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Technical Discussions
Jeffry
R & D,
Advantech Alliance SB, Malaysia, Joined May 2011, 19

Jeffry

R & D,
Advantech Alliance SB,
Malaysia,
Joined May 2011
19
09:57 Jul-04-2017
Corrosion Inspection on Painted Surface using UT/Advanced UT

Dear all,

I required an opinion regarding UT on painted surface using UT/advanced UT for corrosion inspection. Practically, isn't is allowable to utilize UT/Advanced UT on coated surface according to codes and standards?

    
 
 Reply 
 
James Scalf
NDT Inspector,
Global Integrity, Canada, Joined Oct 2012, 273

James Scalf

NDT Inspector,
Global Integrity,
Canada,
Joined Oct 2012
273
20:53 Jul-04-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to Jeffry at 09:57 Jul-04-2017 (Opening).

Jeffry,

It will be entirely dependant on the specification and/or code you are inspecting to. some will stipulate the removal of the surface coating others may provide provision for performing the inspection through the coating.

I have done corrosion mapping and bond testing through surface coatings many times what you need to ensure that the coating is 1) well bonded, 2) of uniform condition and 3) is uniform in thickness.

1) if the coating is not well bonded you will get regions where you have no sonic transmission.
2) if the coating isn't uniform in condition (cracked chipped and/or worn) then the thickness reading will be unreliable as well if it is not uniform you could have a different attenuation in a given area which could affect the measurements
3) if the coating varies then the thickness measurement for corrosion mapping is useless especially if you are looking for a small corrosion material loss.

Bottom line is look at the Specification and/or code you are following if it doesn't state in there check with your client and/or employer.

1    
 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 746

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
746
22:59 Jul-04-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to Jeffry at 09:57 Jul-04-2017 (Opening).

You are generally OK if the coating is tight and the thickness less than 0.25 mm. Otherwise, use transfer correction to measure loss of sound

1    
 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 189

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
189
02:00 Jul-05-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to Jeffry at 09:57 Jul-04-2017 (Opening).

Jeffry:

Also be aware that the thickness of the coating will be included in your readings, but it will affect your measurement by between 2 to 3 times the coating thickness. This is because the velocity of sound through coatings (such as paint) are much slower than through steel.

(Here I assume you're measuring painted steel pipe, and not some exotic Martian alloy with a paint-like material velocity)

The UT set is just a fancy stopwatch. You tell it the velocity of steel, and it trusts that you're telling it the truth. If the outside is painted, then the sound takes 2 to 3 times as long to travel through the paint layer before it hits the steel and takes off like a race car. That extra long time through the paint, even though it might be really thin, fools the UT set and makes the reading look extra thick.

Take for example the 0.25mm of paint that Anmol suggested as a good upper limit for reasonable thickness. Unless you compensate for it, all your readings will be 0.50mm to 0.75mm higher than the actual pipe thickness at that location (approximately, give or take). This estimate gets less reliable the more irregular your coating is (as my friend James has already pointed out).

Good luck

1    
 
 Reply 
 
Jeffry
R & D,
Advantech Alliance SB, Malaysia, Joined May 2011, 19

Jeffry

R & D,
Advantech Alliance SB,
Malaysia,
Joined May 2011
19
03:49 Jul-05-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to Paul Holloway at 02:00 Jul-05-2017 .

Thanks for your feedback and support for this issue.

But when I refer to ASME code stated as per following:

T-471.5 Surface Preparation. When the base material
or weld surface interferes with the examination, the
base material or weld shall be prepared as needed to permit
the examination.

and ASTM Standards stated as per following:

8. Surface Condition
8.1 All surfaces shall be clean and free of scale, dirt,
grease, paint, or other foreign material that could interfere
with interpretation of examination results. The methods
used for cleaning and preparing the surfaces for ultrasonic
examination shall not be detrimental to the base metal or
the surface finish. Excessive surface roughness or scratches
can produce signals that interfere with the examination.

Booth doesn't mention allowable coating thickness (for example 0.25mm stated by Anmol Birring). Based on my understanding and reading by referring these codes and standards mentioned UT through the coating is not allowed. Is that correct?

Please advise.

    
 
 Reply 
 
JohnP
JohnP
10:21 Jul-05-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to Jeffry at 03:49 Jul-05-2017 .

It would be depend on whether you are examining a weld through paint or just doing thickness/corrosion inspection.
Common practice in thickness measurement is to measure between the first and second back wall echo's which gives the wall thickness minus the paint.

