Dear Readers,
the media pressure in reporting on the formation of hexavalent chromium compounds (#Cr6 compounds) such as calcium chromate (CaCrO4) or sodium chromate (Na2CrO4) is growing and many individual reports coming from all over the world are adding up to show the whole disaster:
Only from the German-speaking countries nothing is heard (yet), but it should only be a matter of time until this topic, which has been successfully kept quiet so far, also reaches the German market.
Perhaps because there, in particular, occupational safety and environmental protection have a higher weight, or should we say - should have?
The latest developments:
"Chromium present in stainless steel may form as a residue on the exterior and sometimes interior engine or turbine components. This chromium is hexavalent (Cr6+ ), which is a carcinogen and a skin and respiratory sensitizer. It forms when metal in an oxidizing or corrosive environment is in contact with calcium oxidecontaining materials, such as thread sealants or insulation. The generation of Cr6+ increases at elevated temperatures and often appears as a yellow or white residue on engine components and adjacent insulation surfaces."
What few people know, however, is that the original link to which this warning message refers has been deleted in the meantime.
In a confidential conversation at a #Biogas trade fair in Europe, we were told behind closed doors that the deletion order probably came "from the very top" from the company headquarters.
To avoid copyright discussions, we would like to show our own photos here, which show a clear chromate formation (calcium chromate; <CaCrO4>) on hot engine parts, which we took ourselves during an engine overhaul, please see for yourself:
The warning further states:
What Went Wrong:
The presence of this residue and how it is produced was not known until the last few years.
The residue may often be mistaken for sulfur and can be difficult to see with typical sodium lights.
But where does the yellowish-powdery calcium chromate come from or how can it be formed?
In order to pursue this question and to be able to answer it reliably, we have to do a little more causal research, as already mentioned; the chemical formula is, for example:
Cr2O3 + 2Cao + 3/2 O2 => 2CaCrO4
<1> <2> <3> <4>
<1> Chromium(III) compound | Source: stainless steel alloys
<2> calcium oxide | source: ??
<3> oxygen | source: ambient air
<4> Calcium chromate | Result
![Oxidation of Cr (III) to Cr (VI) [CaCrO4] in the presence of calcium oxide (CaO)](https://static.wixstatic.com/media/d7b443_0b54a0c939514902aaf6a852454acd68~mv2.png/v1/fill/w_52,h_41,al_c,q_85,usm_0.66_1.00_0.01,blur_2,enc_auto/d7b443_0b54a0c939514902aaf6a852454acd68~mv2.png)
The diagram shows how the calcium content affects the high oxidation of chromium (VI) from chromium (III) compounds under the influence of temperature.
From a temperature range above 250°C, the oxidation range starts to increase up to a temperature range of approx. 850°C.
This is exactly the temperature range in which CHP engines or turbines are operated!
So, to solve the problem of calcium chromate formation, you have to look for and find the calcium source!
But this is not so easy to find at first sight.
To locate the chromium(III) compound, a stainless steel or chromium-containing surface is also required.
Both sources can be found in a component that does not always belong directly to a CHP engine, for example.
It is the insulation, often supplied in textile form, but often in metallic form, to insulate the system temperature of the engine, i.e. to store heat, to provide less radiation, etc. pp.
In the past, it was succinctly dismissed as heat protection, but today it is an important component of exhaust gas aftertreatment in many combustion systems, but it always leads a somewhat shadowy existence because, for one thing, it does not necessarily improve the appearance of the engine and, in textile or matte form, it is also a nuisance and generates dust.
These half-shells removed from the engine shown above contain chromium, so we have found the source of the chromium.
These half-shells contain insulating materials as mats or scrims, or they are compacted and filled with an insulating material (colloquially: insulating wool), the actual core of a shell insulation
.
What not everyone knows:
More than 90% of all insulation materials on the market contain calcium in various mass units (between 15 and 40%). If they do not contain calcium, they contain sodium or potassium or a mixture of other metals containing alkali or alkaline earth metals which, as the graph shows, also lead to the formation of chromates at temperature!
And so we can also claim that we have located the components (sources) necessary for the high oxidation process (chromium (III) to chromium (VI)) described at the beginning, the calcium source is simply the insulating material!
As delivered, however, the insulating material, whether metallic as a half or full shell, does not contain any chromium (VI) compounds, and thus all the manufacturers' safety data sheets are flawless.
The real dilemma, known as #TheChromateDisaster, only begins when the systems are put into operation, i.e. when the operating temperature rises and later becomes permanent.
With metallic half-shells e.g., the formation of calcium chromate takes place unnoticed!
The calcium chromate forms inside the half-shells, namely exactly where the calcium-containing insulating material and the chromium-containing cladding permanently form chemical compounds at higher temperatures.
And so the harmless calcium oxide of the insulating material combines with the harmless chromium(III) compounds of the stainless steel foil, but due to the temperature it becomes the non-vanishing and unfortunately carcinogenic element #calciumchromate!
So this is indeed a more than unfortunate thermochemical chain reaction, which unfortunately had not been thought of before, but which is now hitting the entire industry with force and posing new challenges.
In principle, any CHP/CHP machine and any steam or gas turbine can be affected, regardless of the manufacturer, because stainless steel-containing components meet with calcium-containing insulating elements at high temperatures almost everywhere, which makes the formation scheme described above likely.
Unfortunately, the same also applies to piping and automotive components if they contain stainless steel alloys, for example, which is particularly the case with the latest exhaust gas aftertreatment systems (Euro 6, Bharat 6, Tier 5, etc.).
Since calcium chromate is classified as a carcinogen (Carc. 1B) and a substance of very high concern (SVHC), is on the #REACH list, and is assigned H-phrases H350 (may cause cancer) and H410 (very toxic to aquatic organisms with long-term effects), special occupational safety regulations (e.g. Germany: ArbSchG) apply and the Ordinance on Hazardous Substances (e.g. Germany: GefStoffV) must be applied.
The safety officers in the companies know what this means:
Hazard assessments
S-T-O-P principle; substitution obligation
Exposure inventory (40 years retention period!)
Country-specific disposal regulations (Hazardous Waste Ordinance)
With all these aspects in mind, every turbine and engine overhaul will become a special construction site in the future.
Carrying on as before may work for a while, but it is a question of time when trade associations, factory inspectorates and consumer protection organizations or the like will carry out inspections. will carry out inspections.
The first state offices in Germany, for example, are just preparing the first control measures, we know this from safe and trustworthy sources!
Notes on the images used above:
You might get the impression that the problem described is only due to a certain engine manufacturer or a certain type of thermal insulation, as shown at the beginning of this newsletter.
However, as you can see from the following pictures, (almost) all other types of thermal insulation are also affected:
(Left: Cr6 verification turbine insulation | Center: Cr6 verification stainless steel flange | Right: Cr6 verification insulating mattress)
#TheChromateDisaster is a general problem, not a specific one!
More on the chromate problem, which is also more than a cause for concern, e.g. in gas and steam turbines, in the next blog post.