Tube Expansion Guide – Tube Sheet Preparation

October 27, 2021
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Tube Sheet Preparation

RGP-RCB-7.23 TUBE HOLE FINISH

Tube hole finish affects the mechanical strength and leak tightness of an expanded tube-to-tube sheet joint. In general:

  • A rough tube hole provides more mechanical strength than a smooth tube hole. This is influenced by a complex relationship of modulus of elasticity, yield strength and hardness of the materials being used.
  • A smooth tube hole does not provide the mechanical strength that a rough tube hole does, but it can provide a pressure tight joint at a lower level of wall reduction.
  • Very light wall tubes require a smoother tube hole finish than heavier wall tubes.
  • Significant longitudinal scratches can provide leak paths through an expanded tube-to-tube sheet joint and should therefore be removed.
  • The inside edges of tube holes in tube sheets shall be free of burrs to prevent cutting of the tubes. lnternal surfaces shall be given a workmanlike finish

Preparation of Tube Holes

Preparation of tube holes in heat exchangers and condensers is as follows:

  1. Drill and ream tube sheet holes to over the outside diameter of the tube to be used as per TEMA standard.
  2. Be certain the ligaments are sufficient to guarantee a safe and permanent tube joint.
  3. When conditions permit, utilize a sizing or burnishing tool to further assure a good finish in the tube hole. This will also increase the tensile strength of the ligament.
  4. The serrations or grooves to be used will determine the holding power of the tube.
  5. It is extremely important when retubing that the grooves be cleared of all metals or any foreign material

RB-7.24 TUBE HOLE GROOVING

Tube holes for expanded joints for tubes 518″ (15.9mm) OD and larger shall be machined with annular ring groove(s) for additional longitudinal load resistance. For strength welded tube to Tube sheet joints, ring grooves are not required.

For roller expanded tube joints, when tube sheet thickness exceeds 1″ (25.4mm) at least two grooves shall be used, each approximately 118″ (3.2mm) wide by 1/64″ (0.4mm) deep.

Tube sheets with thickness less than or equal to 1″ (25.4mm) may be provided with one groove.

Tube Sheet Grooving Tools are suited for CNC application on account of 1 piece mandrel construction  short design

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