NPRO Journal · ENGINEERING
Tube Hole Design
for Roller Expansion
Tube rolling hole design starts with clearance, grooves, and rolling depth — freeze them on the drawing before the expander touches the sheet.
Tube rolling hole design starts with clearance, grooves, and rolling depth — freeze them on the drawing before the expander touches the sheet.
Answer first: For roller-expanded tube-to-tubesheet joints, the hole is a designed feature — diameter (clearance over tube OD), bore finish, optional grooves, and rolling depth must be frozen with pitch and ligament before CNC drilling. This page is the design explainer; use the tube hole layout calculator to visualise pitch, and expanded vs welded for joint-method selection.
Roller expansion needs a deliberate diametral gap so the tube can enter and then plastically expand into contact with the bore. TEMA hole-oversize practice often varies with unsupported tube length and class context — published discussions commonly reference bands on the order of roughly 0.4 mm to 0.8 mm depending on clause. Do not treat those as universal shop defaults. Put the hole diameter on the drawing and tie it to the TEMA edition named on the datasheet. See tolerances explained and TEMA tolerance reference.
Grooves are annular recesses in the hole wall. During expansion, tube metal flows into the groove, improving mechanical interlock and often leak resistance versus a plain bore. Specify groove count, width, depth, and location only when the purchaser standard or design note requires them — and machine them accordingly. Omitting specified grooves (or adding unspecified ones) is a nonconformance.
A frequently referenced industrial design practice limits the rolled length to about the lesser of 90% of tubesheet thickness or 150 mm, unless the purchaser document states a different rule. Rolling past the far face or through thin ligaments invites distortion. Pair depth limits with controlled wall reduction and recorded expander settings on the ITP.
Hole diameter tolerance, position tolerance, and finish interact with TEMA class expectations and ASME VIII documentation. Class R petroleum duties often carry deeper inspection — but class letters never replace a hole schedule. Align with TEMA Class R explained and standards.
| PARAMETER | GENERAL PRACTICE NOTE | FREEZE ON |
|---|---|---|
| Hole oversize | Per TEMA edition / unsupported length — often discussed ~0.4–0.8 mm bands | Drawing hole Ø + edition |
| Grooves | Only if purchaser / standard requires; geometry is design-owned | Groove detail / ITP |
| Rolling length | Often ≤ min(~90% TS thickness, 150 mm) in published design notes | Joint procedure |
| Inspection | Wall reduction / torque records + hydro / leak checks | ITP hold points |
Tight triangular pitch raises ligament risk when rolling. Validate count and ligament with the layout calculator, then read damaged tube sheet holes for failure modes that start as bad hole design.
It is the engineered combination of hole diameter (clearance), finish, optional grooves, rolling depth, and ligament that makes a roller-expanded joint repeatable and inspectable.
From the purchaser specification and the TEMA edition cited on the exchanger datasheet — not from a generic blog table alone.
Hole design still matters for both. Hybrid joints add a seal weld after seating — see expanded vs welded.
Yes — when the drawing specifies groove geometry. Send the drawing via the enquiry form for manufacturability review.
Send your drawing or RFQ — NPRO India reviews code, material and manufacturability before quoting.
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