Between the corona-related lockdowns in 2020, the most detailed warning to date on "chromium (VI)" deposits on engines comes freely visible and retrievable on the net.
With today's state of knowledge, however, the question arises whether the published information really shows the actual course of the investigation, or whether it is merely an attempt at explanation; on closer inspection, the attentive observer notices things which, to put it mildly, are not entirely plausible, at least not from the point of view of today's knowledge.
"..Hexavalent Cromium or Chromium-6 (Cr-6) is the product of the oxydation of Cr-3 or Cr-4 contained in the alloy of certain stainless steel parts from the exhaust system and/or its thermal insulation. Cr-6 develops under specific conditions: high temperature, oxydising environment, potential presence of catalyst, such as Calcium, present in some greases.
Hexavalent chromium may be encountered in-use from sources such as aftermarket parts, interactions with maintenance materials and/or certain operating environments.
While lab testing is the only sure way to know if hexavalent chromium is present, an indication that hexavalent chromium may be present are yellow residual deposits (See the Illustration below), typically in areas of high heat such as on exhaust manifolds or exhaust insulation.
Furthermore it says:
"If such yellow residual deposits are found on the engine, engine component parts, or associated equipment or package, the maufacturer recommends following local regulations and guidelines and good hygiene and safe work practices.
Precautionary examples are listed below:.
Avoid creation of airborne dust containing the yellow deposits. If generation of airborne dust cannot be avoided, it is advisable to use a face shield or goggles and a negative pressure half mask respirator with P-100 cartridges (or equivalent).
• Wear personal protective equipment to prevent skin and eye exposure. Wear cut proof nitrile gloves and a disposable protective suit.
• Wash hands and face with soap and water prior to eating, drinking, smoking or during rest room breaks to prevent ingestion of any yellow powder.
• Avoid release of the residual deposits to the environment. All waste generated during the repair process including cleaning towels, and used Personal Protective Equipment (PPE) need to be collected and stored in a proper container pending disposal as hazardous waste.
In the event that hexavalent chromium is discovered, Caterpillar recommends following all local guidelines
and wearing the correct PPE during the decontamination and removal process.
A so-called "washing instruction" follows, as if it were about the correct handling of a bought dress, so that this looks like new again afterwards.
Only that this is not about the care of cotton or polyester, but about the handling of a carcinogenic, partly mutagenic, but also acutely environmentally harmful substance.
It is indeed possible to treat hexavalent chromates with liquids that can lead to extensive decontamination.
Such processes are intended, for example, to remove chromium (VI) compounds from screws, flanges, or similar components with deposits.
In this cleaning process, the contaminated parts are placed in a liquid solution so that they can be used again without being contaminated after an appropriate period of time.
But how, for example, does the publisher of the so-called "washing instructions" imagine the process of treating entire pipelines, turbochargers and the related thermal insulation? If you look at the company's website, there is a lot of cleaning to be done
So it is not surprising that the purification process can take several days, as it is described by the publisher of the website, because we read further:
"..The cleaning process is repeated as long as the test remains positive....
...This process can take 1 to 3 days depending on the engine series..."
We don't want to offend our interested readers, but we also know the realities "in the field".
You don't have to have much imagination to doubt that maintenance work carried out under time pressure (overhauls; editor's note) does not include a time window for such cleaning work, especially in view of the fact that, for example, according to the Technical Guidelines for Work with Hazardous Substances (in Germany: TRGS), work rooms for work with hazardous substances should only be accessible to trained employees and these rooms would have to be closed off to all other persons and may only be accessible again when the risk no longer exists.
If the work guidelines are interpreted correctly, the engine room would therefore be closed off for several days and thus only accessible to those familiar with the problem, and would not be allowed to be reopened until everything was "clean" and "safe".
Just a few days ago, the editorial team was at a biogas plant where, among other things, an engine affected according to the safety warning is being operated. When we asked whether there was a risk assessment regarding the possible formation of chromium (VI) compounds on the insulation/motor or even whether a mandatory so-called "exposure register" was kept, we were only looked at incredulously.
