DPC NEWS N°3
Dry powder density
As SUGGESTED by one of our readers, there is a very simple method not to have to check the developer; it is good enough to replace it every day.
Due to the small quantity, it does not raise problem.
Suck up the old developer, check under UV-
This process is very well accepted by auditors.
EDITORIAL -
ONCE AGAIN THE END OF PENETRANT TESTING IS AT OUR HANDS' REACH
Our last month editorial brought us an unexpected number of emails from our readers the world over. Our readers live in more than 110 countries.
As an example we have been allowed to publish in its entirety, at the end of this editorial a point of view we received.
We were far from thinking that this topic would seem valuable to so many people to write about. We cannot publish all the messages we got and the answers we have sent.
We think it more useful to present a summary.
First of all almost all of our readers followed us up and let us know they approved our writings.
Nevertheless some confirmed their aim is to substitute completely, or at least in some areas, PT with alternative methods they qualify as more reliable and "cleaner".
By experience we do not see any method more reliable than PT or MT to detect open to the surface discontinuities on very different parts in many different locations. Trying to replace these two methods, it is commendable...even feasible in specific cases....but what we are sure of is that PT and MT materials manufacturers as well as users (think of service companies which rarely do their tests in workshops!) won't be out of business for decades!
As per environment concerns important improvements have been made, the least one
being lowering of volatile organic compounds (VOC) emissions. We are confident that
constant efforts will lead to other improvements, though the "volatile, non-
All the future PT lines may comprise the waste water treatment installation.
Automatic PT process lines make it easy to comply with all the parameters of every inspection step while deleting manual actions.
But a human being will still be irreplaceable when time comes to inspect parts due to the unique combination: sensor (eyes) + signal processor (brain), of course obsolete...but which is still the only one able to see in a fraction of a second that indications are in line (and shall be considered as ONE indication), that an area currently displaying a background has today an aspect which is more like abnormal porosities; the human being is also unique in that he will have a look to an area of the part he has been instructed not to check (so as to decrease inspection time), and "bingo" he finds indications that "should never have existed" (real cases in nuclear industry: microflaws on reactor covers; in aerospace for different parts; in car industry, etc.) while a computer instructed not to check that area will NEVER take the initiative!
That's why we think hiring, training and increased motivation of inspectors are of the utmost importance.
Deleting PT, well, dream of it and build castles in the air!
Our thinking is unmoved: we are very confident PT is still there for decades!
Here is the point of view that we mentioned at the beginning of this editorial:
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Doubt raising is important but announcing the death of PT is at least...untimely. I know (and often tell) that PT is one of the pillars for our manufacturing quality. I must confess that since the last few years I put my hands in penetrant less and less, but what I see from my job close to the Quality Director in my company makes me dubious:
More and more non-
More and more troubles to design and commission new installations, even if relevant,
due to an insuperable a priori targeting any new means requiring a management according
to ISO 14000 or equivalent and whose commissioning is always hoped for...elsewhere.
Same reaction for surface treatments lines, metal-
More imagination needed to fit PT in a 100% digitalised production line, which is a specific main strength of our Company.
Adding to what was said at this meeting is that our company even if it has to look
forward using TOCCATA's binoculars shall have a long-
I am not sure to have my ticket for Moscow available but I will be happy to hear about discussions and to try and know when the facts meet the fiction.”
Luc BOYER, Level 3, Corporate Quality Management of Dassault Aviation.
Our answer:
« Inspectors are really the keystone of all the manual processes involved in PT, and, as we say, PT puts many people off. Is it possible to make the entire PT process automatic? Sure a higher salary is needed to hire, qualify, motivate inspectors.
As for PT being a part of a 100% digitalised production line... we are at a minimum sceptical. The first example was the 1978 "Integrated Blade Inspection System" (IBIS) tested in the US. In Europe the first fully automatic inspection system, known as AEOS®, commissioned in 1980, was also a failure. Nowadays no equipment is in the process of being put in service. Nor for the next decade, in our opinion.
It is true that in some cases, such as the one you explain, an automatic NDT (UT, ET) during the manufacturing process may be the right choice.”
DPC NEWS N° 017
PT PRODUCTS FOR SPECIAL APPLICATIONS (FOLLOW-
Many of our American friends read the papers that we wrote and published on our website. Quite often we even get support letters and some questions are asked.
We suggest you have a thorough look at the papers published on the monthly "The Penetrant Professor", address as following:
http://www.met-
In its November 2009 issue there is a comment on our own DPCNEWSLETTER #017 issued in October 2009 which deals with PT products for special applications.
In The Penetrant Professor issue you may find a long list of American patents about PT which went nowhere:
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As you may summarise chemists, maybe only to justify themselves to their bosses, or at least to have their names registered, have many ideas... quite close to frenzy!
