How To Achieve A Proper Bead When Using A Roll Bead Expander
Single roll beading expanders simultaneously expand and bead the tube ends in firetube boiler applications. This tool accomplishes the creation of a pressure-tight tube-to-tube sheet joint, and a beaded tube end, by utilizing the natural feed force built into the expander to push the beading roll against the end of the tube while expansion is taking place.
In order to obtain the best results and properly expand using a roll bead expander, tubes ends must be set to the proper projection. Tube projection refers to the distance between a tube end and the tube sheet. While a standard expander may not require any projection, the extra beading operation performed by a roll beading expander requires enough projection to form a bead at the end of the tube. The amount of projection can vary depending on tube diameter and wall thickness. The average tube projection range is between 3/16″ and 9/32″. In most cases, 3/16″ projection is a good starting point and produces an acceptable bead.
While rolling, it is important to maintain constant projection in order to avoid a loss of consistency of the tube ends. Variation of this projection prevents the consistent formation of an acceptable bead. In cases where the tube sheet is bowed or warped, and is not parallel to the end of the tube, the desired projection should be measured at the midpoint.
Standard operating procedures (SOP), as provided in the Operations & Maintenance Instructions that accompany the expander, cover the basics. One of the most important procedures is using vice grips to grip one end of the tube to hold the projection in place. Vice grips are a quick, simple way to secure the tube in position. After all of the tubes have been expanded on one end of the vessel, the opposite end of the tube can be trimmed to the proper projection using a boiler tube cutter. To determine if a boiler tube cutter is suitable for trimming, ensure the cutter has an adjustable collar. Once the collar is in place, the tube end can be set to the appropriate projection and cut.
Single roll beading expanders quickly and consistently expand and bead tubes in one operation.Combining these operations can save significant time and money. It is important that these steps are taken before using a roll bead expander, to obtain the best results.