The number of different industrial tube brushes and cleaning heads to choose from can be overwhelming for plant managers new to boiler and heat exchanger maintenance. Even seasoned pros can use a refresher course when moving to a new facility, or when new systems are installed. Fortunately, there are only 3 basic things you need to know to spec the best one for the job.
1. Tube Size
When it comes to tube brushes and cleaning heads, Inner Diameter (ID) is the measurement that matters most. ID is the distance from one side of the interior tube wall directly across to the other side. If you don’t know the tube ID of the equipment you are cleaning, you can measure it with a mechanical hole gauge, or a digital micrometer. If you know the tube wall gauge and Outer Diameter (OD) you can also use our Tube ID Smart Chart. OD includes the thickness of the tube wall itself. So, it is always slightly larger than ID. Heat exchangers generally have smaller diameter tubes ranging from about 1/4 to 1-1/2 inch. Boilers, in general, have larger diameter tube ranging from 1-1/2 to 4+ inches.
2. Tube Type
In addition to size, you need to know some things about the tubes to be cleaned. For example, are they straight or curved? As you would expect, straight tubes run straight through the length of the pressure vessel, exiting at the opposite end. This is common for fire tube boilers, as well as a lot of shell and tube type heat exchangers in operation today. However, water tube boilers with curved tubes and U-tube exchangers (pronounced the same as YouTube) are also common. Unlike straight tubes, U-tubes do not exit at the opposite end, but rather curve back around and return to the front tube sheet. Curved tubes require a cleaning head that can work its way through the bend.
Some heat exchanger tubes are lined with twisting ridges like rifling. These are called internally enhanced tubes. The spiraling shape allows fluid to flow through the tube more smoothly and efficiently with less turbulence. Dual diameter brushes are designed reach the high and the low areas of internally enhanced tubes.
It is also important to know what type of metal tubes are installed in the pressure vessel to be cleaned. Tube and brush metals should always match to avoid damage that will shorten the service life of tubes made of soft metals. Non-ferrous metals that do not contain iron, including copper, brass, and aluminum, are softer than ferrous metals like steel and stainless steel, which contain iron. So using a harder steel brush in a softer copper tube will score and erode the internal surface, leading to premature corrosion and eventual leaks. Softer bronze brushes can be used with copper and brass tubes. Stainless steel can be used with titanium and copper-nickel alloy tubes (also called Cupronickel). Plastic nylon brushes are safe to use with any metal.
3. Deposit Type
Different heating and cooling systems with varying maintenance histories become fouled by different types of dirt, grime and slime. For example, dry black soot builds up over time in fire tube boiler tubes, whereas mushy gunk, as well as hard scale, can form in chillers, absorbers and water tube boilers. HVAC tube deposits fall into the following 4 basic categories.
Light to Medium Debris
When maintenance is performed on a regular seasonal schedule you will most likely encounter only light to medium debris. In that case spiral brushes will do the trick. They work in conjunction with water delivered via the drive unit shaft to create a flushing action that aids the cleaning process. When the water that streams back out of the tube starts running clear, then you know it’s clean and time to move on to the next one.
Again, always match the spiral brush metal to the tube metal. Only use hard ferrous metals in ferrous tubes and softer non-ferrous metals in non-ferrous tubes.
Soft Powdery Deposits
Sometimes moderate deposits need more than just a spiral brush. For rust, scale and chemical precipitates an expanding brush with replaceable bristles is ideal. As the head spins on the cleaning unit shaft, the bristle cartridges rise via centripetal force, expanding to conform to the interior circumference of the tube. Expanding brushes tend to last longer than spiral brushes too. As the bristles wear down, the cartridges simply rise a little further to contact the tube wall. Once the bristle cartridges have worn to far they can be replaced with new ones. They come in steel, stainless steel, bronze, or nylon to match the tube metal.
A swing frame brush offers similar expanding capability for larger diameter boiler tubes.
Soft, Wet and Gummy Deposits
Microbiological, biofilm, or “mud” is thicker, heavier gunk that needs to be scraped off the tube walls. An expanding scraper is great for sludgy deposits, including marine growth. Just like an expanding brush, the expanding scraper head conforms to changes in the inside of the diameter of the tube to provide a very effective cleaning action throughout the length of the tube. Scraper cartridges are easily replaced after they wear out too. But unlike the bristles of a brush, the scraper blades are a lot less susceptible to becoming packed with wet and gummy debris. Used in conjunction with a flexible holder, an expanding scraper can be used to clean curved tubes in water tube boilers and U-tube heat exchangers.
For extra thick gummy deposits in larger diameter tubes, a cutter head is sometimes needed.
Brittle or Hard Scale
For tubes showing light limescale or calcium scale build-up, a buffing tool is often all that is needed to clear away excess debris after an initial pass with an expanding brush or scraper. Heavier soft or hard scale deposits call for the use of a cutter head.
Cutter heads come in multiple sizes and shapes. They range from a single cutter head for thin scale in smaller diameter tubes to ones with multiple cutters for removing thick encrustations of hard scale in larger diameter tubes.
Systems that have been neglected for some time can become completely plugged with hard scale and coke. These worst-case-scenarios call for a carbide-tipped cutter bit or drill head on a universal joint to bore through the blockage. A P-Brush should then be used to finish the job after punching through the clog.
The TC Wilson experts are available during business hours to answer questions about your specific wet or dry tube cleaning needs. Contact us or use the online chat for advice, including recommended pneumatic or electric drive units for the heating and cooling systems installed at your facility.