Part 1: Getting to the Root of the Problem
Why are contractors surprised when repeated abrasive blast/hydrojet/mechanical cleaning methods (in conjunction with dehumidification, chemical treatments for soluble salt removal) fail to achieve a result good enough to pass pre-coating inspection and/or conductivity testing? Why do the same thing over and over yet expect to achieve a different result? The only difference predictably achieved in that manner is in the expenses and the number of days behind schedule the project accumulates.
Looking into the problem confirms that a different approach is needed. Mechanical cleaning methods and chemical treatments are limited to what they were designed to do: remove macrocontaminants and soluble salts. They can't remove the full array microscopic contaminants responsible for stubborn corrosion-triggering contamination, nor were they ever designed to.
MICROCONTAMINATION CAUSES CORROSION
Abrasive blasting and hydrojetting remove macrocontaminants like oils, dirt, and visible rust. Soluble salt removal chemicals remove water soluble contaminants. Rust inhibitors create a temporary barrier film to keep ambient contaminants from reaching the substrate. Coatings provide a ‘permanently’ bonded barrier film. They all do what they are supposed to do, more or less.
What they don’t do is deal with a particularly nasty microscopic aggregate contaminant: iron sulfide and other ionically bonded compounds. Current steel manufacturing employs closed-loop quench systems that (contaminant-rich) quench water, significantly increasing aggregate contaminant loads. Filtration technologies cannot filter out 100% of these nasty contaminants, and their existence on steel surfaces is ubiquitous.
These compounds penetrate metal substrates over time and are difficult to remove. These contaminants draw soluble salts through ionic attraction, even when sulfur is present at very low ppm. Soluble salts form a very strong bond with these adverse anions, rendering them ‘functionally insoluble’ (not readily removed by abrasive blasting, hydrojetting or mechanical cleaning; and unaffected by soluble salt removers or inhibitors). The strong attraction results in soluble salts that ‘hide’ the salts below oxide films that develop, making them virtually impossible to remove or detect outside the laboratory.
These microscopic contaminants are extremely hygroscopic, meaning they draw in moisture from the air to initiate a corrosion chain reaction that will continue unimpeded to expand corrosion reactions. This adverse process is universal to bare substrates; however, but coated substrates are vulnerable to it as well. In coating protected substrates, atmospheric moisture and chlorides are drawn in through pores and holidays, essentially ‘feeding’ the ionically bonded compounds. Corrosion expands through capillary action causing coatings to disbond, delaminate, blister and fail.
The key to successful contamination control is comprehensive surface preparation that eliminates microcontamination. OxNot is a unique chemical treatment that removes sulfides, destroys oxide films and dissolves ‘hidden’ (bonded) chlorides, in addition to nitrates, microbial byproducts, rust and soluble salts from metal surfaces. The result is a substrate that passes visual, ion detection and conductivity testing, resists rustback and creates the optimal surface for strong, consistent coating adhesion.
OxNot more than met the expectations and standards in the nightmare scenario described above, removing the cause of massive surface contamination that had previously delayed the project for several months and optimally preparing the surface for the coating phase in a few short hours.
A SIMPLE, EFFECTIVE SOLUTION
When it comes to surface preparation, the KISS (keep it simple, stupid) principle applies. More tasks, more complexity. More equipment, more complexity. More settings, more complexity. More complexity, more room for human error. OxNot is a promising new technology that offers a simple, effective solution to the problem of microcontamination.
OxNot CleanBlast is a liquid material designed to be mixed with chlorine-free or activate carbon filtered water in the vapor blaster water supply tank at a 1:100 ratio, then blasted per the manufacturer’s regular blast guidelines on the target surface. A final “rinse-only” phase is recommended after blast cleaning to remove any residual grit particles that may remain on the surface. After air-drying, the surface is then ready for coating. It's that simple.
Vapor blasting with OxNot CleanBlast increases the efficiency and dependability of the entire surface preparation process. Setup and cleanup of vapor blasting equipment is easier and faster than that of older technologies. Surface cleaning, soluble salt removal, decontamination, chemical rust prevention treatment and profiling can be completed simultaneously using one machine, in one step, with zero dwell time. The entire process is condensed. No dehumidification, inhibitors, water supply tankers or waste containment trucks are required.
Simplifying the surface preparation process with OxNot CleanBlast and vapor blasting equipment impacts the entire maintenance process. Low pressure vapor blasting slashes the frequency of blast nozzle and hose replacement as well, for less maintenance downtime across the board.
Low-pressure, low-dispersal vapor blasting won’t impact nearby activities. Coating contractors can opt to directly follow surface preparation crews and begin applying coatings as soon as the surfaces are dry, or even days later (since OxNot delays flash rust). OxNot CleanBlast dries as fast as pure water, leaving zero film or residue on metal surfaces, so there’s no guesswork involved, no secondary rinse, and no coating incompatibility to impede adhesion.
The aim of surface preparation is to eliminate contaminants and control other variables to ensure predictable, desired cleanliness (metal hygiene) to create a pristine surface for uniform coating adhesion and corrosion protection. Controlling more variables simply leads to more predictable outcomes, every time. The reason why contractors seeking to avoid metal contamination nightmares turn to vapor blasting with OxNot, time after time is clear. Controlling more variables generates more “wins”, lowers the investment per job (time, labor and money) for increased profit margin, and permits more and tighter project scheduling.