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Technical Discussions
Andreas
Andreas
12:25 Oct-13-2009
Magnetic Flux Leakage vs SLOFEC

Hello,

currently I'm working on a analysis of tank floor inspection methods. The magnetic flux leakage method seems to be the standard method. Recently I have learned that the so called SLOFEC method is capable to ensure tank floor inspections as well. According to the developer it seems that SLOFEC is superior to the MFL method in almost every comparable aspect.

I wonder if this is a fact and that SLOFEC is going to displace the MFL method or are there any weaknesses of the SLOFEC method, e.g. intense costs.

Other than that, are there any different or similar methods to inspect tank floors?

With kind regards,

Andreas

    
 
 
Geert Bontekoe
Geert Bontekoe
04:03 Oct-14-2009
Re: Magnetic Flux Leakage vs SLOFEC
In Reply to Andreas at 12:25 Oct-13-2009 (Opening).

Dear Andreas, There is a different technique that can be used for floor inspections of AST's. This is an In-Service inspection system that takes UT readings of the floor without removing the product.

Regards Geert

    
 
 
Andreas
NDT Inspector, Specially in the oilfield
Tuboscope Vetco(Deutschland)Gmbh, Germany, Joined Oct 1999, 126

Andreas

NDT Inspector, Specially in the oilfield
Tuboscope Vetco(Deutschland)Gmbh,
Germany,
Joined Oct 1999
126
08:01 Oct-14-2009
Re: Magnetic Flux Leakage vs SLOFEC
In Reply to Andreas at 12:25 Oct-13-2009 (Opening).

You should go to side of siverwing a manufacturer of MFL scanner , there you find some info paper about tank floor inspection.
SLOFEC stands for Satureded Low Frequency Eddy Current it is similar to MFL in my opinion.
I google it and they published in some paper to inspect up to 30 mm wall , how you can satured this wall with a normal crawler?
MFL in tank floor inspection was used to find corrossion/flaw and then verify the finding with a other method.Later on the wall thickness reading was added.


Andreas

    
 
 
John O'Brien
Consultant, -
Chevron ETC , USA, Joined Jan 2000, 278

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
278
13:49 Oct-14-2009
Re: Magnetic Flux Leakage vs SLOFEC
In Reply to Andreas at 08:01 Oct-14-2009 .

The question is not really which is better but which may be most appropriate for a given examination. The MFL scanners are generally limited in wall thickness and the thickness of coating on top of the plate so for example a thick annular plate 0.5" (12.5mm) thick with 0.12" (3 mm) of fibreglass is going to be outside the capability of most MFL scanners.
Just because you scan over an area does not mean the scanner is capable of detecting or accurately sizing everything as all the tools have detection thresholds.
MFL scanners have in general served the industry well for most standard 0.25" (6 mm) bare or thin film coated tank floors. However if your risk assessment indicates MIC to be a threat you probably will not identify reliably with MFL as the pits are below the detection threshold.
SLOFEC does appear to be more sensitive to small flaws in standard plate and performs better in thicker sections. Down side is that the screen data requires a greater degree of operator skill and experience.
SLOFEC may also be slower to some degree to cover the same area as greater sesnsitivity often means more follow up work as more is detected. This then tie sinto your overlal stategy - many operators set a threshold in wall loss and affected area, if you screen quick and cheap and are beyond the costs threashold you just replace the floor - hence MFL is adequete. Larger tanks the cost may drive you to require a higher standard of examination.

    
 
 
Aaron
Aaron
09:51 Jan-06-2010
Re: Magnetic Flux Leakage vs SLOFEC
In Reply to Andreas at 12:25 Oct-13-2009 (Opening).

Andreas,
The main difference between MFL and SLOFEC is that the MFL mtheod uses a passive Hall sensor for monitoring the inspection material whereas the SLOFEC techniques uses eddy currents in a saturation mode, this is far more sensitive. There is a good deal of useful information on the Innospection website if you want to review the information.
www.innospection.com

    
 
 
carlos
carlos
15:00 Jan-08-2010
Re: Magnetic Flux Leakage vs SLOFEC
In Reply to Aaron at 09:51 Jan-06-2010 .

Now a days their are also floorscanner which use combined technology

    
 
 

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