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Technical Discussions
Aleg
Aleg
18:13 Jul-08-2020
Minumum depht of a discontinuaty to be detected by dye penetrant testing

Hello,

please tell, which is the minumum depht
(in microns) of a discontinuaty in steel to be detected by dye penetrant testing?

I see (without a magnifying glassa) a crack (length is 5 mm) on perfectly cleaned tested surface, but using of dye penetrant testing does not give an indication. I understand, that it is a surface crack and want to know what is the minimum depht of a discontinuaty to be detected by dye penetrant testing.

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

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
894
02:08 Jul-09-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Aleg at 18:13 Jul-08-2020 (Opening).

Aleg,

Penetrant Testing is not meant to establish the depth of a defect that is open to the surface. If you really want to know the depth of a surface indication, I recommend using Eddy Current or Ultrasonic Inspection.

 
 Reply 
 
Aleg
Aleg
06:56 Jul-09-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Michel Couture at 02:08 Jul-09-2020 .

Hello.

I do not try to determine depth of a defect by dye penetrant testing. I want to know which is mimimum depth of a defect whicj can give an indication. For example, a crack with depth 1 micron can give an indication?

 
 Reply 
 
Diego
Consultant,
Freelance, Spain, Joined May 2013, 201

Diego

Consultant,
Freelance,
Spain,
Joined May 2013
201
17:28 Jul-09-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Aleg at 06:56 Jul-09-2020 .

There is no minimum depth of a flaw to be detected by PT. This depth will depend mainly on the width of the flaw, the technique and the procedure to be used.

 
 Reply 
 
ashok kumar patra
,
Saudi K-KEM Engineering service co, Saudi Arabia, Joined May 2018, 63

ashok kumar patra

,
Saudi K-KEM Engineering service co,
Saudi Arabia,
Joined May 2018
63
21:16 Jul-09-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Aleg at 06:56 Jul-09-2020 .

You cannot measure depth with PT.

It can detect discontinuity from greater depth :

Provided open to surface discontinuity only

you apply more dwell time for you greater depth if it is open to surface defect only.

it cannot detect subsurface defect below even 0.5 mm if it is not open to surface.

 
 Reply 
 
ezio
Other, Retired ex Laboratory Technical Manager
OMECO Research Centre, Italy, Joined Sep 2008, 278

ezio

Other, Retired ex Laboratory Technical Manager
OMECO Research Centre,
Italy,
Joined Sep 2008
278
00:28 Jul-10-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Aleg at 18:13 Jul-08-2020 (Opening).

caro Aleg, a me è spesso capitato di vedere una cricca ad occhio, ma questa non dava indicazione con i normali liquidi penetranti Questo perchè la cricca era "tappata" o dalla sporcizia o da un fenomeno di incollatura, in un fuso o in una saldatura, o da tensioni residue, specie in materiali molto duttili come alluminio o acciaio inox. In questi casi bisogna pulire accuratamente, riscaldare localmente o addirittura ricorrere ad un attacco acido. Che materiale è il tuo? che trattamenti superficiali ha subito? E' un particolare nuovo o esercito? ecc ecc

 
 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
02:04 Jul-10-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Aleg at 18:13 Jul-08-2020 (Opening).

For PT to detect, the capillary action has to work. That is the key. So as such there is no specific minimum depth

2
 
 Reply 
 
Rafid O. Lopez
, NDT Level 3
Mexico, Joined Jan 2010, 86

Rafid O. Lopez

, NDT Level 3
Mexico,
Joined Jan 2010
86
03:07 Jul-10-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Anmol Birring at 02:04 Jul-10-2020 .

The correct question is?
Why I dont see a crack indication, after I did a PT inspection?

Question: what penetrant did you use? Fluorescent or visible? Solvent removable, water-washable or post-emulsifiable? What level of sensitivity?

Did you use the correct form to remove the penetrant excess?

Perhaps, the real problem is not the depth of the discontinuity, but the form to remove the excess of penetrant of the surface; excesive solvent on the cloth, excesive pressure of the water, incorrect angle or distance of the rinse, excesive emulsifier time, all of this is related to an over-wash and at the end you dont see any penetrant indication.

 
 Reply 
 
Anooj
Engineering,
India, Joined Nov 2017, 1

Anooj

Engineering,
India,
Joined Nov 2017
1
05:46 Jul-10-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Aleg at 18:13 Jul-08-2020 (Opening).

PT for detecting Surface defects.
MT For detecting Surface and Subsurface (0.5mm) defects.

