Dry ice blasting concern on carbon steel 1

[compit]

Hi All,

I have a client’s supplier who is proposing to to use dry ice blasting to remove a leaded epoxy paint from the internal side of a mild (0.3%) carbon steel vertical above ground storage tank.

I have yet to come across dry ice blasting. My initial concern is that the process is quoted as being effective when the area being blasted is temporarily brought well below the Charpy impact test value for the steel. (

https://info.coldjet.com/the-definitive-guide-to-dry-ice-blasting)

The figures I see quoted where the process is effect is -109°F / -78.9°C.
This localised low temperature coupled with impacts from dry ice pellet kinetic energy & impact thermal kinetic effect " "micro-explosions" make me worry that localised embrittlement / cracking or stress raisers may be born out of the process.

Would anyone have any experience with dry ice blasting on mild carbon steel, or would anyone know of any standards that might address this topic?

Many thanks

 

[TugboatEng]

I can only share thoughts as I only know of dry ice blasting and don't have experience or facts.

The dry ice itself is 109°F but the quantity being used should be low enough that it doesn't cool the substrate to anywhere near that temperature. Media blasting typically generates some heat in the material so that may also offset the cooling effect from dry ice.

 

[compit]

Thanks for your thoughts, though I am not sure where the heat you mention would come from, if anything I imagine the phase change of solid dry ice to gas would make the surface even cooler than the temp of the dry ice.

I read this (from the above link) and can imagine negative side effects in the very top microns of the plate or HAZ.

If it can cause "thermodynamic shock, which causes the contaminant to embrittle and shrink", and "creates an extremely large temperature differential between successive micro-layers within the contaminant" and "This sharp thermal gradient produces localized high shear stresses between the micro-layers". I can't see why this would not equally occur in bare metal areas that were blasted as would inevitably occur during overlapping and passing sweeps.

Localised high sheer stresses.... I shiver at the thought....

"The temperature (-109°F / -78.9°C) of the dry ice causes thermodynamic shock, which causes the contaminant to embrittle and shrink. The resulting micro-cracking helps break the bond between the surface and the contaminant.

The instantaneous sublimation (phase change from solid to gas) of dry ice upon impact absorbs maximum heat from the very thin top layer of the surface contaminant. Maximum heat is absorbed due to latent heat of sublimation.

The very rapid transfer of heat into the dry ice from the coating top layer creates an extremely large temperature differential between successive micro-layers within the contaminant. This sharp thermal gradient produces localized high shear stresses between the micro-layers. The shear stresses produced are also dependent upon the contaminant’s thermal conductivity and thermal coefficient of expansion / contraction, as well as the thermal mass of the underlying substrate. The high shear produced over a very brief period of time causes rapid micro-cracking between the layers leading to the failure of the bond between the contaminant and surface of the substrate."

 

[TugboatEng]

Is the heat being absorbed from the metal or is it the heat being absorbed from the kinetic energy of the dry ice that causes it to sublimate?

Then again, a chilling effect may improve the performance on non-metallic substrates as most paints and coatings will become more brittle at lower temperatures.

Metals have a much higher thermal conductivity and won't see as much localized cooling effect.

Most mechanical cleaning methods do put high stresses on the surface. Abrasives shear material away, shots indent the surface. Even ultrasonic cleaning can erode the surfaces by cavitation.

 

[MintJulep]

Seems easy enough to set up a simple test and measure the metal temperature directly.

Pontification on the internet is not likely to confirm nor relive your concern.

 

[compit]

I'm not trying to pontificate, simply responding to someone trying to be helpful.

I'm also not sure what kind of simple test you imagine that could accurately measure the surface temp of the first few microns of the plate or weld surface.

What I was asking was did anyone have experience or know of any codes or standards that address this topic.

Thanks

 

[LittleInch]

I'll admit it's a new one to me, but for something like tank blasting I can't see an issue. Any impact or micro hardening isn't going to affect a tank shell. If the product has been in use this long then they should have a looooong list of satisfied customers and has been proven. Ask them for a reference list and permission to contact people.

I assume you know all about the toxic issues to do with removal of lead paint and materials? Basically full chemical suit / BA stuff and much testing.

I did a course once on cleaning tanks which had held leaded products (Petrol) and it scared the living daylights out of me. Can't see this being any better.

Maybe try the storage tank forum with a similar question and link back to this one?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[blakmax]

I'd be more concerned about the poor fellow doing the blasting in a confined space using a material that gives of a gas that is non-breathable.

 

[LittleInch]

NO.

Lead poisoning is a horrible way to go. By the time you find out you've got too much in your urine / blood your body starts processing it into things which can kill you.

