
: : Anyone else have any thoughts on this?
: : If I am wrong, someone please enlighten me.
------------ End Original Message ------------

Thank you, Charlie. That's exactly what I think, but individuals in power aee accepting less because of lower cost and they won't listen to me.


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

Rohit Bafna

,
TCR Engineering Services,
India,
Joined Sep 2007
18
08:18 Sep-03-2007
Re: TOFD
We perform ToFD Services in Kuwait and Saudi Arabia and have a two member team. The first team member does the scanning (we are doing ToFD projects as per API 650 appendix u, Code case 181 for piping as well as code case 2235-9) while the second person has a manual UT machine with him.

Prior to the start of any project we give out two documents:
- Procedure for examination
- ToFD operating guide for inspectors which illustrates the step by step machine operations. It also includes the timelines of work during the day. For example we prefer to do the scanning in the morning and reporting in the afternoon.

Clients on the other hand are demanding pricing of ToFD services to match that of RT. I for one have more trouble in letting the clients know that ToFD is just another NDT technique and not the one and only tool for evaluation.

We are presenting a paper as well as taking part in the Fourth Middle East Nondestructive Testing Conference and Exhibition (4MENDT 2007) which is being held at the GulfInternational Convention Center, Kingdom of Bahrain from December 2 to 5, 2007. Hopefully during our paper presentation as well as exhibition booth, we will have a better opportunity to explain our viewpoints.


    
 
 
Paulo
Paulo
02:32 Sep-04-2007
Re: TOFD
Hello everybody!
Here, in Brazil, we use TOFD + PE to inspect. We put some probes for TOFD and some for PE (to cover the root and the top of the weld) in the same scanner, and generally we need just one pass to cover all the weld. Using a scanner like that we can provide a better evaluation.
Regards.
Paulo

----------- Start Original Message -----------
: : Frank
: : For many years now TOFD has been sold as a stand alone technique for the inspection of new welds which it is not. The main technical issues raised by the use of TOFD alone as you say is the near surface blind zone caused by the lateral wave and also the blind zone on the lower root edge caused by any misalignment. the procedure should include the use of primary and secondary creep waves to investigate these areas. The operator should also be a fully approved Ascan technician to enable interpretation of indications.
: : Simple answer would be to ensure encumbent inspection companies include above in procedures prior contract commencment and the equipment setup is capable of locating defects of concern.
: : Hope this helps and kind regards Charlie Jackson
: : PS Used together there are few defects that TOFD and PE can locate and position accurately but seperately they have deficiencies.
: :
: : : I have seen a couple of companies coming out with TOFD seervices. These companies are accepting/rejecting indications based on TOFD only. They are using the aceptnce criteria in ASME B31 Case 181. They do no investigating at all. In fact, they don't even bring Manual UT equipment on site with them and the TOFD techncians are sometimes not experienced with manual UT.
: : : My other problemis they are ignoring the dead zone. No backup inspections are being done. One company uses MPI to do this. Not for investigating indications but as a tool to pick up the dead zone. They indicate that theoretically MPI (AC) can penetrate 3-5 mm in the piece. Well I disagree. ASME considers MPI as a surface examination only.
: : : This is not all companies now. I have seen a couple of companies that I have alot of confidence in.
: : : But I have a problem with these companies that are selling TOFD as a stand alone inspection technique and the project teams are accepting this without knowing what they are accepting .
: : : Anyone else have any thoughts on this?
: : : If I am wrong, someone please enlighten me.
: Thank you, Charlie. That's exactly what I think, but individuals in power aee accepting less because of lower cost and they won't listen to me.
------------ End Original Message ------------




    
 
 

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