 
 Reply 
 
ashok kumar patra
,
Saudi K-KEM Engineering service co, Saudi Arabia, Joined May 2018, 63

ashok kumar patra

,
Saudi K-KEM Engineering service co,
Saudi Arabia,
Joined May 2018
63
06:53 Jul-10-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Rafid O. Lopez at 03:07 Jul-10-2020 .

please elaborate on method of cleaning , material, dwell time etc. check your penetrant with star crack panel how many cracks you get are you applying florescent die after visible die?

 
 Reply 
 
ezio
Other, Retired ex Laboratory Technical Manager
OMECO Research Centre, Italy, Joined Sep 2008, 278

ezio

Other, Retired ex Laboratory Technical Manager
OMECO Research Centre,
Italy,
Joined Sep 2008
278
14:56 Jul-10-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Aleg at 18:13 Jul-08-2020 (Opening).

temo che il senso della mia precedente risposta non sia del tutto chiaro nella traduzione in inglese.
Sei sicuro che quello sia un difetto (crack)? Ad esempio sui tondi laminati di acciaio dopo rettifica appaiono talvolta all'esame visivo delle sottilissime indicazioni rettilinee di lunghezza 5-10 mm, che sembrano cricche ma non lo sono, Si tratta di piccole impurità del lingotto di partenza, stirate dal processo di laminazione e finite in superficie, con dimensione trasversale di pochi centesimi di mm, ma molto appariscenti.
Aggiungo un'osservazione generale: tutti parlano di tecnica PT e nessuno della natura del difetto, che a mio parere è essenziale per interpretare tutti gli NDT.

 
 Reply 
 
Aleg
Aleg
18:18 Jul-10-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Rafid O. Lopez at 03:07 Jul-10-2020 .

The tested object (a part of engine) is covered with very (!) thin layer. The object is made from cast iron but the layer is made from other metal. The crack does not go in depth and it is «stopped» on the layer which has very (!) small thickness. In other words, the crack does not go in cast iron ("parent metal") because it is «stopped» on the layer.

I use water-washable penetrant which has 2 level of sensitivity.

The technology is 100% followed.

 
 Reply 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1307

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1307
19:53 Jul-10-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Anmol Birring at 02:04 Jul-10-2020 .

Anmol, I think you have (as we say in English) "hit the nail on the head". Capillary action is required to both pull the dye into the flaw and to pull the dye out. Capillary action is determined by several variables; liquid-air surface tension,liquid contact angle on the acting surface, density of liquid, local acceleration due to gravity and the size of the opening into which the capillary action is to occur. Some penetrants are designed to better remain in broad shallow openings, others are designed to wash off without excessive cleaning. There is no specific depth. Determining the effective depth/opening of flaws to detect is essentially the function of penetrant performance tests, since you can purchase different characteristics of the dye and carrier.

1
 
 Reply 
 
ashok kumar patra
,
Saudi K-KEM Engineering service co, Saudi Arabia, Joined May 2018, 63

ashok kumar patra

,
Saudi K-KEM Engineering service co,
Saudi Arabia,
Joined May 2018
63
09:22 Jul-11-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Aleg at 18:18 Jul-10-2020 .

You are telling thin layer is it a crack or scratch and there you are using waterwashable penetrant please elaborate more

 
 Reply 
 
Osman
Engineering,
USA, Joined Aug 2009, 11

Osman

Engineering,
USA,
Joined Aug 2009
11
11:15 Jul-11-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Aleg at 18:13 Jul-08-2020 (Opening).

There is no value of depth since you are not going to report it, the method itself not providing any information to be used as as reference for comparison purposes.The only thing you need is enough defect volume able to keep amount of penetrant. If you expect very tiny crack as you said , may be you need to consider longer penetrant dwel time/ thin developer coat / sensitive PT techniques

 
 Reply 
 
Aleg
Aleg
18:08 Jul-11-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Osman at 11:15 Jul-11-2020 .

I think, you are right that I shall use more sensitive PT technique. Dwelling time was enough.

I suppose, that the question is in very small depth of the crack. The crack is visible on surface the detail because the surface is smooth and polished.

And I agree with you, that „defect volume shall be able to keep amount of penetrant”. If the depth of the crack is very small (for example 1 micron) and having visible by eye opening, the amount of entered penetrant is so small, that it is 100 % removed when using of a remover.

 
 Reply 
 
Ashok kumar patra
,
Saudi K-KEM Engineering service co, Saudi Arabia, Joined May 2018, 63

Ashok kumar patra

,
Saudi K-KEM Engineering service co,
Saudi Arabia,
Joined May 2018
63
09:20 Jul-12-2020
Re: Minumum depht of a discontinuaty to be detected by dye penetrant testing
In Reply to Aleg at 18:08 Jul-11-2020 .

Yes now you understand you can use post emulsifiable penetrant instead of waterwashable or solvent removable with proper removal of excess penetrant you get the indication.

peace.

Regards.
Ashok patra.

 
 Reply 
 

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