I don't deny the CO2 levels in an enclosed environment might not be great either, but this stuff is deadly if you don't treat it like plutonium.

https://patient.info/doctor/lead-poisoning-pro

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[compit]

He would be on full BA, all lead protocols would be followed, blood testing before after etc.

I'd like to know more than that they have don't it before on other clients equipment, I want to understand the constraints before allowing something that brings even the surface of the steel (and particular the HAZ) to far below the metal design temp and then to boot impacting at those temps.

I'd post this on the storage tanks forum but I think that might go against forum rules on cross posting.

 

[hydtools]

Just end this thread and post elsewhere. The hazard nature of the problem outweighs the rule of cross postings.

Ted

 

[MintJulep]

Well, I know that dry ice blasting has been used on carbon steel sheet, cast iron and cast steel parts of passenger rail cars and bogies over the years during overhauls. Copper HVAC coils, plastic and FRP parts, wire harnesses too.

So far the world hasn't ended as a result.

But that anecdote doesn't assuage your concern does it? Nor should it.

But likely anecdote and testimonial is all that you will find. I can say with confidence that there is no standard for this, because it is not a standard thing.

Maybe, if you're lucky, somebody has had the same worry and has somehow found a satisfactory (to them) answer. Unless that somebody is in academia, it's not likely that their answer is published. Maybe that someone is an Eng-Tips member, and will will willing to share.

What quantifiable proof do you need to give approval? How can that proof be created? Define that and tell the supplier the bar they need to get over. Anything else is not fair to the supplier, and will just drag the process out until either the supplier gives up, or someone over rules your worry and approves it anyway.

I agree about the occupational hazard of this. The flip side of that is that the dry-ice process will greatly reduce the amount of contaminated waste from the process because there will be no contaminated blasting media to dispose of.

If you don't think that you can measure the temperature accurately (enough), then blast some test coupons and examine them for evidence of the damage mechanisms that you are afraid of.

By the way, "creates an extremely large temperature differential between successive micro-layers within the contaminant" and "This sharp thermal gradient produces localized high shear stresses between the micro-layers" is marketing BS from the blasting equipment manufacturer, not the result of rigorous engineering investigation.

 

[LittleInch]

It might also be of interest to the materials forums.

Sub thickness cooling is an interesting area I suspect.

I found this on the web so assume it's ok to attach, but seems to be relevant.
So if it's good enough for Shell, then....

There is also a reference in the back to another report which seems to address the issue, but it doesn't appear on a search.

https://www.jurunature.com/panel/up...chnical Assessment of Dry-Ice Blasting(1).pdf

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MintJulep]

Well I'll be damned.....

 

[LittleInch]

Well if sone can find this that would complete the circle. Enspec appear to be a standalone test house. No search facility so if you want it you will probably need to pay.

http://www.enspectechnology.com/index.html

Review of the effects of the dry-ice cleaning process on the surface embrittlement of
carbon and stainless steels; Enspec Technology, Case No. EN2719 Rev 0, 14th of June
2016.

The original shell report comes from here:

https://jurunature.com/humidur.php?task=product&Gcode=1

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SJones]

@LI

That document is a good score. Download and keep because it is Shell Restricted and copyright, and might soon disappear. I hadn't expected the productivity to be so much more than grit blasting, but that is tempered with the fact that the DIB can't achieve the necessary profile for high performance coatings. The Shell work is for external, atmospheric coatings - it could be a different story if the OP wants to reline an AST where surface (re)preparation is going to be more critical. It could well be that a secondary grit blast is required to get an optimum preparation for lining, particularly if immersion at any elevated temperature is on the menu.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[LittleInch]

I have, don't worry....

I found it on a generic search and it is on that companies website so....

I did read somewhere that they can introduce some grit into the lance if you need a particular surface spec so I suppose they just use less grit than otherwise.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[compit]

What a great find ! Thanks for all the digging.

Absolutely getting eyes on that Enspec report would be interesting, the test method as it is described in the Shell report is vague and leaves room for lots of potential holes.

I think the next way I should approach this is by asking if anyone knows of companies which do not allow dry ice blasting of carbon steel for risk of macro level damage.

 

[mfgenggear]

compit

there has been a wealth of information given all ready. my thoughts is no effect, and you might be over reaction. but to be
sure simulate tensile and charpy test samples and electron microscope and test away. I believe it will not effect the metallurgical , tensile and impact test.

 

[Compositepro]

Dry ice blasting is a well established process with plenty of history. It is a type of grit blasting but with dry ice rather than an abrasive. It is used on composite parts because it is far more gentle on the substrate than abrasive. All this speculation by those unfamiliar with the process is is just that, speculation. Talk to suppliers of equipment.