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Technical Discussions
MG
,
Canada, Joined Nov 2017, 6

MG

,
Canada,
Joined Nov 2017
6
18:41 Sep-25-2018
How to MT pipe bevel prep properly in the field

In another word, MT with yoke.
For example, on a 6"STD pipe T=.280"

Thanks

 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 894

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
894
03:51 Oct-02-2018
Re: How to MT pipe bevel prep properly in the field
In Reply to MG at 18:41 Sep-25-2018 (Opening).

Why don't you do PT Method C instead?

 
 Reply 
 
MG
,
Canada, Joined Nov 2017, 6

MG

,
Canada,
Joined Nov 2017
6
16:54 Oct-02-2018
Re: How to MT pipe bevel prep properly in the field
In Reply to Michel Couture at 03:51 Oct-02-2018 .

Thanks for the reply.

Most of time, it was requested by QC following their documents. It is very hard to change it to PT unless get approval from QA or engineer.

 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 894

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
894
17:33 Oct-03-2018
Re: How to MT pipe bevel prep properly in the field
In Reply to MG at 16:54 Oct-02-2018 .

In reality, there are no difference to doing MT on a weld prep than other surfaces. Using your yoke, you establish two field with a 90 degree seperation to ensure you fiind both longitudinal and transverse cracking on the weld prep surface. My only problem with doing MT is that pipe wall thickness is that you may encounter non relevant indications. This is why I feel that PT in these situations is better suited for the job.

 
 Reply 
 
Bruce McPherson
Consultant
MFL Services, United Kingdom, Joined Mar 2009, 26

Bruce McPherson

Consultant
MFL Services,
United Kingdom,
Joined Mar 2009
26
13:16 Oct-08-2018
Re: How to MT pipe bevel prep properly in the field
In Reply to MG at 18:41 Sep-25-2018 (Opening).

If I have understood you correctly, you are looking to detect laminations within the pipe wall which have become open to the surface when the bevel has been cut and which will be circularly oriented linear indications running around the bevel.
You are also looking for longitudinal defects such as seams or overlaps which will show as linear indications running across the bevel.
Both of these can be detected using an AC yoke and the pipe wall thickness will not be an issue, since the magnetic field will be concentrated on the surface being inspected.
To detect laminations, it is necessary to place one of the yokes pole pieces on the inner wall of the pipe and the other on the outer wall of the pipe.
Both pole pieces should be as near to the end of the pipe as possible.
When the yoke is switched on, a magnetic field is induced in the surface of the bevel and which runs across the bevel.
Magnetic particles applied to the bevel between the yoke contact will indicate the presence of any surface breaking defects running around the bevel
The area inspected for each yoke position is rather limited (roughly the size of the yoke pole faces) so this process will need to be repeated around the bevel until the entire circumference of the bevel has been inspected
To detect defects running across the bevel, place the yoke pole pieces on the surface of the bevel, with a spacing of not more than around 3-4 inches.
When the yoke is switched on a magnetic field is induced in the bevel and which runs around the bevel.
Magnetic particles applied to the bevel between the pole pieces will indicate the presence of any surface breaking defects running across the face of the bevel.
This process needs to be repeated around the bevel until the entire circumference of the bevel has been inspected

Regards

Bruce McPherson

1
 
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