Over the years, several methods have been developed for cleaning boiler firetubes. In decades past, soot blowers were a popular method of keeping tubes clean. Soot blowers consisted of steel tubes fitted with blowing nozzles that were mounted on the tube sheet of the boiler in such a way that the nozzles could be maneuvered to blow steam or air through each tube. Soot blowing was performed at scheduled intervals in hopes that the tubes would be kept clean. This practice was widely accepted when environmental concerns were less important. With soot blowers, the soot was blown out through the smoke stack and into the atmosphere - a practice that is frowned upon today. Today, soot blowers are used mainly in large power utility boilers where the smokestacks are equipped with scrubbers and other environmental devices.
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Another tube cleaning method some boiler tube technicians practiced was washing out the tubes using a fire hose. One can imagine the mess this left behind. Yes, the tubes were cleaned, but the boiler room had a layer of black mud on the floor. It took longer to clean the floor than the tubes. In addition, this was often done on boilers firing Bunker C #6 oil with a high sulfur content, which presented a safety issue - sulfur mixed with water creates an acid.
Another tube cleaning device that has come and gone is a machine that is hung from a system or racks that could be remotely guided to the opening of each tube one by one. Once positioned, the tube cleaning machine mechanically drove a cleaning brush down the tube and back using a cable. It was a great idea, but it took a great deal of time to assemble and disassemble the racks on each boiler.
In most cases, tube cleaning was strictly a manual operation that required much time, labor, mess, and inconvenience. Brushes fastened to long, heavy metal rods were manually pushed and pulled through the soot-laden boiler tubes, resulting in clouds of soot filling the air and settling on every surface in the room. The backbreaking effort went on for hours, followed by the immense task of individually vacuuming each tube and cleaning up the boiler room. Eventually, the issue of worker health was raised with the discovery of Vanadium Poisoning in the s. Vanadium Poisoning is an influenza-like illness that can have permanent effects. Toxic effects were reported from breathing air containing as little as 5 mg per cubic meter. No wonder nobody wanted to clean firetube boilers!
Unfortunately, there are still many operators out there who think this is still the only way to do the job.
Most watertube boilers have tubes in a more or less vertical position. Some watertube boilers have straight tubes, which can be cleaned using methods similar to those described above. However, most watertube boilers also have tubes with bends, making them more difficult to clean. In addition, where firetube boilers commonly have only soot and ash to be removed, water tubes commonly have scale deposits that adhere stubbornly to the tubes. The water quality and the effectiveness of water treatment determine the amount and the nature of the scale. Scale is formed when water is heated, and the suspended solids precipitate out onto the heating surfaces. A well-managed water treatment program is essential to minimizing scale deposits.
Early watertube cleaning devices employed cylindrical air motors fitted with complicated cutter heads fastened to the end of a compressed air hose. The entire motor/cutter assembly was then fed manually through the tubes, and cleaning was performed dry, followed by flushing with a water hose. Each air motor was good for only a narrow range of tube sizes, so if the user had many tube sizes to clean, he had to have multiple air motors, which drove up the cost. Interestingly, this technology started in the U.S. Navy for cleaning ship's boilers.
Over the years, tube cleaning technology has made great strides in developing faster, easier, and more efficient cleaning methods. Equipment that enables a single operator to perform two tasks at once in a fraction of the time required for outdated cleaning methods is now available.
For firetubes with soot deposits, there are tube cleaning machines that mechanically drive brushes or scrapers through the tubes - requiring almost no human effort. These machines are, in turn, connected to powerful vacuums that draw the loosened soot from the tubes, simultaneously leaving the tubes, boiler room, and operator completely clean.
Some firetube boilers develop scale deposits. This is particularly true with waste heat boilers and boilers fired on lesser-quality fuels. Some of the worst waste heat boilers are found at hospitals where medical waste is burned in incinerators, and the boiler is used to capture the heat generated by the incinerator. A straight brushing action is often insufficient, and rotary tube cleaning equipment must be used. Manually-fed rotary systems are available that incorporate simultaneous vacuuming, as well. Many of these systems were based on designs originally intended for condenser and chiller tube cleaning, and they work extremely well on scaled boiler tubes.
Systems are now available that utilize more powerful air motors, which drive flexible shafts fitted with various boiler tube cleaning tools. The flexible shaft, sheathed in a water-tight casing, transports water to the cleaning tool. This feature allows for the tubes to be cleaned and flushed in a single operation, saving time and labor.