1    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1268

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1268
14:49 Jul-05-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to JohnP at 10:21 Jul-05-2017 .

Jeffery, the responses you have obtained from James, Anmol and Paul are all correct and provide good "guidance". You quote ASME and ASTM references without stating the document name/number. The ASME reference appears to reference weld inspection (T-471.5) and ASTM appears to come from E164 (weld inspection). The ASTM document is, you will note, "recommending" to remove weld caps by grinding. Clearly this is not always possible so it is not a standard where all aspects can be applied. Similarly, in E164 para 3.3 it states "there should be agreement between the manufacturer and the purchaser as to the specific reference standards and limits to be used." If a painted surface is the only surface from which to scan you will need to come to an agreement on how to approach this. In some cases it is recommended that the reference standard also be painted using the same process and thickness of coating.
ASME T-471.5 provides you the information required to address the paint but it is up to you or your level 3 to decide how to assess this (with the approval of the AI if they so decide). A poorly bonded thin layer of paint may not be possible to get a useful signal through yet a thick layer of well-bonded paint MIGHT be. ASME V Art. 4 is usually applied in the fabrication process so it is rare that a newly fabricated weld is presented to NDT for inspection AFTER painting. If your application requires UT on a painted surface and you are working in accordance with ASME V Art. 4 there can be uncertainties in the effectiveness of your procedure. In that case you MUST demonstrate the modifications (e.g. scanning from a painted surface) in accordance with T-150 in ASME V Art. 1.
Assessment of the effects of a coating should then be made on coated reference blocks with reference targets as compared to the uncoated condition and the method developed incorporated into a procedure. In our lab we have demonstrated that even a water-gap that is poorly configured can result in up to 12dB attenuation difference due to the quarter-wavelength and half-wavelength matching effect.
Since field conditions can vary widely, Codes will often place the responsibility to assess the effectiveness of a procedure on the Level 3 or company providing the inspection service. Some simply prohibit UT from a painted surface (e.g. API 1104 "All surfaces to be ultrasonically scanned shall be in the uncoated condition. For new construction projects, the coating cutback (bare pipe length) at pipe ends necessary for ultrasonic scanning should be specified prior to the pipe being coated.")

2    
 
 Reply 
 
Jens
Jens
02:46 Jul-06-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to Ed Ginzel at 14:49 Jul-05-2017 .

Hi Ed,

Its that possible UT thickness measurement on 4LPP coating pipeline?

Regards
Jens

    
 
 Reply 
 
JohnP
JohnP
09:38 Jul-06-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to Jens at 02:46 Jul-06-2017 .

Jens,
If the bonding is good you can usually inspect 3LP and 4LP coated pipes.
Sometimes the zero degree probes don't give good signals and repeats from in the coating confuse the measurements.
A pitch catch method gives a more reliable result.
JohnP

    
 
 Reply 
 
Jens
Jens
11:43 Jul-06-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to JohnP at 09:38 Jul-06-2017 .

Hi JohnP,

Thanks for your feedback, does it mean regardless the thickness of 4LPP coating?

Regards
Jens

    
 
 Reply 
 
JohnP
JohnP
11:54 Jul-06-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to Jens at 11:43 Jul-06-2017 .

Jens,

It is a suck it and see situation. Sometimes it works and sometimes it doesn't.
We have had success on 5mm coatings. (and failures)
One coating to avoid is TSA.

Regards

JohnP

    
 
 Reply 
 
Jeffry
R & D,
Advantech Alliance SB, Malaysia, Joined May 2011, 19

Jeffry

R & D,
Advantech Alliance SB,
Malaysia,
Joined May 2011
19
05:13 Jul-07-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to Ed Ginzel at 14:49 Jul-05-2017 .

Dear all,

Thank you for your participants to give a dynamic feedback and idea to me for improvising my understanding in UT inspection on the coating.

Thank you

Jeffry

    
 
 Reply 
 
Jeffry
R & D,
Advantech Alliance SB, Malaysia, Joined May 2011, 19

Jeffry

R & D,
Advantech Alliance SB,
Malaysia,
Joined May 2011
19
05:17 Jul-07-2017
Re: Corrosion Inspection on Painted Surface using UT/Advanced UT
In Reply to Jens at 02:46 Jul-06-2017 .

Hi Jens,

May I know what does it mean of 4LPP coating pipeline? Can you share?

    
 
 Reply 
 

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