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- since 1996 -

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Technical Discussions
Diego Gamarra
NDT Inspector,
Grupo Testek, Venezuela, Joined May 2020, 4

Diego Gamarra

NDT Inspector,
Grupo Testek,
Venezuela,
Joined May 2020
4
01:24 Jul-09-2020
Detection and Characterization of Stress Corrosion Cracking

Hello everybody,

I wanted to know about your thoughts and experience when talking about detecting and characterizing Stress Corrosion Cracks.

Which is the best NDT method for sizing and locating this type of cracks?

What are the differences between Electromagnetic and Ultrasonic methods when talking about stress corrosion cracks? Limitations and Advantages of each one.

Are there other methods that can apply for these?

Thanks,

Diego Gamarra



 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 832

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
832
02:03 Jul-10-2020
Re: Detection and Characterization of Stress Corrosion Cracking
In Reply to Diego Gamarra at 01:24 Jul-09-2020 (Opening).

what are you inspecting? Material ? Where is the SCC ?

 
 Reply 
 
Diego Gamarra
NDT Inspector,
Grupo Testek, Venezuela, Joined May 2020, 4

Diego Gamarra

NDT Inspector,
Grupo Testek,
Venezuela,
Joined May 2020
4
02:32 Jul-10-2020
Re: Detection and Characterization of Stress Corrosion Cracking
In Reply to Anmol Birring at 02:03 Jul-10-2020 .

I wanted to get information about general cases.

But the real case, that made me ask the questions above, is the following:

- Thickness: 35mm
- Material: SS 304
- Location of the SCC: In the Heat Affected Zone, about 25 to 30 mm from the centerline of the weld.

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 832

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
832
03:14 Jul-10-2020
Re: Detection and Characterization of Stress Corrosion Cracking
In Reply to Diego Gamarra at 02:32 Jul-10-2020 .

It will be angle beam UT

 
 Reply 
 
Diego Martínez del Valle
Consultant,
Freelance, Spain, Joined May 2013, 201

Diego Martínez del Valle

Consultant,
Freelance,
Spain,
Joined May 2013
201
13:54 Jul-12-2020
Re: Detection and Characterization of Stress Corrosion Cracking
In Reply to Diego Gamarra at 01:24 Jul-09-2020 (Opening).

Hola Diego.
Como por su nombre y apellidos; así como, por el país desde donde manda su pregunta; son de lengua española, le respondo en esta lengua, que es la mía

Como las grietas por corrosión bajo tensión (SCC) solamente pueden generarse en la superficie que esté en contacto con los elementos que produzcan corrosión (Ejem: cloro para el SS 304), yo le aconsejaría usar el método de líquidos penetrantes, si la superficie es accesible, y, una vez detectada las indicaciones, realizar sobre ellas un estudio mediante réplicas metalográficas.

Un saludo

 
 Reply 
 
Anne-Marie
,
Eddyfi Technologies, Canada, Joined Jul 2020, 1

Anne-Marie

,
Eddyfi Technologies,
Canada,
Joined Jul 2020
1
15:13 Jul-17-2020
Re: Detection and Characterization of Stress Corrosion Cracking
In Reply to Diego Gamarra at 01:24 Jul-09-2020 (Opening).

Hello Diego,

There's a web presentation available on you tube discussing SCC (around 18min 20sec more precisely): https://youtu.be/JIjOgfaDG1w?t=1105

In addition to the video, Eddy current array is a technique that will offer good performances on such type of defects, amongst other benefits. Depending on the cause of the SCC (e.g: chloride induced stress corrosion cracking which starts with small pittings open to the surface), this technique can detect the issue quite early in the process as it is sensitive to small flaws – surface finish will have an impact on minimum detectable flaw size. It will be sensitive to pits and cracks in all orientation, so a single scan will cover all possibilities.
Directly related to your application described above, ECA probes are also offered in flexible casing that will conform to the weld shape, so entire HAZ, toe and cap area can be inspected.
Amongst the other benefits, inspection time (not only scan speed, but getting setup, doing analysis and even reporting) is really interesting when comparing to other techniques like MT or PT. No wait time, automatic detection tools in the software for rapid identification of areas of interest, one-click entry in report, etc.
Once again the application’s specifics will guide the probe choice, but latest equipment available on the market offers wide coverage probes (up to 8in) in order to increase inspection speed and offer clear mapping of the component under inspection, all that with the capability to save and archive the data in order to monitor the asset integrity over time.

One limitation for ECA is capability to perform depth sizing. Scans are encoded so length can be measured precisely, but as for the depth, ECA is a volumetric technique, so it can offer in some cases qualitative sizing, but use of a complementary technique can be needed depending on the inspection requirement.
When working on carbon steel (e.g: carbon steel tanks, vessel, pipeline, etc.) Tangential Eddy Current Array (TECA™) is a complementary inspection technique (basically ECA, with coils in different orientation than standard probes) that offers accurate depth sizing.

Further information on ECA and comparison tables with other technique can be found here: https://eddyfi.com/en/technology/eddy-current-array-eca

Have a great day!!

1
 
 Reply 
 
Simon Amallraja
Consultant, Advanced NDT Methods
Anu Consultants, India, Joined Aug 2013, 45

Simon Amallraja

Consultant, Advanced NDT Methods
Anu Consultants,
India,
Joined Aug 2013
45
11:48 Jul-20-2020
Re: Detection and Characterization of Stress Corrosion Cracking
In Reply to Diego Gamarra at 01:24 Jul-09-2020 (Opening).

Laser UT System can be used for these applications

 
 Reply 
 

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