Chemical cleaning has been used on boilers for many years and is periodically needed to clean the waterside of firetube boilers, where calcium and other mineral-based scale has formed. Industrial boiler scale removal chemicals can effectively remove calcium carbonate and other scales that adhere to heating surfaces. Chemical cleaning is a viable way to clean the waterside of firetube and water tube boilers and should be performed by technicians who are trained and equipped to do the work safely.
Every boiler maintenance program should include regular efficiency testing to reveal trends that indicate it is time to clean the boiler. For example, an increase in stack temperature frequently signals soot or scale build-up. An electronic combustion efficiency tester should be considered standard for the maintenance program. They are essential for tuning the burner properly. Many models of testers are available today with capabilities to measure and/or calculate net stack temperature, oxygen, carbon monoxide, carbon dioxide, nitrous oxide, excess air, combustion efficiency, and other values. There are models available to fit every need and budget. Comparing data from test to test will help pinpoint maintenance requirements.
Regular boiler maintenance that includes thorough boiler tube cleaning will result in lower operating costs and fuel consumption, greater efficiency, and longer heating system life.
Extreme temperatures and high pressures make boiler tube repair vitally important. When done right, re-tubing can give a boiler new life. Replacing cracked pitted or scaled tubes allows the boiler to function properly.
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What Causes Boiler Tube Failure
Raw water from a well or municipality contains impurities such as suspended solids, dissolved solids, and dissolved gases. Feed water can contain these impurities as well as industrial wastes, sediment, and microorganisms. In the Midwest, we most commonly find calcium, magnesium, and silica. These impurities plus the gasses water can contain can wreak havoc on your boiler tubes. That is why having a good boiler feedwater system is so important.
Oxygen and CO2 even in trace amounts as low as 5 ppm (parts per million) will cause major corrosion damage over time. Dissolved oxygen will react with carbon steel throughout the feed water piping, economizers, and boiler, causing oxygen pitting and eventually leaks. Dissolved CO2 can come from poorly deaerated water or as a byproduct of chemical reactions taking place inside your boiler. When this CO2 travels out of the boiler with the steam, it can make the condensate acidic. This acid condensate will corrode your steam piping while also adding iron to your boiler water.
Dissolved solids such as calcium, magnesium, iron, and silica in feedwater can damage a boiler beyond repair. These dissolved solids come out of solution as the temperature of the water increases, forming a scale on nearby surfaces. In many cases, this scale is first seen in the boiler, where the heat transfer occurs. This scale prevents boiler water from cooling metal heat-absorbing surfaces, leading first to a loss of efficiency. As the problem worsens, the boiler will have a number of issues with uneven thermal growth, such as tube roll leaks. When the scale is so thick that it prevents the boiler water from cooling the heat transfer surfaces, the boiler tubes may completely fail.
How Do We Re-tube A Boiler
1. We start by inspecting the boiler looking for welding defects and scaled or pitted tubes. We can also use dye penetrant testing to more easily find areas where cracking has occurred.
2. The second step is to address why the tubes are failing. When re-tubing is necessary, there is often an issue with the system that needs to be diagnosis. This will prevent the new replacement tubes from suffering the same fate as the failed tubes. This often involves looking at the feedwater systems, deaerators, firing rate and more to determine the cause of the issue.
3. After locating all cracks and tube damage, we remove the effected tubes from the boiler. This will occasionally require tube sheet replacement or repair as well.
4. Next, we install new boiler tubes in their place. We can install tubes by rolling, beading or welding depending on the application. This may include the use of XID tubes.
5. Following installation of the new tubes it is time to test the boiler. This involves hydro testing the system while an inspection agency is present. Any of the alterations go to the nation board and any other local regulatory agencies for their records.
Why Use Rasmech For Your Boiler Tube Repair?
We carry boiler tubes in all sizes and thickness to meet the need of your boiler. We are also an R-stamp certified company. This means we meet standards set forth by the National Board of Boiler and Pressure Valve Inspectors code. Finally, we also have a large boiler rental fleet to keep your business online while we are performing the repairs.
Proper boiler tube repair is crucial for maintaining optimal performance and extending the lifespan of boilers subjected to extreme temperatures and high pressures. By replacing cracked, pitted, or scaled tubes, the boiler can regain its intended functionality. This article explores the causes of boiler tube failure, including issues related to water treatment and impurities, such as dissolved solids and gases. It also highlights the step-by-step process of re-tubing a boiler, emphasizing the importance of diagnosing and addressing underlying system issues. Additionally, the article underscores the advantages of choosing an R-stamp certified company with a large boiler rental fleet. This ensures no downtime during repairs. For reliable boiler tube repair services, contact us at 1-800-237-, or via at .
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