PAINTSQUARE BLOG

“Never mistake motion for action.” — Ernest Hemingway

It was early spring of 2007 when my old coating company got the call from Grainger World Headquarters to line the interior of four, identical, stainless steel cooling tower basins. They were small, measuring only 24 feet long by 12 feet wide by 1 foot deep—roughly 360 square feet each.

I specified an elastomer which could be applied in cooler weather, and we went to work.

We needed to abrasive blast the interiors to create a 2.5 to 3.5 mil profile. Visual standards are pretty much useless with stainless steel, so we used one of our more experienced blasters and crews.

Warren Brand

The same job that took my three-man crew six days was able to be done by our subcontractor with only two men in just four days while meeting the same level of quality.

Our three-man crew finished two of the basins in six working days, but we had to pull away before doing the last two, so we subcontracted the last two basins to another contractor.

That contractor sent out two men and completed the exact same job, with the same level of quality, in just four days. 

Let’s do the math:

Whether you’re the owner or the contractor, these numbers should be alarming. 

In this case, Grainger didn’t care how long the job took; it just wasn’t a relevant variable. But as a contractor, these numbers are the difference between staying profitable and going out of business.

Imagine for a moment that this had been a 250-foot-diameter tank of roughly 50,000 square feet. 

Was it a matter of efficiency?

Focus on Efficiency

Efficiency is a complex concept and a disciplined practice, particularly for us coating types. 

For those of you who follow my blog, you’re aware of my dedication to, and practice of, martial arts. There are a number of fundamental principles to the practice, and one of those is efficiency—efficiency in how one moves, how one strikes, where one strikes, the technique one chooses, and so forth.

However, as a corrosion and coatings consultant, efficiency is not necessarily a requirement of the work we do.

While we do take efficiency into consideration when specifying optimal coating systems—in terms of trying to specify a one- or two-coat system in place of multiple-coat systems—we don’t focus on how long blasting should take, the nozzle size, pressure at nozzle, abrasive metering valve, etc. 

As consultants, we don’t focus on efficiency—particularly in surface prep—as most of our projects are bid-based.

The bidding process, however, when combined with a well-written, tight specification, incentivizes contractors to plan their jobs efficiently in order to be competitive.

Then, since bids are designed to be firm, the contractor is further incentivized to run the project efficiently to maximize production and profit, which is all well and good.

While contractors must always be vigilant on their efficiency, there are four cases in which owners must be vigilant about watching how their resources are being allocated:

• Any job that is based on time and material (T&M);
• Contractors who are historically sole-sourced and have not had to face any competition;
• Contractors who have blanket contracts for ongoing work; and
• Whenever a job switches over to T&M.

Now, as those of you who follow this blog know, I’m a fervent supporter of contractors, and I believe they often don’t get the respect they deserve. However, I was a contractor for more than two decades, and I know what can happen—case in point: the Grainger cooling towers.

For the purposes of this blog entry, I’m going to assume that all contractors are well-intentioned and would never purposely be inefficient. That is, of course, the best case scenario.

“Trust but verify.” — Ronald Reagan, in talking about how to interact with the Soviet Union on arms talks

Efficiency Audits for Owners

When our firm considers an efficiency audit, our primary focus is on surface preparation. While there are dozens of different types of surface preparation systems and aggregates, for the purposes of illustration here, I’m going to talk about conventional abrasive blasting with coal slag.  

The basic, fundamental elements of an abrasive blasting system are misleadingly simple. Compressed air is blown through the blast hose, and aggregate (sand, coal slag, garnet, etc.,) is gravity-fed into the air stream at the blast pot. The blend of air and aggregate are then shot out of the blast nozzle at, ideally, 100 psi at roughly 450 miles per hour. That’s it, in a nutshell.

Images courtesy of Blast-One unless otherwise specified

The basic, fundamental elements of an abrasive blasting system are misleadingly simple. Compressed air is blown through the blast hose, and aggregate (sand, coal slag, garnet, etc.,) is gravity-fed into the air stream at the blast pot.

In practice, however, the systems are highly complex and can include dead-man controls, whips, filters, air-driers, aggregate metering valves, CO monitors, cooling vests, electric lights, communication equipment, etc.

For the purposes of this blog, we’re going to focus on only two components of the system, which owners, for very little expense, can monitor in-house.

Contractors are much more sophisticated and understand the importance of all of the elements in a blast system.

“Efficiency is doing things right; effectiveness is doing the right things.” — Peter Drucker

The Blast Nozzle Is Everything

You can have millions of dollars of equipment, manage dozens of tons of blast grit, run hundreds of feet of blast hose all for one, singular purpose—to drive aggregate and compressed air to the blast nozzle. That’s it. That’s the only purpose of any blasting operation.

Modern-day blast nozzles are all venturi as opposed to years ago, when they were straight bore. The venturi nozzle acts much like a jet engine, constricting the passage of the air-aggregate mix briefly at the throat, which then expands into an open cavity. When operating properly, a venturi shoots the aggregate out at roughly 450 mph.

