Expanding Tubes In Heat Exchangers from freeamfva's blog

Expanding Tubes In Heat Exchangers

Before you can start rolling, you will need to select the right expander for the job. Tube OD, and Wall/BWG will determine the size of the expander. However, there are some other factors to consider, such as tube projection, roll length, reach requirements, space constraints, and whether it’s minimum or average wall tubing.Get more news about Condenser Expansion Machine,you can vist our website!

Tube Projection
It’s important to consider if the tube is going to be expanded flush to the tube sheet or if it will have a projection. The most common tube projection for shell and tube heat exchangers is 1/8” from the tube sheet. In situations where all tubes will be rolled to the same projection, an expander with a recess collar should be used. This will accommodate the projection and prevent the tube from being pulled into the expander. The outlet side of surface steam condensers can have varying projections, up to 1X’s the tube diameter in length. In this case a telescoping or full recess collar should be used. If no tube projection is specified, the tube expander will come with a flush collar to expand the tube flush to the tube sheet.

Roll Length
Tube expanders come in two different roll lengths: short and long roll. In order to determine the correct roll length, you will need to know the tube sheet thickness. Choose the roll length that will expand the tube sheet area in the least amount of expansions. If expanding tubes in a double tube sheet, the inner primary tube sheet thickness must be specified so the expander’s rolls can be manufactured to allow for the proper effective expansion length. Whereas, the outer tube sheet would use standard rolls.
Reach Requirements
Generally, tube expanders come in 4”, 8”, 12”, and 18” reaches, but can be made longer to accommodate specific applications. For optimum tool life, use the shortest reach expander that will accommodate the application. Long reach expanders are used in heat exchangers with thick tube sheets or when reaching through water boxes, found in air coolers.

Space Constraints
Heat exchangers with channel boxes or division plates where the tubes are positioned too close to a wall for the expander’s collar to access perimeter tubes will require a friction collar. This collar is smaller in diameter than a standard collar, allowing more access to difficult areas. A friction collar should only be used as needed, as it’s not a replacement for a bearing collar.

Average Wall v Minimum Wall
When ordering tubes, it is very unlikely that each tube wall thickness will be exactly the same. Industry tolerances allow for ±10% thickness. That’s a total variation of up to 20% from the smallest to largest thickness, resulting in a wide range of sizes. For example, if you have .083” average wall tubes, the actual wall could be anywhere between .091” and .075”. If you were to buy a 14 BWG expander to fit .083, it would likely still work for either extreme due to the expansion range that the tool is capable of achieving.
A min wall tube offers the same total variation in wall thickness that an average wall tube does, but the variation is applied differently. It allows for -0% and +20%. So the wall will never be less than the specified thickness. For example, a .083” min wall tube will range from .083” to .100” wall thickness.

At the upper end of that range, a normally sized tube expander will not have enough clearance to enter the tube. If you have min wall tubing, it is recommended that you drop down one expander size. So instead of ordering a 14 BWG expander, you would drop down to a 13 BWG. This ensures that the expander will fit inside of the tubes and still achieve the proper range of expansion.

Setting Up A Condenser Expander
Once the right tool has been selected, the tube expander’s collar will need to be set to the correct roll depth. Generally, you want to set the rolls 1/16” to 1/8” from the back of the tube sheet. This will ensure that the tool does not roll beyond the tube sheet. Simply, loosen the set screw on the collar, adjust the collar threads to the desired roll depth, and tighten the set screw on the expander’s cage flat. This will allow the expander to be adjusted to other depths if necessary.

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