DPC NEWS N°011-
THE VOLATILE ORGANIC COMPOUNDS (VOC)
AND PENETRANT TESTING/MAGNETIC TESTING (PT/MT)
We received an email from a European reader, about the VOC and our DPCNewsletter n° 011.
It comes as follows (edited for clarification):
"Hello Patrick
Just read your DPC newsletter n° 011 about VOC's, etc.
Are you aware there is already a new Directive 2004/42/CE replacing 1999/13/CE? The vapour pressure is no longer the basic but it is the initial boiling point: products boiling at less than 250°C (482°F) are VOC, while those with a higher initial boiling point are not.
Bye T.D."
We warmfully thank this reader for the information. In fact it does not tremendously change the classification: the higher the boiling point, the lower the vapour pressure at 20°C, with very few exceptions.
For instance an hydrocarbon very often used as a basis for red dye penetrants formula
or for oil-
This applies also to the "white-
DPC NEWS N°4
APPLY DRY DEVELOPERS THE RIGHT WAY
One of our readers sent us a comment about dry developer grain size.
Here is his letter, edited for a better understanding:
‘‘The technical data sheet of the dry developer xxx shows there is no particle sized
under 0.1µm, while you state a 1/100 µm (10 nm) figure. If the dust-
Here is our answer:
The dry developer xxx is not the only one of its kind on the market. Further without
giving away any industrial secret, you may know that dry developers comprise magnesium
silicate, alkaline earth carbonates, amorphous silica and other additives, for instance
to enhance whiteness or increase fluorescent indications seeability under (UV-
Top quality dry developers are made from synthetic materials: there is no asbestos
(so no asbestosis risk), silica is crystalline silica-
Amorphous silica as found in some dry developers formulae may have a very small grain size.
As far as we know the first step to amorphous silica is to have silica (SiO2) react
with fluorine, become then the silicon-
The average grain size of this silica is 12 nm, i.e. ca 1/100 µm.
The Van der WALLS forces then helps particles to coalesce together, but a significant part of the powder is made of independent nanoparticles.
DPC NEWS N° 019
TOMORROW'S PENETRANTS (FOLLOW-
Many of our American friends read the papers that we wrote and published on our website. Quite often we even get support letters and some questions are asked.
We received the following e-
‘‘1) There are two ways to make up for lower efficiency of excitation of penetrants by blue light as compared to UV. One is, as you suggest, to make new penetrants that are optimized for the new blue wavelengths. Another is to specify a higher intensity level for blue lights used with existing penetrants. If an excitation wavelength is half as efficient as 365 but you use 2x the intensity you would have used with a 365 source you should get a similar intensity of fluorescence.
2) The situation with magnetic particles is more complicated than with penetrants. As you point out all manufacturers use a similar dye for penetrants, so the excitation spectrum is similar. While there are indeed some similarities, the excitation spectra for the pigments used for magnetic particles are more variable from manufacturer to manufacturer and from product to product within a single manufacturer. And while the excitation spectrum for penetrants is moderately sharply peaked at 365 nm, I have not found this to be so for particles. In many cases the excitation is just as efficient well into the 400's as it is in the UV, and in some cases even more efficient.’’
Our answer:
‘‘An irradiance at 450 nm twice that at 365 nm should make us think... twice!! i.e.,
first, is any effect of saturation of the dyes, as seen with 5,000 µW/cm² and above
at 365 nm, possible when using high 450 nm irradiance? Second: what is the effect
of high irradiance at 450 nm for long exposures, as some times experienced in UV-
These two points will need numerous tests on ALL the penetrants which are currently listed...just to be sure. Sure if these two points are Okayed, better to keep current formulae!!
The other point is more...administrative: no current standard, no specification allows
for using blue light instead of UV-
Maybe not the easiest task to achieve!’’
His answer was:
I absolutely agree that the task of acceptance for primary inspections is difficult, and that great care must be taken to ensure that the same performance as with current methods can be achieved. This will require extensive testing and validation. And if the procedure is ever approved, it will indeed put additional requirements for internal procedure management, auditing, etc.
But now on to the interesting chemistry/physics questions relating to saturation and bleaching. The whole process of fluorescence first requires absorption of a photon to put the fluorescing substance into an excited state. Several things can happen to the excited photon, only one of which is fluorescence. Some can go into mechanical action (heat), and another is that the energy can go into chemical reactions. Is it correct that these chemical reactions are what ‘‘damages’’ the dye and causes bleaching?
A molecule does not ‘‘know how’’ it got into an excited state, whether from absorption
of a UV photon or a blue photon. Once in an excited state the relative probability
of fluorescence or other use of the excited state energy is the same (a little more
on this below). So if blue is for example 50% as efficient at causing fluorescence,
that would mean that it is only 50% as likely to be absorbed in the first place.
