A Chilly Surface Prep Method Gains Steam
- 10 August 2017
- Posted by: Stm Coatech
- Category: Educational Articles
A Chilly Surface Prep Method Gains Steam
In my years in the corrosion mitigation industry, I’ve found that it’s all about change. Don’t get me wrong: If something is not broken, then why fix it? There is no need to reinvent the wheel, as they say. However, if improvements can be made in order to enhance industry practice, improve quality or ensure safety, then believe me, I will try my very best to see if I can make industry changes.
The reason that I bring this up is that people don’t like change. Change unsettles folks; people become scared of the unknown and sometimes cannot see the benefits that change can make.
In the spirit of change: I was recently invited to a demonstration of dry ice blasting.
I am highly open to change and relish new advancements in technology. However, as many of my colleagues will testify, I am also ever skeptical of new technological advancements. There are regular changes within the industry, but rarely changes that are potentially revolutionary and when I am informed of such changes, being the skeptic that I am, I must see for myself before casting judgement or appraisal. Usually, things really are not as good as they seem, and there always are pros and cons of every new advancement; with this is mind, I was determined to find them.
A Cool Way to Blast
Dry ice blasting has been known by many names over the decades, be it “dry ice cleaning,” “dry ice dusting,” “CO2 blasting” and, I am led to believe, “environmentally sustainable cleaning” at some point. However, regardless of the terminology, the process is similar to abrasive blast cleaning, wherein blast media is accelerated within a pressurized airstream to remove surface contaminants and impurities from a designated substrate. The main difference is the medium used.
Dry ice blasting uses frozen carbon dioxide (CO2) dry ice pellets, as opposed to grit, shot or sand.
Dry ice blasting is nothing new: The first patent regarding the development and design of modern-day, single-hosed dry ice blasting technology was awarded in 1986. Since then, it has been a well-used method of surface preparation for years. However, despite the advantages that the method of preparation potentially provides, it has not been the preferred choice in regards to abrasive medium selection within the industry.
One of the main advantages of dry ice blasting is that in this method, unlike all other conventional abrasive mediums, the CO2 sublimes; therefore, there is no generation of secondary waste. Since dry ice evaporates completely as a gas, only the material removed is left for disposal: rust, paint coatings, mill scale etc. This is a huge benefit.
Secondary waste from abrasive media has been known to cause premature coating failures due to excessive dust. Additionally, inclusions contained on the substrate pre-coating the dust particles have also been known to get into sensitive equipment and machinery parts and have led to substantial repair bills for coating contractors. However, this is not the only benefit of dry ice blasting.
I think we all have to agree that safety should come first and this, from an engineering perspective, is what really drew me to researching dry ice blasting. You see, it really is a safer alternative: Many conventional abrasive media are known to contain toxic chemicals and produce harmful emissions. Dry ice blasting does not.
This makes the blast medium far less potentially harmful to production operators and greatly reduces the risk to employee health and safety. It is this factor that we really need to be focusing upon. Plain and simple, operators are not exposed to abrasive media nor the chemicals which they contain.
In addition to the lack of wastage materials and dusts, the CO2 medium also has two other major pros: It’s non-flammable and non-explosive. These are two huge benefits for maintenance work, particularly on oil and gas installations, where blasting works have to be executed during shutdowns in order to prevent live blasting.
Does It Work?
Clearly the environmental uses of this cleaning medium are clear for all who have struggled with abrasive medium removal to see! If you can in effect remove the waste, then why not?
However, this depends upon one thing: Does the dry ice cleaning method produce the same results as conventional blasting medium?
I am steadily starting to believe that it does; you just have to watch this demonstration of dry ice removing PFP. Any of my respected colleagues who have had to endure the painstaking task of removing cured passive fire protection will testify as to how arduous this process is. As per the demonstrations which I witnessed, the dry ice stream removed heavy paint materials and PFP test plates with ease. The post-removal adhesion values were well above 11Mpa prior to removal, and the materials where clearly tightly adherent. In my opinion, this is a remarkable breakthrough in technology.
Dry Ice and Surface Profile
It is common belief that dry ice does not leave a surface profile. That’s a common myth: Dry ice blasting does leave a surface profile, although certainly not in the value range of that produced by abrasive blast media, nor what is typically specified for most conventional coating systems. However, an Ra profile is produced.
To be fair, this was at a company which demonstrated its latest technology and revolutionary delivery systems. I would agree that this is not industry standard; however, it’s clear that major steps and advancements are being made. This was fairly obvious to me upon the demonstrations; the cleanliness could easily be compared to NACE 1/SSPC SP5 in that there remained no visual surface contamination on the test plates after blasting.
Owners and operators are heavily involved in research and developments of the capabilities of CO2 products. The interest has always been there; however, for a number of reasons, in the past the cleaning rates were not as rigorous as they are today, making the process non-feasible from a production perspective.
Challenges to Growth
So what is stopping dry ice blasting? There are two main factors involved.
The first is how I started with this blog: People don’t like change, irrespective of the clearly abundant advantages this medium holds for corrosion mitigation. However, the industry has always been changing, particularly when it comes to surface preparation mediums and cleanliness standards.
The second: the lack of a standard.
There is no standard to date by which to compare the cleanliness achieved. This is a major drawback. Taking into consideration the general appearance of the blast after completion on Rust Grades A,B,C and D, it would be fair to say that visually there is a strong comparison in finish to other abrasive media listed in SSPC Vis 1. I personally do not believe that it is beyond the realm of possibility to have the dry ice abrasive medium added to Vis 1; however, I personally believe that dry ice blasting should have its own separate standard, developed much like the waterjetting standards. This would then save any ambiguities which could be encountered whilst in the field.
Dry Ice Risks
There are, of course, residual risks associated with dry ice blasting. For example, as soon as the dry ice particles impact and penetrate the surface contaminant, energy is released, causing the particles to sublime into a much larger volume of CO2 gas. The gas then rapidly expands, and simply blasts the contaminant away from the substrate, into the airstream.
We have to remember that carbon dioxide is increasingly toxic, starting at concentrations above 1 percent, and can also displace oxygen resulting in asphyxia if equipment is not used in a ventilated area. In addition, because carbon dioxide is heavier than air, exhaust vents are required to be at or near ground level to efficiently remove the gas. At normal pressure, dry ice is −78 °C (−108 °F), and must be handled with insulated gloves. Eye and ear protection are required to safely use dry ice cleaning equipment. Compared to other blasting-cleaning methods, dry ice blasting produces fewer waste products and does not require clean-up of a blasting medium. The waste products can be swept up, vacuumed or washed away depending of course upon the containment.
Information like this would of course be available in a standard if there was one! I will of course be keeping my readers well updated with the standard development; hopefully, one of the leading institutes will soon see the remarkable benefits of having a technical standard based on dry ice media in circulation and I look forward to potentially working with any institute which would like to go down this route.
I am carrying out my own research and development in regards to the medium’s technical abilities for industrial use. There is very little wastage; thick, tightly adherent coatings are now being easily removed with the CO2 medium. It really is impressive stuff, with major leaps in technology since the first patent back in the 1980s.
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Paint Square, A Chilly Surface Prep Method Gains Steam, Erişim Tarihi: 01 Ağustos 2017, http://www.paintsquare.com/blog/?fuseaction=view&blogID=373