The venturi nozzle acts much like a jet engine, constricting the passage of the air-aggregate mix briefly at the throat, which then expands into an open cavity.

The two main issues associated with the blast nozzle are the size of the bore and the pressure at the nozzle. Fortunately, these items are very easy to check and the equipment very inexpensive.

Size of Bore

As you can imagine, the bore (typically made of tungsten carbide or silicon nitride) of the nozzle will, over time, wear out and quickly decrease its effectiveness. After all, you’re running an abrasive through it.

A nozzle that has been worn by 1/16-inch has 50 percent less effectiveness! There are charts that will provide a good estimate of how long a nozzle can be used before replacement, based on the type of aggregate and cubic feet per minute (CFM).

A nozzle that has been worn by 1/16-inch has 50 percent less effectiveness; you can check wear easily with a blast nozzle gauge.

The way to check whether a nozzle is worn out is simple. You take a blast nozzle gauge (about $100), mark it with a grease pencil, put it into the nozzle and twist. When you remove it, there will be a small mark in the grease indicating the size of the nozzle.

Pressure at Nozzle

For reasons far too complex to cover here, optimal efficiency is reached when the pressure at the nozzle is at 100 psi. Now, the CFM may change dramatically; however, the pressure should remain the same.

Checking pressure at the nozzle is also simple and inexpensive. While the blast rig is in operation, a needle gauge (about $150) is inserted into the blast hose near the nozzle, at a 45-degree angle with the flow, and read. It’s that simple. 

Checking pressure at the nozzle is also simple and inexpensive. While the blast rig is in operation, a needle gauge is inserted into the blast hose near the nozzle, at a 45-degree angle with the flow, and read.

How important are just these two items? It’s more difficult to outline the loss of efficiency with the size of nozzle, but the worse the wear is, the straighter the venturi becomes, and the lower the efficiency. 

Also, as the bore gets larger, the compressor has to work harder, which may also reduce the pressure at the nozzle.

I’ve addressed only these two items because, for owners—and contractors as well—they’re easy and inexpensive to check.

Additional Efficiency Bandits

Are there other areas of concern that can have a dramatic impact on efficiency? You bet! They include:

• Humidity of blast air—the dryer the air, the higher the efficiency.
• The metering valve—is the appropriate amount of media (blast grit) being released into the air stream?
• Type of media—is the right size and type of material being used?
• Lighting—is it bright enough for the technician to see what he or she is doing?
• Dust control—is it clear enough for the blaster to see what he or she is doing?
• Is the entire system operating properly? One leak, anywhere, could dramatically drop blast pressure.
• Technician fatigue and morale—is the blaster tired, is he or she maintaining the right angle of the blast nozzle to the surface and the proper distance?

I want to focus a bit more on the technician—the most important link in the blasting system.

A few years ago we were consulting on a large tank lining project which had to be carried out in the winter. The tank, roughly 80 feet tall and 40 feet wide, required scaffolding.

In a meeting including the owner, us and various contractors, the owner indicated he wanted the blasting to be carried out without heat to save money. The tank would then be heated for coating application. 

There were several contractors in the room at the time, who kept silent. However, I recommended that heat be brought in during blasting in order to reduce fatigue on the men blasting inside the tank.

The additional cost was a small fraction of the overall cost of the job, but I explained to the owner that the technician’s comfort was not a small thing and that it would lead to improved efficiency and morale.  

The owner then turned to the contractors, who all nodded their heads enthusiastically. 

After the meeting, they all came up and thanked me, saying that as contractors they really were not in a position to speak up. 

Often, the comfort and well-being of the blasting technician is not taken into consideration. This is a mistake.

Conclusion

Owners:

• Put efficiency issues on your radar for jobs that require them, typically non-bid work. It might be as simple as requiring the contractor to keep logs. Or, better yet, require the contractor to have the appropriate testing equipment on-hand so you can walk over and witness testing, at least for the nozzle bore and pressure. 
• Have the contractor provide you with an estimated productivity rate, or conduct a proof of concept with a known, efficient blast system. This way you can hold the contractor responsible for a predetermined, and mutually agreed-upon, production rate.
• Hire an outside firm to provide random audits.

Contractors:

There are simply too many items to list here to keep track of. And, the larger the contractor, the more difficult the task. However, some options include:

• Conduct internal, random audits. That is, task a person or crew to conduct audits of systems during operations and before rigs are brought to a facility.
• Work with blast equipment and aggregate suppliers. Some of them may provide free inspection of equipment and operations, though likely not as an ongoing service.
• Hire an outside firm to provide random audits.

ABOUT THE THE BLOGGER Warren Brand Warren Brand’s coatings career has ranged from entry-level field painting to the presidency of two successful companies. Over nearly three decades, he has project-managed thousands of coating installations and developed specs for thousands of paint and coating applications. NACE Level 3 and SSPC PCS certified, Brand, an MBA and martial-arts instructor, now heads Chicago Corrosion Group, a leading coatings consultancy. Contact Warren. SEE ALL CONTENT FROM THIS CONTRIBUTOR