Saturation and bleaching both result from excited state electrons, so if blue light
produces only 50% as many excited state electrons for the same input energy, then
by using twice as much blue light you would have the same saturation/bleaching issues
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Is it possible that another factor is whether incoming photons are putting electrons into the first excited state or into a higher excited state? Fluorescence occurs from the first excited state. Could it be that the energy of a UV photon first puts the electron into the 2nd or higher excited state? And if so, could the photobleaching be related to this higher energy level? If so, and if blue photons put the electron only into the 1st excited state, would there then be less potential for bleaching? My own suspicion is that this would not be the case since the higher excited states decay to the lowest excited state very very fast, so the potential for much chemistry to occur would be low.
Is the above discussion correct according to your knowledge, or am I missing important points? I am not arguing here for blue or UV, only trying to fully understand the science behind the process.
Our answer was:
Fluorescence is clearly explained on the following Website:
http://www.ndt-
Then click on ‘‘resources’’, then on ‘‘penetrant testing (PT)’’, then on ‘‘color and fluorescent’’ and also on ‘‘Why Things Fluoresce’’.
Basically, in PT, fluorescence is achieved using 2 dyes: a yellow, yellow-
Both dyes are heterocyclic molecules with N (nitrogen) and C (carbon) atoms with both σ and π linkages. Fluorescence is due to the excitation of the π electrons of the π linkages.
Contrary to σ electrons, π electrons are free electrons moving on an electrons track.
π linkages are not so strong as σ linkages. If some π linkages are destroyed the
fluorescence brightness under UV-
π linkages may be destroyed by:
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When UV-
We could spend quite a long time discussing about the physics of penetrants' fluorescence.
We suggest you contact a PT materials manufacturer, just to make tests comparing
450 and 365 nm responses, as per the American specification SAE-
Should you want to perform the tests by yourself you would need the underneath mentioned equipments:
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UV-
It is likely you may find help, at a lower cost, if working with a manufacturer.
DPC NEWS N°19
TOMORROW'S PENETRANTS (FOLLOW-
In our January, 2010 mail inbox, we answered the e-
We wrote about fluorescence:
‘‘...Basically, in PT, fluorescence is achieved using 2 dyes: a yellow, yellow-
Both dyes are heterocyclic molecules with N (nitrogen) and C (carbon) atoms with both ó and ð linkages. Fluorescence is due to the excitation of the ð electrons of the ð linkages.
Contrary to ó electrons, ð electrons are free electrons moving on an electrons track.
ð linkages are not so strong as ó linkages. If some ð linkages are destroyed the
fluorescent brightness under UV-
ð linkages may be destroyed by:
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A chemical engineer of a PT/MT materials/equipments supplier sent us the following comment:
‘‘Regarding the molecules structure and more exactly p electrons, the sentence «Contrary to ó electrons, ð electrons are free electrons moving on an electrons track», implies that it is an absolute truth. In fact this is true only if the molecule comprises a conjugated system (electrons s and electrons p “alternation” as in butadiene) or if the molecule is aromatic.
The 3 conditions for a molecule to be aromatic are: it must be cyclic, have a conjugated system and have 2n+2 electrons p, n being a whole number. Note that p linkages of an aromatic system, though weaker than the s linkages, are stronger than the classic p linkages.
So in this example, the p electrons are mobile (better to state they are mobile than they are “free” because, in my opinion, this could lead to some confusion with the free electrons of free radicals. So the p electrons are mobile in the conjugated system).
I guess that the heterocyclic molecules you mentioned are aromatic molecules.
A p linkage contains more energy, hence is more fragile than a s linkage.
But this is true even for ethylene (non cyclic and non aromatic).
In your chapter about causes of the p linkages break, I would use the word “light” instead of photolysis, because light is the cause and photolysis is the process.
We may even add that the cause is the free radicals of the light."
Our answer:
‘‘The yellow dye and the optical brightener are aromatic heterocycles. In our mind, it was a given but we understand that we should have stated it.
So, when we write: «Contrary to ó electrons, ð electrons are free electrons moving on an electrons track», this is correct because, as you said, the molecules under scrutiny are aromatic.
We agree with your statement that p electrons are mobile (instead of free).
Agreed also your statement about the causes of the p linkages break: ‘‘light’’ should be used instead of ‘‘photolysis’".
Within a forty year-
As an example: in University, in the ‘60s, our teachers of quantum chemistry talked of “the Heisenberg uncertainty principle’’: it was inaccurate. As a matter of fact, nowadays, they teach ‘‘the Heisenberg’s indetermination principle’’. Indeed, this indetermination is due more to the nature of the particles (we should even talk of “quantons”) than to some insufficient accuracy of our methods of measurement.
A little bit of chemistry cannot hurt our readers.
Thank you very much for the attention you gave to our website”.
N.B. The teacher of quantum chemistry of one of us, in these ‘60s, let us know the mnemonic he asked students to use so as to remember the HEISENBERG’s indetermination principle:
“You only have to answer this question:
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The answer:
Because:
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