Overcoming Challenges in Cleaning Curved Tubes

The main challenge in curved applications is the bend itself. In heat exchangers, particularly those with U-tube bundles, the curves can be extremely tight, like a hairpin. This is because the inner tubes have a very small radius, while the outer tubes have a much larger radius. This variance in bend radius requires a flexible cleaning solution that can adapt to different curve severities within the same bundle, or the use of two different tooling set-ups.

Water tube boilers, on the other hand, typically have less severe bends, often located closer to the mud drum. While the bends aren’t as sharp, they still necessitate specialized equipment.

The tube material is another critical factor. When cleaning anything other than carbon steel, caution must be exercised to prevent scratching or damaging the tube’s inner diameter (ID). This often means using brushes or specialized tooling that won’t abrade the surface.

Finally, the nature of the deposits themselves plays a major role. Deposits can vary in thickness, hardness, and composition. A thin, soft layer of scale can be removed much easier than a thick, hard layer of debris. The amount of build-up is also important; heavily clogged tubes may require a multi-pass approach, starting with a smaller tool to create a pilot hole before using a larger one.

Before any cleaning begins, two key factors must be determined: the tube material and the acceptance criteria for the cleaning. The acceptance criteria, often determined using a borescope, sets a minimum allowance for the percentage of debris remaining in the tube. While removing all debris is ideal, it may not always be feasible, especially in older units or with stubborn deposits.

Once these factors are known, you can select the appropriate cleaning method. This choice generally depends on the deposit type, deposit thickness, and the bend radius of the tube. The more severe the debris buildup, the smaller the initial tool needs to be to navigate through the constricted ID.

A common method for boilers is “rattling” the pipe, which uses an air motor and a cleaning head. The tool vibrates and scrapes the inner walls of the tube, breaking up and dislodging deposits. For heat exchangers, this process can be similar but the tooling may vary.

For tubes with significant debris, a multi-pass cleaning strategy is often necessary. You would start with a smaller tool to bore through the deposit, and as the ID gets larger, you would switch to a larger tool. For example, if you have a 10-inch drill pipe with 2.5 inches of buildup, you’ll need a small tool to start. As this first pass removes the initial layer, the ID will effectively grow. A larger tool can then be used in subsequent passes to clean the remaining deposit.

A key challenge in this scenario is preventing the motor and cleaning head from rattling around inside the larger ID. Excessive movement can damage the tooling or, more critically, the tube itself. To address this, a sleeve or a larger motor may be used on the second pass to keep the tool centered.

In some cases, a single cleaning method may not be enough to meet the acceptance criteria. If mechanical cleaning alone can’t remove all the debris, a hybrid approach may be required. This can involve using a combination of mechanical and chemical cleaning. A chemical wash can help dissolve or loosen any remaining deposits that mechanical cleaning couldn’t reach, especially in tight bend areas.

In general, the more debris you can remove, the better the heat transfer and performance of the unit will be over time. By carefully considering the unique challenges of curved tubes and employing the right tools and techniques, it’s possible to achieve a thorough cleaning that extends the lifespan and efficiency of the equipment.