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Teletest Focus+ was the first system to use long-range guided wave ultrasonic testing to detect corrosion in pipelines.
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Technical Discussions
António P. Sousa
António P. Sousa
02:26 Dec-16-1999
Dissimilar Welds

I have more data for the problem about magnetic particle test on dissimilar welds.
Quality material: SA213T91/ SA213T22.

1- On 180 welds there were detected 92 welds with longitudinal indications on side T91.
2- The length of indications is 10mm at all periphecy.
3- After smooth gunding, the number of welds with indications was 70.
4- On these 70 welds we made a Penetrant test. Result: no indications.
5- Next step- ultrasonic test with 45 Probe (MWB 45 4E). Result: without indications.

Now the question is:
Why do the indications only appear on the Magnetic Particle Test.



 
 Reply 
 
Michael Trinidad
Consultant,
LMATS Pty Ltd , Australia, Joined Jan 2003, 138

Michael Trinidad

Consultant,
LMATS Pty Ltd ,
Australia,
Joined Jan 2003
138
05:40 Dec-21-1999
Re: Dissimilar Welds
My guess would be that the small areas that have indications maybe areas with more significant changes in permeability caused by the welding process. Maybe the segregation or disolution of the parent metals is not uniform giving these localised indications. This could also explain why after grinding some of the indications disapeered as you may have removed the small artifavt causing the permeability change.

Normally you get an indication around the full circumference of the weld when there is a significant change in permeability.

This is my best guess, I think a metalurgist can confirm or deny the theory and I would be most interested in the results

Kind regards

Michael Trinidad
Level III Project Supervisor
SGS Taiwan


 
 Reply 
 
young-jin, hwang
young-jin, hwang
05:44 Jan-10-2000
Re: Dissimilar Welds
: I have more data for the problem about magnetic particle test on dissimilar welds.
: Quality material: SA213T91/ SA213T22.

: 1- On 180 welds there were detected 92 welds with longitudinal indications on side T91.
: 2- The length of indications is 10mm at all periphecy.
: 3- After smooth gunding, the number of welds with indications was 70.
: 4- On these 70 welds we made a Penetrant test. Result: no indications.
: 5- Next step- ultrasonic test with 45 Probe (MWB 45 4E). Result: without indications.

: Now the question is:
: Why do the indications only appear on the Magnetic Particle Test.




 
 Reply 
 
Kåre Johansson
Kåre Johansson
08:26 Jan-12-2000
Re: Dissimilar Welds
This sounds very much like a "problem" we have observed on other materials. The cause is very probably a change in magnetic properties as Mr.Trinidad commented. Considering that the analysis of T91 is close to the border between martensite and ferrite I would expect there there to be some ferrite in the HAZ/fusion line of some welds.
This could be sufficient to cause a magnetic discontinuity which you would only detect using magnetic testing.
The best way to check this is to take a metallographic sample and have a look. Segregation and surface contaminations could also play a role in changing the phase structure locally. This could even give you some areas of retained austemite which would show up exceedingly well using MPI.
Kåre


 
 Reply 
 

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