The questioning of individual employees was also not very informative; although some employees stated that they had heard of this problem before, they did not know any further details.
In the further course of the warning message, the following notes still stand out, which are covered in the FAQ section:
"..Where Cr-6 can be found?.."
"..Cr-6 can be found on engine parts affected by high temperature (over 400°C), mainly on bellows, bellow collars, exhaust manifold screws (nut/bolt), on thermal insulation inner face and on turbocharger..."
"..Can Cr-6 reappear after the clean-up?.."
"..At this stage, there is not enough information to confirm it, however we suppose that the chemical transformation of Cr-6 will continue. As long as Cr-6 development conditions are met – temperature, oxidation – a risk of Chromium transformation might remain."
"..Is it required to change the high-temperature mounting grease?.."
"..Yes, it is required to change it only if your grease contains Calcium.
As previously described, Calcium acts as a catalyst in the Cr-6 chemical reaction. The manufacturer is looking for a commercial calcium-free solution for high temperature screws greasing. The reference of these greases will be communicated as soon as possible. Old Calcium greases shall be removed."
Im FAQ-Bereich finden wir auch noch den Punkt "Vorschriften"
"..The following are the official recommendations:
Protect yourself from the danger,
Stay below the Exposure Limit Value (Professional Exposure Limit Value / Short term limit value),
If technically possible, find a solution to avoid the Cr-6 formation,
As per Labour code ..: “We must replace what is dangerous with what is less dangerous, and what is a little dangerous, with what is not dangerous”.."
In short, it can be concluded that the findings in this magazine series on the connection between stainless steel bodies (engine, turbine; component; editor's note), high temperatures and, in particular, calcium (calcium oxide; editor's note) in the formation of "chromium (VI)" (chromium (VI) compounds, in particular calcium chromate (CaCrO4); editor's note) are also confirmed by the warning message from the engine manufacturer.
However, the critical reader will certainly have asked himself when viewing the page where the calcium source is actually to be found in the pictures.
As delivered, the insulating elements consist of a full stainless steel jacket that encloses an insulating material.
I, too, discovered the decisive detail only after a few months, actually only in the fall of 2020, when I saw a stripped motor from the motor manufacturer for the first time or discovered a certain picture on LinkedIn:
Do you see the handprint above the red arrow?
There was apparently worked without gloves and so the service technician had unprotected contact with the yellow "harmfuldust" calcium chromate , but that is another topic!
This picture brought back memories of the warning message described here, especially because I saw the insulating element that had encased the compensator area in the cutout photo and so I took another close look at the picture of the motor manufacturer!
In the area of the red circle, you can see that the stainless steel protective jacket has probably burst open due to the vibrations; this happens once in a while due to the high temperatures, at least we have seen it many times.
The insulating material protected in the stainless steel jacket until then is released and escapes. Fibers of the insulating mat deposit on the stainless steel foil or other stainless steel bodies and "react".
One of the components of this insulating mat is, you guessed it, and with a mass fraction of about 30%-40%,
Calciumoxid (CaO)
Finally, we quote once again the recommendation already mentioned above:
"..
If technically possible, find a solution to avoid Cr-6 formation,
According to the ... Labor Code, "We must replace the dangerous with the less dangerous and the somewhat dangerous with the non-dangerous."..."
.."
and take another look at the following reference:
"..
The engine manufacturer is looking for a commercial calcium-free solution for high-temperature screw lubrication. The reference of these greases will be communicated as soon as possible. Old calcium greases are to be removed..."
So get rid of the calcium!
At least with the old calcium grease
So if calcium is the reactant and is contained in the grease and this has to be replaced, then wouldn't it also have to be said in reverse, i.e. with insulation containing calcium, which may well be released:
The engine manufacturer is looking for a commercial calcium-free solution for high-temperature insulation?
Old calcium-containing insulation must be removed....
""We must replace the dangerous with the less dangerous and the somewhat dangerous with the non-dangerous.""
Or have we misunderstood something here?
All sources and machine-translated texts can be found here (original in English and French, respectively):
https://www.eneria.fr/en/hexavalent-chromium-or-chromium-6-cr-6-on-engines/