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Technical Discussions
António Pereira de Sousa
António Pereira de Sousa
02:03 Nov-23-1999
Dissimilar Welds

On 460 welds, between SA213T99 and SA213T22(tubes with 0.5x5mm) has been made a magnetic particle testing.
They were detected 50% of welds with longitudinal linear indications on side TA213T91.
After retesting, by Penetrant testing, only 10% of them have shown indications from cracks.
Why?



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

Michael Trinidad

Consultant,
LMATS Pty Ltd ,
Australia,
Joined Jan 2003
138
03:46 Nov-24-1999
Re: Dissimilar Welds
This would most likely be the indications from the magnetic leakage field occuring around the large change in permeability between the two disimilar metals. It has often caught out technicians, we had a similar case in the fourm only a few months back.

Kindest Regards

Michael Trinidad


    
 
 Reply 
 
D. Scott Sullivan
D. Scott Sullivan
01:57 Nov-24-1999
Re: Dissimilar Welds

: This would most likely be the indications from the magnetic leakage field occuring around the large change in permeability between the two disimilar metals. It has often caught out technicians, we had a similar case in the fourm only a few months back.

: Kindest Regards

: Michael Trinidad

: Mr. Trinidad's opinion is most likely correct. Another possibility could be that you were picking up indications of sub-surface lack of fusion with the magnetic particle method. If the lack of fusion was subsurface, the penetrant method would not detect it.
If you cut a cross section and etch the weld, you could confirm this. If you can not cut the weld, a X-ray of the suspect area should be able to readily detect lack of fusion.

:D. Scott Sullivan
Sr. NDT Engineer
RT, ET, MT & PT Level III


    
 
 Reply 
 
Ken Head
Ken Head
07:56 Nov-24-1999
Re: Dissimilar Welds
:
: : This would most likely be the indications from the magnetic leakage field occuring around the large change in permeability between the two disimilar metals. It has often caught out technicians, we had a similar case in the fourm only a few months back.

: : Kindest Regards

: : Michael Trinidad

: : Mr. Trinidad's opinion is most likely correct. Another possibility could be that you were picking up indications of sub-surface lack of fusion with the magnetic particle method. If the lack of fusion was subsurface, the penetrant method would not detect it.
: If you cut a cross section and etch the weld, you could confirm this. If you can not cut the weld, a X-ray of the suspect area should be able to readily detect lack of fusion.

I think you are mistaken on using X-Ray to determine the presence (or
lack there of) of fusion. As a rule, radiography is not the perferred
method for detecting "non-fusion". the method most suited for this task
is UT.
Ken Head
Sr. Level III
: :D. Scott Sullivan
: Sr. NDT Engineer
: RT, ET, MT & PT Level III




    
 
 Reply 
 
D. Scott Sullivan
D. Scott Sullivan
06:03 Nov-29-1999
Re: Dissimilar Welds
Ken,

I don't believe I am mistaken regarding the detection of sidewall lack-of-fussion (LOF).

X-ray would be the preffered method. Although you can detect LOF with the ultrasonic method, LOF, weld root cracks and lack-of-penetration (LOP) all give essentially the same type of ultrasonic signal. The reflected signals are narrow and appear at the same location. These signals can in some cases be differentiated by determining the extent of the flaw in the transverse direction. This is not always possible.

In any case, as far as a back-up inspection to MT, I agree that RT or UT could quickly confirm wether or not the MT indication was relevant.

Best Regards,

D. Scott Sullivan



    
 
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