Basic Guidelines of Tube Expansion

Tight sealing of tubes is a crucial function in the manufacturing of heat exchangers for high pressure steam generators, water tube boilers, fire tube boilers, processing systems and condensers. When considering the best methods and tools to use for tube expanding, manufacturers need to examine critical factors such as safety, speed, cost, operator skill requirements, repeatability and over overall quality.

Considering the wide number of tubes that could be contained within a given sheet—and the possibility that the expansion process could need to be performed manually one by one—it’s very important to maintain best practices and top-quality tools related to tube expansion in order to avoid continual repair costs.

Tube expanding requires the reduction of a tube wall by compressing the tube against a fixed container, such as rolling tubes into tube sheets, drums, ferrules or flanges. While it’s important to understand the process behind wall reduction, it’s equally important to be familiar with the materials often associated with tube expansion. This will help you determine the proper wall reduction necessary as it applies to various metals.

Basically, the harder the material, the less wall reduction required to obtain a tube joint. To make sure you can create a proper tube joint, the tube wall must be reduced by a predetermined percentage. For example, you can assign these as approximate percentages of wall reduction when rolling pressure vessels:

Types of Tube Expansion

Tube expansion can be roughly divided into two categories: parallel tube expansion and flare tube expansion.

• Parallel tube expansion is mainly used in the expansion of tubes of heat exchangers, steam condensers, boilers, etc.
• Flare tube expansion expands tubes by providing a flare shape to the end of the tubes, while also acting as a reinforcement to tensile stress; mostly used for boiler tubes.

What Causes Tube Leaks?

To some degree, all tube-to-tube sheet joints will leak. While welded expanded joints are the most leak-resistant, it may be possible for gases like hydrogen to pass through even welded joints. Unproperly rolled joints—whether they’re under-rolled joints that need to be re-rolled or over-rolled tubes that need to be replaced—can create leaks that cause severe damage and repair expense.

For example, over-rolling can cause a tube sheet to bow or warp so much that a standard-length tube would not work properly until the bowing or warping is repaired. Something like this can be fixed by placing stay rods in the vessel and pulling the tube sheets back to their original position.

Improper preparation of tube holes can also cause tubes to leak. If the tube sheet or drum is gouged, it can be quite difficult to expand the tube properly in order to fill these gouges without over-rolling. In other words, the smoother the tube seat or tube hole, the easier it is to roll an optimum tube joint.

Proper Preparation of Tube Holes

With this in mind, it’s easy to see why proper preparation of tube holes in heat exchangers and condensers is extremely important when it comes to preventing leaks. Following these steps can help prepare tube holes correctly:

• Drill and ream tube sheet holes over the outside diameter of the tube to be used
• Ligaments must be sufficient enough to guarantee a safe and permanent tube joint
• If necessary, use a sizing or burnishing tool to achieve the best finish possible in the tube hole
• Serrations or grooves will determine the holding power of the tube
• Grooves must be cleared of all metals or any foreign material

After tube holes have been prepared, they are usually coated with a rust prevention compound. Before inserting any tube, it is important to remove all traces of this coating. It’s also extremely important to make sure that the tube ends are clear of any foreign material, and that there are no chips on the tubing that might gouge the tube sheet or tube seat when the tube is placed in the vessel.

In some cases, if it ever becomes necessary to force a tube into a tube hole, it will be better to spring the tube than to try to force it with a hammer. If a tube end is kinked or damaged before rolling, the expanded end will be damaged, and a leaky roll joint will result. Paying particular attention to the tube ends and the tube alignment will prevent future troubles.

Determining the Correct Amount of Tube Expansion

The appropriate amount of tube expansion for the tube expander differs depending on the dimensions of the tube sheet hole diameter, outer diameter of the tube, and tube thickness as well as the material of the tube. Use our worksheet as a guide:

Birmingham Wire Gauges:

Here is an example of the application of this method for a 2-inch Outer Diameter 10-gauge tube in a boiler:

Wilson tube expanders are designed to work with tubes in a wide range of sizes. Our mandrel expanders will help you roll tubes in tough-to-reach areas, while our power-driven linsen expanders work well in short bends, U-turns, copper, brass, aluminum, or thin steel tubing. Wilson collet type hydraulic baffle expanders reduce tube wear caused by vibration of baffle plates and support sheets. And we have a wide range of versatile, efficient tools—including parts and accessories — to help make your job easier.

Contact us today or use the online chat for advice from our experts to answer your specific questions about proper tube expansion methods and tools.